view src/mail/ngx_mail_proxy_module.c @ 7354:1812f1d79d84

Fixed socket leak with "return 444" in error_page (ticket #274). Socket leak was observed in the following configuration: error_page 400 = /close; location = /close { return 444; } The problem is that "return 444" triggers termination of the request, and due to error_page termination thinks that it needs to use a posted request to clear stack. But at the early request processing where 400 errors are generated there are no ngx_http_run_posted_requests() calls, so the request is only terminated after an external event. Variants of the problem include "error_page 497" instead (ticket #695) and various other errors generated during early request processing (405, 414, 421, 494, 495, 496, 501, 505). The same problem can be also triggered with "return 499" and "return 408" as both codes trigger ngx_http_terminate_request(), much like "return 444". To fix this, the patch adds ngx_http_run_posted_requests() calls to ngx_http_process_request_line() and ngx_http_process_request_headers() functions, and to ngx_http_v2_run_request() and ngx_http_v2_push_stream() functions in HTTP/2. Since the ngx_http_process_request() function is now only called via other functions which call ngx_http_run_posted_requests(), the call there is no longer needed and was removed.
author Maxim Dounin <mdounin@mdounin.ru>
date Fri, 21 Sep 2018 15:59:30 +0300
parents 9c29644f6d03
children d63c5373b5ba
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>
#include <ngx_event_connect.h>
#include <ngx_mail.h>


typedef struct {
    ngx_flag_t  enable;
    ngx_flag_t  pass_error_message;
    ngx_flag_t  xclient;
    size_t      buffer_size;
    ngx_msec_t  timeout;
} ngx_mail_proxy_conf_t;


static void ngx_mail_proxy_block_read(ngx_event_t *rev);
static void ngx_mail_proxy_pop3_handler(ngx_event_t *rev);
static void ngx_mail_proxy_imap_handler(ngx_event_t *rev);
static void ngx_mail_proxy_smtp_handler(ngx_event_t *rev);
static void ngx_mail_proxy_dummy_handler(ngx_event_t *ev);
static ngx_int_t ngx_mail_proxy_read_response(ngx_mail_session_t *s,
    ngx_uint_t state);
static void ngx_mail_proxy_handler(ngx_event_t *ev);
static void ngx_mail_proxy_upstream_error(ngx_mail_session_t *s);
static void ngx_mail_proxy_internal_server_error(ngx_mail_session_t *s);
static void ngx_mail_proxy_close_session(ngx_mail_session_t *s);
static void *ngx_mail_proxy_create_conf(ngx_conf_t *cf);
static char *ngx_mail_proxy_merge_conf(ngx_conf_t *cf, void *parent,
    void *child);


static ngx_command_t  ngx_mail_proxy_commands[] = {

    { ngx_string("proxy"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, enable),
      NULL },

    { ngx_string("proxy_buffer"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_size_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, buffer_size),
      NULL },

    { ngx_string("proxy_timeout"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, timeout),
      NULL },

    { ngx_string("proxy_pass_error_message"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, pass_error_message),
      NULL },

    { ngx_string("xclient"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, xclient),
      NULL },

      ngx_null_command
};


static ngx_mail_module_t  ngx_mail_proxy_module_ctx = {
    NULL,                                  /* protocol */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    ngx_mail_proxy_create_conf,            /* create server configuration */
    ngx_mail_proxy_merge_conf              /* merge server configuration */
};


ngx_module_t  ngx_mail_proxy_module = {
    NGX_MODULE_V1,
    &ngx_mail_proxy_module_ctx,            /* module context */
    ngx_mail_proxy_commands,               /* module directives */
    NGX_MAIL_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};


static u_char  smtp_auth_ok[] = "235 2.0.0 OK" CRLF;


void
ngx_mail_proxy_init(ngx_mail_session_t *s, ngx_addr_t *peer)
{
    ngx_int_t                  rc;
    ngx_mail_proxy_ctx_t      *p;
    ngx_mail_proxy_conf_t     *pcf;
    ngx_mail_core_srv_conf_t  *cscf;

    s->connection->log->action = "connecting to upstream";

    cscf = ngx_mail_get_module_srv_conf(s, ngx_mail_core_module);

    p = ngx_pcalloc(s->connection->pool, sizeof(ngx_mail_proxy_ctx_t));
    if (p == NULL) {
        ngx_mail_session_internal_server_error(s);
        return;
    }

    s->proxy = p;

