# HG changeset patch
# User Maxim Dounin <mdounin@mdounin.ru>
# Date 1678423430 -10800
# Node ID 8771d35d55d0a2b1cefaab04401d6f837f5a05a2
# Parent  29adacffdefaf7561f610de3408125b302dc028f
Syslog: introduced error log handler.

This ensures that errors which happen during logging to syslog are logged
with proper context, such as "while logging to syslog" and the server name.

Prodded by Safar Safarly.

diff --git a/src/core/ngx_syslog.c b/src/core/ngx_syslog.c
--- a/src/core/ngx_syslog.c
+++ b/src/core/ngx_syslog.c
@@ -18,6 +18,7 @@
 static char *ngx_syslog_parse_args(ngx_conf_t *cf, ngx_syslog_peer_t *peer);
 static ngx_int_t ngx_syslog_init_peer(ngx_syslog_peer_t *peer);
 static void ngx_syslog_cleanup(void *data);
+static u_char *ngx_syslog_log_error(ngx_log_t *log, u_char *buf, size_t len);
 
 
 static char  *facilities[] = {
@@ -67,7 +68,7 @@ ngx_syslog_process_conf(ngx_conf_t *cf, 
     }
 
     peer->hostname = &cf->cycle->hostname;
-    peer->log = &cf->cycle->new_log;
+    peer->logp = &cf->cycle->new_log;
 
     peer->conn.fd = (ngx_socket_t) -1;
 
@@ -289,6 +290,13 @@ ngx_syslog_send(ngx_syslog_peer_t *peer,
 {
     ssize_t  n;
 
+    if (peer->log.handler == NULL) {
+        peer->log = *peer->logp;
+        peer->log.handler = ngx_syslog_log_error;
+        peer->log.data = peer;
+        peer->log.action = "logging to syslog";
+    }
+
     if (peer->conn.fd == (ngx_socket_t) -1) {
         if (ngx_syslog_init_peer(peer) != NGX_OK) {
             return NGX_ERROR;
@@ -306,7 +314,7 @@ ngx_syslog_send(ngx_syslog_peer_t *peer,
     if (n == NGX_ERROR) {
 
         if (ngx_close_socket(peer->conn.fd) == -1) {
-            ngx_log_error(NGX_LOG_ALERT, peer->log, ngx_socket_errno,
+            ngx_log_error(NGX_LOG_ALERT, &peer->log, ngx_socket_errno,
                           ngx_close_socket_n " failed");
         }
 
@@ -324,25 +332,25 @@ ngx_syslog_init_peer(ngx_syslog_peer_t *
 
     fd = ngx_socket(peer->server.sockaddr->sa_family, SOCK_DGRAM, 0);
     if (fd == (ngx_socket_t) -1) {
-        ngx_log_error(NGX_LOG_ALERT, peer->log, ngx_socket_errno,
+        ngx_log_error(NGX_LOG_ALERT, &peer->log, ngx_socket_errno,
                       ngx_socket_n " failed");
         return NGX_ERROR;
     }
 
     if (ngx_nonblocking(fd) == -1) {
-        ngx_log_error(NGX_LOG_ALERT, peer->log, ngx_socket_errno,
+        ngx_log_error(NGX_LOG_ALERT, &peer->log, ngx_socket_errno,
                       ngx_nonblocking_n " failed");
         goto failed;
     }
 
     if (connect(fd, peer->server.sockaddr, peer->server.socklen) == -1) {
-        ngx_log_error(NGX_LOG_ALERT, peer->log, ngx_socket_errno,
+        ngx_log_error(NGX_LOG_ALERT, &peer->log, ngx_socket_errno,
                       "connect() failed");
         goto failed;
     }
 
     peer->conn.fd = fd;
-    peer->conn.log = peer->log;
+    peer->conn.log = &peer->log;
 
     /* UDP sockets are always ready to write */
     peer->conn.write->ready = 1;
@@ -352,7 +360,7 @@ ngx_syslog_init_peer(ngx_syslog_peer_t *
 failed:
 
     if (ngx_close_socket(fd) == -1) {
-        ngx_log_error(NGX_LOG_ALERT, peer->log, ngx_socket_errno,
+        ngx_log_error(NGX_LOG_ALERT, &peer->log, ngx_socket_errno,
                       ngx_close_socket_n " failed");
     }
 
@@ -373,7 +381,30 @@ ngx_syslog_cleanup(void *data)
     }
 
     if (ngx_close_socket(peer->conn.fd) == -1) {
-        ngx_log_error(NGX_LOG_ALERT, peer->log, ngx_socket_errno,
+        ngx_log_error(NGX_LOG_ALERT, &peer->log, ngx_socket_errno,
                       ngx_close_socket_n " failed");
     }
 }
+
+
+static u_char *
+ngx_syslog_log_error(ngx_log_t *log, u_char *buf, size_t len)
+{
+    u_char             *p;
+    ngx_syslog_peer_t  *peer;
+
+    p = buf;
+
+    if (log->action) {
+        p = ngx_snprintf(buf, len, " while %s", log->action);
+        len -= p - buf;
+    }
+
+    peer = log->data;
+
+    if (peer) {
+        p = ngx_snprintf(p, len, ", server: %V", &peer->server.name);
+    }
+
+    return p;
+}
diff --git a/src/core/ngx_syslog.h b/src/core/ngx_syslog.h
--- a/src/core/ngx_syslog.h
+++ b/src/core/ngx_syslog.h
@@ -18,7 +18,8 @@ typedef struct {
     ngx_addr_t         server;
     ngx_connection_t   conn;
 
-    ngx_log_t         *log;
+    ngx_log_t          log;
+    ngx_log_t         *logp;
 
     unsigned           busy:1;
     unsigned           nohostname:1;