bug 771: Remember whether navigation was requested by user

[elinks/kon.git] / src / network / connection.c

/* Connections management */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>
#include <string.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "elinks.h"

#include "cache/cache.h"
#include "config/options.h"
#include "document/document.h"
#include "encoding/encoding.h"
#include "intl/gettext/libintl.h"
#include "main/object.h"
#include "main/select.h"
#include "main/timer.h"
#include "network/connection.h"
#include "network/dns.h"
#include "network/progress.h"
#include "network/socket.h"
#include "network/ssl/ssl.h"
#include "protocol/protocol.h"
#include "protocol/proxy.h"
#include "protocol/uri.h"
#include "session/session.h"
#include "util/error.h"
#include "util/memory.h"
#include "util/string.h"
#include "util/time.h"


struct keepalive_connection {
        LIST_HEAD(struct keepalive_connection);

        /* XXX: This is just the URI of the connection that registered the
         * keepalive connection so only rely on the protocol, user, password,
         * host and port part. */
        struct uri *uri;

        /* Function called when the keepalive has timed out or is deleted */
        void (*done)(struct connection *);

        timeval_T timeout;
        timeval_T creation_time;

        unsigned int protocol_family:1; /* see network/socket.h, EL_PF_INET, EL_PF_INET6 */
        int socket;
};


static unsigned int connection_id = 0;
static int active_connections = 0;
static timer_id_T keepalive_timeout = TIMER_ID_UNDEF;

static INIT_LIST_OF(struct connection, connection_queue);
static INIT_LIST_OF(struct host_connection, host_connections);
static INIT_LIST_OF(struct keepalive_connection, keepalive_connections);

/* Prototypes */
static void notify_connection_callbacks(struct connection *conn);
static void check_keepalive_connections(void);


static /* inline */ enum connection_priority
get_priority(struct connection *conn)
{
        enum connection_priority priority;

        for (priority = 0; priority < PRIORITIES; priority++)
                if (conn->pri[priority])
                        break;

        assertm(priority != PRIORITIES, "Connection has no owner");
        /* Recovery path ;-). (XXX?) */

        return priority;
}

int
get_connections_count(void)
{
        return list_size(&connection_queue);
}

int
get_keepalive_connections_count(void)
{
        return list_size(&keepalive_connections);
}

int
get_connections_connecting_count(void)
{
        struct connection *conn;
        int i = 0;

        foreach (conn, connection_queue)
                i += is_in_connecting_state(conn->state);

        return i;
}

int
get_connections_transfering_count(void)
{
        struct connection *conn;
        int i = 0;

        foreach (conn, connection_queue)
                i += is_in_transfering_state(conn->state);

        return i;
}

/** Check whether the pointer @a conn still points to a connection
 * with the given @a id.  If the struct connection has already been
 * freed, this returns 0.  By comparing connection.id, this function
 * can usually detect even the case where a different connection has
 * been created at the same address.  For that to work, the caller
 * must save the connection.id before the connection can be deleted.  */
static inline int
connection_disappeared(struct connection *conn, unsigned int id)
{
        struct connection *c;

        foreach (c, connection_queue)
                if (conn == c && id == c->id)
                        return 0;

        return 1;
}

/* Host connection management: */
/* Used to keep track on the number of connections to any given host. When
 * trying to setup a new connection the list is searched to see if the maximum
 * number of connection has been reached. If that is the case we try to suspend
 * an already established connection. */
/* Some connections (like file://) that do not involve hosts are not maintained
 * in the list. */

struct host_connection {
        OBJECT_HEAD(struct host_connection);