    p->upstream.sockaddr = peer->sockaddr;
    p->upstream.socklen = peer->socklen;
    p->upstream.name = &peer->name;
    p->upstream.get = ngx_event_get_peer;
    p->upstream.log = s->connection->log;
    p->upstream.log_error = NGX_ERROR_ERR;

    rc = ngx_event_connect_peer(&p->upstream);

    if (rc == NGX_ERROR || rc == NGX_BUSY || rc == NGX_DECLINED) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    ngx_add_timer(p->upstream.connection->read, cscf->timeout);

    p->upstream.connection->data = s;
    p->upstream.connection->pool = s->connection->pool;

    s->connection->read->handler = ngx_mail_proxy_block_read;
    p->upstream.connection->write->handler = ngx_mail_proxy_dummy_handler;

    pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

    s->proxy->buffer = ngx_create_temp_buf(s->connection->pool,
                                           pcf->buffer_size);
    if (s->proxy->buffer == NULL) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->out.len = 0;

    switch (s->protocol) {

    case NGX_MAIL_POP3_PROTOCOL:
        p->upstream.connection->read->handler = ngx_mail_proxy_pop3_handler;
        s->mail_state = ngx_pop3_start;
        break;

    case NGX_MAIL_IMAP_PROTOCOL:
        p->upstream.connection->read->handler = ngx_mail_proxy_imap_handler;
        s->mail_state = ngx_imap_start;
        break;

    default: /* NGX_MAIL_SMTP_PROTOCOL */
        p->upstream.connection->read->handler = ngx_mail_proxy_smtp_handler;
        s->mail_state = ngx_smtp_start;
        break;
    }
}


static void
ngx_mail_proxy_block_read(ngx_event_t *rev)
{
    ngx_connection_t    *c;
    ngx_mail_session_t  *s;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy block read");

    if (ngx_handle_read_event(rev, 0) != NGX_OK) {
        c = rev->data;
        s = c->data;

        ngx_mail_proxy_close_session(s);
    }
}


static void
ngx_mail_proxy_pop3_handler(ngx_event_t *rev)
{
    u_char                 *p;
    ngx_int_t               rc;
    ngx_str_t               line;
    ngx_connection_t       *c;
    ngx_mail_session_t     *s;
    ngx_mail_proxy_conf_t  *pcf;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                   "mail proxy pop3 auth handler");

    c = rev->data;
    s = c->data;

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                      "upstream timed out");
        c->timedout = 1;
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    rc = ngx_mail_proxy_read_response(s, 0);

    if (rc == NGX_AGAIN) {
        return;
    }

    if (rc == NGX_ERROR) {
        ngx_mail_proxy_upstream_error(s);
        return;
    }

    switch (s->mail_state) {

    case ngx_pop3_start:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send user");

        s->connection->log->action = "sending user name to upstream";

        line.len = sizeof("USER ")  - 1 + s->login.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, "USER ", sizeof("USER ") - 1);
        p = ngx_cpymem(p, s->login.data, s->login.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_pop3_user;
        break;

    case ngx_pop3_user:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send pass");

        s->connection->log->action = "sending password to upstream";

        line.len = sizeof("PASS ")  - 1 + s->passwd.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, "PASS ", sizeof("PASS ") - 1);
        p = ngx_cpymem(p, s->passwd.data, s->passwd.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_pop3_passwd;
        break;

    case ngx_pop3_passwd:
        s->connection->read->handler = ngx_mail_proxy_handler;
        s->connection->write->handler = ngx_mail_proxy_handler;
        rev->handler = ngx_mail_proxy_handler;
        c->write->handler = ngx_mail_proxy_handler;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(s->connection->read, pcf->timeout);
        ngx_del_timer(c->read);

        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");

        ngx_mail_proxy_handler(s->connection->write);

        return;

    default:
#if (NGX_SUPPRESS_WARN)
        ngx_str_null(&line);
#endif
        break;
    }

    if (c->send(c, line.data, line.len) < (ssize_t) line.len) {
        /*
         * we treat the incomplete sending as NGX_ERROR
         * because it is very strange here
         */
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->buffer->pos = s->proxy->buffer->start;
    s->proxy->buffer->last = s->proxy->buffer->start;
}


static void
ngx_mail_proxy_imap_handler(ngx_event_t *rev)
{
    u_char                 *p;
    ngx_int_t               rc;
    ngx_str_t               line;
    ngx_connection_t       *c;
    ngx_mail_session_t     *s;
    ngx_mail_proxy_conf_t  *pcf;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                   "mail proxy imap auth handler");

    c = rev->data;
    s = c->data;

