Merge branch 'nix' into 'master'.

13 files changed, 3064 insertions, 0 deletions

diff --git a/nix/libutil/affinity.cc b/nix/libutil/affinity.cc
new file mode 100644
index 0000000000..3e21f43a2e
--- /dev/null
+++ b/nix/libutil/affinity.cc
@@ -0,0 +1,55 @@
+#include "types.hh"
+#include "util.hh"
+#include "affinity.hh"
+
+#if HAVE_SCHED_H
+#include <sched.h>
+#endif
+
+namespace nix {
+
+
+#if HAVE_SCHED_SETAFFINITY
+static bool didSaveAffinity = false;
+static cpu_set_t savedAffinity;
+#endif
+
+
+void setAffinityTo(int cpu)
+{
+#if HAVE_SCHED_SETAFFINITY
+    if (sched_getaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1) return;
+    didSaveAffinity = true;
+    printMsg(lvlDebug, format("locking this thread to CPU %1%") % cpu);
+    cpu_set_t newAffinity;
+    CPU_ZERO(&newAffinity);
+    CPU_SET(cpu, &newAffinity);
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &newAffinity) == -1)
+        printMsg(lvlError, format("failed to lock thread to CPU %1%") % cpu);
+#endif
+}
+
+
+int lockToCurrentCPU()
+{
+#if HAVE_SCHED_SETAFFINITY
+    int cpu = sched_getcpu();
+    if (cpu != -1) setAffinityTo(cpu);
+    return cpu;
+#else
+    return -1;
+#endif
+}
+
+
+void restoreAffinity()
+{
+#if HAVE_SCHED_SETAFFINITY
+    if (!didSaveAffinity) return;
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1)
+        printMsg(lvlError, "failed to restore affinity %1%");
+#endif
+}
+
+
+}
diff --git a/nix/libutil/affinity.hh b/nix/libutil/affinity.hh
new file mode 100644
index 0000000000..c1bd28e136
--- /dev/null
+++ b/nix/libutil/affinity.hh
@@ -0,0 +1,9 @@
+#pragma once
+
+namespace nix {
+
+void setAffinityTo(int cpu);
+int lockToCurrentCPU();
+void restoreAffinity();
+
+}
diff --git a/nix/libutil/archive.cc b/nix/libutil/archive.cc
new file mode 100644
index 0000000000..ab4cd47351
--- /dev/null
+++ b/nix/libutil/archive.cc
@@ -0,0 +1,335 @@
+#include "config.h"
+
+#include <cerrno>
+#include <algorithm>
+#include <vector>
+
+#define _XOPEN_SOURCE 600
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <fcntl.h>
+
+#include "archive.hh"
+#include "util.hh"
+
+
+namespace nix {
+
+
+static string archiveVersion1 = "nix-archive-1";
+
+
+PathFilter defaultPathFilter;
+
+
+static void dump(const string & path, Sink & sink, PathFilter & filter);
+
+
+static void dumpEntries(const Path & path, Sink & sink, PathFilter & filter)
+{
+    Strings names = readDirectory(path);
+    vector<string> names2(names.begin(), names.end());
+    sort(names2.begin(), names2.end());
+
+    for (vector<string>::iterator i = names2.begin();
+         i != names2.end(); ++i)
+    {
+        Path entry = path + "/" + *i;
+        if (filter(entry)) {
+            writeString("entry", sink);
+            writeString("(", sink);
+            writeString("name", sink);
+            writeString(*i, sink);
+            writeString("node", sink);
+            dump(entry, sink, filter);
+            writeString(")", sink);
+        }
+    }
+}
+
+
+static void dumpContents(const Path & path, size_t size, 
+    Sink & sink)
+{
+    writeString("contents", sink);
+    writeLongLong(size, sink);
+
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1) throw SysError(format("opening file `%1%'") % path);
+    
+    unsigned char buf[65536];
+    size_t left = size;
+
+    while (left > 0) {
+        size_t n = left > sizeof(buf) ? sizeof(buf) : left;
+        readFull(fd, buf, n);
+        left -= n;
+        sink(buf, n);
+    }
+
+    writePadding(size, sink);
+}
+
+
+static void dump(const Path & path, Sink & sink, PathFilter & filter)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+
+    writeString("(", sink);
+
+    if (S_ISREG(st.st_mode)) {
+        writeString("type", sink);
+        writeString("regular", sink);
+        if (st.st_mode & S_IXUSR) {
+            writeString("executable", sink);
+            writeString("", sink);
+        }
+        dumpContents(path, (size_t) st.st_size, sink);
+    } 
+
+    else if (S_ISDIR(st.st_mode)) {
+        writeString("type", sink);
+        writeString("directory", sink);
+        dumpEntries(path, sink, filter);
+    }
+
+    else if (S_ISLNK(st.st_mode)) {
+        writeString("type", sink);
+        writeString("symlink", sink);
+        writeString("target", sink);
+        writeString(readLink(path), sink);
+    }
+
+    else throw Error(format("file `%1%' has an unknown type") % path);
+
+    writeString(")", sink);
+}
+
+
+void dumpPath(const Path & path, Sink & sink, PathFilter & filter)
+{
+    writeString(archiveVersion1, sink);
+    dump(path, sink, filter);
+}
+
+
+static SerialisationError badArchive(string s)
+{
+    return SerialisationError("bad archive: " + s);
+}
+
+
+static void skipGeneric(Source & source)
+{
+    if (readString(source) == "(") {
+        while (readString(source) != ")")
+            skipGeneric(source);
+    }
+}
+
+
+static void parse(ParseSink & sink, Source & source, const Path & path);
+
+
+
+static void parseEntry(ParseSink & sink, Source & source, const Path & path)
+{
+    string s, name;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    while (1) {
+        checkInterrupt();
+
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        } else if (s == "name") {
+            name = readString(source);
+        } else if (s == "node") {
+            if (s == "") throw badArchive("entry name missing");
+            parse(sink, source, path + "/" + name);
+        } else {
+            throw badArchive("unknown field " + s);
+            skipGeneric(source);
+        }
+    }
+}
+
+
+static void parseContents(ParseSink & sink, Source & source, const Path & path)
+{
+    unsigned long long size = readLongLong(source);
+    
+    sink.preallocateContents(size);
+
+    unsigned long long left = size;
+    unsigned char buf[65536];
+
+    while (left) {
+        checkInterrupt();
+        unsigned int n = sizeof(buf);
+        if ((unsigned long long) n > left) n = left;
+        source(buf, n);
+        sink.receiveContents(buf, n);
+        left -= n;
+    }
+
+    readPadding(size, source);
+}
+
+
+static void parse(ParseSink & sink, Source & source, const Path & path)
+{
+    string s;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    enum { tpUnknown, tpRegular, tpDirectory, tpSymlink } type = tpUnknown;
+
+    while (1) {
+        checkInterrupt();
+
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        }
+
+        else if (s == "type") {
+            if (type != tpUnknown)
+                throw badArchive("multiple type fields");
+            string t = readString(source);
+
+            if (t == "regular") {
+                type = tpRegular;
+                sink.createRegularFile(path);
+            }
+
+            else if (t == "directory") {
+                sink.createDirectory(path);
+                type = tpDirectory;
+            }
+
+            else if (t == "symlink") {
+                type = tpSymlink;
+            }
+            
+            else throw badArchive("unknown file type " + t);
+            
+        }
+
+        else if (s == "contents" && type == tpRegular) {
+            parseContents(sink, source, path);
+        }
+
+        else if (s == "executable" && type == tpRegular) {
+            readString(source);
+            sink.isExecutable();
+        }
+
+        else if (s == "entry" && type == tpDirectory) {
+            parseEntry(sink, source, path);
+        }
+
+        else if (s == "target" && type == tpSymlink) {
+            string target = readString(source);
+            sink.createSymlink(path, target);
+        }
+
+        else {
+            throw badArchive("unknown field " + s);
+            skipGeneric(source);
+        }
+    }
+}
+
+
+void parseDump(ParseSink & sink, Source & source)
+{
+    string version;    
+    try {
+        version = readString(source);
+    } catch (SerialisationError & e) {
+        /* This generally means the integer at the start couldn't be
+           decoded.  Ignore and throw the exception below. */
+    }
+    if (version != archiveVersion1)
+        throw badArchive("input doesn't look like a Nix archive");
+    parse(sink, source, "");
+}
+
+
+struct RestoreSink : ParseSink
+{
+    Path dstPath;
+    AutoCloseFD fd;
+
+    void createDirectory(const Path & path)
+    {
+        Path p = dstPath + path;
+        if (mkdir(p.c_str(), 0777) == -1)
+            throw SysError(format("creating directory `%1%'") % p);
+    };
+
+    void createRegularFile(const Path & path)
+    {
+        Path p = dstPath + path;
+        fd.close();
+        fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY, 0666);
+        if (fd == -1) throw SysError(format("creating file `%1%'") % p);
+    }
+
+    void isExecutable()
+    {
+        struct stat st;
+        if (fstat(fd, &st) == -1)
+            throw SysError("fstat");
+        if (fchmod(fd, st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
+            throw SysError("fchmod");
+    }
+
+    void preallocateContents(unsigned long long len)
+    {
+#if HAVE_POSIX_FALLOCATE
+        if (len) {
+            errno = posix_fallocate(fd, 0, len);
+            /* Note that EINVAL may indicate that the underlying
+               filesystem doesn't support preallocation (e.g. on
+               OpenSolaris).  Since preallocation is just an
+               optimisation, ignore it. */
+            if (errno && errno != EINVAL)
+                throw SysError(format("preallocating file of %1% bytes") % len);
+        }
+#endif
+    }
+
+    void receiveContents(unsigned char * data, unsigned int len)
+    {
+        writeFull(fd, data, len);
+    }
+
+    void createSymlink(const Path & path, const string & target)
+    {
+        Path p = dstPath + path;
+        nix::createSymlink(target, p);
+    }
+};
+
+ 
+void restorePath(const Path & path, Source & source)
+{
+    RestoreSink sink;
+    sink.dstPath = path;
+    parseDump(sink, source);
+}
+
+ 
+}
diff --git a/nix/libutil/archive.hh b/nix/libutil/archive.hh
new file mode 100644
index 0000000000..ccac92074d
--- /dev/null
+++ b/nix/libutil/archive.hh
@@ -0,0 +1,75 @@
+#pragma once
+
+#include "types.hh"
+#include "serialise.hh"
+
+
+namespace nix {
+
+
+/* dumpPath creates a Nix archive of the specified path.  The format
+   is as follows:
+
+   IF path points to a REGULAR FILE:
+     dump(path) = attrs(
+       [ ("type", "regular")
+       , ("contents", contents(path))
+       ])
+
+   IF path points to a DIRECTORY:
+     dump(path) = attrs(
+       [ ("type", "directory")
+       , ("entries", concat(map(f, sort(entries(path)))))
+       ])
+       where f(fn) = attrs(
+         [ ("name", fn)
+         , ("file", dump(path + "/" + fn))
+         ])
+
+   where:
+
+     attrs(as) = concat(map(attr, as)) + encN(0) 
+     attrs((a, b)) = encS(a) + encS(b)
+
+     encS(s) = encN(len(s)) + s + (padding until next 64-bit boundary)
+
+     encN(n) = 64-bit little-endian encoding of n.
