path: root/guix/scripts/publish.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015 David Thompson <davet@gnu.org>
;;; Copyright © 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix scripts publish)
  #:use-module ((system repl server) #:prefix repl:)
  #:use-module (ice-9 binary-ports)
  #:use-module (ice-9 format)
  #:use-module (ice-9 match)
  #:use-module (ice-9 regex)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 threads)
  #:use-module (rnrs bytevectors)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-2)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:use-module (srfi srfi-19)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-37)
  #:use-module (web http)
  #:use-module (web request)
  #:use-module (web response)
  #:use-module (web server)
  #:use-module (web uri)
  #:autoload   (sxml simple) (sxml->xml)
  #:use-module (guix base32)
  #:use-module (guix base64)
  #:use-module (guix config)
  #:use-module (guix derivations)
  #:use-module (guix hash)
  #:use-module (guix pki)
  #:use-module (guix pk-crypto)
  #:use-module (guix workers)
  #:use-module (guix store)
  #:use-module ((guix serialization) #:select (write-file))
  #:use-module (guix zlib)
  #:use-module (guix cache)
  #:use-module (guix ui)
  #:use-module (guix scripts)
  #:use-module ((guix utils)
                #:select (with-atomic-file-output compressed-file?))
  #:use-module ((guix build utils)
                #:select (dump-port mkdir-p find-files))
  #:export (%public-key
            %private-key

            guix-publish))

(define (show-help)
  (format #t (G_ "Usage: guix publish [OPTION]...
Publish ~a over HTTP.\n") %store-directory)
  (display (G_ "
  -p, --port=PORT        listen on PORT"))
  (display (G_ "
      --listen=HOST      listen on the network interface for HOST"))
  (display (G_ "
  -u, --user=USER        change privileges to USER as soon as possible"))
  (display (G_ "
  -C, --compression[=LEVEL]
                         compress archives at LEVEL"))
  (display (G_ "
  -c, --cache=DIRECTORY  cache published items to DIRECTORY"))
  (display (G_ "
      --workers=N        use N workers to bake items"))
  (display (G_ "
      --ttl=TTL          announce narinfos can be cached for TTL seconds"))
  (display (G_ "
      --nar-path=PATH    use PATH as the prefix for nar URLs"))
  (display (G_ "
      --public-key=FILE  use FILE as the public key for signatures"))
  (display (G_ "
      --private-key=FILE use FILE as the private key for signatures"))
  (display (G_ "
  -r, --repl[=PORT]      spawn REPL server on PORT"))
  (newline)
  (display (G_ "
  -h, --help             display this help and exit"))
  (display (G_ "
  -V, --version          display version information and exit"))
  (newline)
  (show-bug-report-information))

(define (getaddrinfo* host)
  "Like 'getaddrinfo', but properly report errors."
  (catch 'getaddrinfo-error
    (lambda ()
      (getaddrinfo host))
    (lambda (key error)
      (leave (G_ "lookup of host '~a' failed: ~a~%")
             host (gai-strerror error)))))

;; Nar compression parameters.
(define-record-type <compression>
  (compression type level)
  compression?
  (type   compression-type)
  (level  compression-level))

(define %no-compression
  (compression 'none 0))

(define %default-gzip-compression
  ;; Since we compress on the fly, default to fast compression.
  (compression 'gzip 3))

(define (actual-compression item requested)
  "Return the actual compression used for ITEM, which may be %NO-COMPRESSION
if ITEM is already compressed."
  (if (compressed-file? item)
      %no-compression
      requested))

