/* Copyright 2003 Roger Dingledine. */
/* See LICENSE for licensing information */
/* $Id$ */
/**
* \file dns.c
* \brief Resolve hostnames in separate processes.
**/
/* See http://elvin.dstc.com/ListArchive/elvin-dev/archive/2001/09/msg00027.html
* for some approaches to asynchronous dns. We will want to switch once one of
* them becomes more commonly available.
*/
#include "or.h"
#include "tree.h"
extern or_options_t options; /* command-line and config-file options */
/** Longest hostname we're willing to resolve. */
#define MAX_ADDRESSLEN 256
/** Maximum DNS processes to spawn. */
#define MAX_DNSWORKERS 50
/** Minimum DNS processes to spawn. */
#define MIN_DNSWORKERS 3
/** If more than this many processes are idle, shut down the extras. */
#define MAX_IDLE_DNSWORKERS 10
/** Possible outcomes from hostname lookup: permanent failure,
* transient (retryable) failure, and success. */
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3
/** How many dnsworkers we have running right now. */
static int num_dnsworkers=0;
/** How many of the running dnsworkers have an assigned task right now. */
static int num_dnsworkers_busy=0;
/** When did we last rotate the dnsworkers? */
static time_t last_rotation_time=0;
/** Linked list of connections waiting for a DNS answer. */
struct pending_connection_t {
struct connection_t *conn;
struct pending_connection_t *next;
};
/** A DNS request: possibly completed, possibly pending; cached_resolve
* structs are stored at the OR side in a splay tree, and as a linked
* list from oldest to newest.
*/
struct cached_resolve {
SPLAY_ENTRY(cached_resolve) node;
char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
uint32_t addr; /**< IPv4 addr for address. */
char state; /**< 0 is pending; 1 means answer is valid; 2 means resolve failed. */
#define CACHE_STATE_PENDING 0
#define CACHE_STATE_VALID 1
#define CACHE_STATE_FAILED 2
uint32_t expire; /**< Remove items from cache after this time. */
struct pending_connection_t *pending_connections;
struct cached_resolve *next;
};
static void purge_expired_resolves(uint32_t now);
static int assign_to_dnsworker(connection_t *exitconn);
static void dns_purge_resolve(struct cached_resolve *resolve);
static void dns_found_answer(char *address, uint32_t addr, char outcome);
static int dnsworker_main(void *data);
static int spawn_dnsworker(void);
static void spawn_enough_dnsworkers(void);
static void send_resolved_cell(connection_t *conn, uint8_t answer_type);
/** Splay tree of cached_resolve objects. */
static SPLAY_HEAD(cache_tree, cached_resolve) cache_root;
/** Function to compare hashed resolves on their addresses; used to
* implement splay trees. */
static int compare_cached_resolves(struct cached_resolve *a,
struct cached_resolve *b) {
/* make this smarter one day? */
return strncasecmp(a->address, b->address, MAX_ADDRESSLEN);
}
SPLAY_PROTOTYPE(cache_tree, cached_resolve, node, compare_cached_resolves);
SPLAY_GENERATE(cache_tree, cached_resolve, node, compare_cached_resolves);
/** Initialize the DNS cache. */
static void init_cache_tree(void) {
SPLAY_INIT(&cache_root);
}
/** Initialize the DNS subsystem; called by the OR process. */
void dns_init(void) {
init_cache_tree();
last_rotation_time=time(NULL);
spawn_enough_dnsworkers();
}
/** Linked list of resolved addresses, oldest to newest. */
static struct cached_resolve *oldest_cached_resolve = NULL;
static struct cached_resolve *newest_cached_resolve = NULL;
/** Remove every cached_resolve whose expire time is before now
* from the cache. */
static void purge_expired_resolves(uint32_t now) {
struct cached_resolve *resolve;
struct pending_connection_t *pend;
connection_t *pendconn;
/* this is fast because the linked list
* oldest_cached_resolve is ordered by when they came in.
