jsonrpc: use ccan/membuf instead of a string for our output buffer.

This isn't a big change, since we basically dump the entire JSON
resuly string into the membuf then write it out, but it's prep for the
next changes.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/jsonrpc.c

@@ -31,6 +31,16 @@
 #include <sys/types.h>
 #include <sys/un.h>
 
+/* Realloc helper for tal membufs */
+static void *membuf_tal_realloc(struct membuf *mb,
+				void *rawelems, size_t newsize)
+{
+	char *p = rawelems;
+
+	tal_resize(&p, newsize);
+	return p;
+}
+
 /* jcon and cmd have separate lifetimes: we detach them on either destruction */
 static void destroy_jcon(struct json_connection *jcon)
 {
@@ -266,7 +276,11 @@ static void json_done(struct json_connection *jcon,
 		      const char *json TAKES)
 {
 	/* Queue for writing, and wake writer. */
-	jcon->outbuf = tal_strdup(jcon, json);
+	size_t len = strlen(json);
+	char *p = membuf_add(&jcon->outbuf, len);
+	memcpy(p, json, len);
+	if (taken(json))
+		tal_free(json);
 	io_wake(jcon);
 
 	/* Can be NULL if we failed to parse! */
@@ -496,7 +510,7 @@ static struct io_plan *locked_write_json(struct io_conn *conn,
 static struct io_plan *write_json_done(struct io_conn *conn,
 				       struct json_connection *jcon)
 {
-	jcon->outbuf = tal_free(jcon->outbuf);
+	membuf_consume(&jcon->outbuf, jcon->out_amount);
 
 	if (jcon->stop) {
 		log_unusual(jcon->log, "JSON-RPC shutdown");
@@ -516,7 +530,9 @@ static struct io_plan *write_json_done(struct io_conn *conn,
 static struct io_plan *write_json(struct io_conn *conn,
 				  struct json_connection *jcon)
 {
-	return io_write(conn, jcon->outbuf, strlen(jcon->outbuf),
+	jcon->out_amount = membuf_num_elems(&jcon->outbuf);
+	return io_write(conn,
+			membuf_elems(&jcon->outbuf), jcon->out_amount,
 			write_json_done, jcon);
 }
 
@@ -603,7 +619,8 @@ static struct io_plan *jcon_connected(struct io_conn *conn,
 	jcon->buffer = tal_arr(jcon, char, 64);
 	jcon->stop = false;
 	jcon->lock = io_lock_new(jcon);
-	jcon->outbuf = NULL;
+	membuf_init(&jcon->outbuf,
+		    tal_arr(jcon, char, 64), 64, membuf_tal_realloc);
 	jcon->len_read = 0;
 	jcon->command = NULL;
 

lightningd/jsonrpc.h

@@ -4,6 +4,7 @@
 #include <bitcoin/chainparams.h>
 #include <ccan/autodata/autodata.h>
 #include <ccan/list/list.h>
+#include <ccan/membuf/membuf.h>
 #include <common/io_lock.h>
 #include <common/json.h>
 
@@ -62,7 +63,10 @@ struct json_connection {
 	struct command *command;
 
 	/* Current command's output. */
-	const char *outbuf;
+	MEMBUF(char) outbuf;
+
+	/* How much we're writing right now. */
+	size_t out_amount;
 	struct io_lock *lock;
 };