+
+     contents(path) = the contents of a regular file.
+
+     sort(strings) = lexicographic sort by 8-bit value (strcmp).
+
+     entries(path) = the entries of a directory, without `.' and
+     `..'.
+
+     `+' denotes string concatenation. */
+
+struct PathFilter
+{
+    virtual ~PathFilter() { }
+    virtual bool operator () (const Path & path) { return true; }
+};
+
+extern PathFilter defaultPathFilter;
+
+void dumpPath(const Path & path, Sink & sink,
+    PathFilter & filter = defaultPathFilter);
+
+struct ParseSink
+{
+    virtual void createDirectory(const Path & path) { };
+    
+    virtual void createRegularFile(const Path & path) { };
+    virtual void isExecutable() { };
+    virtual void preallocateContents(unsigned long long size) { };
+    virtual void receiveContents(unsigned char * data, unsigned int len) { };
+
+    virtual void createSymlink(const Path & path, const string & target) { };
+};
+    
+void parseDump(ParseSink & sink, Source & source);
+
+void restorePath(const Path & path, Source & source);
+
+ 
+}
diff --git a/nix/libutil/hash.cc b/nix/libutil/hash.cc
new file mode 100644
index 0000000000..050446610f
--- /dev/null
+++ b/nix/libutil/hash.cc
@@ -0,0 +1,382 @@
+#include "config.h"
+
+#include <iostream>
+#include <cstring>
+
+#ifdef HAVE_OPENSSL
+#include <openssl/md5.h>
+#include <openssl/sha.h>
+#else
+extern "C" {
+#include "md5.h"
+#include "sha1.h"
+#include "sha256.h"
+}
+#endif
+
+#include "hash.hh"
+#include "archive.hh"
+#include "util.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+
+namespace nix {
+
+
+Hash::Hash()
+{
+    type = htUnknown;
+    hashSize = 0;
+    memset(hash, 0, maxHashSize);
+}
+
+
+Hash::Hash(HashType type)
+{
+    this->type = type;
+    if (type == htMD5) hashSize = md5HashSize;
+    else if (type == htSHA1) hashSize = sha1HashSize;
+    else if (type == htSHA256) hashSize = sha256HashSize;
+    else throw Error("unknown hash type");
+    assert(hashSize <= maxHashSize);
+    memset(hash, 0, maxHashSize);
+}
+
+
+bool Hash::operator == (const Hash & h2) const
+{
+    if (hashSize != h2.hashSize) return false;
+    for (unsigned int i = 0; i < hashSize; i++)
+        if (hash[i] != h2.hash[i]) return false;
+    return true;
+}
+
+
+bool Hash::operator != (const Hash & h2) const
+{
+    return !(*this == h2);
+}
+
+
+bool Hash::operator < (const Hash & h) const
+{
+    for (unsigned int i = 0; i < hashSize; i++) {
+        if (hash[i] < h.hash[i]) return true;
+        if (hash[i] > h.hash[i]) return false;
+    }
+    return false;
+}
+
+
+const string base16Chars = "0123456789abcdef";
+
+
+string printHash(const Hash & hash)
+{
+    char buf[hash.hashSize * 2];
+    for (unsigned int i = 0; i < hash.hashSize; i++) {
+        buf[i * 2] = base16Chars[hash.hash[i] >> 4];
+        buf[i * 2 + 1] = base16Chars[hash.hash[i] & 0x0f];
+    }
+    return string(buf, hash.hashSize * 2);
+}
+
+    
+Hash parseHash(HashType ht, const string & s)
+{
+    Hash hash(ht);
+    if (s.length() != hash.hashSize * 2)
+        throw Error(format("invalid hash `%1%'") % s);
+    for (unsigned int i = 0; i < hash.hashSize; i++) {
+        string s2(s, i * 2, 2);
+        if (!isxdigit(s2[0]) || !isxdigit(s2[1])) 
+            throw Error(format("invalid hash `%1%'") % s);
+        std::istringstream str(s2);
+        int n;
+        str >> std::hex >> n;
+        hash.hash[i] = n;
+    }
+    return hash;
+}
+
+
+static unsigned char divMod(unsigned char * bytes, unsigned char y)
+{
+    unsigned int borrow = 0;
+
+    int pos = Hash::maxHashSize - 1;
+    while (pos >= 0 && !bytes[pos]) --pos;
+
+    for ( ; pos >= 0; --pos) {
+        unsigned int s = bytes[pos] + (borrow << 8);
+        unsigned int d = s / y;
+        borrow = s % y;
+        bytes[pos] = d;
+    }
+
+    return borrow;
+}
+
+
+unsigned int hashLength32(const Hash & hash)
+{
+    return (hash.hashSize * 8 - 1) / 5 + 1;
+}
+
+
+// omitted: E O U T
+const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
+
+
+string printHash32(const Hash & hash)
+{
+    Hash hash2(hash);
+    unsigned int len = hashLength32(hash);
+
+    const char * chars = base32Chars.data();
+    
+    string s(len, '0');
+
+    int pos = len - 1;
+    while (pos >= 0) {
+        unsigned char digit = divMod(hash2.hash, 32);
+        s[pos--] = chars[digit];
+    }
+
+    for (unsigned int i = 0; i < hash2.maxHashSize; ++i)
+        assert(hash2.hash[i] == 0);
+
+    return s;
+}
+
+
+string printHash16or32(const Hash & hash)
+{
+    return hash.type == htMD5 ? printHash(hash) : printHash32(hash);
+}
+
+
+static bool mul(unsigned char * bytes, unsigned char y, int maxSize)
+{
+    unsigned char carry = 0;
+
+    for (int pos = 0; pos < maxSize; ++pos) {
+        unsigned int m = bytes[pos] * y + carry;
+        bytes[pos] = m & 0xff;
+        carry = m >> 8;
+    }
+
+    return carry;
+}
+
+
+static bool add(unsigned char * bytes, unsigned char y, int maxSize)
+{
+    unsigned char carry = y;
+
+    for (int pos = 0; pos < maxSize; ++pos) {
+        unsigned int m = bytes[pos] + carry;
+        bytes[pos] = m & 0xff;
+        carry = m >> 8;
+        if (carry == 0) break;
+    }
+
+    return carry;
+}
+
+
+Hash parseHash32(HashType ht, const string & s)
+{
+    Hash hash(ht);
+
+    const char * chars = base32Chars.data();
+
+    for (unsigned int i = 0; i < s.length(); ++i) {
+        char c = s[i];
+        unsigned char digit;
+        for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
+            if (chars[digit] == c) break;
+        if (digit >= 32)
+            throw Error(format("invalid base-32 hash `%1%'") % s);
+        if (mul(hash.hash, 32, hash.hashSize) ||
+            add(hash.hash, digit, hash.hashSize))
+            throw Error(format("base-32 hash `%1%' is too large") % s);
+    }
+
+    return hash;
+}
+
+
+Hash parseHash16or32(HashType ht, const string & s)
+{
+    Hash hash(ht);
+    if (s.size() == hash.hashSize * 2)
+        /* hexadecimal representation */
+        hash = parseHash(ht, s);
+    else if (s.size() == hashLength32(hash))
+        /* base-32 representation */
+        hash = parseHash32(ht, s);
+    else
+        throw Error(format("hash `%1%' has wrong length for hash type `%2%'")
+            % s % printHashType(ht));
+    return hash;
+}
+
+
+bool isHash(const string & s)
+{
+    if (s.length() != 32) return false;
+    for (int i = 0; i < 32; i++) {
+        char c = s[i];
+        if (!((c >= '0' && c <= '9') ||
+              (c >= 'a' && c <= 'f')))
+            return false;
+    }
+    return true;
+}
+
+
+struct Ctx
+{
+    MD5_CTX md5;
+    SHA_CTX sha1;
+    SHA256_CTX sha256;
+};
+
+
+static void start(HashType ht, Ctx & ctx)
+{
+    if (ht == htMD5) MD5_Init(&ctx.md5);
+    else if (ht == htSHA1) SHA1_Init(&ctx.sha1);
+    else if (ht == htSHA256) SHA256_Init(&ctx.sha256);
+}
+
+
+static void update(HashType ht, Ctx & ctx,
+    const unsigned char * bytes, unsigned int len)
+{
+    if (ht == htMD5) MD5_Update(&ctx.md5, bytes, len);
+    else if (ht == htSHA1) SHA1_Update(&ctx.sha1, bytes, len);
+    else if (ht == htSHA256) SHA256_Update(&ctx.sha256, bytes, len);
+}
+
+
+static void finish(HashType ht, Ctx & ctx, unsigned char * hash)
+{
+    if (ht == htMD5) MD5_Final(hash, &ctx.md5);
+    else if (ht == htSHA1) SHA1_Final(hash, &ctx.sha1);
+    else if (ht == htSHA256) SHA256_Final(hash, &ctx.sha256);
+}
+
+
+Hash hashString(HashType ht, const string & s)
+{
+    Ctx ctx;
+    Hash hash(ht);
+    start(ht, ctx);
+    update(ht, ctx, (const unsigned char *) s.data(), s.length());
+    finish(ht, ctx, hash.hash);
+    return hash;
+}
+
+
+Hash hashFile(HashType ht, const Path & path)
+{
+    Ctx ctx;
+    Hash hash(ht);
+    start(ht, ctx);
+