*/
while(oldest_cached_resolve && (oldest_cached_resolve->expire < now)) {
resolve = oldest_cached_resolve;
log(LOG_DEBUG,"Forgetting old cached resolve (expires %lu)", (unsigned long)resolve->expire);
if(resolve->state == CACHE_STATE_PENDING) {
log_fn(LOG_WARN,"Expiring a dns resolve that's still pending. Forgot to cull it?");
}
if (resolve->pending_connections) {
log_fn(LOG_WARN, "Closing pending connections on expiring DNS resolve!");
while (resolve->pending_connections) {
pend = resolve->pending_connections;
resolve->pending_connections = pend->next;
/* Connections should only be pending if they have no socket. */
tor_assert(pend->conn->s == -1);
pendconn = pend->conn;
connection_edge_end(pendconn, END_STREAM_REASON_MISC,
pendconn->cpath_layer);
circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
connection_free(pendconn);
tor_free(pend);
}
}
oldest_cached_resolve = resolve->next;
if(!oldest_cached_resolve) /* if there are no more, */
newest_cached_resolve = NULL; /* then make sure the list's tail knows that too */
SPLAY_REMOVE(cache_tree, &cache_root, resolve);
tor_free(resolve);
}
}
static void send_resolved_cell(connection_t *conn, uint8_t answer_type)
{
char buf[RELAY_PAYLOAD_SIZE];
int buflen;
buf[0] = answer_type;
switch (answer_type)
{
case RESOLVED_TYPE_IPV4:
buf[1] = 4;
set_uint32(buf+2, htonl(conn->addr));
buflen = 6;
break;
case RESOLVED_TYPE_ERROR_TRANSIENT:
case RESOLVED_TYPE_ERROR:
buf[1] = 24; /* length of "error resolving hostname" */
strcpy(buf+2, "error resolving hostname");
buflen = 26;
break;
default:
tor_assert(0);
}
connection_edge_send_command(conn, circuit_get_by_conn(conn),
RELAY_COMMAND_RESOLVED, buf, buflen,
conn->cpath_layer);
}
/** See if we have a cache entry for exitconn-\>address. if so,
* if resolve valid, put it into exitconn-\>addr and return 1.
* If resolve failed, return -1.
*
* Else, if seen before and pending, add conn to the pending list,
* and return 0.
*
* Else, if not seen before, add conn to pending list, hand to
* dns farm, and return 0.
*/
int dns_resolve(connection_t *exitconn) {
struct cached_resolve *resolve;
struct cached_resolve search;
struct pending_connection_t *pending_connection;
struct in_addr in;
uint32_t now = time(NULL);
assert_connection_ok(exitconn, 0);
tor_assert(exitconn->s == -1);
/* first check if exitconn->address is an IP. If so, we already
* know the answer. */
if (tor_inet_aton(exitconn->address, &in) != 0) {
exitconn->addr = ntohl(in.s_addr);
return 1;
}
/* then take this opportunity to see if there are any expired
* resolves in the tree. */
purge_expired_resolves(now);
/* now check the tree to see if 'address' is already there. */
strncpy(search.address, exitconn->address, MAX_ADDRESSLEN);
search.address[MAX_ADDRESSLEN-1] = 0;
resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
if(resolve) { /* already there */
switch(resolve->state) {
case CACHE_STATE_PENDING:
/* add us to the pending list */
pending_connection = tor_malloc_zero(
sizeof(struct pending_connection_t));
pending_connection->conn = exitconn;
pending_connection->next = resolve->pending_connections;
resolve->pending_connections = pending_connection;
log_fn(LOG_DEBUG,"Connection (fd %d) waiting for pending DNS resolve of '%s'",
exitconn->s, exitconn->address);
exitconn->state = EXIT_CONN_STATE_RESOLVING;
return 0;
case CACHE_STATE_VALID:
exitconn->addr = resolve->addr;
log_fn(LOG_DEBUG,"Connection (fd %d) found cached answer for '%s'",
