libcbor¶

Documentation for version 0.4.0, updated on Jan 02, 2017.

Overview¶

libcbor is a C library for parsing and generating CBOR, the general-purpose schema-less binary data format.

Main features

Complete RFC conformance [1]
Robust C99 implementation
Layered architecture offers both control and convenience
Flexible memory management
No shared global state - threading friendly [2]
Proper handling of UTF-8
Full support for streams & incremental processing
Extensive documentation and test suite
No runtime dependencies, small footprint

[1]	See RFC conformance

[2]	With the exception of custom memory allocators (see Memory management and reference counting)

Contents¶

Getting started¶

Pre-built Linux packages are distributed from the libcbor website. For other platforms, you will need to compile it from source.

Building & installing libcbor¶

Prerequisites:

C99 compiler
CMake 2.8 or newer (might also be called cmakesetup, cmake-gui or ccmake depending on the installed version and system)
C build system CMake can target (make, Apple Xcode, MinGW, ...)

Note

As of May 2015, not even the 2015 release candidate of Visual Studio supports C99. While CMake will be happy to generate a VS solution that you can play with, libcbor currently cannot be compiled using the MSVC toolchain. ICC, GCC under Cygwin, and MinGW’s GCC will all work. The MinGW build process is described below.

Configuration options

A handful of configuration flags can be passed to cmake. The following table lists libcbor compile-time directives and several important generic flags.

Option	Meaning	Default	Possible values
`CMAKE_C_COMPILER`	C compiler to use	`cc`	`gcc`, `clang`, `clang-3.5`, ...
`CMAKE_INSTALL_PREFIX`	Installation prefix	System-dependent	`/usr/local/lib`, ...
`HUGE_FUZZ`	Fuzz test with 8GB of data	`OFF`	`ON`, `OFF`
`SANE_MALLOC`	Assume `malloc` will refuse unreasonable allocations	`OFF`	`ON`, `OFF`
`COVERAGE`	Generate test coverage instrumentation	`OFF`	`ON`, `OFF`

The following configuration options will also be defined as macros[#]_ in <cbor/common.h> and can therefore be used in client code:

Option	Meaning	Default	Possible values
`CBOR_CUSTOM_ALLOC`	Enable custom allocator support	`OFF`	`ON`, `OFF`
`CBOR_PRETTY_PRINTER`	Include a pretty-printing routine	`ON`	`ON`, `OFF`
`CBOR_BUFFER_GROWTH`	Factor for buffer growth & shrinking	`2`	Decimals > 1

[1]	`ON` & `OFF` will be translated to `1` and `0` using cmakedefine.

If you want to pass other custom configuration options, please refer to http://www.cmake.org/Wiki/CMake_Useful_Variables.

Building using make

CMake will generate a Makefile and other configuration files for the build. As a rule of thumb, you should configure the build outside of the source tree in order to keep different configurations isolated. If you are unsure where to execute the build, just use a temporary directory:

cd $(mktemp -d /tmp/cbor_build.XXXX)

Now, assuming you are in the directory where you want to build, execute the following to configure the build and run make

cmake -DCMAKE_BUILD_TYPE=Release path_to_libcbor_dir
make cbor cbor_shared

Both the shared (libcbor.so) and the static (libcbor.a) libraries should now be in the src subdirectory.

In order to install the libcbor headers and libraries, the usual

make install

is what your’re looking for. Root permissions are required on most systems when using the default installation prefix.

Portability

libcbor is highly portable and works on both little- and big-endian systems regardless of the operating system. After building on an exotic platform, you might wish to verify the result by running the test suite. If you encounter any problems, please report them to the issue tracker.

libcbor is known to successfully work on ARM Android devices. Cross-compilation is possible with arm-linux-gnueabi-gcc.

Linking with libcbor¶

If you include and linker paths include the directories to which libcbor has been installed, compiling programs that uses libcbor requires no extra considerations.

You can verify that everything has been set up properly by creating a file with the following contents

#include <cbor.h>
#include <stdio.h>

int main(int argc, char * argv[])
{
    printf("Hello from libcbor %s\n", CBOR_VERSION);
}

and compiling it

cc hello_cbor.c -lcbor -o hello_cbor

libcbor also comes with pkg-config support. If you install libcbor with a custom prefix, you can use pkg-config to resolve the headers and objects:

cc $(pkg-config --cflags libcbor) hello_cbor.c $(pkg-config --libs libcbor) -o hello_cbor

MinGW build instructions¶

Prerequisites:

MinGW
CMake GUI

First of all, create a folder that will be used for the output. For this demonstration, we will use cbor_out. Start CMake and select the source path and the destination folder.

Then hit the ‘Configure’ button. You will be prompted to select the build system:

Choose MinGW and confirm.

Note

If you select Visual Studio at this point, a MSVC project will be generated for you. This is useful if you just want to browse through the source code.

You can then adjust the build options. The defaults will work just fine. Hit ‘Generate’ when you are done.

You can then adjust the build options. The defaults will work just fine. Hit ‘Generate’ when you are done.

Open the shell, navigate to the output directory, and run mingw32-make cbor cbor_shared.

libcbor will be built and your .dll should be ready at this point

Feel free to also try building and running some of the examples, e.g. mingw32-make sort

Troubleshooting¶

cbor.h not found: The headers directory is probably not in your include path. First, verify the installation location by checking the installation log. If you used make, it will look something like

...
-- Installing: /usr/local/include/cbor
-- Installing: /usr/local/include/cbor/callbacks.h
-- Installing: /usr/local/include/cbor/encoding.h
...