(define %options
  (list (option '(#\h "help") #f #f
                (lambda _
                  (show-help)
                  (exit 0)))
        (option '(#\V "version") #f #f
                (lambda _
                  (show-version-and-exit "guix publish")))
        (option '(#\u "user") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'user arg result)))
        (option '(#\p "port") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'port (string->number* arg) result)))
        (option '("listen") #t #f
                (lambda (opt name arg result)
                  (match (getaddrinfo* arg)
                    ((info _ ...)
                     (alist-cons 'address (addrinfo:addr info)
                                 result))
                    (()
                     (leave (G_ "lookup of host '~a' returned nothing")
                            name)))))
        (option '(#\C "compression") #f #t
                (lambda (opt name arg result)
                  (match (if arg (string->number* arg) 3)
                    (0
                     (alist-cons 'compression %no-compression result))
                    (level
                     (if (zlib-available?)
                         (alist-cons 'compression
                                     (compression 'gzip level)
                                     result)
                         (begin
                           (warning (G_ "zlib support is missing; \
compression disabled~%"))
                           result))))))
        (option '(#\c "cache") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'cache arg result)))
        (option '("workers") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'workers (string->number* arg)
                              result)))
        (option '("ttl") #t #f
                (lambda (opt name arg result)
                  (let ((duration (string->duration arg)))
                    (unless duration
                      (leave (G_ "~a: invalid duration~%") arg))
                    (alist-cons 'narinfo-ttl (time-second duration)
                                result))))
        (option '("nar-path") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'nar-path arg result)))
        (option '("public-key") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'public-key-file arg result)))
        (option '("private-key" "secret-key") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'private-key-file arg result)))
        (option '(#\r "repl") #f #t
                (lambda (opt name arg result)
                  ;; If port unspecified, use default Guile REPL port.
                  (let ((port (and arg (string->number* arg))))
                    (alist-cons 'repl (or port 37146) result))))))

(define %default-options
  `((port . 8080)

    ;; By default, serve nars under "/nar".
    (nar-path . "nar")

    (public-key-file . ,%public-key-file)
    (private-key-file . ,%private-key-file)

    ;; Default to fast & low compression.
    (compression . ,(if (zlib-available?)
                        %default-gzip-compression
                        %no-compression))

    ;; Default number of workers when caching is enabled.
    (workers . ,(current-processor-count))

    (address . ,(make-socket-address AF_INET INADDR_ANY 0))
    (repl . #f)))

;; The key pair used to sign narinfos.
(define %private-key
  (make-parameter #f))
(define %public-key
  (make-parameter #f))

(define %nix-cache-info
  `(("StoreDir" . ,%store-directory)
    ("WantMassQuery" . 0)
    ("Priority" . 100)))

(define (load-derivation file)
  "Read the derivation from FILE."
  (call-with-input-file file read-derivation))

(define (signed-string s)
  "Sign the hash of the string S with the daemon's key."
  (let* ((public-key (%public-key))
         (hash (bytevector->hash-data (sha256 (string->utf8 s))
                                      #:key-type (key-type public-key))))
    (signature-sexp hash (%private-key) public-key)))

(define base64-encode-string
  (compose base64-encode string->utf8))

(define* (narinfo-string store store-path key
                         #:key (compression %no-compression)
                         (nar-path "nar") file-size)
  "Generate a narinfo key/value string for STORE-PATH; an exception is raised
if STORE-PATH is invalid.  Produce a URL that corresponds to COMPRESSION.  The
narinfo is signed with KEY.  NAR-PATH specifies the prefix for nar URLs.
Optionally, FILE-SIZE can specify the size in bytes of the compressed NAR; it
informs the client of how much needs to be downloaded."
  (let* ((path-info  (query-path-info store store-path))
         (compression (actual-compression store-path compression))
         (url        (encode-and-join-uri-path
                      `(,@(split-and-decode-uri-path nar-path)
                        ,@(match compression
                            (($ <compression> 'none)
                             '())
                            (($ <compression> type)
                             (list (symbol->string type))))
                        ,(basename store-path))))
         (hash       (bytevector->nix-base32-string
                      (path-info-hash path-info)))
         (size       (path-info-nar-size path-info))
         (file-size  (or file-size
                         (and (eq? compression %no-compression) size)))
         (references (string-join
                      (map basename (path-info-references path-info))
                      " "))
         (deriver    (path-info-deriver path-info))
         (base-info  (format #f
                             "\
StorePath: ~a
URL: ~a
Compression: ~a
NarHash: sha256:~a
NarSize: ~d
References: ~a~%~a"
                             store-path url
                             (compression-type compression)
                             hash size references
                             (if file-size
                                 (format #f "FileSize: ~a~%" file-size)
                                 "")))
         ;; Do not render a "Deriver" or "System" line if we are rendering
         ;; info for a derivation.
         (info       (if (not deriver)
                         base-info
                         (catch 'system-error
                           (lambda ()
                             (let ((drv (load-derivation deriver)))
                               (format #f "~aSystem: ~a~%Deriver: ~a~%"
                                       base-info (derivation-system drv)
                                       (basename deriver))))
                           (lambda args
                             ;; DERIVER might be missing, but that's fine:
                             ;; it's only used for <substitutable> where it's
                             ;; optional.  'System' is currently unused.
                             (if (= ENOENT (system-error-errno args))
                                 base-info
                                 (apply throw args))))))
         (signature  (base64-encode-string
                      (canonical-sexp->string (signed-string info)))))
    (format #f "~aSignature: 1;~a;~a~%" info (gethostname) signature)))