        /* XXX: This is just the URI of the connection that registered the
         * host connection so only rely on the host part. */
        struct uri *uri;
};

static struct host_connection *
get_host_connection(struct connection *conn)
{
        struct host_connection *host_conn;

        if (!conn->uri->host) return NULL;

        foreach (host_conn, host_connections)
                if (compare_uri(host_conn->uri, conn->uri, URI_HOST))
                        return host_conn;

        return NULL;
}

/* Returns if the connection was successfully added. */
/* Don't add hostnameless host connections but they're valid. */
static int
add_host_connection(struct connection *conn)
{
        struct host_connection *host_conn = get_host_connection(conn);

        if (!host_conn && conn->uri->host) {
                host_conn = mem_calloc(1, sizeof(*host_conn));
                if (!host_conn) return 0;

                host_conn->uri = get_uri_reference(conn->uri);
                object_nolock(host_conn, "host_connection");
                add_to_list(host_connections, host_conn);
        }
        if (host_conn) object_lock(host_conn);

        return 1;
}

/* Decrements and free()s the host connection if it is the last 'refcount'. */
static void
done_host_connection(struct connection *conn)
{
        struct host_connection *host_conn = get_host_connection(conn);

        if (!host_conn) return;

        object_unlock(host_conn);
        if (is_object_used(host_conn)) return;

        del_from_list(host_conn);
        done_uri(host_conn->uri);
        mem_free(host_conn);
}


static void sort_queue();

#ifdef CONFIG_DEBUG
static void
check_queue_bugs(void)
{
        struct connection *conn;
        enum connection_priority prev_priority = 0;
        int cc = 0;

        foreach (conn, connection_queue) {
                enum connection_priority priority = get_priority(conn);

                cc += conn->running;

                assertm(priority >= prev_priority, "queue is not sorted");
                assertm(is_in_progress_state(conn->state),
                        "interrupted connection on queue (conn %s, state %d)",
                        struri(conn->uri), conn->state);
                prev_priority = priority;
        }

        assertm(cc == active_connections,
                "bad number of active connections (counted %d, stored %d)",
                cc, active_connections);
}
#else
#define check_queue_bugs()
#endif

static void
set_connection_socket_state(struct socket *socket, struct connection_state state)
{
        assert(socket);
        set_connection_state(socket->conn, state);
}

static void
set_connection_socket_timeout(struct socket *socket, struct connection_state state)
{
        assert(socket);
        set_connection_timeout(socket->conn);
}

static void
retry_connection_socket(struct socket *socket, struct connection_state state)
{
        assert(socket);
        retry_connection(socket->conn, state);
}

static void
done_connection_socket(struct socket *socket, struct connection_state state)
{
        assert(socket);
        abort_connection(socket->conn, state);
}

static struct connection *
init_connection(struct uri *uri, struct uri *proxied_uri, struct uri *referrer,
                off_t start, enum cache_mode cache_mode,
                enum connection_priority priority)
{
        static struct socket_operations connection_socket_operations = {
                set_connection_socket_state,
                set_connection_socket_timeout,
                retry_connection_socket,
                done_connection_socket,
        };
        struct connection *conn = mem_calloc(1, sizeof(*conn));

        if (!conn) return NULL;

        assert(proxied_uri->protocol != PROTOCOL_PROXY);

        conn->socket = init_socket(conn, &connection_socket_operations);
        if (!conn->socket) {
                mem_free(conn);
                return NULL;
        }

        conn->data_socket = init_socket(conn, &connection_socket_operations);
        if (!conn->data_socket) {
                mem_free(conn->socket);
                mem_free(conn);
                return NULL;
        }

        conn->progress = init_progress(start);
        if (!conn->progress) {
                mem_free(conn->data_socket);
                mem_free(conn->socket);
                mem_free(conn);
                return NULL;
        }

        /* load_uri() gets the URI from get_proxy() which grabs a reference for
         * us. */
        conn->uri = uri;
        conn->proxied_uri = proxied_uri;
        conn->id = connection_id++;
        conn->pri[priority] = 1;
        conn->cache_mode = cache_mode;

        conn->content_encoding = ENCODING_NONE;
        conn->stream_pipes[0] = conn->stream_pipes[1] = -1;
        init_list(conn->downloads);
        conn->est_length = -1;
        conn->timer = TIMER_ID_UNDEF;

        if (referrer) {
                /* Don't set referrer when it is the file protocol and the URI
                 * being loaded is not. This means CGI scripts will have it
                 * available while preventing information about the local
                 * system from being leaked to external servers. */
                if (referrer->protocol != PROTOCOL_FILE
                    || uri->protocol == PROTOCOL_FILE)
                        conn->referrer = get_uri_reference(referrer);
        }

        return conn;
}

static void
update_connection_progress(struct connection *conn)
{
        update_progress(conn->progress, conn->received, conn->est_length, conn->from);
}