exitconn->s, exitconn->address);
if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
return 1;
case CACHE_STATE_FAILED:
if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR);
return -1;
}
tor_assert(0);
}
/* not there, need to add it */
resolve = tor_malloc_zero(sizeof(struct cached_resolve));
resolve->state = CACHE_STATE_PENDING;
resolve->expire = now + MAX_DNS_ENTRY_AGE;
strncpy(resolve->address, exitconn->address, MAX_ADDRESSLEN);
resolve->address[MAX_ADDRESSLEN-1] = 0;
/* add us to the pending list */
pending_connection = tor_malloc_zero(sizeof(struct pending_connection_t));
pending_connection->conn = exitconn;
pending_connection->next = NULL;
resolve->pending_connections = pending_connection;
exitconn->state = EXIT_CONN_STATE_RESOLVING;
/* add us to the linked list of resolves */
if (!oldest_cached_resolve) {
oldest_cached_resolve = resolve;
} else {
newest_cached_resolve->next = resolve;
}
newest_cached_resolve = resolve;
SPLAY_INSERT(cache_tree, &cache_root, resolve);
return assign_to_dnsworker(exitconn);
}
/** Find or spawn a dns worker process to handle resolving
* exitconn-\>address; tell that dns worker to begin resolving.
*/
static int assign_to_dnsworker(connection_t *exitconn) {
connection_t *dnsconn;
unsigned char len;
tor_assert(exitconn->state == EXIT_CONN_STATE_RESOLVING);
tor_assert(exitconn->s == -1);
spawn_enough_dnsworkers(); /* respawn here, to be sure there are enough */
dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
if(!dnsconn) {
log_fn(LOG_WARN,"no idle dns workers. Failing.");
dns_cancel_pending_resolve(exitconn->address);
send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR_TRANSIENT);
return -1;
}
log_fn(LOG_DEBUG, "Connection (fd %d) needs to resolve '%s'; assigning to DNSWorker (fd %d)",
exitconn->s, exitconn->address, dnsconn->s);
tor_free(dnsconn->address);
dnsconn->address = tor_strdup(exitconn->address);
dnsconn->state = DNSWORKER_STATE_BUSY;
num_dnsworkers_busy++;
len = strlen(dnsconn->address);
connection_write_to_buf(&len, 1, dnsconn);
connection_write_to_buf(dnsconn->address, len, dnsconn);
// log_fn(LOG_DEBUG,"submitted '%s'", exitconn->address);
return 0;
}
/** Remove conn from the list of connections waiting for conn-\>address.
*/
void connection_dns_remove(connection_t *conn)
{
struct pending_connection_t *pend, *victim;
struct cached_resolve search;
struct cached_resolve *resolve;
tor_assert(conn->type == CONN_TYPE_EXIT);
tor_assert(conn->state == EXIT_CONN_STATE_RESOLVING);
strncpy(search.address, conn->address, MAX_ADDRESSLEN);
search.address[MAX_ADDRESSLEN-1] = 0;
resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
if(!resolve) {
log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", conn->address);
return;
}
tor_assert(resolve->pending_connections);
assert_connection_ok(conn,0);
pend = resolve->pending_connections;
if(pend->conn == conn) {
resolve->pending_connections = pend->next;
tor_free(pend);
log_fn(LOG_DEBUG, "First connection (fd %d) no longer waiting for resolve of '%s'",
conn->s, conn->address);
return;
} else {
for( ; pend->next; pend = pend->next) {
if(pend->next->conn == conn) {
victim = pend->next;
pend->next = victim->next;
tor_free(victim);
log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
conn->s, conn->address);
return; /* more are pending */
}
}
tor_assert(0); /* not reachable unless onlyconn not in pending list */
}
}
/** Log an error and abort if conn is waiting for a DNS resolve.