(define (not-found request)
  "Render 404 response for REQUEST."
  (values (build-response #:code 404)
          (string-append "Resource not found: "
                         (uri-path (request-uri request)))))

(define (render-nix-cache-info)
  "Render server information."
  (values '((content-type . (text/plain)))
          (lambda (port)
            (for-each (match-lambda
                       ((key . value)
                        (format port "~a: ~a~%" key value)))
                      %nix-cache-info))))

(define* (render-narinfo store request hash
                         #:key ttl (compression %no-compression)
                         (nar-path "nar"))
  "Render metadata for the store path corresponding to HASH.  If TTL is true,
advertise it as the maximum validity period (in seconds) via the
'Cache-Control' header.  This allows 'guix substitute' to cache it for an
appropriate duration.  NAR-PATH specifies the prefix for nar URLs."
  (let ((store-path (hash-part->path store hash)))
    (if (string-null? store-path)
        (not-found request)
        (values `((content-type . (application/x-nix-narinfo))
                  ,@(if ttl
                        `((cache-control (max-age . ,ttl)))
                        '()))
                (cut display
                  (narinfo-string store store-path (%private-key)
                                  #:nar-path nar-path
                                  #:compression compression)
                  <>)))))

(define* (nar-cache-file directory item
                             #:key (compression %no-compression))
  (string-append directory "/"
                 (symbol->string (compression-type compression))
                 "/" (basename item) ".nar"))

(define* (narinfo-cache-file directory item
                             #:key (compression %no-compression))
  (string-append directory "/"
                 (symbol->string (compression-type compression))
                 "/" (basename item)
                 ".narinfo"))

(define run-single-baker
  (let ((baking (make-weak-value-hash-table))
        (mutex  (make-mutex)))
    (lambda (item thunk)
      "Run THUNK, which is supposed to bake ITEM, but make sure only one
thread is baking ITEM at a given time."
      (define selected?
        (with-mutex mutex
          (and (not (hash-ref baking item))
               (begin
                 (hash-set! baking item (current-thread))
                 #t))))

      (when selected?
        (dynamic-wind
          (const #t)
          thunk
          (lambda ()
            (with-mutex mutex
              (hash-remove! baking item))))))))

(define-syntax-rule (single-baker item exp ...)
  "Bake ITEM by evaluating EXP, but make sure there's only one baker for ITEM
at a time."
  (run-single-baker item (lambda () exp ...)))


(define (narinfo-files cache)
  "Return the list of .narinfo files under CACHE."
  (if (file-is-directory? cache)
      (find-files cache
                  (lambda (file stat)
                    (string-suffix? ".narinfo" file)))
      '()))

(define* (render-narinfo/cached store request hash
                                #:key ttl (compression %no-compression)
                                (nar-path "nar")
                                cache pool)
  "Respond to the narinfo request for REQUEST.  If the narinfo is available in
CACHE, then send it; otherwise, return 404 and \"bake\" that nar and narinfo
requested using POOL."
  (define (delete-entry narinfo)
    ;; Delete NARINFO and the corresponding nar from CACHE.
    (let ((nar (string-append (string-drop-right narinfo
                                                 (string-length ".narinfo"))
                              ".nar")))
      (delete-file* narinfo)
      (delete-file* nar)))