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1) throw SysError(format("opening file `%1%'") % path);
+
+    unsigned char buf[8192];
+    ssize_t n;
+    while ((n = read(fd, buf, sizeof(buf)))) {
+        checkInterrupt();
+        if (n == -1) throw SysError(format("reading file `%1%'") % path);
+        update(ht, ctx, buf, n);
+    }
+    
+    finish(ht, ctx, hash.hash);
+    return hash;
+}
+
+
+HashSink::HashSink(HashType ht) : ht(ht)
+{
+    ctx = new Ctx;
+    bytes = 0;
+    start(ht, *ctx);
+}
+    
+HashSink::~HashSink()
+{
+    bufPos = 0;
+    delete ctx;
+}
+
+void HashSink::write(const unsigned char * data, size_t len)
+{
+    bytes += len;
+    update(ht, *ctx, data, len);
+}
+
+HashResult HashSink::finish()
+{
+    flush();
+    Hash hash(ht);
+    nix::finish(ht, *ctx, hash.hash);
+    return HashResult(hash, bytes);
+}
+
+HashResult HashSink::currentHash()
+{
+    flush();
+    Ctx ctx2 = *ctx;
+    Hash hash(ht);
+    nix::finish(ht, ctx2, hash.hash);
+    return HashResult(hash, bytes);
+}
+
+
+HashResult hashPath(
+    HashType ht, const Path & path, PathFilter & filter)
+{
+    HashSink sink(ht);
+    dumpPath(path, sink, filter);
+    return sink.finish();
+}
+
+
+Hash compressHash(const Hash & hash, unsigned int newSize)
+{
+    Hash h;
+    h.hashSize = newSize;
+    for (unsigned int i = 0; i < hash.hashSize; ++i)
+        h.hash[i % newSize] ^= hash.hash[i];
+    return h;
+}
+
+
+HashType parseHashType(const string & s)
+{
+    if (s == "md5") return htMD5;
+    else if (s == "sha1") return htSHA1;
+    else if (s == "sha256") return htSHA256;
+    else return htUnknown;
+}
+
+ 
+string printHashType(HashType ht)
+{
+    if (ht == htMD5) return "md5";
+    else if (ht == htSHA1) return "sha1";
+    else if (ht == htSHA256) return "sha256";
+    else throw Error("cannot print unknown hash type");
+}
+
+ 
+}
diff --git a/nix/libutil/hash.hh b/nix/libutil/hash.hh
new file mode 100644
index 0000000000..8f099c4f07
--- /dev/null
+++ b/nix/libutil/hash.hh
@@ -0,0 +1,113 @@
+#pragma once
+
+#include "types.hh"
+#include "serialise.hh"
+
+
+namespace nix {
+
+
+typedef enum { htUnknown, htMD5, htSHA1, htSHA256 } HashType;
+
+
+const int md5HashSize = 16;
+const int sha1HashSize = 20;
+const int sha256HashSize = 32;
+
+extern const string base32Chars;
+
+
+struct Hash
+{
+    static const unsigned int maxHashSize = 32;
+    unsigned int hashSize;
+    unsigned char hash[maxHashSize];
+
+    HashType type;
+
+    /* Create an unusable hash object. */
+    Hash();
+
+    /* Create a zero-filled hash object. */
+    Hash(HashType type);
+
+    /* Check whether two hash are equal. */
+    bool operator == (const Hash & h2) const;
+
+    /* Check whether two hash are not equal. */
+    bool operator != (const Hash & h2) const;
+
+    /* For sorting. */
+    bool operator < (const Hash & h) const;
+};
+
+
+/* Convert a hash to a hexadecimal representation. */
+string printHash(const Hash & hash);
+
+/* Parse a hexadecimal representation of a hash code. */
+Hash parseHash(HashType ht, const string & s);
+
+/* Returns the length of a base-32 hash representation. */
+unsigned int hashLength32(const Hash & hash);
+
+/* Convert a hash to a base-32 representation. */
+string printHash32(const Hash & hash);
+
+/* Print a hash in base-16 if it's MD5, or base-32 otherwise. */
+string printHash16or32(const Hash & hash);
+
+/* Parse a base-32 representation of a hash code. */
+Hash parseHash32(HashType ht, const string & s);
+
+/* Parse a base-16 or base-32 representation of a hash code. */
+Hash parseHash16or32(HashType ht, const string & s);
+
+/* Verify that the given string is a valid hash code. */
+bool isHash(const string & s);
+
+/* Compute the hash of the given string. */
+Hash hashString(HashType ht, const string & s);
+
+/* Compute the hash of the given file. */
+Hash hashFile(HashType ht, const Path & path);
+
+/* Compute the hash of the given path.  The hash is defined as
+   (essentially) hashString(ht, dumpPath(path)). */
+struct PathFilter;
+extern PathFilter defaultPathFilter;
+typedef std::pair<Hash, unsigned long long> HashResult;
+HashResult hashPath(HashType ht, const Path & path,
+    PathFilter & filter = defaultPathFilter);
+
+/* Compress a hash to the specified number of bytes by cyclically
+   XORing bytes together. */
+Hash compressHash(const Hash & hash, unsigned int newSize);
+
+/* Parse a string representing a hash type. */
+HashType parseHashType(const string & s);
+
+/* And the reverse. */
+string printHashType(HashType ht);
+
+
+struct Ctx;
+
+class HashSink : public BufferedSink
+{
+private:
+    HashType ht;
+    Ctx * ctx;
+    unsigned long long bytes;
+
+public:
+    HashSink(HashType ht);
+    HashSink(const HashSink & h);
+    ~HashSink();
+    void write(const unsigned char * data, size_t len);
+    HashResult finish();
+    HashResult currentHash();
+};
+
+
+}
diff --git a/nix/libutil/serialise.cc b/nix/libutil/serialise.cc
new file mode 100644
index 0000000000..6b71f52c15
--- /dev/null
+++ b/nix/libutil/serialise.cc
@@ -0,0 +1,259 @@
+#include "serialise.hh"
+#include "util.hh"
+
+#include <cstring>
+#include <cerrno>
+
+
+namespace nix {
+
+
+BufferedSink::~BufferedSink()
+{
+    /* We can't call flush() here, because C++ for some insane reason
+       doesn't allow you to call virtual methods from a destructor. */
+    assert(!bufPos);
+    delete[] buffer;
+}
+
+    
+void BufferedSink::operator () (const unsigned char * data, size_t len)
+{
+    if (!buffer) buffer = new unsigned char[bufSize];
+    
+    while (len) {
+        /* Optimisation: bypass the buffer if the data exceeds the
+           buffer size. */
+        if (bufPos + len >= bufSize) {
+            flush();
+            write(data, len);
+            break;
+        }
+        /* Otherwise, copy the bytes to the buffer.  Flush the buffer
+           when it's full. */
+        size_t n = bufPos + len > bufSize ? bufSize - bufPos : len;
+        memcpy(buffer + bufPos, data, n);
+        data += n; bufPos += n; len -= n;
+        if (bufPos == bufSize) flush();
+    }
+}
+
+
+void BufferedSink::flush()
+{
+    if (bufPos == 0) return;
+    size_t n = bufPos;
+    bufPos = 0; // don't trigger the assert() in ~BufferedSink()
+    write(buffer, n);
+}
+
+
+FdSink::~FdSink()
+{
+    try { flush(); } catch (...) { ignoreException(); }
+}
+
+
+void FdSink::write(const unsigned char * data, size_t len)
+{
+    writeFull(fd, data, len);
+}
+
+
+void Source::operator () (unsigned char * data, size_t len)
+{
+    while (len) {
+        size_t n = read(data, len);
+        data += n; len -= n;
+    }
+}
+
+
+BufferedSource::~BufferedSource()
+{
+    delete[] buffer;
+}
+
+
+size_t BufferedSource::read(unsigned char * data, size_t len)
+{
+    if (!buffer) buffer = new unsigned char[bufSize];
+
+    if (!bufPosIn) bufPosIn = readUnbuffered(buffer, bufSize);
+            
+    /* Copy out the data in the buffer. */
+    size_t n = len > bufPosIn - bufPosOut ? bufPosIn - bufPosOut : len;
+    memcpy(data, buffer + bufPosOut, n);
+    bufPosOut += n;
+    if (bufPosIn == bufPosOut) bufPosIn = bufPosOut = 0;
+    return n;
+}
+
+
+bool BufferedSource::hasData()
+{
+    return bufPosOut < bufPosIn;
+}
+
+
+size_t FdSource::readUnbuffered(unsigned char * data, size_t len)
+{
+    ssize_t n;
+    do {
+        checkInterrupt();
+        n = ::read(fd, (char *) data, bufSize);
+    } while (n == -1 && errno == EINTR);
+    if (n == -1) throw SysError("reading from file");
+    if (n == 0) throw EndOfFile("unexpected end-of-file");
+    return n;
+}
+
+
+size_t StringSource::read(unsigned char * data, size_t len)
+{
+    if (pos == s.size()) throw EndOfFile("end of string reached");
+    size_t n = s.copy((char *) data, len, pos);
+    pos += n;
+    return n;
+}
+
+
