view src/mail/ngx_mail_proxy_module.c @ 7790:da0a85e91587

Mail: added missing event handling after reading data. If we need to be notified about further events, ngx_handle_read_event() needs to be called after a read event is processed. Without this, an event can be removed from the kernel and won't be reported again, notably when using oneshot event methods, such as eventport on Solaris. For consistency, existing ngx_handle_read_event() call removed from ngx_mail_read_command(), as this call only covers one of the code paths where ngx_mail_read_command() returns NGX_AGAIN. Instead, appropriate processing added to the callers, covering all code paths where NGX_AGAIN is returned.
author Maxim Dounin <mdounin@mdounin.ru>
date Fri, 05 Mar 2021 17:16:17 +0300
parents d63c5373b5ba
children 4b8f23a36ebf
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;
    ngx_flag_t  smtp_auth;
    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_string("proxy_smtp_auth"),
      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, smtp_auth),
      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) {
        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        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;
    }

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

        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;
    }

    if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
        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, auth, encoded;
    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) {
        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        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 if (pcf->smtp_auth) {
            s->mail_state = ngx_smtp_helo_auth;

        } 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);

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

        if (s->login.len && !pcf->smtp_auth) {
            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 if (pcf->smtp_auth) {
            s->mail_state = ngx_smtp_xclient_auth;

        } 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;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

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

        } else if (pcf->smtp_auth) {
            s->mail_state = ngx_smtp_helo_auth;

        } else {
            s->mail_state = ngx_smtp_helo;
        }

        break;

    case ngx_smtp_helo_auth:
    case ngx_smtp_xclient_auth:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send auth");

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

        if (s->passwd.data == NULL) {
            ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                          "no password available");
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

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

        auth.len = ngx_sprintf(auth.data, "%Z%V%Z%V", &s->login, &s->passwd)
                   - auth.data;

        line.len = sizeof("AUTH PLAIN " CRLF) - 1
                   + ngx_base64_encoded_length(auth.len);

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

        encoded.data = ngx_cpymem(line.data, "AUTH PLAIN ",
                                  sizeof("AUTH PLAIN ") - 1);

        ngx_encode_base64(&encoded, &auth);

        p = encoded.data + encoded.len;
        *p++ = CR; *p = LF;

        s->mail_state = ngx_smtp_auth_plain;

        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_auth_plain:
    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;
    }

    if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
        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_helo_auth:
        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:
        case ngx_smtp_xclient_auth:
            if (p[0] == '2' && (p[1] == '2' || p[1] == '5') && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_auth_plain:
            if (p[0] == '2' && p[1] == '3' && p[2] == '5') {
                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->smtp_auth = 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_value(conf->smtp_auth, prev->smtp_auth, 0);
    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;
}