gossip: Implement gossip_store compaction

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

gossipd/gossip_store.c

@@ -15,6 +15,7 @@
 #include <wire/wire.h>
 
 #define GOSSIP_STORE_FILENAME "gossip_store"
+#define GOSSIP_STORE_TEMP_FILENAME "gossip_store.tmp"
 #define MAX_COUNT_TO_STALE_RATE 10
 static u8 gossip_store_version = 0x02;
 
@@ -145,6 +146,63 @@ static bool gossip_store_append(int fd, struct routing_state *rstate, const u8 *
 		write(fd, msg, msglen) == msglen);
 }
 
+/**
+ * Rewrite the on-disk gossip store, compacting it along the way
+ *
+ * Creates a new file, writes all the updates from the `broadcast_state`, and
+ * then atomically swaps the files.
+ */
+
+static void gossip_store_compact(struct gossip_store *gs)
+{
+	size_t count = 0;
+	u64 index = 0;
+	int fd;
+	const u8 *msg;
+
+	assert(gs->broadcast);
+	status_trace(
+	    "Compacting gossip_store with %zu entries, %zu of which are stale",
+	    gs->count, gs->count - gs->broadcast->count);
+
+	fd = open(GOSSIP_STORE_TEMP_FILENAME, O_RDWR|O_APPEND|O_CREAT, 0600);
+
+	if (fd < 0)
+		status_failed(
+		    STATUS_FAIL_INTERNAL_ERROR,
+		    "Could not open file for gossip_store compaction");
+
+	if (write(fd, &gossip_store_version, sizeof(gossip_store_version))
+	    != sizeof(gossip_store_version))
+		status_failed(STATUS_FAIL_INTERNAL_ERROR,
+			      "Writing version to store: %s", strerror(errno));
+
+	while ((msg = next_broadcast(gs->broadcast, 0, UINT32_MAX, &index)) != NULL) {
+		if (!gossip_store_append(fd, gs->rstate, msg)) {
+			status_broken("Failed writing to gossip store: %s",
+				      strerror(errno));
+			unlink(GOSSIP_STORE_TEMP_FILENAME);
+			return;
+		}
+		count++;
+	}
+
+	if (rename(GOSSIP_STORE_TEMP_FILENAME, GOSSIP_STORE_FILENAME) == -1) {
+		status_broken(
+		    "Error swapping compacted gossip_store into place: %s",
+		    strerror(errno));
+		unlink(GOSSIP_STORE_TEMP_FILENAME);
+		return;
+	}
+
+	status_trace(
+	    "Compaction completed: dropped %zu messages, new count %zu",
+	    gs->count - count, count);
+	gs->count = count;
+	close(gs->fd);
+	gs->fd = fd;
+}
+
 void gossip_store_add(struct gossip_store *gs, const u8 *gossip_msg)
 {
 	size_t stale;
@@ -161,9 +219,8 @@ void gossip_store_add(struct gossip_store *gs, const u8 *gossip_msg)
 
 	gs->count++;
 	stale = gs->count - gs->broadcast->count;
-	if (gs->count >= 100 && stale * MAX_COUNT_TO_STALE_RATE > gs->count) {
-		/* FIXME(cdecker) Implement rewriting of gossip_store */
-	}
+	if (gs->count >= 100 && stale * MAX_COUNT_TO_STALE_RATE > gs->count)
+		gossip_store_compact(gs);
 }
 
 void gossip_store_add_channel_delete(struct gossip_store *gs,

gossipd/test/run-bench-find_route.c

@@ -99,6 +99,11 @@ bool fromwire_wireaddr(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, struct
 u64 insert_broadcast(struct broadcast_state *bstate UNNEEDED, const u8 *msg UNNEEDED,
 		     u32 timestamp UNNEEDED)
 { fprintf(stderr, "insert_broadcast called!\n"); abort(); }
+/* Generated stub for next_broadcast */
+const u8 *next_broadcast(struct broadcast_state *bstate UNNEEDED,
+			 u32 timestamp_min UNNEEDED, u32 timestamp_max UNNEEDED,
+			 u64 *last_index UNNEEDED)
+{ fprintf(stderr, "next_broadcast called!\n"); abort(); }
 /* Generated stub for onion_type_name */
 const char *onion_type_name(int e UNNEEDED)
 { fprintf(stderr, "onion_type_name called!\n"); abort(); }

gossipd/test/run-find_route-specific.c

@@ -63,6 +63,11 @@ bool fromwire_wireaddr(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, struct
 u64 insert_broadcast(struct broadcast_state *bstate UNNEEDED, const u8 *msg UNNEEDED,
 		     u32 timestamp UNNEEDED)
 { fprintf(stderr, "insert_broadcast called!\n"); abort(); }
+/* Generated stub for next_broadcast */
+const u8 *next_broadcast(struct broadcast_state *bstate UNNEEDED,
+			 u32 timestamp_min UNNEEDED, u32 timestamp_max UNNEEDED,
+			 u64 *last_index UNNEEDED)
+{ fprintf(stderr, "next_broadcast called!\n"); abort(); }
 /* Generated stub for onion_type_name */
 const char *onion_type_name(int e UNNEEDED)
 { fprintf(stderr, "onion_type_name called!\n"); abort(); }

gossipd/test/run-find_route.c

@@ -61,6 +61,11 @@ bool fromwire_wireaddr(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, struct
 u64 insert_broadcast(struct broadcast_state *bstate UNNEEDED, const u8 *msg UNNEEDED,
 		     u32 timestamp UNNEEDED)
 { fprintf(stderr, "insert_broadcast called!\n"); abort(); }
+/* Generated stub for next_broadcast */
+const u8 *next_broadcast(struct broadcast_state *bstate UNNEEDED,
+			 u32 timestamp_min UNNEEDED, u32 timestamp_max UNNEEDED,
+			 u64 *last_index UNNEEDED)
+{ fprintf(stderr, "next_broadcast called!\n"); abort(); }
 /* Generated stub for onion_type_name */
 const char *onion_type_name(int e UNNEEDED)
 { fprintf(stderr, "onion_type_name called!\n"); abort(); }