+void writePadding(size_t len, Sink & sink)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        memset(zero, 0, sizeof(zero));
+        sink(zero, 8 - (len % 8));
+    }
+}
+
+
+void writeInt(unsigned int n, Sink & sink)
+{
+    unsigned char buf[8];
+    memset(buf, 0, sizeof(buf));
+    buf[0] = n & 0xff;
+    buf[1] = (n >> 8) & 0xff;
+    buf[2] = (n >> 16) & 0xff;
+    buf[3] = (n >> 24) & 0xff;
+    sink(buf, sizeof(buf));
+}
+
+
+void writeLongLong(unsigned long long n, Sink & sink)
+{
+    unsigned char buf[8];
+    buf[0] = n & 0xff;
+    buf[1] = (n >> 8) & 0xff;
+    buf[2] = (n >> 16) & 0xff;
+    buf[3] = (n >> 24) & 0xff;
+    buf[4] = (n >> 32) & 0xff;
+    buf[5] = (n >> 40) & 0xff;
+    buf[6] = (n >> 48) & 0xff;
+    buf[7] = (n >> 56) & 0xff;
+    sink(buf, sizeof(buf));
+}
+
+
+void writeString(const unsigned char * buf, size_t len, Sink & sink)
+{
+    writeInt(len, sink);
+    sink(buf, len);
+    writePadding(len, sink);
+}
+
+
+void writeString(const string & s, Sink & sink)
+{
+    writeString((const unsigned char *) s.data(), s.size(), sink);
+}
+
+
+template<class T> void writeStrings(const T & ss, Sink & sink)
+{
+    writeInt(ss.size(), sink);
+    foreach (typename T::const_iterator, i, ss)
+        writeString(*i, sink);
+}
+
+template void writeStrings(const Paths & ss, Sink & sink);
+template void writeStrings(const PathSet & ss, Sink & sink);
+
+
+void readPadding(size_t len, Source & source)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        size_t n = 8 - (len % 8);
+        source(zero, n);
+        for (unsigned int i = 0; i < n; i++)
+            if (zero[i]) throw SerialisationError("non-zero padding");
+    }
+}
+
+
+unsigned int readInt(Source & source)
+{
+    unsigned char buf[8];
+    source(buf, sizeof(buf));
+    if (buf[4] || buf[5] || buf[6] || buf[7])
+        throw SerialisationError("implementation cannot deal with > 32-bit integers");
+    return
+        buf[0] |
+        (buf[1] << 8) |
+        (buf[2] << 16) |
+        (buf[3] << 24);
+}
+
+
+unsigned long long readLongLong(Source & source)
+{
+    unsigned char buf[8];
+    source(buf, sizeof(buf));
+    return
+        ((unsigned long long) buf[0]) |
+        ((unsigned long long) buf[1] << 8) |
+        ((unsigned long long) buf[2] << 16) |
+        ((unsigned long long) buf[3] << 24) |
+        ((unsigned long long) buf[4] << 32) |
+        ((unsigned long long) buf[5] << 40) |
+        ((unsigned long long) buf[6] << 48) |
+        ((unsigned long long) buf[7] << 56);
+}
+
+
+size_t readString(unsigned char * buf, size_t max, Source & source)
+{
+    size_t len = readInt(source);
+    if (len > max) throw Error("string is too long");
+    source(buf, len);
+    readPadding(len, source);
+    return len;
+}
+
+ 
+string readString(Source & source)
+{
+    size_t len = readInt(source);
+    unsigned char * buf = new unsigned char[len];
+    AutoDeleteArray<unsigned char> d(buf);
+    source(buf, len);
+    readPadding(len, source);
+    return string((char *) buf, len);
+}
+
+ 
+template<class T> T readStrings(Source & source)
+{
+    unsigned int count = readInt(source);
+    T ss;
+    while (count--)
+        ss.insert(ss.end(), readString(source));
+    return ss;
+}
+
+template Paths readStrings(Source & source);
+template PathSet readStrings(Source & source);
+
+
+}
diff --git a/nix/libutil/serialise.hh b/nix/libutil/serialise.hh
new file mode 100644
index 0000000000..e5a9df1d05
--- /dev/null
+++ b/nix/libutil/serialise.hh
@@ -0,0 +1,133 @@
+#pragma once
+
+#include "types.hh"
+
+
+namespace nix {
+
+
+/* Abstract destination of binary data. */
+struct Sink 
+{
+    virtual ~Sink() { }
+    virtual void operator () (const unsigned char * data, size_t len) = 0;
+};
+
+
+/* A buffered abstract sink. */
+struct BufferedSink : Sink
+{
+    size_t bufSize, bufPos;
+    unsigned char * buffer;
+
+    BufferedSink(size_t bufSize = 32 * 1024)
+        : bufSize(bufSize), bufPos(0), buffer(0) { }
+    ~BufferedSink();
+
+    void operator () (const unsigned char * data, size_t len);
+    
+    void flush();
+    
+    virtual void write(const unsigned char * data, size_t len) = 0;
+};
+
+
+/* Abstract source of binary data. */
+struct Source
+{
+    virtual ~Source() { }
+    
+    /* Store exactly ‘len’ bytes in the buffer pointed to by ‘data’.
+       It blocks until all the requested data is available, or throws
+       an error if it is not going to be available.   */
+    void operator () (unsigned char * data, size_t len);
+
+    /* Store up to ‘len’ in the buffer pointed to by ‘data’, and
+       return the number of bytes stored.  If blocks until at least
+       one byte is available. */
+    virtual size_t read(unsigned char * data, size_t len) = 0;
+};
+
+
+/* A buffered abstract source. */
+struct BufferedSource : Source
+{
+    size_t bufSize, bufPosIn, bufPosOut;
+    unsigned char * buffer;
+
+    BufferedSource(size_t bufSize = 32 * 1024)
+        : bufSize(bufSize), bufPosIn(0), bufPosOut(0), buffer(0) { }
+    ~BufferedSource();
+    
+    size_t read(unsigned char * data, size_t len);
+    
+    /* Underlying read call, to be overridden. */
+    virtual size_t readUnbuffered(unsigned char * data, size_t len) = 0;
+
+    bool hasData();
+};
+
+
+/* A sink that writes data to a file descriptor. */
+struct FdSink : BufferedSink
+{
+    int fd;
+
+    FdSink() : fd(-1) { }
+    FdSink(int fd) : fd(fd) { }
+    ~FdSink();
+    
+    void write(const unsigned char * data, size_t len);
+};
+
+
+/* A source that reads data from a file descriptor. */
+struct FdSource : BufferedSource
+{
+    int fd;
+    FdSource() : fd(-1) { }
+    FdSource(int fd) : fd(fd) { }
+    size_t readUnbuffered(unsigned char * data, size_t len);
+};
+
+
+/* A sink that writes data to a string. */
+struct StringSink : Sink
+{
+    string s;
+    void operator () (const unsigned char * data, size_t len)
+    {
+        s.append((const char *) data, len);
+    }
+};
+
+
+/* A source that reads data from a string. */
+struct StringSource : Source
+{
+    const string & s;
+    size_t pos;
+    StringSource(const string & _s) : s(_s), pos(0) { }
+    size_t read(unsigned char * data, size_t len);    
+};
+
+
+void writePadding(size_t len, Sink & sink);
+void writeInt(unsigned int n, Sink & sink);
+void writeLongLong(unsigned long long n, Sink & sink);
+void writeString(const unsigned char * buf, size_t len, Sink & sink);
+void writeString(const string & s, Sink & sink);
+template<class T> void writeStrings(const T & ss, Sink & sink);
+
+void readPadding(size_t len, Source & source);
+unsigned int readInt(Source & source);
+unsigned long long readLongLong(Source & source);
+size_t readString(unsigned char * buf, size_t max, Source & source);
+string readString(Source & source);
+template<class T> T readStrings(Source & source);
+
+
+MakeError(SerialisationError, Error)
+
+
+}
diff --git a/nix/libutil/types.hh b/nix/libutil/types.hh
new file mode 100644
index 0000000000..4b5ce9a78c
--- /dev/null
+++ b/nix/libutil/types.hh
@@ -0,0 +1,86 @@
+#pragma once
+
+#include "config.h"
+
+#include <string>
+#include <list>
+#include <set>
+
+#include <boost/format.hpp>
+
+
+namespace nix {
+
+
+/* Inherit some names from other namespaces for convenience. */
+using std::string;
+using std::list;
+using std::set;
+using std::vector;
+using boost::format;
+
+
+struct FormatOrString
+{
+    string s;
+    FormatOrString(const string & s) : s(s) { };
+    FormatOrString(const format & f) : s(f.str()) { };
+    FormatOrString(const char * s) : s(s) { };
+};
+
+
+/* BaseError should generally not be caught, as it has Interrupted as
+   a subclass. Catch Error instead. */
+class BaseError : public std::exception
+{
+protected:
+    string prefix_; // used for location traces etc.
