Improve json_object -> string performance

Removes variadic prints for ~3x performance improvement.

json_object.c

@@ -147,9 +147,13 @@ static int json_escape_str(struct printbuf *pb, const char *str, int len, int fl
 					printbuf_memappend(pb,
 							   str + start_offset,
 							   pos - start_offset);
-				sprintbuf(pb, "\\u00%c%c",
-				json_hex_chars[c >> 4],
-				json_hex_chars[c & 0xf]);
+				static char sbuf[7];
+				snprintf(sbuf, sizeof(sbuf),
+                                        "\\u00%c%c",
+                                        json_hex_chars[c >> 4],
+                                        json_hex_chars[c & 0xf]);
+				printbuf_memappend (pb, sbuf, sizeof(sbuf) - 1);
+
 				start_offset = ++pos;
 			} else
 				pos++;
@@ -585,7 +589,10 @@ static int json_object_int_to_json_string(struct json_object* jso,
 					  int level,
 					  int flags)
 {
-	return sprintbuf(pb, "%" PRId64, jso->o.c_int64);
+	/* room for 19 digits, the sign char, and a null term */
+	static char sbuf[21];
+	snprintf(sbuf, sizeof(sbuf), "%"PRId64, jso->o.c_int64);
+	return sprintbuf(pb, sbuf);
 }
 
 struct json_object* json_object_new_int(int32_t i)

printbuf.c

@@ -85,6 +85,7 @@ int printbuf_memappend(struct printbuf *p, const char *buf, int size)
     if (printbuf_extend(p, p->bpos + size + 1) < 0)
       return -1;
   }
+
   memcpy(p->buf + p->bpos, buf, size);
   p->bpos += size;
   p->buf[p->bpos]= '\0';
@@ -111,34 +112,6 @@ int printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len)
 	return 0;
 }
 
-int sprintbuf(struct printbuf *p, const char *msg, ...)
-{
-  va_list ap;
-  char *t;
-  int size;
-  char buf[128];
-
-  /* user stack buffer first */
-  va_start(ap, msg);
-  size = vsnprintf(buf, 128, msg, ap);
-  va_end(ap);
-  /* if string is greater than stack buffer, then use dynamic string
-     with vasprintf.  Note: some implementation of vsnprintf return -1
-     if output is truncated whereas some return the number of bytes that
-     would have been written - this code handles both cases. */
-  if(size == -1 || size > 127) {
-    va_start(ap, msg);
-    if((size = vasprintf(&t, msg, ap)) < 0) { va_end(ap); return -1; }
-    va_end(ap);
-    printbuf_memappend(p, t, size);
-    free(t);
-    return size;
-  } else {
-    printbuf_memappend(p, buf, size);
-    return size;
-  }
-}
-
 void printbuf_reset(struct printbuf *p)
 {
   p->buf[0] = '\0';
@@ -152,3 +125,8 @@ void printbuf_free(struct printbuf *p)
     free(p);
   }
 }
+
+inline int sprintbuf(struct printbuf *p, const char *buf)
+{
+  return printbuf_memappend(p, buf, strlen(buf));
+}

printbuf.h

@@ -62,7 +62,7 @@ extern int
 printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len);
 
 extern int
-sprintbuf(struct printbuf *p, const char *msg, ...);
+sprintbuf(struct printbuf *p, const char *msg);
 
 extern void
 printbuf_reset(struct printbuf *p);

tests/test_printbuf.c

@@ -17,7 +17,7 @@ static void test_basic_printbuf_memset()
 
 	printf("%s: starting test\n", __func__);
 	pb = printbuf_new();
-	sprintbuf(pb, "blue:%d", 1);
+	sprintbuf(pb, "blue:1");
 	printbuf_memset(pb, -1, 'x', 52);
 	printf("Buffer contents:%.*s\n", printbuf_length(pb), pb->buf);
 	printbuf_free(pb);
@@ -111,42 +111,6 @@ static void test_printbuf_memappend(int *before_resize)
 	printf("%s: end test\n", __func__);
 }
 
-static void test_sprintbuf(int before_resize);
-static void test_sprintbuf(int before_resize)
-{
-	struct printbuf *pb;
-
-	printf("%s: starting test\n", __func__);
-	pb = printbuf_new();
-	printf("Buffer length: %d\n", printbuf_length(pb));
-
-	char *data = malloc(before_resize + 1 + 1);
-	memset(data, 'X', before_resize + 1 + 1);
-	data[before_resize + 1] = '\0';
-	sprintbuf(pb, "%s", data);
-	free(data);
-	printf("sprintbuf to just after resize(%d+1): %d, [%s], strlen(buf)=%d\n", before_resize, printbuf_length(pb), pb->buf, (int)strlen(pb->buf));
-
-	printbuf_reset(pb);
-	sprintbuf(pb, "plain");
-	printf("%d, [%s]\n", printbuf_length(pb), pb->buf);
-
-	sprintbuf(pb, "%d", 1);
-	printf("%d, [%s]\n", printbuf_length(pb), pb->buf);
-
-	sprintbuf(pb, "%d", INT_MAX);
-	printf("%d, [%s]\n", printbuf_length(pb), pb->buf);
-
-	sprintbuf(pb, "%d", INT_MIN);
-	printf("%d, [%s]\n", printbuf_length(pb), pb->buf);
-
-	sprintbuf(pb, "%s", "%s");
-	printf("%d, [%s]\n", printbuf_length(pb), pb->buf);
-
-	printbuf_free(pb);
-	printf("%s: end test\n", __func__);
-}
-
 int main(int argc, char **argv)
 {
 	int before_resize = 0;
@@ -159,8 +123,6 @@ int main(int argc, char **argv)
 	printf("========================================\n");
 	test_printbuf_memappend(&before_resize);
 	printf("========================================\n");
-	test_sprintbuf(before_resize);
-	printf("========================================\n");
 
 	return 0;
 }

tests/test_printbuf.expected

@@ -20,13 +20,3 @@ Append to just before resize: 31, [XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX]
 Append to just after resize: 32, [XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX]
 test_printbuf_memappend: end test
 ========================================
-test_sprintbuf: starting test
-Buffer length: 0
-sprintbuf to just after resize(31+1): 32, [XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX], strlen(buf)=32
-5, [plain]
-6, [plain1]
-16, [plain12147483647]
-27, [plain12147483647-2147483648]
-29, [plain12147483647-2147483648%s]
-test_sprintbuf: end test
-========================================