Make sure that CMAKE_INSTALL_PREFIX (if you provided it) was correct. Including the path path during compilation should suffice, e.g.:

cc -I/usr/local/include hello_cbor.c -lcbor -o hello_cbor

cannot find -lcbor during linking: Most likely the same problem as before. Include the installation directory in the linker shared path using -R, e.g.:

cc -Wl,-rpath,/usr/local/lib -lcbor -o hello_cbor

shared library missing during execution: Verify the linkage using ldd, otool, or similar and adjust the compilation directives accordingly:

⇒  ldd hello_cbor
    linux-vdso.so.1 =>  (0x00007ffe85585000)
    libcbor.so => /usr/local/lib/libcbor.so (0x00007f9af69da000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f9af65eb000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f9af6be9000)

compilation failed: If your compiler supports C99 yet the compilation has failed, please report the issue to the issue tracker.

Usage & preliminaries¶

Version information¶

libcbor exports its version using three self-explanatory macros:

CBOR_MAJOR_VERSION

CBOR_MINOR_VERSION

CBOR_PATCH_VERSION

The CBOR_VERSION is a string concatenating these three identifiers into one (e.g. 0.2.0).

In order to simplify version comparisons, the version is also exported as

#define CBOR_HEX_VERSION ((CBOR_MAJOR_VERSION << 16) | (CBOR_MINOR_VERSION << 8) | CBOR_PATCH_VERSION)

Since macros are difficult to work with through FFIs, the same information is also available through three uint8_t constants, namely

cbor_major_version

cbor_minor_version

cbor_patch_version

Headers to include¶

The cbor.h header includes all the symbols. If, for any reason, you don’t want to include all the exported symbols, feel free to use just some of the cbor/*.h headers:

cbor/arrays.h - Type 4 – Arrays

cbor/bytestrings.h - Type 2 – Byte strings

cbor/callbacks.h - Callbacks used for Decoding

cbor/common.h - Common utilities - always transitively included

cbor/data.h - Data types definitions - always transitively included

cbor/encoding.h - Streaming encoders for Encoding

cbor/floats_ctrls.h - Type 7 – Floats & control tokens

cbor/ints.h - Types 0 & 1 – Positive and negative integers

cbor/maps.h - Type 5 – Maps

cbor/serialization.h - High level serialization such as cbor_serialize()

cbor/streaming.h - Home of cbor_stream_decode()

cbor/strings.h - Type 3 – UTF-8 strings

cbor/tags.h - Type 6 – Semantic tags

Using libcbor¶

If you want to get more familiar with CBOR, we recommend the cbor.io website. Once you get the grasp of what is it CBOR does, the examples (located in the examples directory) should give you a good feel of the API. The API documentation should then provide with all the information you may need.

Creating and serializing items

#include "cbor.h"
#include <stdio.h>

int main(int argc, char * argv[])
{
    /* Preallocate the map structure */
    cbor_item_t * root = cbor_new_definite_map(2);
    /* Add the content */
    cbor_map_add(root, (struct cbor_pair) {
        .key = cbor_move(cbor_build_string("Is CBOR awesome?")),
        .value = cbor_move(cbor_build_bool(true))
    });
    cbor_map_add(root, (struct cbor_pair) {
        .key = cbor_move(cbor_build_uint8(42)),
        .value = cbor_move(cbor_build_string("Is the answer"))
    });
    /* Output: `length` bytes of data in the `buffer` */
    unsigned char * buffer;
    size_t buffer_size, length = cbor_serialize_alloc(root, &buffer, &buffer_size);

    fwrite(buffer, 1, length, stdout);
    free(buffer);

    fflush(stdout);
    cbor_decref(&root);
}

Reading serialized data

#include "cbor.h"
#include <stdio.h>

/*
 * Reads data from a file. Example usage:
 * $ ./examples/readfile examples/data/nested_array.cbor
 */

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    /* Assuming `buffer` contains `info.st_size` bytes of input data */
    struct cbor_load_result result;
    cbor_item_t * item = cbor_load(buffer, length, &result);
    /* Pretty-print the result */
    cbor_describe(item, stdout);
    fflush(stdout);
    /* Deallocate the result */
    cbor_decref(&item);

    fclose(f);
}

Using the streaming parser

#include "cbor.h"
#include <stdio.h>
#include <string.h>

/*
 * Illustrates how one might skim through a map (which is assumed to have
 * string keys and values only), looking for the value of a specific key
 *
 * Use the examples/data/map.cbor input to test this.
 */

const char * key = "a secret key";
bool key_found = false;

void find_string(void * _ctx, cbor_data buffer, size_t len)
{
    if (key_found) {
        printf("Found the value: %*s\n", (int) len, buffer);
        key_found = false;
    } else if (len == strlen(key)) {
        key_found = (memcmp(key, buffer, len) == 0);
    }
}

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    struct cbor_callbacks callbacks = cbor_empty_callbacks;
    struct cbor_decoder_result decode_result;
    size_t bytes_read = 0;
    callbacks.string = find_string;
    while (bytes_read < length) {
        decode_result = cbor_stream_decode(buffer + bytes_read,
                                           length - bytes_read,
                                           &callbacks, NULL);
        bytes_read += decode_result.read;
    }

    fclose(f);
}

API¶

The data API is centered around cbor_item_t, a generic handle for any CBOR item. There are functions to

create items,

set items’ data,

parse serialized data into items,

manage, move, and links item together.

The single most important thing to keep in mind is: cbor_item_t is an opaque type and should only be manipulated using the appropriate functions! Think of it as an object.

The libcbor API closely follows the semantics outlined by CBOR standard. This part of the documentation provides a short overview of the CBOR constructs, as well as a general introduction to the libcbor API. Remaining reference can be found in the following files structured by data types.