*/
void assert_connection_edge_not_dns_pending(connection_t *conn) {
struct pending_connection_t *pend;
struct cached_resolve *resolve;
SPLAY_FOREACH(resolve, cache_tree, &cache_root) {
for(pend = resolve->pending_connections;
pend;
pend = pend->next) {
tor_assert(pend->conn != conn);
}
}
}
/** Log an error and abort if any connection waiting for a DNS resolve is
* corrupted. */
void assert_all_pending_dns_resolves_ok(void) {
struct pending_connection_t *pend;
struct cached_resolve *resolve;
SPLAY_FOREACH(resolve, cache_tree, &cache_root) {
for(pend = resolve->pending_connections;
pend;
pend = pend->next) {
assert_connection_ok(pend->conn, 0);
tor_assert(pend->conn->s == -1);
tor_assert(!connection_in_array(pend->conn));
}
}
}
/** Mark all connections waiting for address for close. Then cancel
* the resolve for address itself, and remove any cached results for
* address from the cache.
*/
void dns_cancel_pending_resolve(char *address) {
struct pending_connection_t *pend;
struct cached_resolve search;
struct cached_resolve *resolve;
connection_t *pendconn;
strncpy(search.address, address, MAX_ADDRESSLEN);
search.address[MAX_ADDRESSLEN-1] = 0;
resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
if(!resolve) {
log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", address);
return;
}
tor_assert(resolve->pending_connections);
/* mark all pending connections to fail */
log_fn(LOG_DEBUG, "Failing all connections waiting on DNS resolve of '%s'",
address);
while(resolve->pending_connections) {
pend = resolve->pending_connections;
pend->conn->state = EXIT_CONN_STATE_RESOLVEFAILED;
pendconn = pend->conn;
tor_assert(pendconn->s == -1);
if(!pendconn->marked_for_close) {
connection_edge_end(pendconn, END_STREAM_REASON_MISC, pendconn->cpath_layer);
}
circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
connection_free(pendconn);
resolve->pending_connections = pend->next;
tor_free(pend);
}
dns_purge_resolve(resolve);
}
/** Remove resolve from the cache.
*/
static void dns_purge_resolve(struct cached_resolve *resolve) {
struct cached_resolve *tmp;
/* remove resolve from the linked list */
if(resolve == oldest_cached_resolve) {
oldest_cached_resolve = resolve->next;
if(oldest_cached_resolve == NULL)
newest_cached_resolve = NULL;
} else {
/* FFFF make it a doubly linked list if this becomes too slow */
for(tmp=oldest_cached_resolve; tmp && tmp->next != resolve; tmp=tmp->next) ;
tor_assert(tmp); /* it's got to be in the list, or we screwed up somewhere else */
tmp->next = resolve->next; /* unlink it */
if(newest_cached_resolve == resolve)
newest_cached_resolve = tmp;
}
/* remove resolve from the tree */
SPLAY_REMOVE(cache_tree, &cache_root, resolve);
tor_free(resolve);
}
/** Called on the OR side when a DNS worker tells us the outcome of a DNS
* resolve: tell all pending connections about the result of the lookup, and
* cache the value. (address is a NUL-terminated string containing the
* address to look up; addr is an IPv4 address in host order;
* outcome is one of
* DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}.