/* Progress timer callback for @conn->progress.  As explained in
 * @start_update_progress, this function must erase the expired timer
 * ID from @conn->progress->timer.  */
static void
stat_timer(struct connection *conn)
{
        update_connection_progress(conn);
        /* The expired timer ID has now been erased.  */
        notify_connection_callbacks(conn);
}

void
set_connection_state(struct connection *conn, struct connection_state state)
{
        struct download *download;
        struct progress *progress = conn->progress;

        if (is_in_result_state(conn->state) && is_in_progress_state(state))
                conn->prev_error = conn->state;

        conn->state = state;
        if (is_in_state(conn->state, S_TRANS)) {
                if (progress->timer == TIMER_ID_UNDEF) {
                        const unsigned int id = conn->id;

                        start_update_progress(progress, (void (*)(void *)) stat_timer, conn);
                        update_connection_progress(conn);
                        if (connection_disappeared(conn, id))
                                return;
                }

        } else {
                kill_timer(&progress->timer);
        }

        foreach (download, conn->downloads) {
                download->state = state;
                download->prev_error = conn->prev_error;
        }

        if (is_in_progress_state(state)) notify_connection_callbacks(conn);
}

void
shutdown_connection_stream(struct connection *conn)
{
        if (conn->stream) {
                close_encoded(conn->stream);
                conn->stream = NULL;
        } else if (conn->stream_pipes[0] >= 0) {
                /* close_encoded() usually closes this end of the pipe,
                 * but open_encoded() apparently failed this time.  */
                close(conn->stream_pipes[0]);
        }
        if (conn->stream_pipes[1] >= 0)
                close(conn->stream_pipes[1]);
        conn->stream_pipes[0] = conn->stream_pipes[1] = -1;
}

static void
free_connection_data(struct connection *conn)
{
        assertm(conn->running, "connection already suspended");
        /* XXX: Recovery path? Originally, there was none. I think we'll get
         * at least active_connections underflows along the way. --pasky */
        conn->running = 0;

        active_connections--;
        assertm(active_connections >= 0, "active connections underflow");
        if_assert_failed active_connections = 0;

#ifdef CONFIG_SSL
        if (conn->socket->ssl && conn->cached)
                mem_free_set(&conn->cached->ssl_info, get_ssl_connection_cipher(conn->socket));
#endif

        if (conn->done)
                conn->done(conn);

        done_socket(conn->socket);
        done_socket(conn->data_socket);

        shutdown_connection_stream(conn);

        mem_free_set(&conn->info, NULL);

        kill_timer(&conn->timer);

        if (!is_in_state(conn->state, S_WAIT))
                done_host_connection(conn);
}

void
notify_connection_callbacks(struct connection *conn)
{
        struct connection_state state = conn->state;
        unsigned int id = conn->id;
        struct download *download, *next;

        foreachsafe (download, next, conn->downloads) {
                download->cached = conn->cached;
                if (download->callback)
                        download->callback(download, download->data);
                if (is_in_progress_state(state)
                    && connection_disappeared(conn, id))
                        return;
        }
}

static void
done_connection(struct connection *conn)
{
        /* When removing the connection callbacks should always be aware of it
         * so they can unregister themselves. We do this by enforcing that the
         * connection is in a result state. If it is not already it is an
         * internal bug. This should never happen but it does. ;) --jonas */
        if (!is_in_result_state(conn->state))
                set_connection_state(conn, connection_state(S_INTERNAL));

        del_from_list(conn);
        notify_connection_callbacks(conn);
        if (conn->referrer) done_uri(conn->referrer);
        done_uri(conn->uri);
        done_uri(conn->proxied_uri);
        mem_free(conn->socket);
        mem_free(conn->data_socket);
        done_progress(conn->progress);
        mem_free(conn);
        check_queue_bugs();
}