The API is designed to allow both very tight control & flexibility and general convenience with sane defaults. [1] For example, client with very specific requirements (constrained environment, custom application protocol built on top of CBOR, etc.) may choose to take full control (and responsibility) of memory and data structures management by interacting directly with the decoder. Other clients might want to take control of specific aspects (streamed collections, hash maps storage), but leave other responsibilities to libcbor. More general clients might prefer to be abstracted away from all aforementioned details and only be presented complete data structures.

libcbor provides

stateless encoders and decoders
encoding and decoding drivers, routines that coordinate encoding and decoding of complex structures
data structures to represent and transform CBOR structures
routines for building and manipulating these structures
utilities for inspection and debugging

Types of items¶

Every cbor_item_t has a cbor_type associated with it - these constants correspond to the types specified by the CBOR standard:

enum type cbor_type¶

Specifies the Major type of cbor_item_t.

Values:

: 0 - positive integers

: 1 - negative integers

: 2 - byte strings

: 3 - strings

: 4 - arrays

: 5 - maps

: 6 - tags

: 7 - decimals and special values (true, false, nil, ...)

To find out the type of an item, one can use

Warning

doxygenfunction: Cannot find function “cbor_typeof” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Please note the distinction between functions like cbor_isa_uint() and cbor_is_int(). The following functions work solely with the major type value.

Binary queries¶

Alternatively, there are functions to query each particular type.

Warning

Passing an invalid cbor_item_t reference to any of these functions results in undefined behavior.

Warning

doxygenfunction: Cannot find function “cbor_isa_uint” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_negint” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_bytestring” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_string” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_array” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_map” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_tag” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_isa_float_ctrl” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Logical queries¶

These functions provide information about the item type from a more high-level perspective

Warning

doxygenfunction: Cannot find function “cbor_is_int” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_is_float” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_is_bool” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_is_null” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_is_undef” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Memory management and reference counting¶

Due to the nature of its domain libcbor will need to work with heap memory. The stateless decoder and encoder don’t allocate any memory.

If you have specific requirements, you should consider rolling your own driver for the stateless API.

Using custom allocator¶

libcbor gives you with the ability to provide your own implementations of malloc, realloc, and free. This can be useful if you are using a custom allocator throughout your application, or if you want to implement custom policies (e.g. tighter restrictions on the amount of allocated memory).

In order to use this feature, libcbor has to be compiled with the appropriate flags. You can verify the configuration using the CBOR_CUSTOM_ALLOC macro. A simple usage might be as follows:

#if CBOR_CUSTOM_ALLOC
    cbor_set_allocs(malloc, realloc, free);
#else
   #error "libcbor built with support for custom allocation is required"
#endif

Warning

doxygenfunction: Cannot find function “cbor_set_allocs” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Reference counting¶

As CBOR items may require complex cleanups at the end of their lifetime, there is a reference counting mechanism in place. This also enables very simple GC when integrating libcbor into managed environment. Every item starts its life (by either explicit creation, or as a result of parsing) with reference count set to 1. When the refcount reaches zero, it will be destroyed.

Items containing nested items will be destroyed recursively - refcount of every nested item will be decreased by one.

The destruction is synchronous and renders any pointers to items with refcount zero invalid immediately after calling the cbor_decref().

Warning

doxygenfunction: Cannot find function “cbor_incref” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_decref” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_intermediate_decref” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_refcount” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

Warning

doxygenfunction: Cannot find function “cbor_move” in doxygen xml output for project “libcbor” from directory: ../build/doxygen/xml

cbor_item_t *cbor_copy(cbor_item_t *item)¶

Deep copy of an item.

All the reference counts in the new structure are set to one.

Return

new CBOR deep copy

Parameters

item[borrow]: item to copy

Decoding¶

The following diagram illustrates the relationship among different parts of libcbor from the decoding standpoint.

┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│                                                                                              │
│                                      Client application                                      │
│                                                                                              │
│                                                 ┌────────────────────────────────────────────┘
│                                                 │                     ↕
│                                                 │ ┌──────────────────────────────────────────┐
│                                                 │ │                                          │
│                                                 │ │          Manipulation routines           │
│                                                 │ │                                          │
│           ┌─────────────────────────────────────┘ └──────────────────────────────────────────┘
│           │     ↑    ↑                  ↑                              ↑
│           │     │    │    ┌─────────────╫──────────┬───────────────────┴─┐
│           │     │   CDS   │             ║          │                     │
│           │     │    │   PDS            ║         PDS                   PDS
│           │     ↓    ↓    ↓             ↓          ↓                     ↓
│           │ ┌─────────────────┐   ┌────────────────────┐   ┌────────────────────────────┐
│           │ │                 │   │                    │   │                            │
│           │ │  Custom driver  │ ↔ │  Streaming driver  │ ↔ │       Default driver       │ ↔ CD
│           │ │                 │   │                    │   │                            │
└───────────┘ └─────────────────┘   └────────────────────┘   └────────────────────────────┘
      ↕                ↕                        ↕                           ↕
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│                                                                                              │
│                            Stateless event─driven decoder                                    │
│                                                                                              │
└──────────────────────────────────────────────────────────────────────────────────────────────┘

              (PSD = Provided Data Structures, CDS = Custom Data Structures)

This section will deal with the API that is labeled as the “Default driver” in the diagram. That is, routines that decode complete libcbor data items

cbor_item_t *cbor_load(cbor_data source, size_t source_size, struct cbor_load_result *result)¶

Loads data item from a buffer.