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                      "upstream timed out");
        c->timedout = 1;
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    rc = ngx_mail_proxy_read_response(s, s->mail_state);

    if (rc == NGX_AGAIN) {
        return;
    }

    if (rc == NGX_ERROR) {
        ngx_mail_proxy_upstream_error(s);
        return;
    }

    switch (s->mail_state) {

    case ngx_imap_start:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send login");

        s->connection->log->action = "sending LOGIN command to upstream";

        line.len = s->tag.len + sizeof("LOGIN ") - 1
                   + 1 + NGX_SIZE_T_LEN + 1 + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        line.len = ngx_sprintf(line.data, "%VLOGIN {%uz}" CRLF,
                               &s->tag, s->login.len)
                   - line.data;

        s->mail_state = ngx_imap_login;
        break;

    case ngx_imap_login:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send user");

        s->connection->log->action = "sending user name to upstream";

        line.len = s->login.len + 1 + 1 + NGX_SIZE_T_LEN + 1 + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        line.len = ngx_sprintf(line.data, "%V {%uz}" CRLF,
                               &s->login, s->passwd.len)
                   - line.data;

        s->mail_state = ngx_imap_user;
        break;

    case ngx_imap_user:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send passwd");

        s->connection->log->action = "sending password to upstream";

        line.len = s->passwd.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, s->passwd.data, s->passwd.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_imap_passwd;
        break;

    case ngx_imap_passwd:
        s->connection->read->handler = ngx_mail_proxy_handler;
        s->connection->write->handler = ngx_mail_proxy_handler;
        rev->handler = ngx_mail_proxy_handler;
        c->write->handler = ngx_mail_proxy_handler;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(s->connection->read, pcf->timeout);
        ngx_del_timer(c->read);

        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");

        ngx_mail_proxy_handler(s->connection->write);

        return;

    default:
#if (NGX_SUPPRESS_WARN)
        ngx_str_null(&line);
#endif
        break;
    }

    if (c->send(c, line.data, line.len) < (ssize_t) line.len) {
        /*
         * we treat the incomplete sending as NGX_ERROR
         * because it is very strange here
         */
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->buffer->pos = s->proxy->buffer->start;
    s->proxy->buffer->last = s->proxy->buffer->start;
}


static void
ngx_mail_proxy_smtp_handler(ngx_event_t *rev)
{
    u_char                    *p;
    ngx_int_t                  rc;
    ngx_str_t                  line;
    ngx_buf_t                 *b;
    ngx_connection_t          *c;
    ngx_mail_session_t        *s;
    ngx_mail_proxy_conf_t     *pcf;
    ngx_mail_core_srv_conf_t  *cscf;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                   "mail proxy smtp auth handler");

    c = rev->data;
    s = c->data;

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                      "upstream timed out");
        c->timedout = 1;
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    rc = ngx_mail_proxy_read_response(s, s->mail_state);

    if (rc == NGX_AGAIN) {
        return;
    }

    if (rc == NGX_ERROR) {
        ngx_mail_proxy_upstream_error(s);
        return;
    }

    switch (s->mail_state) {

    case ngx_smtp_start:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send ehlo");

        s->connection->log->action = "sending HELO/EHLO to upstream";

        cscf = ngx_mail_get_module_srv_conf(s, ngx_mail_core_module);

        line.len = sizeof("HELO ")  - 1 + cscf->server_name.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

        p = ngx_cpymem(line.data,
                       ((s->esmtp || pcf->xclient) ? "EHLO " : "HELO "),
                       sizeof("HELO ") - 1);

        p = ngx_cpymem(p, cscf->server_name.data, cscf->server_name.len);
        *p++ = CR; *p = LF;

        if (pcf->xclient) {
            s->mail_state = ngx_smtp_helo_xclient;

        } else if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            s->mail_state = ngx_smtp_helo_from;

        } else {
            s->mail_state = ngx_smtp_helo;
        }

        break;

    case ngx_smtp_helo_xclient:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send xclient");

        s->connection->log->action = "sending XCLIENT to upstream";

        line.len = sizeof("XCLIENT ADDR= LOGIN= NAME="
                          CRLF) - 1
                   + s->connection->addr_text.len + s->login.len + s->host.len;

#if (NGX_HAVE_INET6)
        if (s->connection->sockaddr->sa_family == AF_INET6) {
            line.len += sizeof("IPV6:") - 1;
        }
#endif