static inline void
add_to_queue(struct connection *conn)
{
        struct connection *c;
        enum connection_priority priority = get_priority(conn);

        foreach (c, connection_queue)
                if (get_priority(c) > priority)
                        break;

        add_at_pos(c->prev, conn);
}


/* Returns zero if no callback was done and the keepalive connection should be
 * deleted or non-zero if the keepalive connection should not be deleted. */
static int
do_keepalive_connection_callback(struct keepalive_connection *keep_conn)
{
        struct uri *proxied_uri = get_proxied_uri(keep_conn->uri);
        struct uri *proxy_uri   = get_proxy_uri(keep_conn->uri, NULL);

        if (proxied_uri && proxy_uri) {
                struct connection *conn;

                conn = init_connection(proxy_uri, proxied_uri, NULL, 0,
                                       CACHE_MODE_NEVER, PRI_CANCEL);

                if (conn) {
                        void (*done)(struct connection *) = keep_conn->done;

                        add_to_queue(conn);

                        /* Get the keepalive info and let it clean up */
                        if (!has_keepalive_connection(conn)
                            || !add_host_connection(conn)) {
                                free_connection_data(conn);
                                done_connection(conn);
                                return 0;
                        }

                        active_connections++;
                        conn->running = 1;
                        done(conn);
                        return 1;
                }
        }

        if (proxied_uri) done_uri(proxied_uri);
        if (proxy_uri) done_uri(proxy_uri);

        return 0;
}

static inline void
done_keepalive_connection(struct keepalive_connection *keep_conn)
{
        if (keep_conn->done && do_keepalive_connection_callback(keep_conn))
                return;

        del_from_list(keep_conn);
        if (keep_conn->socket != -1) close(keep_conn->socket);
        done_uri(keep_conn->uri);
        mem_free(keep_conn);
}

static struct keepalive_connection *
init_keepalive_connection(struct connection *conn, long timeout_in_seconds,
                          void (*done)(struct connection *))
{
        struct keepalive_connection *keep_conn;
        struct uri *uri = conn->uri;

        assert(uri->host);
        if_assert_failed return NULL;

        keep_conn = mem_calloc(1, sizeof(*keep_conn));
        if (!keep_conn) return NULL;

        keep_conn->uri = get_uri_reference(uri);
        keep_conn->done = done;
        keep_conn->protocol_family = conn->socket->protocol_family;
        keep_conn->socket = conn->socket->fd;
        timeval_from_seconds(&keep_conn->timeout, timeout_in_seconds);
        timeval_now(&keep_conn->creation_time);

        return keep_conn;
}

static struct keepalive_connection *
get_keepalive_connection(struct connection *conn)
{
        struct keepalive_connection *keep_conn;

        if (!conn->uri->host) return NULL;

        foreach (keep_conn, keepalive_connections)
                if (compare_uri(keep_conn->uri, conn->uri, URI_KEEPALIVE))
                        return keep_conn;

        return NULL;
}

int
has_keepalive_connection(struct connection *conn)
{
        struct keepalive_connection *keep_conn = get_keepalive_connection(conn);

        if (!keep_conn) return 0;

        conn->socket->fd = keep_conn->socket;
        conn->socket->protocol_family = keep_conn->protocol_family;

        /* Mark that the socket should not be closed and the callback should be
         * ignored. */
        keep_conn->socket = -1;
        keep_conn->done = NULL;
        done_keepalive_connection(keep_conn);

        return 1;
}

void
add_keepalive_connection(struct connection *conn, long timeout_in_seconds,
                         void (*done)(struct connection *))
{
        struct keepalive_connection *keep_conn;

        assertm(conn->socket->fd != -1, "keepalive connection not connected");
        if_assert_failed goto done;

        keep_conn = init_keepalive_connection(conn, timeout_in_seconds, done);
        if (keep_conn) {
                /* Make sure that the socket descriptor will not periodically be
                 * checked or closed by free_connection_data(). */
                clear_handlers(conn->socket->fd);
                conn->socket->fd = -1;
                add_to_list(keepalive_connections, keep_conn);