Return

new CBOR item or NULL on failure. In that case, result contains location and description of the error.

Parameters

source: The buffer
source_size:
result[out]: Result indicator. CBOR_ERR_NONE on success

Associated data structures¶

enum type cbor_error_code¶

Possible decoding errors.

Values:

Memory error - item allocation failed.

Is it too big for your allocator?

: Stack parsing algorithm failed.

struct

High-level decoding result.

Public Members

struct cbor_error cbor_load_result::error¶: Error indicator.

size_t cbor_load_result::read¶: Number of bytes read.

struct

High-level decoding error.

Public Members

size_t cbor_error::position¶: Aproximate position.

cbor_error_code cbor_error::code¶: Description.

Encoding¶

The easiest way to encode data items is using the cbor_serialize() or cbor_serialize_alloc() functions:

size_t cbor_serialize(const cbor_item_t *item, cbor_mutable_data buffer, size_t buffer_size)¶

Serialize the given item.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A data item
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_alloc(const cbor_item_t *item, cbor_mutable_data *buffer, size_t *buffer_size)¶

Serialize the given item, allocating buffers as needed.

Warning

It is your responsibility to free the buffer using an appropriate free implementation.

Return

Length of the result. 0 on failure, in which case buffer is NULL.

Parameters

item[borrow]: A data item
buffer[out]: Buffer containing the result
buffer_size[out]: Size of the buffer

Type-specific serializers¶

In case you know the type of the item you want to serialize beforehand, you can use one of the type-specific serializers.

Note

Unless compiled in debug mode, these do not verify the type. Passing an incorrect item will result in an undefined behavior.

size_t cbor_serialize_uint(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize an uint.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A uint
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_negint(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize a negint.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A neging
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_bytestring(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize a bytestring.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A bytestring
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_string(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize a string.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A string
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_array(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize an array.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: An array
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_map(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize a map.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A map
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_tag(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize a tag.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A tag
buffer: Buffer to serialize to
buffer_size: Size of the buffer

size_t cbor_serialize_float_ctrl(const cbor_item_t *, cbor_mutable_data, size_t)¶

Serialize a.

Return

Length of the result. 0 on failure.

Parameters

item[borrow]: A float or ctrl
buffer: Buffer to serialize to
buffer_size: Size of the buffer

Types 0 & 1 – Positive and negative integers¶

CBOR has two types of integers – positive (which may be effectively regarded as unsigned), and negative. There are four possible widths for an integer – 1, 2, 4, or 8 bytes. These are represented by

enum type cbor_int_width¶

Possible widths of CBOR_TYPE_UINT items.

Values:

Type 0 - positive integers¶

Corresponding `cbor_type`	`CBOR_TYPE_UINT`
Number of allocations	One per lifetime
Storage requirements	`sizeof(cbor_item_t) + sizeof(uint*_t)`

Note: once a positive integer has been created, its width cannot be changed.

Type 1 - negative integers¶

Corresponding `cbor_type`	`CBOR_TYPE_NEGINT`
Number of allocations	One per lifetime
Storage requirements	`sizeof(cbor_item_t) + sizeof(uint*_t)`

Note: once a positive integer has been created, its width cannot be changed.

Type 0 & 1¶

Due to their largely similar semantics, the following functions can be used for both Type 0 and Type 1 items. One can convert between them freely using the conversion functions.

Actual Type of the integer can be checked using item types API.

An integer item is created with one of the four widths. Because integers’ storage is bundled together with the handle, the width cannot be changed over its lifetime.

Warning

Due to the fact that CBOR negative integers represent integers in the range \([-1, -2^N]\), cbor_set_uint API is somewhat counter-intuitive as the resulting logical value is 1 less. This behavior is necessary in order to permit uniform manipulation with the full range of permitted values. For example, the following snippet

cbor_item_t * item = cbor_new_int8();
cbor_mark_negint(item);
cbor_set_uint8(0);

will produce an item with the logical value of \(-1\). There is, however, an upside to this as well: There is only one representation of zero.

Building new items¶

cbor_item_t *cbor_build_uint8(uint8_t value)¶

Constructs a new positive integer.

Return

new positive integer

Parameters

value: the value to use

cbor_item_t *cbor_build_uint16(uint16_t value)¶

Constructs a new positive integer.

Return

new positive integer

Parameters

value: the value to use

cbor_item_t *cbor_build_uint32(uint32_t value)¶

Constructs a new positive integer.

Return

new positive integer

Parameters

value: the value to use

cbor_item_t *cbor_build_uint64(uint64_t value)¶

Constructs a new positive integer.

Return

new positive integer

Parameters

value: the value to use

Retrieving values¶

uint8_t cbor_get_uint8(const cbor_item_t *item)¶

Extracts the integer value.

Return

the value

Parameters

item[borrow]: positive or negative integer

uint16_t cbor_get_uint16(const cbor_item_t *item)¶

Extracts the integer value.

Return

the value

Parameters

item[borrow]: positive or negative integer

uint32_t cbor_get_uint32(const cbor_item_t *item)¶

Extracts the integer value.

Return

the value

Parameters

item[borrow]: positive or negative integer

uint64_t cbor_get_uint64(const cbor_item_t *item)¶

Extracts the integer value.

Return

the value

Parameters

item[borrow]: positive or negative integer

Setting values¶

void cbor_set_uint8(cbor_item_t *item, uint8_t value)¶

Assigns the integer value.

Parameters

item[borrow]: positive or negative integer item
value: the value to assign. For negative integer, the logical value is -value - 1

void cbor_set_uint16(cbor_item_t *item, uint16_t value)¶

Assigns the integer value.

