Found udp_connection to be null when statsd server is not available

[janmejay]

ngx_http_statsd_udp_send calls uc->connection and when uc is null it generates segfault.

Here is the trace:

Program received signal SIGSEGV, Segmentation fault.
0x00000000004c1301 in ngx_http_statsd_udp_send (l=0xf54590,
    buf=0xfb98a8 "retail.pricing.fk_proxy.ip_10_98_169_234.80.status.200:1|c\003\243FB\a\356\001", len=58) at ../nginx-statsd/ngx_http_statsd.c:382
382     ../nginx-statsd/ngx_http_statsd.c: No such file or directory.
        in ../nginx-statsd/ngx_http_statsd.c
(gdb) bt
#0  0x00000000004c1301 in ngx_http_statsd_udp_send (l=0xf54590,
    buf=0xfb98a8 "retail.pricing.fk_proxy.ip_10_98_169_234.80.status.200:1|c\003\243FB\a\356\001", len=58) at ../nginx-statsd/ngx_http_statsd.c:382
#1  0x00000000004c10a2 in ngx_http_statsd_handler (r=0xf45960) at ../nginx-statsd/ngx_http_statsd.c:313
#2  0x000000000045c465 in ngx_http_log_request (r=0xf45960) at src/http/ngx_http_request.c:3455
#3  0x000000000045c2d6 in ngx_http_free_request (r=0xf45960, rc=0) at src/http/ngx_http_request.c:3402
#4  0x000000000045af7b in ngx_http_set_keepalive (r=0xf45960) at src/http/ngx_http_request.c:2840
#5  0x000000000045a3f5 in ngx_http_finalize_connection (r=0xf45960) at src/http/ngx_http_request.c:2483
#6  0x000000000045a058 in ngx_http_finalize_request (r=0xf45960, rc=0) at src/http/ngx_http_request.c:2384
#7  0x0000000000477feb in ngx_http_upstream_finalize_request (r=0xf45960, u=0xfb66f0, rc=0) at src/http/ngx_http_upstream.c:3560
#8  0x00000000004770eb in ngx_http_upstream_process_request (r=0xf45960) at src/http/ngx_http_upstream.c:3161
#9  0x0000000000476e08 in ngx_http_upstream_process_upstream (r=0xf45960, u=0xfb66f0) at src/http/ngx_http_upstream.c:3092
#10 0x00000000004721db in ngx_http_upstream_handler (ev=0x1005230) at src/http/ngx_http_upstream.c:977
#11 0x000000000043b78e in ngx_epoll_process_events (cycle=0xf38620, timer=60000, flags=1) at src/event/modules/ngx_epoll_module.c:691
#12 0x000000000042bfd4 in ngx_process_events_and_timers (cycle=0xf38620) at src/event/ngx_event.c:248
#13 0x0000000000439696 in ngx_worker_process_cycle (cycle=0xf38620, data=0x0) at src/os/unix/ngx_process_cycle.c:816
#14 0x0000000000435ef6 in ngx_spawn_process (cycle=0xf38620, proc=0x439490 , data=0x0, name=0x4c69c3 "worker process",
    respawn=0) at src/os/unix/ngx_process.c:198
#15 0x0000000000439089 in ngx_reap_children (cycle=0xf38620) at src/os/unix/ngx_process_cycle.c:627
#16 0x0000000000437d19 in ngx_master_process_cycle (cycle=0xf38620) at src/os/unix/ngx_process_cycle.c:180
#17 0x000000000040727f in main (argc=1, argv=0x7fffd7f4cee8) at src/core/nginx.c:407

[janmejay]

Added a null check to fix it, here is the patch.

Please advice if there is a better way of fixing this.

From 7105230479ed6ee89371bae2d6655429c9efa515 Mon Sep 17 00:00:00 2001
From: Janmejay Singh 
Date: Fri, 17 Jan 2014 16:12:55 +0530
Subject: [PATCH] check that udp_connection exists before trying
 to use it, absense of this segfaults the worker
---
 ngx_http_statsd.c | 3 +++
 1 file changed, 3 insertions(+)
diff --git a/ngx_http_statsd.c b/ngx_http_statsd.c
index c2f1041..939ce43 100644
--- a/ngx_http_statsd.c
+++ b/ngx_http_statsd.c
@@ -379,6 +379,9 @@ ngx_http_statsd_udp_send(ngx_udp_endpoint_t *l, u_char *buf, size_t len)
     ngx_udp_connection_t  *uc;
 
     uc = l->udp_connection;
+    if (! uc) {
+        return NGX_ERROR;
+    }
     if (uc->connection == NULL) {
 
         uc->log = *l->log;
-- 
1.8.3.2