        } else if (done) {
                /* It will take just a little more time */
                done(conn);
                return;
        }

done:
        free_connection_data(conn);
        done_connection(conn);
        register_check_queue();
}

/* Timer callback for @keepalive_timeout.  As explained in @install_timer,
 * this function must erase the expired timer ID from all variables.  */
static void
keepalive_timer(void *x)
{
        keepalive_timeout = TIMER_ID_UNDEF;
        /* The expired timer ID has now been erased.  */
        check_keepalive_connections();
}

void
check_keepalive_connections(void)
{
        struct keepalive_connection *keep_conn, *next;
        timeval_T now;
        int p = 0;

        timeval_now(&now);

        kill_timer(&keepalive_timeout);

        foreachsafe (keep_conn, next, keepalive_connections) {
                timeval_T age;

                if (can_read(keep_conn->socket)) {
                        done_keepalive_connection(keep_conn);
                        continue;
                }

                timeval_sub(&age, &keep_conn->creation_time, &now);
                if (timeval_cmp(&age, &keep_conn->timeout) > 0) {
                        done_keepalive_connection(keep_conn);
                        continue;
                }

                p++;
        }

        for (; p > MAX_KEEPALIVE_CONNECTIONS; p--) {
                assertm(!list_empty(keepalive_connections), "keepalive list empty");
                if_assert_failed return;
                done_keepalive_connection(keepalive_connections.prev);
        }

        if (!list_empty(keepalive_connections))
                install_timer(&keepalive_timeout, KEEPALIVE_CHECK_TIME,
                              keepalive_timer, NULL);
}

static inline void
abort_all_keepalive_connections(void)
{
        while (!list_empty(keepalive_connections))
                done_keepalive_connection(keepalive_connections.next);

        check_keepalive_connections();
}


static void
sort_queue(void)
{
        while (1) {
                struct connection *conn;
                int swp = 0;

                foreach (conn, connection_queue) {
                        if (!list_has_next(connection_queue, conn)) break;

                        if (get_priority(conn->next) < get_priority(conn)) {
                                struct connection *c = conn->next;

                                del_from_list(conn);
                                add_at_pos(c, conn);
                                swp = 1;
                        }
                }

                if (!swp) break;
        };
}

static void
interrupt_connection(struct connection *conn)
{
        free_connection_data(conn);
}

static inline void
suspend_connection(struct connection *conn)
{
        interrupt_connection(conn);
        set_connection_state(conn, connection_state(S_WAIT));
}

static void
run_connection(struct connection *conn)
{
        protocol_handler_T *func = get_protocol_handler(conn->uri->protocol);

        assert(func);

        assertm(!conn->running, "connection already running");
        if_assert_failed return;

        if (!add_host_connection(conn)) {
                set_connection_state(conn, connection_state(S_OUT_OF_MEM));
                done_connection(conn);
                return;
        }

        active_connections++;
        conn->running = 1;

        func(conn);
}

/* Set certain state on a connection and then abort the connection. */
void
abort_connection(struct connection *conn, struct connection_state state)
{
        assertm(is_in_result_state(state),
                "connection didn't end in result state (%d)", state);

        if (is_in_state(state, S_OK) && conn->cached)
                normalize_cache_entry(conn->cached, conn->from);

        set_connection_state(conn, state);

        if (conn->running) interrupt_connection(conn);
        done_connection(conn);
        register_check_queue();
}