Parameters

item[borrow]: positive or negative integer item
value: the value to assign. For negative integer, the logical value is -value - 1

void cbor_set_uint32(cbor_item_t *item, uint32_t value)¶

Assigns the integer value.

Parameters

item[borrow]: positive or negative integer item
value: the value to assign. For negative integer, the logical value is -value - 1

void cbor_set_uint64(cbor_item_t *item, uint64_t value)¶

Assigns the integer value.

Parameters

item[borrow]: positive or negative integer item
value: the value to assign. For negative integer, the logical value is -value - 1

Dealing with width¶

cbor_int_width cbor_int_get_width(const cbor_item_t *item)¶

Queries the integer width.

Return

the width

Parameters

item[borrow]: positive or negative integer item

Dealing with signedness¶

void cbor_mark_uint(cbor_item_t *item)¶

Marks the integer item as a positive integer.

The data value is not changed

Parameters

item[borrow]: positive or negative integer item

void cbor_mark_negint(cbor_item_t *item)¶

Marks the integer item as a negative integer.

The data value is not changed

Parameters

item[borrow]: positive or negative integer item

Creating new items¶

cbor_item_t *cbor_new_int8()¶

Allocates new integer with 1B width.

The width cannot be changed once allocated

Return: new positive integer. The value is not initialized.

cbor_item_t *cbor_new_int16()¶

Allocates new integer with 2B width.

The width cannot be changed once allocated

Return: new positive integer. The value is not initialized.

cbor_item_t *cbor_new_int32()¶

Allocates new integer with 4B width.

The width cannot be changed once allocated

Return: new positive integer. The value is not initialized.

cbor_item_t *cbor_new_int64()¶

Allocates new integer with 8B width.

The width cannot be changed once allocated

Return: new positive integer. The value is not initialized.

Type 2 – Byte strings¶

CBOR byte strings are just (ordered) series of bytes without further interpretation (unless there is a tag). Byte string’s length may or may not be known during encoding. These two kinds of byte strings can be distinguished using cbor_bytestring_is_definite() and cbor_bytestring_is_indefinite() respectively.

In case a byte string is indefinite, it is encoded as a series of definite byte strings. These are called “chunks”. For example, the encoded item

0xf5            Start indefinite byte string
    0x41        Byte string (1B long)
        0x00
    0x41        Byte string (1B long)
        0xff
    0xff        "Break" control token

represents two bytes, 0x00 and 0xff. This on one hand enables streaming messages even before they are fully generated, but on the other hand it adds more complexity to the client code.

Corresponding `cbor_type`	`CBOR_TYPE_BYTESTRING`
Number of allocations (definite)	One plus any manipulations with the data
Number of allocations (indefinite)	One plus logarithmically many reallocations relative to chunk count
Storage requirements (definite)	`sizeof(cbor_item_t) + length(handle)`
Storage requirements (indefinite)	`sizeof(cbor_item_t) * (1 + chunk_count) + chunks`

Streaming indefinite byte strings¶

Please refer to Streaming & indefinite items.

Getting metadata¶

size_t cbor_bytestring_length(const cbor_item_t *item)¶

Returns the length of the binary data.

For definite byte strings only

Return

length of the binary data. Zero if no chunk has been attached yet

Parameters

item[borrow]: a definite bytestring

bool cbor_bytestring_is_definite(const cbor_item_t *item)¶

Is the byte string definite?

Return

Is the byte string definite?

Parameters

item[borrow]: a byte string

bool cbor_bytestring_is_indefinite(const cbor_item_t *item)¶

Is the byte string indefinite?

Return

Is the byte string indefinite?

Parameters

item[borrow]: a byte string

size_t cbor_bytestring_chunk_count(const cbor_item_t *item)¶

Get the number of chunks this string consist of.

Return

The chunk count. 0 for freshly created items.

Parameters

item[borrow]: A indefinite bytestring

Reading data¶

cbor_mutable_data cbor_bytestring_handle(const cbor_item_t *item)¶

Get the handle to the binary data.

Definite items only. Modifying the data is allowed. In that case, the caller takes responsibility for the effect on items this item might be a part of

Return

The address of the binary data. NULL if no data have been assigned yet.

Parameters

item[borrow]: A definite byte string

cbor_item_t **cbor_bytestring_chunks_handle(const cbor_item_t *item)¶

Get the handle to the array of chunks.

Manipulations with the memory block (e.g. sorting it) are allowed, but the validity and the number of chunks must be retained.

Return

array of cbor_bytestring_chunk_count definite bytestrings

Parameters

item[borrow]: A indefinite byte string

Creating new items¶

cbor_item_t *cbor_new_definite_bytestring()¶

Creates a new definite byte string.

The handle is initialized to NULL and length to 0

Return: new definite bytestring. NULL on malloc failure.

cbor_item_t *cbor_new_indefinite_bytestring()¶

Creates a new indefinite byte string.

The chunks array is initialized to NULL and chunkcount to 0

Return: new indefinite bytestring. NULL on malloc failure.

Building items¶

cbor_item_t *cbor_build_bytestring(cbor_data handle, size_t length)¶

Creates a new byte string and initializes it.

The handle will be copied to a newly allocated block

Return

A new byte string with content handle. NULL on malloc failure.

Parameters

handle: Block of binary data
length: Length of data

Manipulating existing items¶

void cbor_bytestring_set_handle(cbor_item_t * item, cbor_mutable_data restrict data, size_t length)

Set the handle to the binary data.