+    string err;
+public:
+    unsigned int status; // exit status
+    BaseError(const FormatOrString & fs, unsigned int status = 1);
+    ~BaseError() throw () { };
+    const char * what() const throw () { return err.c_str(); }
+    const string & msg() const throw () { return err; }
+    const string & prefix() const throw () { return prefix_; }
+    BaseError & addPrefix(const FormatOrString & fs);
+};
+
+#define MakeError(newClass, superClass) \
+    class newClass : public superClass                  \
+    {                                                   \
+    public:                                             \
+        newClass(const FormatOrString & fs, unsigned int status = 1) : superClass(fs, status) { }; \
+    };
+
+MakeError(Error, BaseError)
+
+class SysError : public Error
+{
+public:
+    int errNo;
+    SysError(const FormatOrString & fs);
+};
+
+
+typedef list<string> Strings;
+typedef set<string> StringSet;
+
+
+/* Paths are just strings. */
+typedef string Path;
+typedef list<Path> Paths;
+typedef set<Path> PathSet;
+
+
+typedef enum {
+    lvlError = 0,
+    lvlInfo,
+    lvlTalkative,
+    lvlChatty,
+    lvlDebug,
+    lvlVomit
+} Verbosity;
+
+
+}
diff --git a/nix/libutil/util.cc b/nix/libutil/util.cc
new file mode 100644
index 0000000000..15c462ce4e
--- /dev/null
+++ b/nix/libutil/util.cc
@@ -0,0 +1,1105 @@
+#include "config.h"
+
+#include <iostream>
+#include <cerrno>
+#include <cstdio>
+#include <cstdlib>
+#include <sstream>
+#include <cstring>
+
+#include <sys/wait.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <limits.h>
+
+#ifdef __APPLE__
+#include <sys/syscall.h>
+#endif
+
+#include "util.hh"
+
+
+extern char * * environ;
+
+
+namespace nix {
+
+
+BaseError::BaseError(const FormatOrString & fs, unsigned int status)
+    : status(status)
+{
+    err = fs.s;
+}
+
+
+BaseError & BaseError::addPrefix(const FormatOrString & fs)
+{
+    prefix_ = fs.s + prefix_;
+    return *this;
+}
+
+
+SysError::SysError(const FormatOrString & fs)
+    : Error(format("%1%: %2%") % fs.s % strerror(errno))
+    , errNo(errno)
+{
+}
+
+
+string getEnv(const string & key, const string & def)
+{
+    char * value = getenv(key.c_str());
+    return value ? string(value) : def;
+}
+
+
+Path absPath(Path path, Path dir)
+{
+    if (path[0] != '/') {
+        if (dir == "") {
+#ifdef __GNU__
+            /* GNU (aka. GNU/Hurd) doesn't have any limitation on path
+               lengths and doesn't define `PATH_MAX'.  */
+            char *buf = getcwd(NULL, 0);
+            if (buf == NULL)
+#else
+            char buf[PATH_MAX];
+            if (!getcwd(buf, sizeof(buf)))
+#endif
+                throw SysError("cannot get cwd");
+            dir = buf;
+#ifdef __GNU__
+            free(buf);
+#endif
+        }
+        path = dir + "/" + path;
+    }
+    return canonPath(path);
+}
+
+
+Path canonPath(const Path & path, bool resolveSymlinks)
+{
+    string s;
+
+    if (path[0] != '/')
+        throw Error(format("not an absolute path: `%1%'") % path);
+
+    string::const_iterator i = path.begin(), end = path.end();
+    string temp;
+
+    /* Count the number of times we follow a symlink and stop at some
+       arbitrary (but high) limit to prevent infinite loops. */
+    unsigned int followCount = 0, maxFollow = 1024;
+
+    while (1) {
+
+        /* Skip slashes. */
+        while (i != end && *i == '/') i++;
+        if (i == end) break;
+
+        /* Ignore `.'. */
+        if (*i == '.' && (i + 1 == end || i[1] == '/'))
+            i++;
+
+        /* If `..', delete the last component. */
+        else if (*i == '.' && i + 1 < end && i[1] == '.' &&
+            (i + 2 == end || i[2] == '/'))
+        {
+            if (!s.empty()) s.erase(s.rfind('/'));
+            i += 2;
+        }
+
+        /* Normal component; copy it. */
+        else {
+            s += '/';
+            while (i != end && *i != '/') s += *i++;
+
+            /* If s points to a symlink, resolve it and restart (since
+               the symlink target might contain new symlinks). */
+            if (resolveSymlinks && isLink(s)) {
+                if (++followCount >= maxFollow)
+                    throw Error(format("infinite symlink recursion in path `%1%'") % path);
+                temp = absPath(readLink(s), dirOf(s))
+                    + string(i, end);
+                i = temp.begin(); /* restart */
+                end = temp.end();
+                s = "";
+                /* !!! potential for infinite loop */
+            }
+        }
+    }
+
+    return s.empty() ? "/" : s;
+}
+
+
+Path dirOf(const Path & path)
+{
+    Path::size_type pos = path.rfind('/');
+    if (pos == string::npos)
+        throw Error(format("invalid file name `%1%'") % path);
+    return pos == 0 ? "/" : Path(path, 0, pos);
+}
+
+
+string baseNameOf(const Path & path)
+{
+    Path::size_type pos = path.rfind('/');
+    if (pos == string::npos)
+        throw Error(format("invalid file name `%1%'") % path);
+    return string(path, pos + 1);
+}
+
+
+bool isInDir(const Path & path, const Path & dir)
+{
+    return path[0] == '/'
+        && string(path, 0, dir.size()) == dir
+        && path.size() >= dir.size() + 2
+        && path[dir.size()] == '/';
+}
+
+
+struct stat lstat(const Path & path)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting status of `%1%'") % path);
+    return st;
+}
+
+
+bool pathExists(const Path & path)
+{
+    int res;
+    struct stat st;
+    res = lstat(path.c_str(), &st);
+    if (!res) return true;
+    if (errno != ENOENT && errno != ENOTDIR)
+        throw SysError(format("getting status of %1%") % path);
+    return false;
+}
+
+
+Path readLink(const Path & path)
+{
+    checkInterrupt();
+    struct stat st = lstat(path);
+    if (!S_ISLNK(st.st_mode))
+        throw Error(format("`%1%' is not a symlink") % path);
+    char buf[st.st_size];
+    if (readlink(path.c_str(), buf, st.st_size) != st.st_size)
+        throw SysError(format("reading symbolic link `%1%'") % path);
+    return string(buf, st.st_size);
+}
+
+
+bool isLink(const Path & path)
+{
+    struct stat st = lstat(path);
+    return S_ISLNK(st.st_mode);
+}
+
+
+Strings readDirectory(const Path & path)
+{
+    Strings names;
+
+    AutoCloseDir dir = opendir(path.c_str());
+    if (!dir) throw SysError(format("opening directory `%1%'") % path);
+
+    struct dirent * dirent;
+    while (errno = 0, dirent = readdir(dir)) { /* sic */
+        checkInterrupt();
+        string name = dirent->d_name;
+        if (name == "." || name == "..") continue;
+        names.push_back(name);
+    }
+    if (errno) throw SysError(format("reading directory `%1%'") % path);
+
+    return names;
+}
+
+
+string readFile(int fd)
+{
+    struct stat st;
+    if (fstat(fd, &st) == -1)
+        throw SysError("statting file");
+
+    unsigned char * buf = new unsigned char[st.st_size];
+    AutoDeleteArray<unsigned char> d(buf);
+    readFull(fd, buf, st.st_size);
+
+    return string((char *) buf, st.st_size);
+}
+
+
+string readFile(const Path & path, bool drain)
+{
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1)
+        throw SysError(format("opening file `%1%'") % path);
+    return drain ? drainFD(fd) : readFile(fd);
+}
+
+
+void writeFile(const Path & path, const string & s)
+{
+    AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
+    if (fd == -1)
+        throw SysError(format("opening file `%1%'") % path);
+    writeFull(fd, (unsigned char *) s.data(), s.size());
+}
+
+
+string readLine(int fd)
+{
+    string s;
+    while (1) {
+        checkInterrupt();
+        char ch;
+        ssize_t rd = read(fd, &ch, 1);
+        if (rd == -1) {
+            if (errno != EINTR)
+                throw SysError("reading a line");
+        } else if (rd == 0)
+            throw EndOfFile("unexpected EOF reading a line");
+        else {
+            if (ch == '\n') return s;
+            s += ch;
+        }
+    }
+}
+
+
+void writeLine(int fd, string s)
+{
+    s += '\n';
+    writeFull(fd, (const unsigned char *) s.data(), s.size());
+}
+
+
+static void _deletePath(const Path & path, unsigned long long & bytesFreed)
+{
+    checkInterrupt();
+
+    printMsg(lvlVomit, format("%1%") % path);
+
+    struct stat st = lstat(path);
+
+    if (!S_ISDIR(st.st_mode) && st.st_nlink == 1)
+        bytesFreed += st.st_blocks * 512;
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+
+        /* Make the directory writable. */
+        if (!(st.st_mode & S_IWUSR)) {
+            if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
+                throw SysError(format("making `%1%' writable") % path);
+        }
+
+        for (Strings::iterator i = names.begin(); i != names.end(); ++i)
+            _deletePath(path + "/" + *i, bytesFreed);
+    }
+
+    if (remove(path.c_str()) == -1)
+        throw SysError(format("cannot unlink `%1%'") % path);
+}
+
+
+void deletePath(const Path & path)
+{
+    unsigned long long dummy;
+    deletePath(path, dummy);
+}
+
+
+void deletePath(const Path & path, unsigned long long & bytesFreed)
+{
+    startNest(nest, lvlDebug,
+        format("recursively deleting path `%1%'") % path);
+    bytesFreed = 0;
+    _deletePath(path, bytesFreed);
+}
+
+
+static Path tempName(Path tmpRoot, const Path & prefix, bool includePid,
+    int & counter)
+{
+    tmpRoot = canonPath(tmpRoot.empty() ? getEnv("TMPDIR", "/tmp") : tmpRoot, true);
+    if (includePid)
+        return (format("%1%/%2%-%3%-%4%") % tmpRoot % prefix % getpid() % counter++).str();
+    else
+        return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
+}
+
+
+Path createTempDir(const Path & tmpRoot, const Path & prefix,
+    bool includePid, bool useGlobalCounter, mode_t mode)
+{
+    static int globalCounter = 0;
+    int localCounter = 0;
+    int & counter(useGlobalCounter ? globalCounter : localCounter);
+
+    while (1) {
+        checkInterrupt();
