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- /* Copyright 2003 Roger Dingledine. */
- /* See LICENSE for licensing information */
- /* $Id$ */
- /* 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"
- #define MAX_ADDRESSLEN 256
- #define MAX_DNSWORKERS 50
- #define MIN_DNSWORKERS 3
- #define MAX_IDLE_DNSWORKERS 10
- int num_dnsworkers=0;
- int num_dnsworkers_busy=0;
- static void purge_expired_resolves(uint32_t now);
- static int assign_to_dnsworker(connection_t *exitconn);
- static void dns_found_answer(char *question, uint32_t answer);
- int dnsworker_main(void *data);
- static int spawn_dnsworker(void);
- static void spawn_enough_dnsworkers(void);
- struct pending_connection_t {
- struct connection_t *conn;
- struct pending_connection_t *next;
- };
- struct cached_resolve {
- SPLAY_ENTRY(cached_resolve) node;
- char question[MAX_ADDRESSLEN]; /* the hostname to be resolved */
- uint32_t answer; /* in host order. I know I'm horrible for assuming ipv4 */
- 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 untouched items from cache after some time? */
- struct pending_connection_t *pending_connections;
- struct cached_resolve *next;
- };
- SPLAY_HEAD(cache_tree, cached_resolve) cache_root;
- static int compare_cached_resolves(struct cached_resolve *a, struct cached_resolve *b) {
- /* make this smarter one day? */
- return strncasecmp(a->question, b->question, MAX_ADDRESSLEN);
- }
- SPLAY_PROTOTYPE(cache_tree, cached_resolve, node, compare_cached_resolves);
- SPLAY_GENERATE(cache_tree, cached_resolve, node, compare_cached_resolves);
- static void init_cache_tree(void) {
- SPLAY_INIT(&cache_root);
- }
- void dns_init(void) {
- init_cache_tree();
- spawn_enough_dnsworkers();
- }
- static struct cached_resolve *oldest_cached_resolve = NULL; /* linked list, */
- static struct cached_resolve *newest_cached_resolve = NULL; /* oldest to newest */
- static void purge_expired_resolves(uint32_t now) {
- struct cached_resolve *resolve;
- /* 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 %d)", resolve->expire);
- 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);
- free(resolve);
- }
- }
- /* See if the question 'exitconn->address' has been answered. 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;
- uint32_t now = time(NULL);
- /* first 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 'question' is already there. */
- strncpy(search.question, exitconn->address, MAX_ADDRESSLEN);
- 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(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);
-
- return 0;
- case CACHE_STATE_VALID:
- exitconn->addr = resolve->answer;
- log_fn(LOG_DEBUG,"Connection (fd %d) found cached answer for '%s'",
- exitconn->s, exitconn->address);
- return 1;
- case CACHE_STATE_FAILED:
- return -1;
- }
- } else { /* need to add it */
- resolve = tor_malloc_zero(sizeof(struct cached_resolve));
- resolve->state = CACHE_STATE_PENDING;
- resolve->expire = now + 15*60; /* 15 minutes */
- strncpy(resolve->question, exitconn->address, MAX_ADDRESSLEN);
- /* add us to the pending list */
- pending_connection = tor_malloc(sizeof(struct pending_connection_t));
- pending_connection->conn = exitconn;
- pending_connection->next = resolve->pending_connections;
- resolve->pending_connections = pending_connection;
- /* 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);
- }
- assert(0);
- return 0; /* not reached; keep gcc happy */
- }
- static int assign_to_dnsworker(connection_t *exitconn) {
- connection_t *dnsconn;
- unsigned char len;
- 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, NULL);
- return -1;
- }
- log_fn(LOG_DEBUG, "Connection (fd %d) needs to resolve '%s'; assigning to DNSWorker (fd %d)",
- exitconn->s, exitconn->address, dnsconn->s);
- 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;
- }
- /* if onlyconn is NULL, cancel the whole thing. if onlyconn is defined,
- * then remove onlyconn from the pending list, and if the pending list
- * is now empty, cancel the whole thing.