  (let* ((item        (hash-part->path store hash))
         (compression (actual-compression item compression))
         (cached      (and (not (string-null? item))
                           (narinfo-cache-file cache item
                                               #:compression compression))))
    (cond ((string-null? item)
           (not-found request))
          ((file-exists? cached)
           ;; Narinfo is in cache, send it.
           (values `((content-type . (application/x-nix-narinfo))
                     ,@(if ttl
                           `((cache-control (max-age . ,ttl)))
                           '()))
                   (lambda (port)
                     (display (call-with-input-file cached
                                read-string)
                              port))))
          ((valid-path? store item)
           ;; Nothing in cache: bake the narinfo and nar in the background and
           ;; return 404.
           (eventually pool
             (single-baker item
               ;; (format #t "baking ~s~%" item)
               (bake-narinfo+nar cache item
                                 #:ttl ttl
                                 #:compression compression
                                 #:nar-path nar-path))

             (when ttl
               (single-baker 'cache-cleanup
                 (maybe-remove-expired-cache-entries cache
                                                     narinfo-files
                                                     #:entry-expiration
                                                     (file-expiration-time ttl)
                                                     #:delete-entry delete-entry
                                                     #:cleanup-period ttl))))
           (not-found request))
          (else
           (not-found request)))))

(define* (bake-narinfo+nar cache item
                           #:key ttl (compression %no-compression)
                           (nar-path "/nar"))
  "Write the narinfo and nar for ITEM to CACHE."
  (let* ((compression (actual-compression item compression))
         (nar         (nar-cache-file cache item
                                      #:compression compression))
         (narinfo     (narinfo-cache-file cache item
                                          #:compression compression)))

    (mkdir-p (dirname nar))
    (match (compression-type compression)
      ('gzip
       ;; Note: the file port gets closed along with the gzip port.
       (call-with-gzip-output-port (open-output-file (string-append nar ".tmp"))
         (lambda (port)
           (write-file item port))
         #:level (compression-level compression)
         #:buffer-size (* 128 1024))
       (rename-file (string-append nar ".tmp") nar))
      ('none
       ;; When compression is disabled, we retrieve files directly from the
       ;; store; no need to cache them.
       #t))

    (mkdir-p (dirname narinfo))
    (with-atomic-file-output narinfo
      (lambda (port)
        ;; Open a new connection to the store.  We cannot reuse the main
        ;; thread's connection to the store since we would end up sending
        ;; stuff concurrently on the same channel.
        (with-store store
          (display (narinfo-string store item
                                   (%private-key)
                                   #:nar-path nar-path
                                   #:compression compression
                                   #:file-size (stat:size (stat nar)))
                   port))))))

;; XXX: Declare the 'Guix-Compression' HTTP header, which is in fact for
;; internal consumption: it allows us to pass the compression info to
;; 'http-write', as part of the workaround to <http://bugs.gnu.org/21093>.
(declare-header! "Guix-Nar-Compression"
                 (lambda (str)
                   (match (call-with-input-string str read)
                     (('compression type level)
                      (compression type level))))
                 compression?
                 (lambda (compression port)
                   (match compression
                     (($ <compression> type level)
                      (write `(compression ,type ,level) port)))))

(define* (render-nar store request store-item
                     #:key (compression %no-compression))
  "Render archive of the store path corresponding to STORE-ITEM."
  (let ((store-path (string-append %store-directory "/" store-item)))
    ;; The ISO-8859-1 charset *must* be used otherwise HTTP clients will
    ;; interpret the byte stream as UTF-8 and arbitrarily change invalid byte
    ;; sequences.
    (if (valid-path? store store-path)
        (values `((content-type . (application/x-nix-archive
                                   (charset . "ISO-8859-1")))
                  (guix-nar-compression . ,compression))
                ;; XXX: We're not returning the actual contents, deferring
                ;; instead to 'http-write'.  This is a hack to work around
                ;; <http://bugs.gnu.org/21093>.
                store-path)
        (not-found request))))

