diff --git a/daemon/cli.c b/daemon/cli.c
index 958149128..35afe336c 100644
--- a/daemon/cli.c
+++ b/daemon/cli.c
@@ -1265,11 +1265,12 @@ static void cli_incoming(struct streambuf_stream *s) {
    ilogs(control, LOG_INFO, "New cli connection from %s", s->addr);
 }
 
-static void cli_streambuf_printf(struct cli_writer *cw, const char *fmt, ...) {
+static size_t cli_streambuf_printf(struct cli_writer *cw, const char *fmt, ...) {
 	va_list va;
 	va_start(va, fmt);
-	streambuf_vprintf(cw->ptr, fmt, va);
+	size_t ret = streambuf_vprintf(cw->ptr, fmt, va);
 	va_end(va);
+	return ret;
 }
 
 static void cli_stream_readable(struct streambuf_stream *s) {
@@ -2059,12 +2060,15 @@ static void cli_incoming_media_evict_players(str *instr, struct cli_writer *cw,
 }
 #endif
 
-static void ng_printf(struct cli_writer *cw, const char *fmt, ...) {
+static size_t ng_printf(struct cli_writer *cw, const char *fmt, ...) {
 	GString *s = cw->ptr;
+	size_t ret = s->len;
 	va_list va;
 	va_start(va, fmt);
 	g_string_append_vprintf(s, fmt, va);
 	va_end(va);
+	ret = s->len - ret;
+	return ret;
 }
 
 const char *cli_ng(ng_command_ctx_t *ctx) {
diff --git a/daemon/websocket.c b/daemon/websocket.c
index 5819fa967..f413dd4ba 100644
--- a/daemon/websocket.c
+++ b/daemon/websocket.c
@@ -424,13 +424,15 @@ static const char *websocket_http_metrics(struct websocket_message *wm) {
 
 
 // adds printf string to output buffer without triggering response
-static void websocket_queue_printf(struct cli_writer *cw, const char *fmt, ...) {
+static size_t websocket_queue_printf(struct cli_writer *cw, const char *fmt, ...) {
 	va_list va;
 	va_start(va, fmt);
 	char *s = g_strdup_vprintf(fmt, va);
+	size_t ret = strlen(s);
 	va_end(va);
-	websocket_queue_raw(cw->ptr, s, strlen(s));
+	websocket_queue_raw(cw->ptr, s, ret);
 	g_free(s);
+	return ret;
 }
 
 
diff --git a/include/cli.h b/include/cli.h
index 8c0e05f7b..84bc8e22c 100644
--- a/include/cli.h
+++ b/include/cli.h
@@ -16,7 +16,7 @@ struct cli_writer;
 struct call_monologue;
 
 struct cli_writer {
-	void (*cw_printf)(struct cli_writer *, const char *, ...) __attribute__ ((format (printf, 2, 3)));
+	size_t (*cw_printf)(struct cli_writer *, const char *, ...) __attribute__ ((format (printf, 2, 3)));
 	void *ptr;
 	call_t *call;
 	struct call_monologue *ml;
diff --git a/lib/streambuf.c b/lib/streambuf.c
index e3f36e17a..c30fecdfb 100644
--- a/lib/streambuf.c
+++ b/lib/streambuf.c
@@ -182,22 +182,27 @@ size_t streambuf_bufsize(struct streambuf *b) {
 }
 
 
-void streambuf_vprintf(struct streambuf *b, const char *f, va_list va) {
+size_t streambuf_vprintf(struct streambuf *b, const char *f, va_list va) {
 	GString *gs;
 
 	gs = g_string_new("");
 	g_string_vprintf(gs, f, va);
 
+	size_t ret = gs->len;
 	streambuf_write(b, gs->str, gs->len);
 	g_string_free(gs, TRUE);
+
+	return ret;
 }
 
-void streambuf_printf(struct streambuf *b, const char *f, ...) {
+size_t streambuf_printf(struct streambuf *b, const char *f, ...) {
 	va_list va;
 
 	va_start(va, f);
-	streambuf_vprintf(b, f, va);
+	size_t ret = streambuf_vprintf(b, f, va);
 	va_end(va);
+
+	return ret;
 }
 
 void streambuf_write(struct streambuf *b, const char *s, unsigned int len) {
diff --git a/lib/streambuf.h b/lib/streambuf.h
index ea4919936..c1f9612d0 100644
--- a/lib/streambuf.h
+++ b/lib/streambuf.h
@@ -42,8 +42,8 @@ int streambuf_writeable(struct streambuf *);
 int streambuf_readable(struct streambuf *);
 char *streambuf_getline(struct streambuf *);
 size_t streambuf_bufsize(struct streambuf *);
-void streambuf_printf(struct streambuf *, const char *, ...) __attribute__ ((format (printf, 2, 3)));
-void streambuf_vprintf(struct streambuf *, const char *, va_list);
+size_t streambuf_printf(struct streambuf *, const char *, ...) __attribute__ ((format (printf, 2, 3)));
+size_t streambuf_vprintf(struct streambuf *, const char *, va_list);
 void streambuf_write(struct streambuf *, const char *, unsigned int);
 INLINE void streambuf_write_str(struct streambuf *b, str *s) {
 	streambuf_write(b, s->s, s->len);