- */
- void dns_cancel_pending_resolve(char *question, connection_t *onlyconn) {
- struct pending_connection_t *pend, *victim;
- struct cached_resolve search;
- struct cached_resolve *resolve, *tmp;
- strncpy(search.question, question, MAX_ADDRESSLEN);
- resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
- if(!resolve) {
- log_fn(LOG_WARN,"Question '%s' is not pending. Dropping.", question);
- return;
- }
- assert(resolve->state == CACHE_STATE_PENDING);
- assert(resolve->pending_connections);
- if(onlyconn) {
- pend = resolve->pending_connections;
- if(pend->conn == onlyconn) {
- resolve->pending_connections = pend->next;
- free(pend);
- if(resolve->pending_connections) {/* more pending, don't cancel it */
- log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
- onlyconn->s, question);
- return;
- }
- } else {
- for( ; pend->next; pend = pend->next) {
- if(pend->next->conn == onlyconn) {
- victim = pend->next;
- pend->next = victim->next;
- free(victim);
- log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
- onlyconn->s, question);
- return; /* more are pending */
- }
- }
- assert(0); /* not reachable unless onlyconn not in pending list */
- }
- } else {
- /* mark all pending connections to fail */
- log_fn(LOG_DEBUG, "Failing all connections waiting on DNS resolve of '%s'",
- question);
- while(resolve->pending_connections) {
- pend = resolve->pending_connections;
- connection_edge_end(pend->conn, END_STREAM_REASON_MISC, NULL);
- resolve->pending_connections = pend->next;
- free(pend);
- }
- }
- /* 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) ;
- 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);
- free(resolve);
- }
- static void dns_found_answer(char *question, uint32_t answer) {
- struct pending_connection_t *pend;
- struct cached_resolve search;
- struct cached_resolve *resolve;
- strncpy(search.question, question, MAX_ADDRESSLEN);
- resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
- if(!resolve) {
- log_fn(LOG_WARN,"Answer to unasked question '%s'? Dropping.", question);
- /* 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) {
- log_fn(LOG_WARN, "Duplicate answer to question '%s'; ignoring",
- question);
- 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. */
- /* assert(resolve->state == CACHE_STATE_PENDING); */
- resolve->answer = ntohl(answer);
- if(resolve->answer)
- resolve->state = CACHE_STATE_VALID;
- else
- resolve->state = CACHE_STATE_FAILED;
- while(resolve->pending_connections) {
- pend = resolve->pending_connections;
- pend->conn->addr = resolve->answer;
- if(resolve->state == CACHE_STATE_FAILED)
- connection_edge_end(pend->conn, END_STREAM_REASON_RESOLVEFAILED, NULL);
- else
- connection_exit_connect(pend->conn);
- resolve->pending_connections = pend->next;
- free(pend);
- }
- }
- /******************************************************************/
- int connection_dns_finished_flushing(connection_t *conn) {
- assert(conn && conn->type == CONN_TYPE_DNSWORKER);
- connection_stop_writing(conn);
- return 0;
- }
- int connection_dns_process_inbuf(connection_t *conn) {
- uint32_t answer;
- assert(conn && conn->type == CONN_TYPE_DNSWORKER);
- if(conn->inbuf_reached_eof) {
- log_fn(LOG_WARN,"Read eof. Worker dying.");
- if(conn->state == DNSWORKER_STATE_BUSY) {
- dns_cancel_pending_resolve(conn->address, NULL);
- num_dnsworkers_busy--;
- }
- num_dnsworkers--;
- return -1;
- }
- assert(conn->state == DNSWORKER_STATE_BUSY);
- if(buf_datalen(conn->inbuf) < 4) /* entire answer available? */
- return 0; /* not yet */
- assert(buf_datalen(conn->inbuf) == 4);
- connection_fetch_from_buf((char*)&answer,sizeof(answer),conn);
- log_fn(LOG_DEBUG, "DNSWorker (fd %d) returned answer for '%s'",
- conn->s, conn->address);
- dns_found_answer(conn->address, answer);
- free(conn->address);
- conn->address = tor_strdup("<idle>");
- conn->state = DNSWORKER_STATE_IDLE;
- num_dnsworkers_busy--;
- return 0;
- }
- int dnsworker_main(void *data) {
- char question[MAX_ADDRESSLEN];
- unsigned char question_len;
- struct hostent *rent;
- int *fdarray = data;
- int fd;
- close(fdarray[0]); /* this is the side of the socketpair the parent uses */
- fd = fdarray[1]; /* this side is ours */
- for(;;) {
- if(read(fd, &question_len, 1) != 1) {
- log_fn(LOG_ERR,"read length failed. Child exiting.");
- spawn_exit();
- }
- assert(question_len > 0);
- if(read_all(fd, question, question_len) != question_len) {
- log_fn(LOG_ERR,"read hostname failed. Child exiting.");
- spawn_exit();
- }
- question[question_len] = 0; /* null terminate it */
- rent = gethostbyname(question);
- if (!rent) {
- log_fn(LOG_INFO,"Could not resolve dest addr %s. Returning nulls.",question);
- if(write_all(fd, "\0\0\0\0", 4) != 4) {
- log_fn(LOG_ERR,"writing nulls failed. Child exiting.");
- spawn_exit();
- }
- } else {
- assert(rent->h_length == 4); /* break to remind us if we move away from ipv4 */
- if(write_all(fd, rent->h_addr, 4) != 4) {
- log_fn(LOG_INFO,"writing answer failed. Child exiting.");
- spawn_exit();
- }
- log_fn(LOG_INFO,"Answered question '%s'.",question);
- }
- }
- return 0; /* windows wants this function to return an int */
- }
- 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", strerror(errno));
- exit(1);
- }
- spawn_func(dnsworker_main, (void*)fd);
- log_fn(LOG_DEBUG,"just spawned a worker.");
- close(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("<unused>");
- 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 */
- }
- 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
- * XXX requests until the old ones finish or time out: otherwise, if
- * XXX the connection requests come fast enough, we never get any DNS done.
- */
- 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);
- assert(dnsconn);
- log_fn(LOG_DEBUG, "Max DNS workers spawned; all are busy. Killing one.");
- /* tell the exit connection that it's failed */
- dns_cancel_pending_resolve(dnsconn->address, NULL);
- dnsconn->marked_for_close = 1;
- 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_needed+MAX_IDLE_DNSWORKERS) { /* too many idle? */
- /* cull excess workers */
- dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
- assert(dnsconn);
- dnsconn->marked_for_close = 1;
- num_dnsworkers--;
- }
- }
- /*
- Local Variables:
- mode:c
- indent-tabs-mode:nil
- c-basic-offset:2
- End:
- */
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