Parameters

item[borrow]: A definite byte string
data: The memory block. The caller gives up the ownership of the block. libcbor will deallocate it when appropriate using its free function
length: Length of the data block

bool cbor_bytestring_add_chunk(cbor_item_t *item, cbor_item_t *chunk)¶

Appends a chunk to the bytestring.

Indefinite byte strings only.

May realloc the chunk storage.

Return

true on success, false on realloc failure. In that case, the refcount of chunk is not increased and the item is left intact.

Parameters

item[borrow]: An indefinite byte string
item[incref]: A definite byte string

Type 3 – UTF-8 strings¶

CBOR strings work in much the same ways as Type 2 – Byte strings.

Corresponding `cbor_type`	`CBOR_TYPE_STRING`
Number of allocations (definite)	One plus any manipulations with the data
Number of allocations (indefinite)	One plus logarithmically many reallocations relative to chunk count
Storage requirements (definite)	`sizeof(cbor_item_t) + length(handle)`
Storage requirements (indefinite)	`sizeof(cbor_item_t) * (1 + chunk_count) + chunks`

Streaming indefinite strings¶

Please refer to Streaming & indefinite items.

UTF-8 encoding validation¶

libcbor considers UTF-8 encoding validity to be a part of the well-formedness notion of CBOR and therefore invalid UTF-8 strings will be rejected by the parser. Strings created by the user are not checked.

Getting metadata¶

size_t cbor_string_length(const cbor_item_t *item)¶

Returns the length of the underlying string.

For definite strings only

Return

length of the string. Zero if no chunk has been attached yet

Parameters

item[borrow]: a definite string

bool cbor_string_is_definite(const cbor_item_t *item)¶

Is the string definite?

Return

Is the string definite?

Parameters

item[borrow]: a string

bool cbor_string_is_indefinite(const cbor_item_t *item)¶

Is the string indefinite?

Return

Is the string indefinite?

Parameters

item[borrow]: a string

size_t cbor_string_chunk_count(const cbor_item_t *item)¶

Get the number of chunks this string consist of.

Return

The chunk count. 0 for freshly created items.

Parameters

item[borrow]: A indefinite string

Reading data¶

cbor_mutable_data cbor_string_handle(const cbor_item_t *item)¶

Get the handle to the underlying string.

Definite items only. Modifying the data is allowed. In that case, the caller takes responsibility for the effect on items this item might be a part of

Return

The address of the underlying string. NULL if no data have been assigned yet.

Parameters

item[borrow]: A definite string

cbor_item_t **cbor_string_chunks_handle(const cbor_item_t *item)¶

Get the handle to the array of chunks.

Manipulations with the memory block (e.g. sorting it) are allowed, but the validity and the number of chunks must be retained.

Return

array of cbor_string_chunk_count definite strings

Parameters

item[borrow]: A indefinite string

Creating new items¶

cbor_item_t *cbor_new_definite_string()¶

Creates a new definite string.

The handle is initialized to NULL and length to 0

Return: new definite string. NULL on malloc failure.

cbor_item_t *cbor_new_indefinite_string()¶

Creates a new indefinite string.

The chunks array is initialized to NULL and chunkcount to 0

Return: new indefinite string. NULL on malloc failure.

Building items¶

cbor_item_t *cbor_build_string(const char *val)¶

Creates a new string and initializes it.

The val will be copied to a newly allocated block

Return

A new string with content handle. NULL on malloc failure.

Parameters

val: A null-terminated UTF-8 string

Manipulating existing items¶

void cbor_string_set_handle(cbor_item_t * item, cbor_mutable_data restrict data, size_t length)

Set the handle to the underlying string.

Warning

Using a pointer to a stack allocated constant is a common mistake. Lifetime of the string will expire when it goes out of scope and the CBOR item will be left inconsistent.

Parameters

item[borrow]: A definite string
data: The memory block. The caller gives up the ownership of the block. libcbor will deallocate it when appropriate using its free function
length: Length of the data block

bool cbor_string_add_chunk(cbor_item_t *item, cbor_item_t *chunk)¶

Appends a chunk to the string.

Indefinite strings only.

May realloc the chunk storage.

Return

true on success. false on realloc failure. In that case, the refcount of chunk is not increased and the item is left intact.

Parameters

item[borrow]: An indefinite string
item[incref]: A definite string

Type 4 – Arrays¶

CBOR arrays, just like byte strings and strings, can be encoded either as definite, or as indefinite.

Corresponding `cbor_type`	`CBOR_TYPE_ARRAY`
Number of allocations (definite)	Two plus any manipulations with the data
Number of allocations (indefinite)	Two plus logarithmically many reallocations relative to additions
Storage requirements (definite)	`(sizeof(cbor_item_t) + 1) * size`
Storage requirements (indefinite)	`<= sizeof(cbor_item_t) + sizeof(cbor_item_t) * size * BUFFER_GROWTH`

Examples¶

0x9f        Start indefinite array
    0x01        Unsigned integer 1
    0xff        "Break" control token

0x9f        Start array, 1B length follows
0x20        Unsigned integer 32
    ...        32 items follow

Streaming indefinite arrays¶

Please refer to Streaming & indefinite items.

Getting metadata¶

size_t cbor_array_size(const cbor_item_t *item)¶

Get the number of members.

Return

The number of members

Parameters

item[borrow]: An array

size_t cbor_array_allocated(const cbor_item_t *item)¶

Get the size of the allocated storage.

Return

The size of the allocated storage (number of items)

Parameters

item[borrow]: An array

bool cbor_array_is_definite(const cbor_item_t *item)¶

Is the array definite?

Return

Is the array definite?

Parameters

item[borrow]: An array

bool cbor_array_is_indefinite(const cbor_item_t *item)¶

Is the array indefinite?