(define* (render-nar/cached store cache request store-item
                            #:key (compression %no-compression))
  "Respond to REQUEST with a nar for STORE-ITEM.  If the nar is in CACHE,
return it; otherwise, return 404."
  (let ((cached (nar-cache-file cache store-item
                                #:compression compression)))
    (if (file-exists? cached)
        (values `((content-type . (application/octet-stream
                                   (charset . "ISO-8859-1"))))
                ;; XXX: We're not returning the actual contents, deferring
                ;; instead to 'http-write'.  This is a hack to work around
                ;; <http://bugs.gnu.org/21093>.
                cached)
        (not-found request))))

(define (render-content-addressed-file store request
                                       name algo hash)
  "Return the content of the result of the fixed-output derivation NAME that
has the given HASH of type ALGO."
  ;; TODO: Support other hash algorithms.
  (if (and (eq? algo 'sha256) (= 32 (bytevector-length hash)))
      (let ((item (fixed-output-path name hash
                                     #:hash-algo algo
                                     #:recursive? #f)))
        (if (valid-path? store item)
            (values `((content-type . (application/octet-stream
                                       (charset . "ISO-8859-1"))))
                    ;; XXX: We're not returning the actual contents, deferring
                    ;; instead to 'http-write'.  This is a hack to work around
                    ;; <http://bugs.gnu.org/21093>.
                    item)
            (not-found request)))
      (not-found request)))

(define (render-home-page request)
  "Render the home page."
  (values `((content-type . (text/html (charset . "UTF-8"))))
          (call-with-output-string
            (lambda (port)
              (sxml->xml '(html
                           (head (title "GNU Guix Substitute Server"))
                           (body
                            (h1 "GNU Guix Substitute Server")
                            (p "Hi, "
                               (a (@ (href
                                      "https://gnu.org/s/guix/manual/html_node/Invoking-guix-publish.html"))
                                  (tt "guix publish"))
                               " speaking.  Welcome!")))
                         port)))))

(define extract-narinfo-hash
  (let ((regexp (make-regexp "^([a-df-np-sv-z0-9]{32}).narinfo$")))
    (lambda (str)
      "Return the hash within the narinfo resource string STR, or false if STR
is invalid."
      (and=> (regexp-exec regexp str)
             (cut match:substring <> 1)))))

(define (get-request? request)
  "Return #t if REQUEST uses the GET method."
  (eq? (request-method request) 'GET))

(define (request-path-components request)
  "Split the URI path of REQUEST into a list of component strings.  For
example: \"/foo/bar\" yields '(\"foo\" \"bar\")."
  (split-and-decode-uri-path (uri-path (request-uri request))))


;;;
;;; Server.
;;;

(define %http-write
  (@@ (web server http) http-write))

(define (sans-content-length response)
  "Return RESPONSE without its 'content-length' header."
  (set-field response (response-headers)
             (alist-delete 'content-length
                           (response-headers response)
                           eq?)))

(define (with-content-length response length)
  "Return RESPONSE with a 'content-length' header set to LENGTH."
  (set-field response (response-headers)
             (alist-cons 'content-length length
                         (alist-delete 'content-length
                                       (response-headers response)
                                       eq?))))

(define-syntax-rule (swallow-EPIPE exp ...)
  "Swallow EPIPE errors raised by EXP..."
  (catch 'system-error
    (lambda ()
      exp ...)
    (lambda args
      (if (= EPIPE (system-error-errno args))
          (values)
          (apply throw args)))))

(define-syntax-rule (swallow-zlib-error exp ...)
  "Swallow 'zlib-error' exceptions raised by EXP..."
  (catch 'zlib-error
    (lambda ()
      exp ...)
    (const #f)))