        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, "XCLIENT ADDR=", sizeof("XCLIENT ADDR=") - 1);

#if (NGX_HAVE_INET6)
        if (s->connection->sockaddr->sa_family == AF_INET6) {
            p = ngx_cpymem(p, "IPV6:", sizeof("IPV6:") - 1);
        }
#endif

        p = ngx_copy(p, s->connection->addr_text.data,
                     s->connection->addr_text.len);

        if (s->login.len) {
            p = ngx_cpymem(p, " LOGIN=", sizeof(" LOGIN=") - 1);
            p = ngx_copy(p, s->login.data, s->login.len);
        }

        p = ngx_cpymem(p, " NAME=", sizeof(" NAME=") - 1);
        p = ngx_copy(p, s->host.data, s->host.len);

        *p++ = CR; *p++ = LF;

        line.len = p - line.data;

        if (s->smtp_helo.len) {
            s->mail_state = ngx_smtp_xclient_helo;

        } else if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            s->mail_state = ngx_smtp_xclient_from;

        } else {
            s->mail_state = ngx_smtp_xclient;
        }

        break;

    case ngx_smtp_xclient_helo:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send client ehlo");

        s->connection->log->action = "sending client HELO/EHLO to upstream";

        line.len = sizeof("HELO " CRLF) - 1 + s->smtp_helo.len;

        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        line.len = ngx_sprintf(line.data,
                       ((s->esmtp) ? "EHLO %V" CRLF : "HELO %V" CRLF),
                       &s->smtp_helo)
                   - line.data;

        s->mail_state = (s->auth_method == NGX_MAIL_AUTH_NONE) ?
                            ngx_smtp_helo_from : ngx_smtp_helo;

        break;

    case ngx_smtp_helo_from:
    case ngx_smtp_xclient_from:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send mail from");

        s->connection->log->action = "sending MAIL FROM to upstream";

        line.len = s->smtp_from.len + sizeof(CRLF) - 1;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, s->smtp_from.data, s->smtp_from.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_smtp_from;

        break;

    case ngx_smtp_from:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send rcpt to");

        s->connection->log->action = "sending RCPT TO to upstream";

        line.len = s->smtp_to.len + sizeof(CRLF) - 1;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, s->smtp_to.data, s->smtp_to.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_smtp_to;

        break;

    case ngx_smtp_helo:
    case ngx_smtp_xclient:
    case ngx_smtp_to:

        b = s->proxy->buffer;

        if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            b->pos = b->start;

        } else {
            ngx_memcpy(b->start, smtp_auth_ok, sizeof(smtp_auth_ok) - 1);
            b->last = b->start + sizeof(smtp_auth_ok) - 1;
        }

        s->connection->read->handler = ngx_mail_proxy_handler;
        s->connection->write->handler = ngx_mail_proxy_handler;
        rev->handler = ngx_mail_proxy_handler;
        c->write->handler = ngx_mail_proxy_handler;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(s->connection->read, pcf->timeout);
        ngx_del_timer(c->read);

        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");

        if (s->buffer->pos == s->buffer->last) {
            ngx_mail_proxy_handler(s->connection->write);

        } else {
            ngx_mail_proxy_handler(c->write);
        }

        return;

    default:
#if (NGX_SUPPRESS_WARN)
        ngx_str_null(&line);
#endif
        break;
    }

    if (c->send(c, line.data, line.len) < (ssize_t) line.len) {
        /*
         * we treat the incomplete sending as NGX_ERROR
         * because it is very strange here
         */
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->buffer->pos = s->proxy->buffer->start;
    s->proxy->buffer->last = s->proxy->buffer->start;
}


static void
ngx_mail_proxy_dummy_handler(ngx_event_t *wev)
{
    ngx_connection_t    *c;
    ngx_mail_session_t  *s;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, wev->log, 0, "mail proxy dummy handler");

    if (ngx_handle_write_event(wev, 0) != NGX_OK) {
        c = wev->data;
        s = c->data;

        ngx_mail_proxy_close_session(s);
    }
}


static ngx_int_t
ngx_mail_proxy_read_response(ngx_mail_session_t *s, ngx_uint_t state)
{
    u_char                 *p, *m;
    ssize_t                 n;
    ngx_buf_t              *b;
    ngx_mail_proxy_conf_t  *pcf;

    s->connection->log->action = "reading response from upstream";

    b = s->proxy->buffer;

    n = s->proxy->upstream.connection->recv(s->proxy->upstream.connection,
                                            b->last, b->end - b->last);