*/
static void dns_found_answer(char *address, uint32_t addr, char outcome) {
struct pending_connection_t *pend;
struct cached_resolve search;
struct cached_resolve *resolve;
connection_t *pendconn;
circuit_t *circ;
strncpy(search.address, address, MAX_ADDRESSLEN);
search.address[MAX_ADDRESSLEN-1] = 0;
resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
if(!resolve) {
log_fn(LOG_INFO,"Resolved unasked address '%s'? Dropping.", address);
/* XXX Why drop? Just because we don't care now doesn't mean we shouldn't
* XXX cache the result for later. */
return;
}
if (resolve->state != CACHE_STATE_PENDING) {
/* XXXX Maybe update addr? or check addr for consistency? Or let
* VALID replace FAILED? */
log_fn(LOG_WARN, "Resolved '%s' which was already resolved; ignoring",
address);
tor_assert(resolve->pending_connections == NULL);
return;
}
/* Removed this assertion: in fact, we'll sometimes get a double answer
* to the same question. This can happen when we ask one worker to resolve
* X.Y.Z., then we cancel the request, and then we ask another worker to
* resolve X.Y.Z. */
/* tor_assert(resolve->state == CACHE_STATE_PENDING); */
resolve->addr = ntohl(addr);
if(outcome == DNS_RESOLVE_SUCCEEDED)
resolve->state = CACHE_STATE_VALID;
else
resolve->state = CACHE_STATE_FAILED;
while(resolve->pending_connections) {
pend = resolve->pending_connections;
assert_connection_ok(pend->conn,time(NULL));
pend->conn->addr = resolve->addr;
pendconn = pend->conn; /* don't pass complex things to the
connection_mark_for_close macro */
if(resolve->state == CACHE_STATE_FAILED) {
/* prevent double-remove. */
pendconn->state = EXIT_CONN_STATE_RESOLVEFAILED;
if (pendconn->purpose == EXIT_PURPOSE_CONNECT) {
/*XXXX can we safely raise the detach here to happen after we
* send the end cell? */
circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
connection_edge_end(pendconn, END_STREAM_REASON_MISC, pendconn->cpath_layer);
} else {
send_resolved_cell(pendconn, RESOLVED_TYPE_ERROR);
/* This detach must happen after we send the resolved cell. */
circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
}
connection_free(pendconn);
} else {
if (pendconn->purpose == EXIT_PURPOSE_CONNECT) {
/* prevent double-remove. */
pend->conn->state = EXIT_CONN_STATE_CONNECTING;
circ = circuit_get_by_conn(pend->conn);
tor_assert(circ);
/* unlink pend->conn from resolving_streams, */
circuit_detach_stream(circ, pend->conn);
/* and link it to n_streams */
pend->conn->next_stream = circ->n_streams;
circ->n_streams = pend->conn;
connection_exit_connect(pend->conn);
} else {
/* prevent double-remove. This isn't really an accurate state,
* but it does the right thing. */
pendconn->state = EXIT_CONN_STATE_RESOLVEFAILED;
send_resolved_cell(pendconn, RESOLVED_TYPE_IPV4);
circ = circuit_get_by_conn(pendconn);
tor_assert(circ);
circuit_detach_stream(circ, pendconn);
connection_free(pendconn);
}
}
resolve->pending_connections = pend->next;
tor_free(pend);
}
if(outcome == DNS_RESOLVE_FAILED_TRANSIENT) { /* remove from cache */
dns_purge_resolve(resolve);
}
}
/******************************************************************/
/*
* Connection between OR and dnsworker
*/
/** Write handler: called when we've pushed a request to a dnsworker. */
int connection_dns_finished_flushing(connection_t *conn) {
tor_assert(conn && conn->type == CONN_TYPE_DNSWORKER);
connection_stop_writing(conn);
return 0;
}
/** Read handler: called when we get data from a dnsworker. If the
* connection is closed, mark the dnsworker as dead. Otherwise, see
* if we have a complete answer. If so, call dns_found_answer on the
* result. If not, wait. Returns 0. */
int connection_dns_process_inbuf(connection_t *conn) {
char success;
uint32_t addr;
tor_assert(conn && conn->type == CONN_TYPE_DNSWORKER);
if(conn->inbuf_reached_eof) {