Return

Is the array indefinite?

Parameters

item[borrow]: An array

Reading data¶

cbor_item_t **cbor_array_handle(const cbor_item_t *item)¶

Get the array contents.

The items may be reordered and modified as long as references remain consistent.

Return

cbor_array_size items

Parameters

item[borrow]: An array

cbor_item_t *cbor_array_get(const cbor_item_t *item, size_t index)¶

Get item by index.

Return

incref The item, or NULL in case of boundary violation

Parameters

item[borrow]: An array
index: The index

Creating new items¶

cbor_item_t *cbor_new_definite_array(const size_t size)¶

Create new definite array.

Return

new array or NULL upon malloc failure

Parameters

size: Number of slots to preallocate

cbor_item_t *cbor_new_indefinite_array()¶

Create new indefinite array.

Return: new array or NULL upon malloc failure

Modifying items¶

bool cbor_array_push(cbor_item_t *array, cbor_item_t *pushee)¶

Append to the end.

For indefinite items, storage may be realloacted. For definite items, only the preallocated capacity is available.

Return

true on success, false on failure

Parameters

array[borrow]: An array
pushee[incref]: The item to push

bool cbor_array_replace(cbor_item_t *item, size_t index, cbor_item_t *value)¶

Replace item at an index.

The item being replace will be cbor_decref ‘ed.

Return

true on success, false on allocation failure.

Parameters

item[borrow]: An array
value[incref]: The item to assign
index: The index

bool cbor_array_set(cbor_item_t *item, size_t index, cbor_item_t *value)¶

Set item by index.

Creating arrays with holes is not possible

Return

true on success, false on allocation failure.

Parameters

item[borrow]: An array
value[incref]: The item to assign
index: The index

Type 5 – Maps¶

CBOR maps are the plain old associate hash maps known from JSON and many other formats and languages, with one exception: any CBOR data item can be a key, not just strings. This is somewhat unusual and you, as an application developer, should keep that in mind.

Maps can be either definite or indefinite, in much the same way as Type 4 – Arrays.

Corresponding `cbor_type`	`CBOR_TYPE_MAP`
Number of allocations (definite)	Two plus any manipulations with the data
Number of allocations (indefinite)	Two plus logarithmically many reallocations relative to additions
Storage requirements (definite)	`sizeof(cbor_pair) * size + sizeof(cbor_item_t)`
Storage requirements (indefinite)	`<= sizeof(cbor_item_t) + sizeof(cbor_pair) * size * BUFFER_GROWTH`

Streaming maps¶

Please refer to Streaming & indefinite items.

Getting metadata¶

size_t cbor_map_size(const cbor_item_t *item)¶

Get the number of pairs.

Return

The number of pairs

Parameters

item[borrow]: A map

size_t cbor_map_allocated(const cbor_item_t *item)¶

Get the size of the allocated storage.

Return

Allocated storage size (as the number of cbor_pair items)

Parameters

item[borrow]: A map

bool cbor_map_is_definite(const cbor_item_t *item)¶

Is this map definite?

Return

Is this map definite?

Parameters

item[borrow]: A map

bool cbor_map_is_indefinite(const cbor_item_t *item)¶

Is this map indefinite?

Return

Is this map indefinite?

Parameters

item[borrow]: A map

Reading data¶

struct cbor_pair *cbor_map_handle(const cbor_item_t *item)¶

Get the pairs storage.

Return

Array of cbor_map_size pairs. Manipulation is possible as long as references remain valid.

Parameters

item[borrow]: A map

Creating new items¶

cbor_item_t *cbor_new_definite_map(const size_t size)¶

Create a new definite map.

Return

new definite map. NULL on malloc failure.

Parameters

size: The number of slots to preallocate

cbor_item_t *cbor_new_indefinite_map()¶

Create a new indefinite map.

Return

new definite map. NULL on malloc failure.

Parameters

size: The number of slots to preallocate

Modifying items¶

bool cbor_map_add(cbor_item_t *item, struct cbor_pair pair)¶

Add a pair to the map.

For definite maps, items can only be added to the preallocated space. For indefinite maps, the storage will be expanded as needed

Return

true on success, false if either reallocation failed or the preallcoated storage is full

Parameters

item[borrow]: A map
pair[incref]: The key-value pair to add (incref is member-wise)

Type 6 – Semantic tags¶

Tag are additional metadata that can be used to extend or specialize the meaning or interpretation of the other data items.

For example, one might tag an array of numbers to communicate that it should be interpreted as a vector.

Please consult the official IANA repository of CBOR tags before inventing new ones.

cbor_item_t *cbor_new_tag(uint64_t value)¶

Create a new tag.

Return

new tag. Item reference is NULL.

Parameters

value: The tag value. Please consult the tag repository

cbor_item_t *cbor_tag_item(const cbor_item_t *item)¶

Get the tagged item.

Return

incref the tagged item

Parameters

item[borrow]: A tag

uint64_t cbor_tag_value(const cbor_item_t *item)¶

Get tag value.

Return

The tag value. Please consult the tag repository

Parameters

item[borrow]: A tag

void cbor_tag_set_item(cbor_item_t *item, cbor_item_t *tagged_item)¶

Set the tagged item.

Parameters

item[borrow]: A tag
tagged_item[incref]: The item to tag

Type 7 – Floats & control tokens¶

This type combines two completely unrelated types of items – floating point numbers and special values such as true, false, null, etc. We refer to these special values as ‘control values’ or ‘ctrls’ for short throughout the code.

Just like integers, they have different possible width (resulting in different value ranges and precisions).

enum type cbor_float_width¶

Possible widths of CBOR_TYPE_FLOAT_CTRL items.