    if (n == NGX_ERROR || n == 0) {
        return NGX_ERROR;
    }

    if (n == NGX_AGAIN) {
        return NGX_AGAIN;
    }

    b->last += n;

    if (b->last - b->pos < 4) {
        return NGX_AGAIN;
    }

    if (*(b->last - 2) != CR || *(b->last - 1) != LF) {
        if (b->last == b->end) {
            *(b->last - 1) = '\0';
            ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                          "upstream sent too long response line: \"%s\"",
                          b->pos);
            return NGX_ERROR;
        }

        return NGX_AGAIN;
    }

    p = b->pos;

    switch (s->protocol) {

    case NGX_MAIL_POP3_PROTOCOL:
        if (p[0] == '+' && p[1] == 'O' && p[2] == 'K') {
            return NGX_OK;
        }
        break;

    case NGX_MAIL_IMAP_PROTOCOL:
        switch (state) {

        case ngx_imap_start:
            if (p[0] == '*' && p[1] == ' ' && p[2] == 'O' && p[3] == 'K') {
                return NGX_OK;
            }
            break;

        case ngx_imap_login:
        case ngx_imap_user:
            if (p[0] == '+') {
                return NGX_OK;
            }
            break;

        case ngx_imap_passwd:
            if (ngx_strncmp(p, s->tag.data, s->tag.len) == 0) {
                p += s->tag.len;
                if (p[0] == 'O' && p[1] == 'K') {
                    return NGX_OK;
                }
            }
            break;
        }

        break;

    default: /* NGX_MAIL_SMTP_PROTOCOL */

        if (p[3] == '-') {
            /* multiline reply, check if we got last line */

            m = b->last - (sizeof(CRLF "200" CRLF) - 1);

            while (m > p) {
                if (m[0] == CR && m[1] == LF) {
                    break;
                }

                m--;
            }

            if (m <= p || m[5] == '-') {
                return NGX_AGAIN;
            }
        }

        switch (state) {

        case ngx_smtp_start:
            if (p[0] == '2' && p[1] == '2' && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_helo:
        case ngx_smtp_helo_xclient:
        case ngx_smtp_helo_from:
        case ngx_smtp_from:
            if (p[0] == '2' && p[1] == '5' && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_xclient:
        case ngx_smtp_xclient_from:
        case ngx_smtp_xclient_helo:
            if (p[0] == '2' && (p[1] == '2' || p[1] == '5') && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_to:
            return NGX_OK;
        }

        break;
    }

    pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

    if (pcf->pass_error_message == 0) {
        *(b->last - 2) = '\0';
        ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                      "upstream sent invalid response: \"%s\"", p);
        return NGX_ERROR;
    }

    s->out.len = b->last - p - 2;
    s->out.data = p;

    ngx_log_error(NGX_LOG_INFO, s->connection->log, 0,
                  "upstream sent invalid response: \"%V\"", &s->out);

    s->out.len = b->last - b->pos;
    s->out.data = b->pos;

    return NGX_ERROR;
}


static void
ngx_mail_proxy_handler(ngx_event_t *ev)
{
    char                   *action, *recv_action, *send_action;
    size_t                  size;
    ssize_t                 n;
    ngx_buf_t              *b;
    ngx_uint_t              do_write;
    ngx_connection_t       *c, *src, *dst;
    ngx_mail_session_t     *s;
    ngx_mail_proxy_conf_t  *pcf;

    c = ev->data;
    s = c->data;

    if (ev->timedout || c->close) {
        c->log->action = "proxying";

        if (c->close) {
            ngx_log_error(NGX_LOG_INFO, c->log, 0, "shutdown timeout");

        } else if (c == s->connection) {
            ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                          "client timed out");
            c->timedout = 1;

        } else {
            ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                          "upstream timed out");
        }

        ngx_mail_proxy_close_session(s);
        return;
    }

    if (c == s->connection) {
        if (ev->write) {
            recv_action = "proxying and reading from upstream";
            send_action = "proxying and sending to client";
            src = s->proxy->upstream.connection;
            dst = c;
            b = s->proxy->buffer;

        } else {
            recv_action = "proxying and reading from client";
            send_action = "proxying and sending to upstream";
            src = c;
            dst = s->proxy->upstream.connection;
            b = s->buffer;
        }

    } else {
        if (ev->write) {
            recv_action = "proxying and reading from client";
            send_action = "proxying and sending to upstream";
            src = s->connection;
            dst = c;
            b = s->buffer;