(define (nar-response-port response)
  "Return a port on which to write the body of RESPONSE, the response of a
/nar request, according to COMPRESSION."
  (match (assoc-ref (response-headers response) 'guix-nar-compression)
    (($ <compression> 'gzip level)
     ;; Note: We cannot used chunked encoding here because
     ;; 'make-gzip-output-port' wants a file port.
     (make-gzip-output-port (response-port response)
                            #:level level
                            #:buffer-size (* 64 1024)))
    (($ <compression> 'none)
     (response-port response))
    (#f
     (response-port response))))

(define (http-write server client response body)
  "Write RESPONSE and BODY to CLIENT, possibly in a separate thread to avoid
blocking."
  (match (response-content-type response)
    (('application/x-nix-archive . _)
     ;; Sending the the whole archive can take time so do it in a separate
     ;; thread so that the main thread can keep working in the meantime.
     (call-with-new-thread
      (lambda ()
        (let* ((response (write-response (sans-content-length response)
                                         client))
               (port     (begin
                           (force-output client)
                           (nar-response-port response))))
          ;; XXX: Given our ugly workaround for <http://bugs.gnu.org/21093> in
          ;; 'render-nar', BODY here is just the file name of the store item.
          ;; We call 'write-file' from here because we know that's the only
          ;; way to avoid building the whole nar in memory, which could
          ;; quickly become a real problem.  As a bonus, we even do
          ;; sendfile(2) directly from the store files to the socket.
          (swallow-zlib-error
           (swallow-EPIPE
            (write-file (utf8->string body) port)))
          (swallow-zlib-error
           (close-port port))
          (values)))))
    (('application/octet-stream . _)
     ;; Send a raw file in a separate thread.
     (call-with-new-thread
      (lambda ()
        (catch 'system-error
          (lambda ()
            (call-with-input-file (utf8->string body)
              (lambda (input)
                (let* ((size     (stat:size (stat input)))
                       (response (write-response (with-content-length response
                                                                      size)
                                                 client))
                       (output   (response-port response)))
                  (if (file-port? output)
                      (sendfile output input size)
                      (dump-port input output))
                  (close-port output)
                  (values)))))
          (lambda args
            ;; If the file was GC'd behind our back, that's fine.  Likewise if
            ;; the client closes the connection.
            (unless (memv (system-error-errno args)
                          (list ENOENT EPIPE ECONNRESET))
              (apply throw args))
            (values))))))
    (_
     ;; Handle other responses sequentially.
     (%http-write server client response body))))

(define-server-impl concurrent-http-server
  ;; A variant of Guile's built-in HTTP server that offloads possibly long
  ;; responses to a different thread.
  (@@ (web server http) http-open)
  (@@ (web server http) http-read)
  http-write
  (@@ (web server http) http-close))

(define* (make-request-handler store
                               #:key
                               cache pool
                               narinfo-ttl
                               (nar-path "nar")
                               (compression %no-compression))
  (define nar-path?
    (let ((expected (split-and-decode-uri-path nar-path)))
      (cut equal? expected <>)))

  (lambda (request body)
    (format #t "~a ~a~%"
            (request-method request)
            (uri-path (request-uri request)))
    (if (get-request? request)                    ;reject POST, PUT, etc.
        (match (request-path-components request)
          ;; /nix-cache-info
          (("nix-cache-info")
           (render-nix-cache-info))
          ;; /
          ((or () ("index.html"))
           (render-home-page request))
          ;; /<hash>.narinfo
          (((= extract-narinfo-hash (? string? hash)))
           ;; TODO: Register roots for HASH that will somehow remain for
           ;; NARINFO-TTL.
           (if cache
               (render-narinfo/cached store request hash
                                      #:cache cache
                                      #:pool pool
                                      #:ttl narinfo-ttl
                                      #:nar-path nar-path
                                      #:compression compression)
               (render-narinfo store request hash
                               #:ttl narinfo-ttl
                               #:nar-path nar-path
                               #:compression compression)))
          ;; /nar/file/NAME/sha256/HASH
          (("file" name "sha256" hash)
           (guard (c ((invalid-base32-character? c)
                      (not-found request)))
             (let ((hash (nix-base32-string->bytevector hash)))
               (render-content-addressed-file store request
                                              name 'sha256 hash))))

          ;; Use different URLs depending on the compression type.  This
          ;; guarantees that /nar URLs remain valid even when 'guix publish'
          ;; is restarted with different compression parameters.

