gossip: Separate writing to gossip_store fd from append

We write both when coming from outside, as well as when compacting, so we
extract the write functionality to use it in both cases.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

gossipd/gossip_store.c

@@ -74,33 +74,45 @@ struct gossip_store *gossip_store_new(const tal_t *ctx,
 			      "Writing version to store: %s", strerror(errno));
 	return gs;
 }
+
 /**
- * Write an incoming message to the `gossip_store`
+ * Given a message and a file descriptor append the message to it.
  *
- * @param gs  The gossip_store to write to
- * @param msg The message to write
- * @return The newly created and initialized `gossip_store`
+ * Returns true on success, false on error.
  */
-static void gossip_store_append(struct gossip_store *gs, const u8 *msg)
+static bool gossip_store_file_append(int fd, const u8 *msg)
 {
 	u32 msglen = tal_len(msg);
 	beint32_t checksum, belen = cpu_to_be32(msglen);
-	size_t stale;
 
 	/* Only give error message once. */
-	if (gs->fd == -1)
-		return;
+	if (fd == -1)
+		return true;
 
 	checksum = cpu_to_be32(crc32c(0, msg, msglen));
 
-	/* FORTIFY_SOURCE gets upset if we don't check return. */
-	if (write(gs->fd, &belen, sizeof(belen)) != sizeof(belen) ||
-	    write(gs->fd, &checksum, sizeof(checksum)) != sizeof(checksum) ||
-	    write(gs->fd, msg, msglen) != msglen) {
-              status_broken("Failed writing to gossip store: %s",
-			    strerror(errno));
-	      gs->fd = -1;
+	return (write(fd, &belen, sizeof(belen)) == sizeof(belen) &&
+		write(fd, &checksum, sizeof(checksum)) == sizeof(checksum) &&
+		write(fd, msg, msglen) == msglen);
+}
+
+/**
+ * Write an incoming message to the `gossip_store`
+ *
+ * @param gs  The gossip_store to write to
+ * @param msg The message to write
+ * @return The newly created and initialized `gossip_store`
+ */
+static void gossip_store_append(struct gossip_store *gs, const u8 *msg)
+{
+	size_t stale;
+	if (!gossip_store_file_append(gs->fd, msg)) {
+		status_broken("Failed writing to gossip store: %s",
+			      strerror(errno));
+		gs->fd = -1;
+		return;
 	}
+
 	gs->count++;
 	stale = gs->count - gs->broadcast->count;