        } else {
            recv_action = "proxying and reading from upstream";
            send_action = "proxying and sending to client";
            src = c;
            dst = s->connection;
            b = s->proxy->buffer;
        }
    }

    do_write = ev->write ? 1 : 0;

    ngx_log_debug3(NGX_LOG_DEBUG_MAIL, ev->log, 0,
                   "mail proxy handler: %ui, #%d > #%d",
                   do_write, src->fd, dst->fd);

    for ( ;; ) {

        if (do_write) {

            size = b->last - b->pos;

            if (size && dst->write->ready) {
                c->log->action = send_action;

                n = dst->send(dst, b->pos, size);

                if (n == NGX_ERROR) {
                    ngx_mail_proxy_close_session(s);
                    return;
                }

                if (n > 0) {
                    b->pos += n;

                    if (b->pos == b->last) {
                        b->pos = b->start;
                        b->last = b->start;
                    }
                }
            }
        }

        size = b->end - b->last;

        if (size && src->read->ready) {
            c->log->action = recv_action;

            n = src->recv(src, b->last, size);

            if (n == NGX_AGAIN || n == 0) {
                break;
            }

            if (n > 0) {
                do_write = 1;
                b->last += n;

                continue;
            }

            if (n == NGX_ERROR) {
                src->read->eof = 1;
            }
        }

        break;
    }

    c->log->action = "proxying";

    if ((s->connection->read->eof && s->buffer->pos == s->buffer->last)
        || (s->proxy->upstream.connection->read->eof
            && s->proxy->buffer->pos == s->proxy->buffer->last)
        || (s->connection->read->eof
            && s->proxy->upstream.connection->read->eof))
    {
        action = c->log->action;
        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "proxied session done");
        c->log->action = action;

        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_write_event(dst->write, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_read_event(dst->read, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_write_event(src->write, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_read_event(src->read, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (c == s->connection) {
        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(c->read, pcf->timeout);
    }
}


static void
ngx_mail_proxy_upstream_error(ngx_mail_session_t *s)
{
    if (s->proxy->upstream.connection) {
        ngx_log_debug1(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                       "close mail proxy connection: %d",
                       s->proxy->upstream.connection->fd);

        ngx_close_connection(s->proxy->upstream.connection);
    }

    if (s->out.len == 0) {
        ngx_mail_session_internal_server_error(s);
        return;
    }

    s->quit = 1;
    ngx_mail_send(s->connection->write);
}


static void
ngx_mail_proxy_internal_server_error(ngx_mail_session_t *s)
{
    if (s->proxy->upstream.connection) {
        ngx_log_debug1(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                       "close mail proxy connection: %d",
                       s->proxy->upstream.connection->fd);

        ngx_close_connection(s->proxy->upstream.connection);
    }

    ngx_mail_session_internal_server_error(s);
}


static void
ngx_mail_proxy_close_session(ngx_mail_session_t *s)
{
    if (s->proxy->upstream.connection) {
        ngx_log_debug1(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                       "close mail proxy connection: %d",
                       s->proxy->upstream.connection->fd);

        ngx_close_connection(s->proxy->upstream.connection);
    }

    ngx_mail_close_connection(s->connection);
}


static void *
ngx_mail_proxy_create_conf(ngx_conf_t *cf)
{
    ngx_mail_proxy_conf_t  *pcf;

    pcf = ngx_pcalloc(cf->pool, sizeof(ngx_mail_proxy_conf_t));
    if (pcf == NULL) {
        return NULL;
    }

    pcf->enable = NGX_CONF_UNSET;
    pcf->pass_error_message = NGX_CONF_UNSET;
    pcf->xclient = NGX_CONF_UNSET;
    pcf->buffer_size = NGX_CONF_UNSET_SIZE;
    pcf->timeout = NGX_CONF_UNSET_MSEC;

    return pcf;
}


static char *
ngx_mail_proxy_merge_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_mail_proxy_conf_t *prev = parent;
    ngx_mail_proxy_conf_t *conf = child;

    ngx_conf_merge_value(conf->enable, prev->enable, 0);
    ngx_conf_merge_value(conf->pass_error_message, prev->pass_error_message, 0);
    ngx_conf_merge_value(conf->xclient, prev->xclient, 1);
    ngx_conf_merge_size_value(conf->buffer_size, prev->buffer_size,
                              (size_t) ngx_pagesize);
    ngx_conf_merge_msec_value(conf->timeout, prev->timeout, 24 * 60 * 60000);

    return NGX_CONF_OK;
}