+        Path tmpDir = tempName(tmpRoot, prefix, includePid, counter);
+        if (mkdir(tmpDir.c_str(), mode) == 0) {
+            /* Explicitly set the group of the directory.  This is to
+               work around around problems caused by BSD's group
+               ownership semantics (directories inherit the group of
+               the parent).  For instance, the group of /tmp on
+               FreeBSD is "wheel", so all directories created in /tmp
+               will be owned by "wheel"; but if the user is not in
+               "wheel", then "tar" will fail to unpack archives that
+               have the setgid bit set on directories. */
+            if (chown(tmpDir.c_str(), (uid_t) -1, getegid()) != 0)
+                throw SysError(format("setting group of directory `%1%'") % tmpDir);
+            return tmpDir;
+        }
+        if (errno != EEXIST)
+            throw SysError(format("creating directory `%1%'") % tmpDir);
+    }
+}
+
+
+Paths createDirs(const Path & path)
+{
+    Paths created;
+    if (path == "/") return created;
+
+    struct stat st;
+    if (lstat(path.c_str(), &st) == -1) {
+        created = createDirs(dirOf(path));
+        if (mkdir(path.c_str(), 0777) == -1 && errno != EEXIST)
+            throw SysError(format("creating directory `%1%'") % path);
+        st = lstat(path);
+        created.push_back(path);
+    }
+
+    if (!S_ISDIR(st.st_mode)) throw Error(format("`%1%' is not a directory") % path);
+
+    return created;
+}
+
+
+void createSymlink(const Path & target, const Path & link)
+{
+    if (symlink(target.c_str(), link.c_str()))
+        throw SysError(format("creating symlink from `%1%' to `%2%'") % link % target);
+}
+
+
+LogType logType = ltPretty;
+Verbosity verbosity = lvlInfo;
+
+static int nestingLevel = 0;
+
+
+Nest::Nest()
+{
+    nest = false;
+}
+
+
+Nest::~Nest()
+{
+    close();
+}
+
+
+static string escVerbosity(Verbosity level)
+{
+    return int2String((int) level);
+}
+
+
+void Nest::open(Verbosity level, const FormatOrString & fs)
+{
+    if (level <= verbosity) {
+        if (logType == ltEscapes)
+            std::cerr << "\033[" << escVerbosity(level) << "p"
+                      << fs.s << "\n";
+        else
+            printMsg_(level, fs);
+        nest = true;
+        nestingLevel++;
+    }
+}
+
+
+void Nest::close()
+{
+    if (nest) {
+        nestingLevel--;
+        if (logType == ltEscapes)
+            std::cerr << "\033[q";
+        nest = false;
+    }
+}
+
+
+void printMsg_(Verbosity level, const FormatOrString & fs)
+{
+    checkInterrupt();
+    if (level > verbosity) return;
+    string prefix;
+    if (logType == ltPretty)
+        for (int i = 0; i < nestingLevel; i++)
+            prefix += "|   ";
+    else if (logType == ltEscapes && level != lvlInfo)
+        prefix = "\033[" + escVerbosity(level) + "s";
+    string s = (format("%1%%2%\n") % prefix % fs.s).str();
+    writeToStderr(s);
+}
+
+
+void warnOnce(bool & haveWarned, const FormatOrString & fs)
+{
+    if (!haveWarned) {
+        printMsg(lvlError, format("warning: %1%") % fs.s);
+        haveWarned = true;
+    }
+}
+
+
+void writeToStderr(const string & s)
+{
+    try {
+        _writeToStderr((const unsigned char *) s.data(), s.size());
+    } catch (SysError & e) {
+        /* Ignore failing writes to stderr if we're in an exception
+           handler, otherwise throw an exception.  We need to ignore
+           write errors in exception handlers to ensure that cleanup
+           code runs to completion if the other side of stderr has
+           been closed unexpectedly. */
+        if (!std::uncaught_exception()) throw;
+    }
+}
+
+
+static void defaultWriteToStderr(const unsigned char * buf, size_t count)
+{
+    writeFull(STDERR_FILENO, buf, count);
+}
+
+
+void (*_writeToStderr) (const unsigned char * buf, size_t count) = defaultWriteToStderr;
+
+
+void readFull(int fd, unsigned char * buf, size_t count)
+{
+    while (count) {
+        checkInterrupt();
+        ssize_t res = read(fd, (char *) buf, count);
+        if (res == -1) {
+            if (errno == EINTR) continue;
+            throw SysError("reading from file");
+        }
+        if (res == 0) throw EndOfFile("unexpected end-of-file");
+        count -= res;
+        buf += res;
+    }
+}
+
+
+void writeFull(int fd, const unsigned char * buf, size_t count)
+{
+    while (count) {
+        checkInterrupt();
+        ssize_t res = write(fd, (char *) buf, count);
+        if (res == -1) {
+            if (errno == EINTR) continue;
+            throw SysError("writing to file");
+        }
+        count -= res;
+        buf += res;
+    }
+}
+
+
+string drainFD(int fd)
+{
+    string result;
+    unsigned char buffer[4096];
+    while (1) {
+        checkInterrupt();
+        ssize_t rd = read(fd, buffer, sizeof buffer);
+        if (rd == -1) {
+            if (errno != EINTR)
+                throw SysError("reading from file");
+        }
+        else if (rd == 0) break;
+        else result.append((char *) buffer, rd);
+    }
+    return result;
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+AutoDelete::AutoDelete(const string & p, bool recursive) : path(p)
+{
+    del = true;
+    this->recursive = recursive;
+}
+
+AutoDelete::~AutoDelete()
+{
+    try {
+        if (del) {
+            if (recursive)
+                deletePath(path);
+            else {
+                if (remove(path.c_str()) == -1)
+                    throw SysError(format("cannot unlink `%1%'") % path);
+            }
+        }
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+void AutoDelete::cancel()
+{
+    del = false;
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+AutoCloseFD::AutoCloseFD()
+{
+    fd = -1;
+}
+
+
+AutoCloseFD::AutoCloseFD(int fd)
+{
+    this->fd = fd;
+}
+
+
+AutoCloseFD::AutoCloseFD(const AutoCloseFD & fd)
+{
+    /* Copying an AutoCloseFD isn't allowed (who should get to close
+       it?).  But as an edge case, allow copying of closed
+       AutoCloseFDs.  This is necessary due to tiresome reasons
+       involving copy constructor use on default object values in STL
+       containers (like when you do `map[value]' where value isn't in
+       the map yet). */
+    this->fd = fd.fd;
+    if (this->fd != -1) abort();
+}
+
+
+AutoCloseFD::~AutoCloseFD()
+{
+    try {
+        close();
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void AutoCloseFD::operator =(int fd)
+{
+    if (this->fd != fd) close();
+    this->fd = fd;
+}
+
+
+AutoCloseFD::operator int() const
+{
+    return fd;
+}
+
+
+void AutoCloseFD::close()
+{
+    if (fd != -1) {
+        if (::close(fd) == -1)
+            /* This should never happen. */
+            throw SysError(format("closing file descriptor %1%") % fd);
+        fd = -1;
+    }
+}
+
+
+bool AutoCloseFD::isOpen()
+{
+    return fd != -1;
+}
+
+
+/* Pass responsibility for closing this fd to the caller. */
+int AutoCloseFD::borrow()
+{
+    int oldFD = fd;
+    fd = -1;
+    return oldFD;
+}
+
+
+void Pipe::create()
+{
+    int fds[2];
+    if (pipe(fds) != 0) throw SysError("creating pipe");
+    readSide = fds[0];
+    writeSide = fds[1];
+    closeOnExec(readSide);
+    closeOnExec(writeSide);
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+AutoCloseDir::AutoCloseDir()
+{
+    dir = 0;
+}
+
+
+AutoCloseDir::AutoCloseDir(DIR * dir)
+{
+    this->dir = dir;
+}
+
+
+AutoCloseDir::~AutoCloseDir()
+{
+    close();
+}
+
+
+void AutoCloseDir::operator =(DIR * dir)
+{
+    this->dir = dir;
+}
+
+
+AutoCloseDir::operator DIR *()
+{
+    return dir;
+}
+
+
+void AutoCloseDir::close()
+{
+    if (dir) {
+        closedir(dir);
+        dir = 0;
+    }
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+Pid::Pid()
+{
+    pid = -1;
+    separatePG = false;
+    killSignal = SIGKILL;
+}
+
+
+Pid::~Pid()
+{
+    kill();
+}
+
+
+void Pid::operator =(pid_t pid)
+{
+    if (this->pid != pid) kill();
+    this->pid = pid;
+    killSignal = SIGKILL; // reset signal to default
+}
+
+
+Pid::operator pid_t()
+{
+    return pid;
+}
+
+
+void Pid::kill()
+{
+    if (pid == -1 || pid == 0) return;
+
+    printMsg(lvlError, format("killing process %1%") % pid);
+
+    /* Send the requested signal to the child.  If it has its own
+       process group, send the signal to every process in the child
+       process group (which hopefully includes *all* its children). */
+    if (::kill(separatePG ? -pid : pid, killSignal) != 0)
+        printMsg(lvlError, (SysError(format("killing process %1%") % pid).msg()));
+
+    /* Wait until the child dies, disregarding the exit status. */
+    int status;
+    while (waitpid(pid, &status, 0) == -1) {
+        checkInterrupt();
+        if (errno != EINTR) {
+            printMsg(lvlError,
+                (SysError(format("waiting for process %1%") % pid).msg()));
+            break;
+        }
+    }
+
+    pid = -1;
+}
+
+
+int Pid::wait(bool block)
+{
+    assert(pid != -1);
+    while (1) {
+        int status;
+        int res = waitpid(pid, &status, block ? 0 : WNOHANG);
+        if (res == pid) {
+            pid = -1;
+            return status;
+        }
+        if (res == 0 && !block) return -1;
+        if (errno != EINTR)
+            throw SysError("cannot get child exit status");
+        checkInterrupt();
+    }
+}
+
+
+void Pid::setSeparatePG(bool separatePG)
+{
+    this->separatePG = separatePG;
+}
+
+
+void Pid::setKillSignal(int signal)
+{
+    this->killSignal = signal;
+}
+
+
+void killUser(uid_t uid)
+{
+    debug(format("killing all processes running under uid `%1%'") % uid);
+
+    assert(uid != 0); /* just to be safe... */
+
+    /* The system call kill(-1, sig) sends the signal `sig' to all
+       users to which the current process can send signals.  So we
+       fork a process, switch to uid, and send a mass kill. */
+
+    Pid pid;
+    pid = fork();
