out_gelf: port the plugin to Windows (fluent#2574)

With this patch, the GELF Output plugin can be compiled and linked
on Windows.

This commit also fixes a few bugs in GELF plugin:

 * The message header was not constructed properly. In particular,
   11-12th bytes were filled in the reversed order.

 * The message id generation was bogus (e.g. it did "tv_nsec*1000000
   + tm.tm.tv_nsec" to generate a timestamp)

Fix these glitches and add detailed documentation to each function.

Signed-off-by: Fujimoto Seiji <fujimoto@ceptord.net>

Author: fujimotos

cmake/windows-setup.cmake

@@ -49,7 +49,7 @@ set(FLB_OUT_DATADOG           Yes)
 set(FLB_OUT_ES                Yes)
 set(FLB_OUT_EXIT               No)
 set(FLB_OUT_FORWARD           Yes)
-set(FLB_OUT_GELF               No)
+set(FLB_OUT_GELF              Yes)
 set(FLB_OUT_HTTP              Yes)
 set(FLB_OUT_INFLUXDB          Yes)
 set(FLB_OUT_NATS               No)

plugins/out_gelf/gelf.c

@@ -75,6 +75,51 @@
  * server nodes omit this field automatically.
  */
 
+/*
+ * Generate a unique message ID. The upper 48-bit is milliseconds
+ * since the Epoch, the lower 16-bit is a random nonce.
+ */
+static uint64_t message_id(void)
+{
+    uint64_t now;
+    uint16_t nonce;
+    struct flb_time tm;
+
+    if (flb_time_get(&tm) != -1) {
+        now = (uint64_t) tm.tm.tv_sec * 1000 + tm.tm.tv_nsec / 1000000;
+    }
+    else {
+        now = (uint64_t) time(NULL) * 1000;
+    }
+    nonce = (uint16_t) rand();
+
+    return (now << 16) | nonce;
+}
+
+/*
+ * A GELF header is 12 bytes in size. It has the following
+ * structure:
+ *
+ * +---+---+---+---+---+---+---+---+---+---+---+---+
+ * | MAGIC |           MESSAGE ID          |SEQ|NUM|
+ * +---+---+---+---+---+---+---+---+---+---+---+---+
+ *
+ * NUM is the total number of packets to send. SEQ is the
+ * unique sequence number for each packet (zero-indexed).
+ */
+#define GELF_MAGIC "\x1e\x0f"
+#define GELF_HEADER_SIZE 12
+
+static void init_chunk_header(uint8_t *buf, int count)
+{
+    uint64_t msgid = message_id();
+
+    memcpy(buf, GELF_MAGIC, 2);
+    memcpy(buf + 2, &msgid, 8);
+    buf[10] = 0;
+    buf[11] = count;
+}
+
 /*
  * Chunked GELF
  * Prepend the following structure to your GELF message to make it chunked:
@@ -89,66 +134,45 @@
  * already arrived and still arriving chunks.
  * A message MUST NOT consist of more than 128 chunks.
  */
-
 static int gelf_send_udp_chunked(struct flb_out_gelf_config *ctx, void *msg,
                                  size_t msg_size)
 {
     int ret;
-    uint8_t header[12];
     uint8_t n;
     size_t chunks;
     size_t offset;
-    struct flb_time tm;
-    uint64_t messageid;
-    struct msghdr msghdr;
-    struct iovec iov[2];
+    size_t len;
+    uint8_t *buf = (uint8_t *) ctx->pckt_buf;
 
     chunks = msg_size / ctx->pckt_size;
-    if ((msg_size % ctx->pckt_size) != 0)
+    if (msg_size % ctx->pckt_size != 0) {
         chunks++;
+    }
 
     if (chunks > 128) {
-        flb_plg_error(ctx->ins, "message too big: %zd bytes, too many chunks",
-                      msg_size);
+        flb_plg_error(ctx->ins, "message too big: %zd bytes", msg_size);
         return -1;
     }
 
-    flb_time_get(&tm);
-
-    messageid = ((uint64_t)(tm.tm.tv_nsec*1000000 + tm.tm.tv_nsec) << 32) |
-                (uint64_t)rand_r(&(ctx->seed));
-
-    header[0] = 0x1e;
-    header[1] = 0x0f;
-    memcpy (header+2, &messageid, 8);
-    header[10] = chunks;
-
-    iov[0].iov_base = header;
-    iov[0].iov_len = 12;
-
-    memset(&msghdr, 0, sizeof(struct msghdr));
-    msghdr.msg_iov = iov;
-    msghdr.msg_iovlen = 2;
+    init_chunk_header(buf, chunks);
 
     offset = 0;
     for (n = 0; n < chunks; n++) {
-        header[11] = n;
+        buf[10] = n;
 
-        iov[1].iov_base = msg + offset;
-        if ((msg_size - offset) < ctx->pckt_size) {
-            iov[1].iov_len = msg_size - offset;
-        }
-        else {
-            iov[1].iov_len = ctx->pckt_size;
+        len = msg_size - offset;
+        if (ctx->pckt_size < len) {
+            len = ctx->pckt_size;
         }
+        memcpy(buf + GELF_HEADER_SIZE, (char *) msg + offset, len);
 
-        ret = sendmsg(ctx->fd, &msghdr, MSG_DONTWAIT | MSG_NOSIGNAL);
+        ret = send(ctx->fd, buf, len + GELF_HEADER_SIZE,
+                   MSG_DONTWAIT | MSG_NOSIGNAL);
         if (ret == -1) {
             flb_errno();
         }
         offset += ctx->pckt_size;
     }
-
     return 0;
 }
 
@@ -399,14 +423,23 @@ static int cb_gelf_init(struct flb_output_instance *ins, struct flb_config *conf
         }
         close(fd);
     }
+    srand(ctx->seed);
 
     ctx->fd = -1;
+    ctx->pckt_buf = NULL;
+
     if (ctx->mode == FLB_GELF_UDP) {
         ctx->fd = flb_net_udp_connect(ins->host.name, ins->host.port);
         if (ctx->fd < 0) {
             flb_free(ctx);
             return -1;
         }
+        ctx->pckt_buf = flb_malloc(GELF_HEADER_SIZE + ctx->pckt_size);
+        if (ctx->pckt_buf == NULL) {
+            flb_socket_close(ctx->fd);
+            flb_free(ctx);
+            return -1;
+        }
     }
     else {
         int io_flags = FLB_IO_TCP;
@@ -449,6 +482,7 @@ static int cb_gelf_exit(void *data, struct flb_config *config)
     flb_sds_destroy(ctx->fields.full_message_key);
     flb_sds_destroy(ctx->fields.level_key);
 
+    flb_free(ctx->pckt_buf);
     flb_free(ctx);
 
     return 0;

plugins/out_gelf/gelf.h

@@ -35,6 +35,7 @@ struct flb_out_gelf_config {
     flb_sockfd_t fd;
 
     int pckt_size;
+    char *pckt_buf;
     int compress;
     unsigned int seed;