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+WRAP-JSON facility
+==================
+
+The facility wrap-json is based on the pack/unpack API on the
+libray jansson. The two chapters below are copied from the
+documentation of jansson library copyrighted by Petri Lehtinen
+(see at end).
+
+Building Values
+---------------
+
+This section describes functions that help to create, or *pack*, complex
+JSON values, especially nested objects and arrays. Value building is
+based on a *format string* that is used to tell the functions about the
+expected arguments.
+
+For example, the format string `"i"` specifies a single integer value,
+while the format string `"[ssb]"` or the equivalent `"[s, s, b]"`
+specifies an array value with two strings and a boolean as its items:
+
+    /* Create the JSON integer 42 */
+    wrap_json_pack(&result, "i", 42);
+
+    /* Create the JSON array ["foo", "bar", true] */
+    wrap_json_pack(&result, "[ssb]", "foo", "bar", 1);
+
+Here's the full list of format specifiers. The type in parentheses
+denotes the resulting JSON type, and the type in brackets (if any)
+denotes the C type that is expected as the corresponding argument or
+arguments.
+
+`s` (string) \[const char \*\]
+
+:   Convert a null terminated UTF-8 string to a JSON string.
+
+`s?` (string) \[const char \*\]
+
+:   Like `s`, but if the argument is *NULL*, output a JSON null value.
+
+`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.
+
+`s#` (string) \[const char \*, int\]
+
+:   Convert a UTF-8 buffer of a given length to a JSON string.
+
+`s%` (string) \[const char \*, size\_t\]
+
+:   Like `s#` but the length argument is of type size\_t.
+
+`+` \[const char \*\]
+
+:   Like `s`, but concatenate to the previous string. Only valid after
+    `s`, `s#`, `+` or `+#`.
+
+`+#` \[const char \*, int\]
+
+:   Like `s#`, but concatenate to the previous string. Only valid after
+    `s`, `s#`, `+` or `+#`.
+
+`+%` (string) \[const char \*, size\_t\]
+
+:   Like `+#` but the length argument is of type size\_t.
+
+`n` (null)
+
+:   Output a JSON null value. No argument is consumed.
+
+`b` (boolean) \[int\]
+
+:   Convert a C int to JSON boolean value. Zero is converted to `false`
+    and non-zero to `true`.
+
+`i` (integer) \[int\]
+
+:   Convert a C int to JSON integer.
+
+`I` (integer) \[json\_int\_t\]
+
+:   Convert a C json\_int\_t to JSON integer.
+
+`f` (real) \[double\]
+
+:   Convert a C double to JSON real.
+
+`o` (any value) \[json\_t \*\]
+
+:   Output any given JSON value as-is. If the value is added to an array
+    or object, the reference to the value passed to `o` is stolen by the
+    container.
+
+`O` (any value) \[json\_t \*\]
+
+:   Like `o`, but the argument's reference count is incremented. This is
+    useful if you pack into an array or object and want to keep the
+    reference for the JSON value consumed by `O` to yourself.
+
+`o?`, `O?` (any value) \[json\_t \*\]
+
+:   Like `o` and `O`, respectively, but if the argument is *NULL*,
+    output a JSON null value.
+
+`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.
+
+`[fmt]` (array)
+
+:   Build an array with contents from the inner format string. `fmt` may
+    contain objects and arrays, i.e. recursive value building is
+    supported.
+
+`{fmt}` (object)
+
+:   Build an object with contents from the inner format string `fmt`.
+    The first, third, etc. format specifier represent a key, and must be
+    a string (see `s`, `s#`, `+` and `+#` above), as object keys are
+    always strings. The second, fourth, etc. format specifier represent
+    a value. Any value may be an object or array, i.e. recursive value
+    building is supported.
+
+Whitespace, `:` and `,` are ignored.
+
+More examples:
+
+    /* Build an empty JSON object */
+    wrap_json_pack(&result, "{}");
+
+    /* Build the JSON object {"foo": 42, "bar": 7} */
+    wrap_json_pack(&result, "{sisi}", "foo", 42, "bar", 7);
+
+    /* Like above, ':', ',' and whitespace are ignored */
+    wrap_json_pack(&result, "{s:i, s:i}", "foo", 42, "bar", 7);
+
+    /* Build the JSON array [[1, 2], {"cool": true}] */
+    wrap_json_pack(&result, "[[i,i],{s:b}]", 1, 2, "cool", 1);
+
+    /* Build a string from a non-null terminated buffer */
+    char buffer[4] = {'t', 'e', 's', 't'};
+    wrap_json_pack(&result, "s#", buffer, 4);
+
+    /* Concatenate strings together to build the JSON string "foobarbaz" */
+    wrap_json_pack(&result, "s++", "foo", "bar", "baz");
+
+    /* Create an empty object or array when optional members are missing */
+    wrap_json_pack(&result, "{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL);
+    wrap_json_pack(&result, "[s*,o*,O*]", NULL, NULL, NULL);
+
+Parsing and Validating Values
+-----------------------------
+
+This section describes functions that help to validate complex values
+and extract, or *unpack*, data from them. Like building values
+<apiref-pack>, this is also based on format strings.