+    switch (pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0:
+        try { /* child */
+
+            if (setuid(uid) == -1)
+                throw SysError("setting uid");
+
+            while (true) {
+#ifdef __APPLE__
+                /* OSX's kill syscall takes a third parameter that, among other
+                   things, determines if kill(-1, signo) affects the calling
+                   process. In the OSX libc, it's set to true, which means
+                   "follow POSIX", which we don't want here
+                 */
+                if (syscall(SYS_kill, -1, SIGKILL, false) == 0) break;
+#else
+                if (kill(-1, SIGKILL) == 0) break;
+#endif
+                if (errno == ESRCH) break; /* no more processes */
+                if (errno != EINTR)
+                    throw SysError(format("cannot kill processes for uid `%1%'") % uid);
+            }
+
+        } catch (std::exception & e) {
+            writeToStderr((format("killing processes belonging to uid `%1%': %2%\n") % uid % e.what()).str());
+            _exit(1);
+        }
+        _exit(0);
+    }
+
+    /* parent */
+    int status = pid.wait(true);
+    if (status != 0)
+        throw Error(format("cannot kill processes for uid `%1%': %2%") % uid % statusToString(status));
+
+    /* !!! We should really do some check to make sure that there are
+       no processes left running under `uid', but there is no portable
+       way to do so (I think).  The most reliable way may be `ps -eo
+       uid | grep -q $uid'. */
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+string runProgram(Path program, bool searchPath, const Strings & args)
+{
+    checkInterrupt();
+
+    std::vector<const char *> cargs; /* careful with c_str()! */
+    cargs.push_back(program.c_str());
+    for (Strings::const_iterator i = args.begin(); i != args.end(); ++i)
+        cargs.push_back(i->c_str());
+    cargs.push_back(0);
+
+    /* Create a pipe. */
+    Pipe pipe;
+    pipe.create();
+
+    /* Fork. */
+    Pid pid;
+    pid = maybeVfork();
+
+    switch (pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0: /* child */
+        try {
+            if (dup2(pipe.writeSide, STDOUT_FILENO) == -1)
+                throw SysError("dupping stdout");
+
+            if (searchPath)
+                execvp(program.c_str(), (char * *) &cargs[0]);
+            else
+                execv(program.c_str(), (char * *) &cargs[0]);
+            throw SysError(format("executing `%1%'") % program);
+
+        } catch (std::exception & e) {
+            writeToStderr("error: " + string(e.what()) + "\n");
+        }
+        _exit(1);
+    }
+
+    /* Parent. */
+
+    pipe.writeSide.close();
+
+    string result = drainFD(pipe.readSide);
+
+    /* Wait for the child to finish. */
+    int status = pid.wait(true);
+    if (!statusOk(status))
+        throw Error(format("program `%1%' %2%")
+            % program % statusToString(status));
+
+    return result;
+}
+
+
+void closeMostFDs(const set<int> & exceptions)
+{
+    int maxFD = 0;
+    maxFD = sysconf(_SC_OPEN_MAX);
+    for (int fd = 0; fd < maxFD; ++fd)
+        if (fd != STDIN_FILENO && fd != STDOUT_FILENO && fd != STDERR_FILENO
+            && exceptions.find(fd) == exceptions.end())
+            close(fd); /* ignore result */
+}
+
+
+void closeOnExec(int fd)
+{
+    int prev;
+    if ((prev = fcntl(fd, F_GETFD, 0)) == -1 ||
+        fcntl(fd, F_SETFD, prev | FD_CLOEXEC) == -1)
+        throw SysError("setting close-on-exec flag");
+}
+
+
+#if HAVE_VFORK
+pid_t (*maybeVfork)() = vfork;
+#else
+pid_t (*maybeVfork)() = fork;
+#endif
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+volatile sig_atomic_t _isInterrupted = 0;
+
+void _interrupted()
+{
+    /* Block user interrupts while an exception is being handled.
+       Throwing an exception while another exception is being handled
+       kills the program! */
+    if (!std::uncaught_exception()) {
+        _isInterrupted = 0;
+        throw Interrupted("interrupted by the user");
+    }
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+template<class C> C tokenizeString(const string & s, const string & separators)
+{
+    C result;
+    string::size_type pos = s.find_first_not_of(separators, 0);
+    while (pos != string::npos) {
+        string::size_type end = s.find_first_of(separators, pos + 1);
+        if (end == string::npos) end = s.size();
+        string token(s, pos, end - pos);
+        result.insert(result.end(), token);
+        pos = s.find_first_not_of(separators, end);
+    }
+    return result;
+}
+
+template Strings tokenizeString(const string & s, const string & separators);
+template StringSet tokenizeString(const string & s, const string & separators);
+template vector<string> tokenizeString(const string & s, const string & separators);
+
+
+string concatStringsSep(const string & sep, const Strings & ss)
+{
+    string s;
+    foreach (Strings::const_iterator, i, ss) {
+        if (s.size() != 0) s += sep;
+        s += *i;
+    }
+    return s;
+}
+
+
+string concatStringsSep(const string & sep, const StringSet & ss)
+{
+    string s;
+    foreach (StringSet::const_iterator, i, ss) {
+        if (s.size() != 0) s += sep;
+        s += *i;
+    }
+    return s;
+}
+
+
+string chomp(const string & s)
+{
+    size_t i = s.find_last_not_of(" \n\r\t");
+    return i == string::npos ? "" : string(s, 0, i + 1);
+}
+
+
+string statusToString(int status)
+{
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+        if (WIFEXITED(status))
+            return (format("failed with exit code %1%") % WEXITSTATUS(status)).str();
+        else if (WIFSIGNALED(status)) {
+            int sig = WTERMSIG(status);
+#if HAVE_STRSIGNAL
+            const char * description = strsignal(sig);
+            return (format("failed due to signal %1% (%2%)") % sig % description).str();
+#else
+            return (format("failed due to signal %1%") % sig).str();
+#endif
+        }
+        else
+            return "died abnormally";
+    } else return "succeeded";
+}
+
+
+bool statusOk(int status)
+{
+    return WIFEXITED(status) && WEXITSTATUS(status) == 0;
+}
+
+
+bool hasSuffix(const string & s, const string & suffix)
+{
+    return s.size() >= suffix.size() && string(s, s.size() - suffix.size()) == suffix;
+}
+
+
+void expect(std::istream & str, const string & s)
+{
+    char s2[s.size()];
+    str.read(s2, s.size());
+    if (string(s2, s.size()) != s)
+        throw Error(format("expected string `%1%'") % s);
+}
+
+
+string parseString(std::istream & str)
+{
+    string res;
+    expect(str, "\"");
+    int c;
+    while ((c = str.get()) != '"')
+        if (c == '\\') {
+            c = str.get();
+            if (c == 'n') res += '\n';
+            else if (c == 'r') res += '\r';
+            else if (c == 't') res += '\t';
+            else res += c;
+        }
+        else res += c;
+    return res;
+}
+
+
+bool endOfList(std::istream & str)
+{
+    if (str.peek() == ',') {
+        str.get();
+        return false;
+    }
+    if (str.peek() == ']') {
+        str.get();
+        return true;
+    }
+    return false;
+}
+
+
+string decodeOctalEscaped(const string & s)
+{
+    string r;
+    for (string::const_iterator i = s.begin(); i != s.end(); ) {
+        if (*i != '\\') { r += *i++; continue; }
+        unsigned char c = 0;
+        ++i;
+        while (i != s.end() && *i >= '0' && *i < '8')
+            c = c * 8 + (*i++ - '0');
+        r += c;
+    }
+    return r;
+}
+
+
+void ignoreException()
+{
+    try {
+        throw;
+    } catch (std::exception & e) {
+        printMsg(lvlError, format("error (ignored): %1%") % e.what());
+    }
+}
+
+
+}
diff --git a/nix/libutil/util.hh b/nix/libutil/util.hh
new file mode 100644
index 0000000000..8bedfea9a0
--- /dev/null
+++ b/nix/libutil/util.hh
@@ -0,0 +1,349 @@
+#pragma once
+
+#include "types.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <unistd.h>
+#include <signal.h>
+
+#include <cstdio>
+
+
+namespace nix {
+
+
+#define foreach(it_type, it, collection)                                \
+    for (it_type it = (collection).begin(); it != (collection).end(); ++it)
+
+#define foreach_reverse(it_type, it, collection)                                \
+    for (it_type it = (collection).rbegin(); it != (collection).rend(); ++it)
+
+
+/* Return an environment variable. */
+string getEnv(const string & key, const string & def = "");
+
+/* Return an absolutized path, resolving paths relative to the
+   specified directory, or the current directory otherwise.  The path
+   is also canonicalised. */
+Path absPath(Path path, Path dir = "");
+
+/* Canonicalise a path by removing all `.' or `..' components and
+   double or trailing slashes.  Optionally resolves all symlink
+   components such that each component of the resulting path is *not*
+   a symbolic link. */
+Path canonPath(const Path & path, bool resolveSymlinks = false);
+
+/* Return the directory part of the given canonical path, i.e.,
+   everything before the final `/'.  If the path is the root or an
+   immediate child thereof (e.g., `/foo'), this means an empty string
+   is returned. */
+Path dirOf(const Path & path);
+
+/* Return the base name of the given canonical path, i.e., everything
+   following the final `/'. */
+string baseNameOf(const Path & path);
+
+/* Check whether a given path is a descendant of the given
+   directory. */
+bool isInDir(const Path & path, const Path & dir);
+
+/* Get status of `path'. */
+struct stat lstat(const Path & path);
+
+/* Return true iff the given path exists. */
+bool pathExists(const Path & path);
+
+/* Read the contents (target) of a symbolic link.  The result is not
+   in any way canonicalised. */
+Path readLink(const Path & path);
+
+bool isLink(const Path & path);
+
+/* Read the contents of a directory.  The entries `.' and `..' are
+   removed. */
+Strings readDirectory(const Path & path);
+