          ;; /nar/gzip/<store-item>
          ((components ... "gzip" store-item)
           (if (and (nar-path? components) (zlib-available?))
               (let ((compression (match compression
                                    (($ <compression> 'gzip)
                                     compression)
                                    (_
                                     %default-gzip-compression))))
                 (if cache
                     (render-nar/cached store cache request store-item
                                        #:compression compression)
                     (render-nar store request store-item
                                 #:compression compression)))
               (not-found request)))

          ;; /nar/<store-item>
          ((components ... store-item)
           (if (nar-path? components)
               (render-nar store request store-item
                           #:compression %no-compression)
               (not-found request)))

          (x (not-found request)))
        (not-found request))))

(define* (run-publish-server socket store
                             #:key (compression %no-compression)
                             (nar-path "nar") narinfo-ttl
                             cache pool)
  (run-server (make-request-handler store
                                    #:cache cache
                                    #:pool pool
                                    #:nar-path nar-path
                                    #:narinfo-ttl narinfo-ttl
                                    #:compression compression)
              concurrent-http-server
              `(#:socket ,socket)))

(define (open-server-socket address)
  "Return a TCP socket bound to ADDRESS, a socket address."
  (let ((sock (socket (sockaddr:fam address) SOCK_STREAM 0)))
    (setsockopt sock SOL_SOCKET SO_REUSEADDR 1)
    (bind sock address)
    sock))

(define (gather-user-privileges user)
  "Switch to the identity of USER, a user name."
  (catch 'misc-error
    (lambda ()
      (let ((user (getpw user)))
        (setgroups #())
        (setgid (passwd:gid user))
        (setuid (passwd:uid user))))
    (lambda (key proc message args . rest)
      (leave (G_ "user '~a' not found: ~a~%")
             user (apply format #f message args)))))


;;;
;;; Entry point.
;;;

(define (guix-publish . args)
  (with-error-handling
    (let* ((opts    (args-fold* args %options
                                (lambda (opt name arg result)
                                  (leave (G_ "~A: unrecognized option~%") name))
                                (lambda (arg result)
                                  (leave (G_ "~A: extraneous argument~%") arg))
                                %default-options))
           (user    (assoc-ref opts 'user))
           (port    (assoc-ref opts 'port))
           (ttl     (assoc-ref opts 'narinfo-ttl))
           (compression (assoc-ref opts 'compression))
           (address (let ((addr (assoc-ref opts 'address)))
                      (make-socket-address (sockaddr:fam addr)
                                           (sockaddr:addr addr)
                                           port)))
           (socket  (open-server-socket address))
           (nar-path  (assoc-ref opts 'nar-path))
           (repl-port (assoc-ref opts 'repl))
           (cache     (assoc-ref opts 'cache))
           (workers   (assoc-ref opts 'workers))

           ;; Read the key right away so that (1) we fail early on if we can't
           ;; access them, and (2) we can then drop privileges.
           (public-key  (read-file-sexp (assoc-ref opts 'public-key-file)))
           (private-key (read-file-sexp (assoc-ref opts 'private-key-file))))

      (when user
        ;; Now that we've read the key material and opened the socket, we can
        ;; drop privileges.
        (gather-user-privileges user))

      (when (zero? (getuid))
        (warning (G_ "server running as root; \
consider using the '--user' option!~%")))

      (parameterize ((%public-key public-key)
                     (%private-key private-key))
        (format #t (G_ "publishing ~a on ~a, port ~d~%")
                %store-directory
                (inet-ntop (sockaddr:fam address) (sockaddr:addr address))
                (sockaddr:port address))
        (when repl-port
          (repl:spawn-server (repl:make-tcp-server-socket #:port repl-port)))
        (with-store store
          (run-publish-server socket store
                              #:cache cache
                              #:pool (and cache (make-pool workers))
                              #:nar-path nar-path
                              #:compression compression
                              #:narinfo-ttl ttl))))))

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