log_fn(LOG_WARN,"Read eof. Worker died unexpectedly.");
if(conn->state == DNSWORKER_STATE_BUSY) {
dns_cancel_pending_resolve(conn->address);
num_dnsworkers_busy--;
}
num_dnsworkers--;
connection_mark_for_close(conn);
return 0;
}
if(conn->state != DNSWORKER_STATE_BUSY) {
log_fn(LOG_WARN,"Bug: poll() indicated than an idle dns worker was readable. Please report.");
return 0;
}
if(buf_datalen(conn->inbuf) < 5) /* entire answer available? */
return 0; /* not yet */
tor_assert(conn->state == DNSWORKER_STATE_BUSY);
tor_assert(buf_datalen(conn->inbuf) == 5);
connection_fetch_from_buf(&success,1,conn);
connection_fetch_from_buf((char *)&addr,sizeof(uint32_t),conn);
log_fn(LOG_DEBUG, "DNSWorker (fd %d) returned answer for '%s'",
conn->s, conn->address);
tor_assert(success >= DNS_RESOLVE_FAILED_TRANSIENT);
tor_assert(success <= DNS_RESOLVE_SUCCEEDED);
dns_found_answer(conn->address, addr, success);
tor_free(conn->address);
conn->address = tor_strdup("");
conn->state = DNSWORKER_STATE_IDLE;
num_dnsworkers_busy--;
if (conn->timestamp_created < last_rotation_time) {
connection_mark_for_close(conn);
num_dnsworkers--;
spawn_enough_dnsworkers();
}
return 0;
}
/** Close and re-open all idle dnsworkers; schedule busy ones to be closed
* and re-opened once they're no longer busy.
**/
void dnsworkers_rotate(void)
{
connection_t *dnsconn;
while ((dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER,
DNSWORKER_STATE_IDLE))) {
connection_mark_for_close(dnsconn);
num_dnsworkers--;
}
last_rotation_time = time(NULL);
spawn_enough_dnsworkers();
}
/** Implementation for DNS workers; this code runs in a separate
* execution context. It takes as its argument an fdarray as returned
* by socketpair(), and communicates via fdarray[1]. The protocol is
* as follows:
* - The OR says:
* - ADDRESSLEN [1 byte]
* - ADDRESS [ADDRESSLEN bytes]
* - The DNS worker does the lookup, and replies:
* - OUTCOME [1 byte]
* - IP [4 bytes]
*
* OUTCOME is one of DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}.
* IP is in host order.
*
* The dnsworker runs indefinitely, until its connection is closed or an error
* occurs.
*/
static int dnsworker_main(void *data) {
char address[MAX_ADDRESSLEN];
unsigned char address_len;
char answer[5];
uint32_t ip;
int *fdarray = data;
int fd;
int result;
tor_close_socket(fdarray[0]); /* this is the side of the socketpair the parent uses */
fd = fdarray[1]; /* this side is ours */
#ifndef MS_WINDOWS
connection_free_all(); /* so the child doesn't hold the parent's fd's open */
#endif
handle_signals(0); /* ignore interrupts from the keyboard, etc */
for(;;) {
if(recv(fd, &address_len, 1, 0) != 1) {
log_fn(LOG_INFO,"dnsworker exiting because tor process closed connection (either pruned idle dnsworker or died).");
spawn_exit();
}
if(address_len && read_all(fd, address, address_len, 1) != address_len) {
log_fn(LOG_ERR,"read hostname failed. Child exiting.");
spawn_exit();
}
address[address_len] = 0; /* null terminate it */
result = tor_lookup_hostname(address, &ip);
/* Make 0.0.0.0 an error, so that we can use "0" to mean "no addr") */
if (!ip)
result = -1;
switch (result) {
case 1:
/* XXX008 result can never be 1, because we set it to -1 above on error */
log_fn(LOG_INFO,"Could not resolve dest addr %s (transient).",address);
answer[0] = DNS_RESOLVE_FAILED_TRANSIENT;
break;
case -1:
log_fn(LOG_INFO,"Could not resolve dest addr %s (permanent).",address);
answer[0] = DNS_RESOLVE_FAILED_PERMANENT;
break;
case 0:
log_fn(LOG_INFO,"Resolved address '%s'.",address);
answer[0] = DNS_RESOLVE_SUCCEEDED;
break;
}
set_uint32(answer+1, ip);
if(write_all(fd, answer, 5, 1) != 5) {
log_fn(LOG_ERR,"writing answer failed. Child exiting.");
spawn_exit();
}
}
return 0; /* windows wants this function to return an int */
}
/** Launch a new DNS worker; return 0 on success, -1 on failure.
