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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;
return 0;
case CACHE_STATE_VALID:
exitconn->addr = resolve->answer;
return 1;
case CACHE_STATE_FAILED:
return -1;
}
} else { /* need to add it */
resolve = tor_malloc(sizeof(struct cached_resolve));
memset(resolve, 0, sizeof(struct cached_resolve));
resolve->state = CACHE_STATE_PENDING;
resolve->expire = now + 100; /* XXX for testing. when we're confident, switch it back */
// resolve->expire = now + 86400; /* now + 1 day */
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_INFO,"no idle dns workers. Failing.");
dns_cancel_pending_resolve(exitconn->address, NULL);
return -1;
}
dnsconn->address = strdup(exitconn->address);
dnsconn->state = DNSWORKER_STATE_BUSY;
num_dnsworkers_busy++;
len = strlen(dnsconn->address);
/* FFFF we should have it retry if the first worker bombs out */
if(connection_write_to_buf(&len, 1, dnsconn) < 0 ||
connection_write_to_buf(dnsconn->address, len, dnsconn) < 0) {
log_fn(LOG_NOTICE,"Write failed. Closing worker and failing resolve.");
dnsconn->marked_for_close = 1;
dns_cancel_pending_resolve(exitconn->address, NULL);
return -1;
}
// 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_INFO,"Answer to unasked question '%s'? 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 */
return;
} else {
for( ; pend->next; pend = pend->next) {
if(pend->next->conn == onlyconn) {
victim = pend->next;
pend->next = victim->next;
free(victim);
return; /* more are pending */
}
}
assert(0); /* not reachable unless onlyconn not in pending list */
}
} else {
/* mark all pending connections to fail */
while(resolve->pending_connections) {
pend = resolve->pending_connections;
pend->conn->marked_for_close = 1;
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_INFO,"Answer to unasked question '%s'? Dropping.", question);
return;
}
assert(resolve->state == CACHE_STATE_PENDING);
/* XXX sometimes this still gets triggered. :( */
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_exit_connect(pend->conn) < 0) {
pend->conn->marked_for_close = 1;
}
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(LOG_ERR,"connection_dnsworker_process_inbuf(): 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(conn->inbuf_datalen < 4) /* entire answer available? */
return 0; /* not yet */
assert(conn->inbuf_datalen == 4);
connection_fetch_from_buf((char*)&answer,sizeof(answer),conn);
dns_found_answer(conn->address, answer);
free(conn->address);
conn->address = NULL;
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(LOG_INFO,"dnsworker_main(): read length failed. Exiting.");
spawn_exit();
}
assert(question_len > 0);
if(read(fd, question, question_len) != question_len) {
log(LOG_INFO,"dnsworker_main(): read hostname failed. Exiting.");
spawn_exit();
}
question[question_len] = 0; /* null terminate it */
rent = gethostbyname(question);
if (!rent) {
log(LOG_INFO,"dnsworker_main(): Could not resolve dest addr %s. Returning nulls.",question);
if(write_all(fd, "\0\0\0\0", 4) != 4) {
log(LOG_INFO,"dnsworker_main(): writing nulls failed. 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(LOG_INFO,"dnsworker_main(): writing answer failed. Exiting.");
spawn_exit();
}
log(LOG_INFO,"dnsworker_main(): 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) {
perror("socketpair");
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);
if(!conn) {
close(fd[0]);
return -1;
}
set_socket_nonblocking(fd[0]);
/* set up conn so it's got all the data we need to remember */
conn->receiver_bucket = -1; /* non-cell connections don't do receiver buckets */
conn->bandwidth = -1;
conn->s = fd[0];
if(connection_add(conn) < 0) { /* no space, forget it */
log_fn(LOG_INFO,"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;
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);
/* tell the exit connection that it's failed */
dns_cancel_pending_resolve(dnsconn->address, NULL);
dnsconn->marked_for_close = 1;
num_dnsworkers_busy--;
}
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_ERR,"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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