/* Set certain state on a connection and then retry the connection. */
void
retry_connection(struct connection *conn, struct connection_state state)
{
        int max_tries = get_opt_int("connection.retries");

        assertm(is_in_result_state(state),
                "connection didn't end in result state (%d)", state);

        set_connection_state(conn, state);

        interrupt_connection(conn);
        if (conn->uri->post || (max_tries && ++conn->tries >= max_tries)) {
                done_connection(conn);
                register_check_queue();
        } else {
                conn->prev_error = conn->state;
                run_connection(conn);
        }
}

static int
try_to_suspend_connection(struct connection *conn, struct uri *uri)
{
        enum connection_priority priority = get_priority(conn);
        struct connection *c;

        foreachback (c, connection_queue) {
                if (get_priority(c) <= priority) return -1;
                if (is_in_state(c->state, S_WAIT)) continue;
                if (c->uri->post && get_priority(c) < PRI_CANCEL) continue;
                if (uri && !compare_uri(uri, c->uri, URI_HOST)) continue;
                suspend_connection(c);
                return 0;
        }

        return -1;
}

static inline int
try_connection(struct connection *conn, int max_conns_to_host, int max_conns)
{
        struct host_connection *host_conn = get_host_connection(conn);

        if (host_conn && get_object_refcount(host_conn) >= max_conns_to_host)
                return try_to_suspend_connection(conn, host_conn->uri) ? 0 : -1;

        if (active_connections >= max_conns)
                return try_to_suspend_connection(conn, NULL) ? 0 : -1;

        run_connection(conn);
        return 1;
}

static void
check_queue(void)
{
        struct connection *conn;
        int max_conns_to_host = get_opt_int("connection.max_connections_to_host");
        int max_conns = get_opt_int("connection.max_connections");

again:
        conn = connection_queue.next;
        check_queue_bugs();
        check_keepalive_connections();

        while (conn != (struct connection *) &connection_queue) {
                struct connection *c;
                enum connection_priority pri = get_priority(conn);

                for (c = conn; c != (struct connection *) &connection_queue && get_priority(c) == pri;) {
                        struct connection *cc = c;

                        c = c->next;
                        if (is_in_state(cc->state, S_WAIT)
                            && get_keepalive_connection(cc)
                            && try_connection(cc, max_conns_to_host, max_conns))
                                goto again;
                }

                for (c = conn; c != (struct connection *) &connection_queue && get_priority(c) == pri;) {
                        struct connection *cc = c;

                        c = c->next;
                        if (is_in_state(cc->state, S_WAIT)
                            && try_connection(cc, max_conns_to_host, max_conns))
                                goto again;
                }
                conn = c;
        }

again2:
        foreachback (conn, connection_queue) {
                if (get_priority(conn) < PRI_CANCEL) break;
                if (is_in_state(conn->state, S_WAIT)) {
                        set_connection_state(conn, connection_state(S_INTERRUPTED));
                        done_connection(conn);
                        goto again2;
                }
        }

        check_queue_bugs();
}

int
register_check_queue(void)
{
        return register_bottom_half(check_queue, NULL);
}

int
load_uri(struct uri *uri, struct uri *referrer, struct download *download,
         enum connection_priority pri, enum cache_mode cache_mode, off_t start)
{
        struct cache_entry *cached;
        struct connection *conn;
        struct uri *proxy_uri, *proxied_uri;
        struct connection_state error_state = connection_state(S_OK);

        if (download) {
                download->conn = NULL;
                download->cached = NULL;
                download->pri = pri;
                download->state = connection_state(S_OUT_OF_MEM);
                download->prev_error = connection_state(0);
        }

#ifdef CONFIG_DEBUG
        foreach (conn, connection_queue) {
                struct download *assigned;

                foreach (assigned, conn->downloads) {
                        assertm(assigned != download, "Download assigned to '%s'", struri(conn->uri));
                        if_assert_failed {
                                download->state = connection_state(S_INTERNAL);
                                if (download->callback)
                                        download->callback(download, download->data);
                                return 0;
                        }
                        /* No recovery path should be necessary. */
                }
        }
#endif

        cached = get_validated_cache_entry(uri, cache_mode);
        if (cached) {
                if (download) {
                        download->cached = cached;
                        download->state = connection_state(S_OK);
                        /* XXX:
                         * This doesn't work since sometimes |download->progress|
                         * is undefined and contains random memory locations.
                         * It's not supposed to point on anything here since
                         * |download| has no connection attached.
                         * Downloads resuming will probably break in some
                         * cases without this, though.
                         * FIXME: Needs more investigation. --pasky */
                        /* if (download->progress) download->progress->start = start; */
                        if (download->callback)
                                download->callback(download, download->data);
                }
                return 0;
        }

