json_object: Introduce json_object_new_string_ext().

This function helps to reduce code duplication, as it can be easily
extended for different ways how a new json string-object will be
created from a given string buffer.

json_object.c

@@ -1138,60 +1138,63 @@ static void json_object_string_delete(struct json_object *jso)
 	json_object_generic_delete(jso);
 }
 
-struct json_object *json_object_new_string(const char *s)
+struct json_object *json_object_new_string_ext(const char *s, const int len,
+                                               int flags)
 {
-	struct json_object *jso = json_object_new(json_type_string);
-	if (!jso)
+	if (len <= 0 || flags == 0)
 		return NULL;
-	jso->_delete = &json_object_string_delete;
-	jso->_to_json_string = &json_object_string_to_json_string;
-	jso->o.c_string.len = strlen(s);
-	if (jso->o.c_string.len < LEN_DIRECT_STRING_DATA)
-	{
-		memcpy(jso->o.c_string.str.data, s, jso->o.c_string.len);
-	}
-	else
-	{
-		jso->o.c_string.str.ptr = strdup(s);
-		if (!jso->o.c_string.str.ptr)
-		{
-			json_object_generic_delete(jso);
-			errno = ENOMEM;
-			return NULL;
-		}
-	}
-	return jso;
-}
 
-struct json_object *json_object_new_string_len(const char *s, const int len)
-{
-	char *dstbuf;
 	struct json_object *jso = json_object_new(json_type_string);
 	if (!jso)
 		return NULL;
+	char *dstbuf = NULL;
 	jso->_delete = &json_object_string_delete;
 	jso->_to_json_string = &json_object_string_to_json_string;
+	jso->o.c_string.len = len;
+
+	/* short cut if the internal string buffer of jso is big enough */
 	if (len < LEN_DIRECT_STRING_DATA)
 	{
 		dstbuf = jso->o.c_string.str.data;
+		memcpy(dstbuf, s, jso->o.c_string.len);
+		dstbuf[len] = '\0';
+		return jso;
 	}
-	else
+
+	if (flags & JSON_C_NEW_STRING_STRDUP)
+		dstbuf = strdup(s);
+	else if (flags & JSON_C_NEW_STRING_LENGTH)
 	{
-		jso->o.c_string.str.ptr = (char *)malloc(len + 1);
-		if (!jso->o.c_string.str.ptr)
+		dstbuf = malloc(len + 1);
+		if (dstbuf)
 		{
-			json_object_generic_delete(jso);
-			errno = ENOMEM;
-			return NULL;
+			memcpy(dstbuf, s, len);
+			dstbuf[len] = '\0';
 		}
-		dstbuf = jso->o.c_string.str.ptr;
 	}
-	memcpy(dstbuf, (const void *)s, len);
-	dstbuf[len] = '\0';
-	jso->o.c_string.len = len;
+
+	/* cannot be reached if o.c_string.str.data is used */
+	if (!dstbuf)
+	{
+		/* errno has already been set by malloc or strdup */
+		json_object_generic_delete(jso);
+		return NULL;
+	}
+
+	jso->o.c_string.str.ptr = dstbuf;
 	return jso;
 }
 
+struct json_object *json_object_new_string(const char *s)
+{
+	return json_object_new_string_ext(s, strlen(s), JSON_C_NEW_STRING_STRDUP);
+}
+
+struct json_object *json_object_new_string_len(const char *s, const int len)
+{
+	return json_object_new_string_ext(s, len, JSON_C_NEW_STRING_LENGTH);
+}
+
 const char *json_object_get_string(struct json_object *jso)
 {
 	if (!jso)

json_object.h

@@ -45,6 +45,16 @@ extern "C" {
 
 #define JSON_OBJECT_DEF_HASH_ENTRIES 16
 
+/**
+ * A copy of the string is made and the memory is managed by the json_object.
+ */
+#define JSON_C_NEW_STRING_STRDUP (1 << 0)
+/**
+ * A copy of the string with a maximum of len characters is made and the
+ * memory is managed by the json_object.
+ */
+#define JSON_C_NEW_STRING_LENGTH (1 << 1)
+
 /**
  * A flag for the json_object_to_json_string_ext() and
  * json_object_to_file_ext() functions which causes the output
@@ -867,13 +877,27 @@ JSON_EXPORT int json_object_set_double(struct json_object *obj, double new_value
 
 /* string type methods */
 
+/** Create a new json_object of type json_type_string in a configurable way
+ *
+ * The string will be embedded into the new object as specified by the given
+ * flags parameter.
+ *
+ * @param s the string
+ * @param len the size of the string buffer in bytes
+ * @param flags process-modifying options, MUST NOT equal zero, and only one
+ * option can be specified.
+ * @returns a json_object of type json_type_string
+ */
+JSON_EXPORT struct json_object *json_object_new_string_ext(const char *s, const int len,
+                                                           int flags);
+
 /** Create a new empty json_object of type json_type_string
  *
  * A copy of the string is made and the memory is managed by the json_object
  *
  * @param s the string
  * @returns a json_object of type json_type_string
- * @see json_object_new_string_len()
+ * @see json_object_new_string_ext()
  */
 JSON_EXPORT struct json_object *json_object_new_string(const char *s);
 
@@ -883,9 +907,9 @@ JSON_EXPORT struct json_object *json_object_new_string(const char *s);
  * A copy of the string is made and the memory is managed by the json_object
  *
  * @param s the string
- * @param len max length of the new string
+ * @param len max length of the new string, must be >= 1
  * @returns a json_object of type json_type_string
- * @see json_object_new_string()
+ * @see json_object_new_string_ext()
  */
 JSON_EXPORT struct json_object *json_object_new_string_len(const char *s, const int len);