*/
static int spawn_dnsworker(void) {
int fd[2];
connection_t *conn;
if(tor_socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0) {
log(LOG_ERR, "Couldn't construct socketpair: %s",
tor_socket_strerror(tor_socket_errno(-1)));
tor_cleanup();
exit(1);
}
spawn_func(dnsworker_main, (void*)fd);
log_fn(LOG_DEBUG,"just spawned a worker.");
tor_close_socket(fd[1]); /* we don't need the worker's side of the pipe */
conn = connection_new(CONN_TYPE_DNSWORKER);
set_socket_nonblocking(fd[0]);
/* set up conn so it's got all the data we need to remember */
conn->s = fd[0];
conn->address = tor_strdup("");
if(connection_add(conn) < 0) { /* no space, forget it */
log_fn(LOG_WARN,"connection_add failed. Giving up.");
connection_free(conn); /* this closes fd[0] */
return -1;
}
conn->state = DNSWORKER_STATE_IDLE;
connection_start_reading(conn);
return 0; /* success */
}
/** If we have too many or too few DNS workers, spawn or kill some.
*/
static void spawn_enough_dnsworkers(void) {
int num_dnsworkers_needed; /* aim to have 1 more than needed,
* but no less than min and no more than max */
connection_t *dnsconn;
/* XXX This may not be the best strategy. Maybe we should queue pending
* requests until the old ones finish or time out: otherwise, if
* the connection requests come fast enough, we never get any DNS done. -NM
* XXX But if we queue them, then the adversary can pile even more
* queries onto us, blocking legitimate requests for even longer.
* Maybe we should compromise and only kill if it's been at it for
* more than, e.g., 2 seconds. -RD
*/
if(num_dnsworkers_busy == MAX_DNSWORKERS) {
/* We always want at least one worker idle.
* So find the oldest busy worker and kill it.
*/
dnsconn = connection_get_by_type_state_lastwritten(CONN_TYPE_DNSWORKER,
DNSWORKER_STATE_BUSY);
tor_assert(dnsconn);
log_fn(LOG_WARN, "%d DNS workers are spawned; all are busy. Killing one.",
MAX_DNSWORKERS);
connection_mark_for_close(dnsconn);
num_dnsworkers_busy--;
num_dnsworkers--;
}
if(num_dnsworkers_busy >= MIN_DNSWORKERS)
num_dnsworkers_needed = num_dnsworkers_busy+1;
else
num_dnsworkers_needed = MIN_DNSWORKERS;
while(num_dnsworkers < num_dnsworkers_needed) {
if(spawn_dnsworker() < 0) {
log(LOG_WARN,"spawn_enough_dnsworkers(): spawn failed!");
return;
}
num_dnsworkers++;
}
while(num_dnsworkers > num_dnsworkers_busy+MAX_IDLE_DNSWORKERS) { /* too many idle? */
/* cull excess workers */
log_fn(LOG_WARN,"%d of %d dnsworkers are idle. Killing one.",
num_dnsworkers-num_dnsworkers_needed, num_dnsworkers);
dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
tor_assert(dnsconn);
connection_mark_for_close(dnsconn);
num_dnsworkers--;
}
}
/*
Local Variables:
mode:c
indent-tabs-mode:nil
c-basic-offset:2
End:
*/