in_syslog: added buffer_rcv_size option to set socket receiving buffer

With default value of 208kb some UDP syslogs packet are lost at 10000 logs/s.
Using the option set to a high value a steady stream of 10000 log/s can be
processed without losing any log (on localhost).

Signed-off-by: Benoît GARNIER <[email protected]>

plugins/in_syslog/syslog.c

@@ -227,6 +227,11 @@ static struct flb_config_map config_map[] = {
      0, FLB_TRUE, offsetof(struct flb_syslog, parser_name),
      "Set the parser"
     },
+    {
+      FLB_CONFIG_MAP_SIZE, "buffer_rcv_size", (char *)NULL,
+      0, FLB_TRUE, offsetof(struct flb_syslog, buffer_rcv_size),
+      "Set the socket receiving buffer size"
+    },
     /* EOF */
     {0}
 };

plugins/in_syslog/syslog.h

@@ -49,6 +49,7 @@ struct flb_syslog {
     flb_sds_t unix_path;
     flb_sds_t unix_perm_str;
     unsigned int unix_perm;
+    size_t buffer_rcv_size;
 
     /* UDP buffer, data length and buffer size */
         // char *buffer_data;

plugins/in_syslog/syslog_conf.c

@@ -116,6 +116,13 @@ struct flb_syslog *syslog_conf_create(struct flb_input_instance *ins,
         ctx->buffer_max_size = ctx->buffer_chunk_size;
     }
 
+    /* Socket rcv buffer size */
+    if (ctx->buffer_rcv_size == -1 || ctx->buffer_rcv_size>INT_MAX) {
+        flb_plg_error(ins, "invalid buffer_rcv_size");
+        flb_free(ctx);
+        return NULL;
+    }
+
     /* Parser */
     if (ctx->parser_name) {
         ctx->parser = flb_parser_get(ctx->parser_name, config);

plugins/in_syslog/syslog_server.c

@@ -166,6 +166,14 @@ static int syslog_server_net_create(struct flb_syslog *ctx)
         return -1;
     }
 
+    if (ctx->buffer_rcv_size) {
+        if (flb_net_socket_rcv_buffer(ctx->downstream->server_fd, ctx->buffer_rcv_size)) {
+            flb_error("[in_syslog] could not set rcv buffer to %ld. Aborting",
+                      ctx->buffer_rcv_size);
+            return -1;
+        }
+    }
+
     flb_net_socket_nonblocking(ctx->downstream->server_fd);
 
     return 0;