        proxied_uri = get_proxied_uri(uri);
        proxy_uri   = get_proxy_uri(uri, &error_state);

        if (!proxy_uri
            || !proxied_uri
            || (get_protocol_need_slash_after_host(proxy_uri->protocol)
                && !proxy_uri->hostlen)) {

                if (download) {
                        if (is_in_state(error_state, S_OK)) {
                                error_state = proxy_uri && proxied_uri
                                        ? connection_state(S_BAD_URL)
                                        : connection_state(S_OUT_OF_MEM);
                        }

                        download->state = error_state;
                        download->callback(download, download->data);
                }
                if (proxy_uri) done_uri(proxy_uri);
                if (proxied_uri) done_uri(proxied_uri);
                return -1;
        }

        foreach (conn, connection_queue) {
                if (conn->detached
                    || !compare_uri(conn->uri, proxy_uri, 0))
                        continue;

                done_uri(proxy_uri);
                done_uri(proxied_uri);

                if (get_priority(conn) > pri) {
                        del_from_list(conn);
                        conn->pri[pri]++;
                        add_to_queue(conn);
                        register_check_queue();
                } else {
                        conn->pri[pri]++;
                }

                if (download) {
                        download->progress = conn->progress;
                        download->conn = conn;
                        download->cached = conn->cached;
                        add_to_list(conn->downloads, download);
                        /* This is likely to call download->callback() now! */
                        set_connection_state(conn, conn->state);
                }
                check_queue_bugs();
                return 0;
        }

        conn = init_connection(proxy_uri, proxied_uri, referrer, start, cache_mode, pri);
        if (!conn) {
                if (download) {
                        download->state = connection_state(S_OUT_OF_MEM);
                        download->callback(download, download->data);
                }
                if (proxy_uri) done_uri(proxy_uri);
                if (proxied_uri) done_uri(proxied_uri);
                return -1;
        }

        if (cache_mode < CACHE_MODE_FORCE_RELOAD && cached && !list_empty(cached->frag)
            && !((struct fragment *) cached->frag.next)->offset)
                conn->from = ((struct fragment *) cached->frag.next)->length;

        if (download) {
                download->progress = conn->progress;
                download->conn = conn;
                download->cached = NULL;
                download->state = connection_state(S_OK);
                add_to_list(conn->downloads, download);
        }

        add_to_queue(conn);
        set_connection_state(conn, connection_state(S_WAIT));

        check_queue_bugs();

        register_check_queue();
        return 0;
}


/* FIXME: one object in more connections */
void
cancel_download(struct download *download, int interrupt)
{
        struct connection *conn;

        assert(download);
        if_assert_failed return;

        /* Did the connection already end? */
        if (is_in_result_state(download->state))
                return;

        assertm(download->conn != NULL, "last state is %d", download->state);

        check_queue_bugs();

        download->state = connection_state(S_INTERRUPTED);
        del_from_list(download);

        conn = download->conn;

        conn->pri[download->pri]--;
        assertm(conn->pri[download->pri] >= 0, "priority counter underflow");
        if_assert_failed conn->pri[download->pri] = 0;

        if (list_empty(conn->downloads)) {
                /* Necessary because of assertion in get_priority(). */
                conn->pri[PRI_CANCEL]++;

                if (conn->detached || interrupt)
                        abort_connection(conn, connection_state(S_INTERRUPTED));
        }

        sort_queue();
        check_queue_bugs();

        register_check_queue();
}

void
move_download(struct download *old, struct download *new,
              enum connection_priority newpri)
{
        struct connection *conn;

        assert(old);