+/* Read the contents of a file into a string. */
+string readFile(int fd);
+string readFile(const Path & path, bool drain = false);
+
+/* Write a string to a file. */
+void writeFile(const Path & path, const string & s);
+
+/* Read a line from a file descriptor. */
+string readLine(int fd);
+
+/* Write a line to a file descriptor. */
+void writeLine(int fd, string s);
+
+/* Delete a path; i.e., in the case of a directory, it is deleted
+   recursively.  Don't use this at home, kids.  The second variant
+   returns the number of bytes and blocks freed. */
+void deletePath(const Path & path);
+
+void deletePath(const Path & path, unsigned long long & bytesFreed);
+
+/* Create a temporary directory. */
+Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",
+    bool includePid = true, bool useGlobalCounter = true, mode_t mode = 0755);
+
+/* Create a directory and all its parents, if necessary.  Returns the
+   list of created directories, in order of creation. */
+Paths createDirs(const Path & path);
+
+/* Create a symlink. */
+void createSymlink(const Path & target, const Path & link);
+
+
+template<class T, class A>
+T singleton(const A & a)
+{
+    T t;
+    t.insert(a);
+    return t;
+}
+
+
+/* Messages. */
+
+
+typedef enum {
+    ltPretty,   /* nice, nested output */
+    ltEscapes,  /* nesting indicated using escape codes (for log2xml) */
+    ltFlat      /* no nesting */
+} LogType;
+
+extern LogType logType;
+extern Verbosity verbosity; /* suppress msgs > this */
+
+class Nest
+{
+private:
+    bool nest;
+public:
+    Nest();
+    ~Nest();
+    void open(Verbosity level, const FormatOrString & fs);
+    void close();
+};
+
+void printMsg_(Verbosity level, const FormatOrString & fs);
+
+#define startNest(varName, level, f) \
+    Nest varName; \
+    if (level <= verbosity) { \
+      varName.open(level, (f)); \
+    }
+
+#define printMsg(level, f) \
+    do { \
+        if (level <= verbosity) { \
+            printMsg_(level, (f)); \
+        } \
+    } while (0)
+
+#define debug(f) printMsg(lvlDebug, f)
+
+void warnOnce(bool & haveWarned, const FormatOrString & fs);
+
+void writeToStderr(const string & s);
+
+extern void (*_writeToStderr) (const unsigned char * buf, size_t count);
+
+
+/* Wrappers arount read()/write() that read/write exactly the
+   requested number of bytes. */
+void readFull(int fd, unsigned char * buf, size_t count);
+void writeFull(int fd, const unsigned char * buf, size_t count);
+
+MakeError(EndOfFile, Error)
+
+
+/* Read a file descriptor until EOF occurs. */
+string drainFD(int fd);
+
+
+
+/* Automatic cleanup of resources. */
+
+
+template <class T>
+struct AutoDeleteArray
+{
+    T * p;
+    AutoDeleteArray(T * p) : p(p) { }
+    ~AutoDeleteArray()
+    {
+        delete [] p;
+    }
+};
+
+
+class AutoDelete
+{
+    Path path;
+    bool del;
+    bool recursive;
+public:
+    AutoDelete(const Path & p, bool recursive = true);
+    ~AutoDelete();
+    void cancel();
+};
+
+
+class AutoCloseFD
+{
+    int fd;
+public:
+    AutoCloseFD();
+    AutoCloseFD(int fd);
+    AutoCloseFD(const AutoCloseFD & fd);
+    ~AutoCloseFD();
+    void operator =(int fd);
+    operator int() const;
+    void close();
+    bool isOpen();
+    int borrow();
+};
+
+
+class Pipe
+{
+public:
+    AutoCloseFD readSide, writeSide;
+    void create();
+};
+
+
+class AutoCloseDir
+{
+    DIR * dir;
+public:
+    AutoCloseDir();
+    AutoCloseDir(DIR * dir);
+    ~AutoCloseDir();
+    void operator =(DIR * dir);
+    operator DIR *();
+    void close();
+};
+
+
+class Pid
+{
+    pid_t pid;
+    bool separatePG;
+    int killSignal;
+public:
+    Pid();
+    ~Pid();
+    void operator =(pid_t pid);
+    operator pid_t();
+    void kill();
+    int wait(bool block);
+    void setSeparatePG(bool separatePG);
+    void setKillSignal(int signal);
+};
+
+
+/* Kill all processes running under the specified uid by sending them
+   a SIGKILL. */
+void killUser(uid_t uid);
+
+
+/* Run a program and return its stdout in a string (i.e., like the
+   shell backtick operator). */
+string runProgram(Path program, bool searchPath = false,
+    const Strings & args = Strings());
+
+/* Close all file descriptors except stdin, stdout, stderr, and those
+   listed in the given set.  Good practice in child processes. */
+void closeMostFDs(const set<int> & exceptions);
+
+/* Set the close-on-exec flag for the given file descriptor. */
+void closeOnExec(int fd);
+
+/* Call vfork() if available, otherwise fork(). */
+extern pid_t (*maybeVfork)();
+
+
+/* User interruption. */
+
+extern volatile sig_atomic_t _isInterrupted;
+
+void _interrupted();
+
+void inline checkInterrupt()
+{
+    if (_isInterrupted) _interrupted();
+}
+
+MakeError(Interrupted, BaseError)
+
+
+/* String tokenizer. */
+template<class C> C tokenizeString(const string & s, const string & separators = " \t\n\r");
+
+
+/* Concatenate the given strings with a separator between the
+   elements. */
+string concatStringsSep(const string & sep, const Strings & ss);
+string concatStringsSep(const string & sep, const StringSet & ss);
+
+
+/* Remove trailing whitespace from a string. */
+string chomp(const string & s);
+
+
+/* Convert the exit status of a child as returned by wait() into an
+   error string. */
+string statusToString(int status);
+
+bool statusOk(int status);
+
+
+/* Parse a string into an integer. */
+template<class N> bool string2Int(const string & s, N & n)
+{
+    std::istringstream str(s);
+    str >> n;
+    return str && str.get() == EOF;
+}
+
+template<class N> string int2String(N n)
+{
+    std::ostringstream str;
+    str << n;
+    return str.str();
+}
+
+
+/* Return true iff `s' ends in `suffix'. */
+bool hasSuffix(const string & s, const string & suffix);
+
+
+/* Read string `s' from stream `str'. */
+void expect(std::istream & str, const string & s);
+
+
+/* Read a C-style string from stream `str'. */
+string parseString(std::istream & str);
+
+
+/* Utility function used to parse legacy ATerms. */
+bool endOfList(std::istream & str);
+
+
+/* Escape a string that contains octal-encoded escape codes such as
+   used in /etc/fstab and /proc/mounts (e.g. "foo\040bar" decodes to
+   "foo bar"). */
+string decodeOctalEscaped(const string & s);
+
+
+/* Exception handling in destructors: print an error message, then
+   ignore the exception. */
+void ignoreException();
+
+
+}
diff --git a/nix/libutil/xml-writer.cc b/nix/libutil/xml-writer.cc
new file mode 100644
index 0000000000..01794001b2
--- /dev/null
+++ b/nix/libutil/xml-writer.cc
@@ -0,0 +1,94 @@
+#include <assert.h>
+
+#include "xml-writer.hh"
+
+
+namespace nix {
+    
+
+XMLWriter::XMLWriter(bool indent, std::ostream & output)
+    : output(output), indent(indent)
+{
+    output << "<?xml version='1.0' encoding='utf-8'?>" << std::endl;
+    closed = false;
+}
+
+
+XMLWriter::~XMLWriter()
+{
+    close();
+}
+
+
+void XMLWriter::close()
+{
+    if (closed) return;
+    while (!pendingElems.empty()) closeElement();
+    closed = true;
+}
+
+
+void XMLWriter::indent_(unsigned int depth)
+{
+    if (!indent) return;
+    output << string(depth * 2, ' ');
+}
+
+
+void XMLWriter::openElement(const string & name,
+    const XMLAttrs & attrs)
+{
+    assert(!closed);
+    indent_(pendingElems.size());
+    output << "<" << name;
+    writeAttrs(attrs);
+    output << ">";
+    if (indent) output << std::endl;
+    pendingElems.push_back(name);
+}
+
+
+void XMLWriter::closeElement()
+{
+    assert(!pendingElems.empty());
+    indent_(pendingElems.size() - 1);
+    output << "</" << pendingElems.back() << ">";
+    if (indent) output << std::endl;
+    pendingElems.pop_back();
+    if (pendingElems.empty()) closed = true;
+}
+
+
+void XMLWriter::writeEmptyElement(const string & name,
+    const XMLAttrs & attrs)
+{
+    assert(!closed);
+    indent_(pendingElems.size());
+    output << "<" << name;
+    writeAttrs(attrs);
+    output << " />";
+    if (indent) output << std::endl;
+}
+
+
+void XMLWriter::writeAttrs(const XMLAttrs & attrs)
+{
+    for (XMLAttrs::const_iterator i = attrs.begin(); i != attrs.end(); ++i) {
+        output << " " << i->first << "=\"";
+        for (unsigned int j = 0; j < i->second.size(); ++j) {
+            char c = i->second[j];
+            if (c == '"') output << "&quot;";
+            else if (c == '<') output << "&lt;";
+            else if (c == '>') output << "&gt;";
+            else if (c == '&') output << "&amp;";
+            /* Escape newlines to prevent attribute normalisation (see
+               XML spec, section 3.3.3. */
+            else if (c == '\n') output << "&#xA;";
+            else output << c;
+        }
+        output << "\"";
+    }
+}
+
+
+}
diff --git a/nix/libutil/xml-writer.hh b/nix/libutil/xml-writer.hh
new file mode 100644
index 0000000000..3cefe3712c
--- /dev/null
+++ b/nix/libutil/xml-writer.hh
@@ -0,0 +1,69 @@
+#pragma once
+
+#include <iostream>
+#include <string>
+#include <list>
+#include <map>
+
+
+namespace nix {
+
+using std::string;
+using std::map;
+using std::list;
+
+
+typedef map<string, string> XMLAttrs;
+
+
+class XMLWriter
+{
+private:
+
+    std::ostream & output;
+
+    bool indent;
+    bool closed;
+
+    list<string> pendingElems;
+
+public:
+
+    XMLWriter(bool indent, std::ostream & output);
+    ~XMLWriter();
+
+    void close();
+
+    void openElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+    void closeElement();
+
+    void writeEmptyElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+
+private:
+    void writeAttrs(const XMLAttrs & attrs);
+
+    void indent_(unsigned int depth);
+};
+
+
+class XMLOpenElement
+{
+private:
+    XMLWriter & writer;
+public:
+    XMLOpenElement(XMLWriter & writer, const string & name,
+        const XMLAttrs & attrs = XMLAttrs())
+        : writer(writer)
+    {
+        writer.openElement(name, attrs);
+    }
+    ~XMLOpenElement()
+    {
+        writer.closeElement();
+    }
+};
+
+
+}