UDP input: Add support for getting max size of UDP receive buffer in BSD compatible way

Author: sedmicha

src/plugins/input/udp/udp.c

@@ -446,8 +446,33 @@ listener_init(struct udp_data *instance)
     const char *err_str;
 
     // Get maximum socket receive buffer size (in bytes)
-    FILE *f;
     int sock_rmax = 0;
+
+#if defined(__FreeBSD__) || defined(__OpenBSD__)
+    unsigned long space = 0;
+    size_t n = sizeof(space);
+    int sock = socket(PF_INET, SOCK_DGRAM, 0);
+    if (sock < 0) {
+        ipx_strerror(errno, err_str);
+        IPX_CTX_WARNING(instance->ctx, "Unable to get the maximum socket receive buffer size "
+            "(socket() failed: %s). Due to potentially small buffers, some records may be lost!",
+            err_str);
+    }
+
+    if (getsockopt(sock, SOL_SOCKET, SO_RCVBUF, &space, (socklen_t*)&n) != 0) {
+        ipx_strerror(errno, err_str);
+        IPX_CTX_WARNING(instance->ctx, "Unable to get the maximum socket receive buffer size "
+            "(getsockopt() failed: %s). Due to potentially small buffers, some records may be lost!",
+            err_str);
+    } else {
+        sock_rmax = (int) space;
+    }
+
+    if (sock != 0) {
+        close(sock);
+    }
+#else
+    FILE *f;
     static const char *sys_cfg = "/proc/sys/net/core/rmem_max";
     if ((f = fopen(sys_cfg, "r")) == NULL || fscanf(f, "%d", &sock_rmax) != 1 || sock_rmax < 0) {
         ipx_strerror(errno, err_str);
@@ -457,10 +482,12 @@ listener_init(struct udp_data *instance)
         sock_rmax = 0;
     }
 
-    instance->listen.rmem_size = sock_rmax;
     if (f != NULL) {
         fclose(f);
     }
+#endif
+
+    instance->listen.rmem_size = sock_rmax;
 
     if (sock_rmax != 0 && sock_rmax < UDP_RMEM_REQ) {
         IPX_CTX_WARNING(instance->ctx, "The maximum socket receive buffer size is too small "