        /* The download doesn't necessarily have a connection attached, for
         * example the file protocol loads it's object immediately. This is
         * catched by the result state check below. */

        conn = old->conn;

        new->conn       = conn;
        new->cached     = old->cached;
        new->prev_error = old->prev_error;
        new->progress   = old->progress;
        new->state      = old->state;
        new->pri        = newpri;

        if (is_in_result_state(old->state)) {
                /* Ensure that new->conn is always "valid", that is NULL if the
                 * connection has been detached and non-NULL otherwise. */
                if (new->callback) {
                        new->conn = NULL;
                        new->progress = NULL;
                        new->callback(new, new->data);
                }
                return;
        }

        assertm(old->conn != NULL, "last state is %d", old->state);

        conn->pri[new->pri]++;
        add_to_list(conn->downloads, new);
        /* In principle, we need to sort_queue() only if conn->pri[new->pri]
         * just changed from 0 to 1.  But the risk of bugs is smaller if we
         * sort every time.  */
        sort_queue();

        cancel_download(old, 0);
}


/* This will remove 'pos' bytes from the start of the cache for the specified
 * connection, if the cached object is already too big. */
void
detach_connection(struct download *download, off_t pos)
{
        struct connection *conn = download->conn;

        if (is_in_result_state(download->state)) return;

        if (!conn->detached) {
                off_t total_len;
                off_t i, total_pri = 0;

                if (!conn->cached)
                        return;

                total_len = (conn->est_length == -1) ? conn->from
                                                     : conn->est_length;

                if (total_len < (get_opt_long("document.cache.memory.size")
                                 * MAX_CACHED_OBJECT_PERCENT / 100)) {
                        /* This whole thing will fit to the memory anyway, so
                         * there's no problem in detaching the connection. */
                        return;
                }

                for (i = 0; i < PRI_CANCEL; i++)
                        total_pri += conn->pri[i];
                assertm(total_pri, "detaching free connection");
                /* No recovery path should be necessary...? */

                /* Pre-clean cache. */
                shrink_format_cache(0);

                if (total_pri != 1 || is_object_used(conn->cached)) {
                        /* We're too important, or someone uses our cache
                         * entry. */
                        return;
                }

                /* DBG("detached"); */

                /* We aren't valid cache entry anymore. */
                conn->cached->valid = 0;
                conn->detached = 1;
        }

        /* Strip the entry. */
        free_entry_to(conn->cached, pos);
}

/* Timer callback for @conn->timer.  As explained in @install_timer,
 * this function must erase the expired timer ID from all variables.  */
static void
connection_timeout(struct connection *conn)
{
        conn->timer = TIMER_ID_UNDEF;
        /* The expired timer ID has now been erased.  */
        timeout_socket(conn->socket);
}

/* Timer callback for @conn->timer.  As explained in @install_timer,
 * this function must erase the expired timer ID from all variables.
 *
 * Huh, using two timers? Is this to account for changes of c->unrestartable
 * or can it be reduced? --jonas */
static void
connection_timeout_1(struct connection *conn)
{
        install_timer(&conn->timer, (milliseconds_T)
                        ((conn->unrestartable
                         ? get_opt_int("connection.unrestartable_receive_timeout")
                         : get_opt_int("connection.receive_timeout"))
                        * 500), (void (*)(void *)) connection_timeout, conn);
        /* The expired timer ID has now been erased.  */
}

void
set_connection_timeout(struct connection *conn)
{
        kill_timer(&conn->timer);

        install_timer(&conn->timer, (milliseconds_T)
                        ((conn->unrestartable
                         ? get_opt_int("connection.unrestartable_receive_timeout")
                         : get_opt_int("connection.receive_timeout"))
                        * 500), (void (*)(void *)) connection_timeout_1, conn);
}


void
abort_all_connections(void)
{
        while (!list_empty(connection_queue)) {
                abort_connection(connection_queue.next,
                                 connection_state(S_INTERRUPTED));
        }

        abort_all_keepalive_connections();
}

void
abort_background_connections(void)
{
        struct connection *conn, *next;

        foreachsafe (conn, next, connection_queue) {
                if (get_priority(conn) >= PRI_CANCEL)
                        abort_connection(conn, connection_state(S_INTERRUPTED));
        }
}

int
is_entry_used(struct cache_entry *cached)
{
        struct connection *conn;

        foreach (conn, connection_queue)
                if (conn->cached == cached)
                        return 1;

        return 0;
}