+
+While a JSON value is unpacked, the type specified in the format string
+is checked to match that of the JSON value. This is the validation part
+of the process. In addition to this, the unpacking functions can also
+check that all items of arrays and objects are unpacked. This check be
+enabled with the format specifier `!` or by using the flag
+`JSON_STRICT`. See below for details.
+
+Here's the full list of format specifiers. The type in parentheses
+denotes the JSON type, and the type in brackets (if any) denotes the C
+type whose address should be passed.
+
+`s` (string) \[const char \*\]
+
+:   Convert a JSON string to a pointer to a null terminated UTF-8
+    string. The resulting string is extracted by using
+    json\_string\_value() internally, so it exists as long as there are
+    still references to the corresponding JSON string.
+
+`s%` (string) \[const char \*, size\_t \*\]
+
+:   Convert a JSON string to a pointer to a null terminated UTF-8 string
+    and its length.
+
+`n` (null)
+
+:   Expect a JSON null value. Nothing is extracted.
+
+`b` (boolean) \[int\]
+
+:   Convert a JSON boolean value to a C int, so that `true` is converted
+    to 1 and `false` to 0.
+
+`i` (integer) \[int\]
+
+:   Convert a JSON integer to C int.
+
+`I` (integer) \[json\_int\_t\]
+
+:   Convert a JSON integer to C json\_int\_t.
+
+`f` (real) \[double\]
+
+:   Convert a JSON real to C double.
+
+`F` (integer or real) \[double\]
+
+:   Convert a JSON number (integer or real) to C double.
+
+`o` (any value) \[json\_t \*\]
+
+:   Store a JSON value with no conversion to a json\_t pointer.
+
+`O` (any value) \[json\_t \*\]
+
+:   Like `O`, but the JSON value's reference count is incremented.
+
+`[fmt]` (array)
+
+:   Convert each item in the JSON array according to the inner format
+    string. `fmt` may contain objects and arrays, i.e. recursive value
+    extraction is supported.
+
+`{fmt}` (object)
+
+:   Convert each item in the JSON object according to the inner format
+    string `fmt`. The first, third, etc. format specifier represent a
+    key, and must be `s`. The corresponding argument to unpack functions
+    is read as the object key. The second fourth, etc. format specifier
+    represent a value and is written to the address given as the
+    corresponding argument. **Note** that every other argument is read
+    from and every other is written to.
+
+    `fmt` may contain objects and arrays as values, i.e. recursive value
+    extraction is supported.
+
+`!`
+
+:   This special format specifier is used to enable the check that all
+    object and array items are accessed, on a per-value basis. It must
+    appear inside an array or object as the last format specifier before
+    the closing bracket or brace.
+
+`*`
+
+:   This special format specifier is the opposite of `!`. This is the default.
+    It must appear inside an array or object as the last format specifier
+    before the closing bracket or brace.
+
+Whitespace, `:` and `,` are ignored.
+
+Examples:
+
+    /* root is the JSON integer 42 */
+    int myint;
+    wrap_json_unpack(root, "i", &myint);
+    assert(myint == 42);
+
+    /* root is the JSON object {"foo": "bar", "quux": true} */
+    const char *str;
+    int boolean;
+    wrap_json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
+    assert(strcmp(str, "bar") == 0 && boolean == 1);
+
+    /* root is the JSON array [[1, 2], {"baz": null} */
+    wrap_json_check(root, "[[i,i], {s:n}]", "baz");
+    /* returns 0 for validation success, nothing is extracted */
+
+    /* root is the JSON array [1, 2, 3, 4, 5] */
+    int myint1, myint2;
+    wrap_json_unpack(root, "[ii!]", &myint1, &myint2);
+    /* returns -1 for failed validation */
+
+    /* root is an empty JSON object */
+    int myint = 0, myint2 = 0, myint3 = 0;
+    wrap_json_unpack(root, "{s?i, s?[ii]}",
+                "foo", &myint1,
+                "bar", &myint2, &myint3);
+    /* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */
+
+
+Copyright
+---------
+
+Copyright (c) 2009-2016 Petri Lehtinen <petri@digip.org>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+