Enable optional object/array members in json_pack()

doc/apiref.rst

@@ -1269,6 +1269,14 @@ arguments.
 
     .. versionadded:: 2.8
 
+``s*`` (string) [const char \*]
+    Like ``s``, but if the argument is *NULL*, do not output any value.
+    This format can only be used inside an object or an array. If used
+    inside an object, the corresponding key is additionally suppressed
+    when the value is omitted. See below for an example.
+
+    .. versionadded:: 2.11
+
 ``s#`` (string) [const char \*, int]
     Convert a UTF-8 buffer of a given length to a JSON string.
 
@@ -1324,11 +1332,20 @@ arguments.
     yourself.
 
 ``o?``, ``O?`` (any value) [json_t \*]
-    Like ``o`` and ``O?``, respectively, but if the argument is
+    Like ``o`` and ``O``, respectively, but if the argument is
     *NULL*, output a JSON null value.
 
     .. versionadded:: 2.8
 
+``o*``, ``O*`` (any value) [json_t \*]
+    Like ``o`` and ``O``, respectively, but if the argument is
+    *NULL*, do not output any value. This format can only be used
+    inside an object or an array. If used inside an object, the
+    corresponding key is additionally suppressed. See below for an
+    example.
+
+    .. versionadded:: 2.11
+
 ``[fmt]`` (array)
     Build an array with contents from the inner format string. ``fmt``
     may contain objects and arrays, i.e. recursive value building is
@@ -1387,6 +1404,10 @@ More examples::
   /* Concatenate strings together to build the JSON string "foobarbaz" */
   json_pack("s++", "foo", "bar", "baz");
 
+  /* Create an empty object or array when optional members are missing */
+  json_pack("{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL);
+  json_pack("[s*,o*,O*]", NULL, NULL, NULL);
+
 
 .. _apiref-unpack:
 

src/pack_unpack.c

@@ -235,6 +235,12 @@ static json_t *pack_object(scanner_t *s, va_list *ap)
             if(ours)
                 jsonp_free(key);
 
+            if(strchr("soO", token(s)) && s->next_token.token == '*') {
+                next_token(s);
+                next_token(s);
+                continue;
+            }
+
             goto error;
         }
 
@@ -249,6 +255,8 @@ static json_t *pack_object(scanner_t *s, va_list *ap)
         if(ours)
             jsonp_free(key);
 
+        if(strchr("soO", token(s)) && s->next_token.token == '*')
+            next_token(s);
         next_token(s);
     }
 
@@ -273,14 +281,23 @@ static json_t *pack_array(scanner_t *s, va_list *ap)
         }
 
         value = pack(s, ap);
-        if(!value)
+        if(!value) {
+            if(strchr("soO", token(s)) && s->next_token.token == '*') {
+                next_token(s);
+                next_token(s);
+                continue;
+            }
+
             goto error;
+        }
 
         if(json_array_append_new(array, value)) {
             set_error(s, "<internal>", "Unable to append to array");
             goto error;
         }
 
+        if(strchr("soO", token(s)) && s->next_token.token == '*')
+            next_token(s);
         next_token(s);
     }
     return array;

test/suites/api/test_pack.c

@@ -240,6 +240,18 @@ static void run_tests()
         fail("json_pack object refcount failed");
     json_decref(value);
 
+    /* object with optional members */
+    value = json_pack("{s:s,s:o,s:O}", "a", NULL, "b", NULL, "c", NULL);
+    if(value)
+        fail("json_pack object optional incorrectly succeeded");
+    value = json_pack("{s:**}", "a", NULL);
+    if(value)
+        fail("json_pack object optional invalid incorrectly succeeded");
+    value = json_pack("{s:s*,s:o*,s:O*}", "a", NULL, "b", NULL, "c", NULL);
+    if(!json_is_object(value) || json_object_size(value) != 0)
+        fail("json_pack object optional failed");
+    json_decref(value);
+
     /* simple array */
     value = json_pack("[i,i,i]", 0, 1, 2);
     if(!json_is_array(value) || json_array_size(value) != 3)
@@ -253,6 +265,18 @@ static void run_tests()
     }
     json_decref(value);
 
+    /* simple array with optional members */
+    value = json_pack("[s,o,O]", NULL, NULL, NULL);
+    if(value)
+        fail("json_pack array optional incorrectly succeeded");
+    value = json_pack("[**]", NULL);
+    if(value)
+        fail("json_pack array optional invalid incorrectly succeeded");
+    value = json_pack("[s*,o*,O*]", NULL, NULL, NULL);
+    if(!json_is_array(value) || json_array_size(value) != 0)
+        fail("json_pack array optional failed");
+    json_decref(value);
+
     /* Whitespace; regular string */
     value = json_pack(" s ", "test");
     if(!json_is_string(value) || strcmp("test", json_string_value(value)))