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author | 2020-11-30 03:44:47 +0530 | |
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committer | 2020-11-29 23:20:37 +0000 | |
commit | 5727bbb99921a741ee7203a070f580a026f37bc8 (patch) | |
tree | d92b1d1d61fb3e9e3ca7b7fac7e521ad2c35e40a /docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md | |
parent | e5e292979e4a08e036e6545d55dd8515a8b6c280 (diff) |
Added AFB Helper Guide in Developer Guides
Revised and added AFB Helper Guide as a part of Developer Guides.
Bug-AGL: [SPEC-3633]
Signed-off-by: Shankho Boron Ghosh <shankhoghosh123@gmail.com>
Change-Id: I3df9265ae0570e987d80bc4bd2d3d14e7743b26a
Diffstat (limited to 'docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md')
-rw-r--r-- | docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md | 341 |
1 files changed, 341 insertions, 0 deletions
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md new file mode 100644 index 0000000..e106a18 --- /dev/null +++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md @@ -0,0 +1,341 @@ +--- +title: C JSON Wrapper +--- + +<!-- WARNING: This file is generated by fetch_docs.js using /home/boron/Documents/AGL/docs-webtemplate/site/_data/tocs/devguides/master/afb-helpers-function-references-afb-helpers-book.yml --> + +WRAP-JSON facility +================== + +The facility wrap-json is based on the pack/unpack API on the +library 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. + +- `y` (byte array) \[const uint8_t \*, size\_t\] + + Convert the byte array whose length is given to + its base64url string representation. + +- `Y` (byte array) \[const uint8_t \*, size\_t\] + + Like 'y' but output is base64. + +- `y?`, `Y?` (byte array or null) \[const uint8_t \*, size\_t\] + + Like 'y' or 'Y' but allows to output a JSON null value + either when the buffer is *NULL* or when the size is *0*. + +- `y*`, `y*` (optional byte array) \[const uint8_t \*, size\_t\] + + Like 'y' or 'Y' but do not put JSON value + either when the buffer is *NULL* or when the size is *0*. + 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. + +- `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. + +- `y` (byte array) \[uint8_t \*\*, size\_t \*\] + + Convert an input string base64url encoded to its + byte array representation. The result and its length + are stored. The returned buffer must be freed by the caller. + +- `Y` (byte array) \[uint8_t \*\*, size\_t \*\] + + Like 'y' but input is base64. + +- `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. |