Values:

: Internal use - ctrl and special values.

: Half float.

: Single float.

: Double.

Corresponding `cbor_type`	`CBOR_TYPE_FLOAT_CTRL`
Number of allocations	One per lifetime
Storage requirements	`sizeof(cbor_item_t) + 1/4/8`

Getting metadata¶

bool cbor_float_ctrl_is_ctrl(const cbor_item_t *item)¶

Is this a ctrl value?

Return

Is this a ctrl value?

Parameters

item[borrow]: A float or ctrl item

cbor_float_width cbor_float_get_width(const cbor_item_t *item)¶

Get the float width.

Return

The width.

Parameters

item[borrow]: A float or ctrl item

bool cbor_ctrl_is_bool(const cbor_item_t *item)¶

Is this ctrl item a boolean?

Return

Is this ctrl item a boolean?

Parameters

item[borrow]: A ctrl item

Reading data¶

float cbor_float_get_float2(const cbor_item_t *item)¶

Get a half precision float.

The item must have the corresponding width

Return

half precision value

Parameters

borrow]: A half precision float

float cbor_float_get_float4(const cbor_item_t *item)¶

Get a single precision float.

The item must have the corresponding width

Return

single precision value

Parameters

borrow]: A signle precision float

double cbor_float_get_float8(const cbor_item_t *item)¶

Get a double precision float.

The item must have the corresponding width

Return

double precision value

Parameters

borrow]: A double precision float

double cbor_float_get_float(const cbor_item_t *item)¶

Get the float value represented as double.

Can be used regardless of the width.

Return

double precision value

Parameters

borrow]: Any float

uint8_t cbor_ctrl_value(const cbor_item_t *item)¶

Reads the control value.

Return

the simple value

Parameters

item[borrow]: A ctrl item

Creating new items¶

cbor_item_t *cbor_new_ctrl()¶

Constructs a new ctrl item.

The width cannot be changed once the item is created

Return: new 1B ctrl

cbor_item_t *cbor_new_float2()¶

Constructs a new float item.

The width cannot be changed once the item is created

Return: new 2B float

cbor_item_t *cbor_new_float4()¶

Constructs a new float item.

The width cannot be changed once the item is created

Return: new 4B float

cbor_item_t *cbor_new_float8()¶

Constructs a new float item.

The width cannot be changed once the item is created

Return: new 8B float

cbor_item_t *cbor_new_null()¶

Constructs new null ctrl item.

Return: new null ctrl item

cbor_item_t *cbor_new_undef()¶

Constructs new under ctrl item.

Return: new under ctrl item

Building items¶

cbor_item_t *cbor_build_bool(bool value)¶

Constructs new boolean ctrl item.

Return

new boolen ctrl item

Parameters

value: The value to use

cbor_item_t *cbor_build_ctrl(uint8_t value)¶

Constructs a ctrl item.

Return

new ctrl item

Parameters

value: the value to use

cbor_item_t *cbor_build_float2(float value)¶

Constructs a new float.

Return

new float

Parameters

value: the value to use

cbor_item_t *cbor_build_float4(float value)¶

Constructs a new float.

Return

new float

Parameters

value: the value to use

cbor_item_t *cbor_build_float8(double value)¶

Constructs a new float.

Return

new float

Parameters

value: the value to use

Manipulating existing items¶

void cbor_set_ctrl(cbor_item_t *item, uint8_t value)¶

Assign a control value.

Warning

It is possible to produce an invalid CBOR value by assigning a invalid value using this mechanism. Please consult the standard before use.

Parameters

item[borrow]: A ctrl item
value: The simple value to assign. Please consult the standard for allowed values

void cbor_set_float2(cbor_item_t *item, float value)¶

Assigns a float value.

Parameters

item[borrow]: A half precision float
value: The value to assign

void cbor_set_float4(cbor_item_t *item, float value)¶

Assigns a float value.

Parameters

item[borrow]: A single precision float
value: The value to assign

void cbor_set_float8(cbor_item_t *item, double value)¶

Assigns a float value.

Parameters

item[borrow]: A double precision float
value: The value to assign

[1]	http://softwareengineering.vazexqi.com/files/pattern.html

Streaming & indefinite items¶

CBOR strings, byte strings, arrays, and maps can be encoded as indefinite, meaning their length or size is not specified. Instead, they are divided into chunks (strings, byte strings), or explicitly terminated (arrays, maps).

This is one of the most important (and due to poor implementations, underutilized) features of CBOR. It enables low-overhead streaming just about anywhere without dealing with channels or pub/sub mechanism. It is, however, important to recognize that CBOR streaming is not a substitute for Websockets [1] and similar technologies.

[1]	RFC 6455

Decoding¶

Another way to decode data using libcbor is to specify a callbacks that will be invoked when upon finding certain items in the input. This service is provided by

struct cbor_decoder_result cbor_stream_decode(cbor_data buffer, size_t buffer_size, const struct cbor_callbacks *callbacks, void *context)¶

Stateless decoder.

Will try parsing the buffer and will invoke the appropriate callback on success. Decodes one item at a time. No memory allocations occur.

Parameters

buffer: Input buffer
buffer_size: Length of the buffer
callbacks: The callback bundle
context: An arbitrary pointer to allow for maintaining context.

To get started, you might want to have a look at the simple streaming example:

#include "cbor.h"
#include <stdio.h>
#include <string.h>

/*
 * Illustrates how one might skim through a map (which is assumed to have
 * string keys and values only), looking for the value of a specific key
 *
 * Use the examples/data/map.cbor input to test this.
 */

const char * key = "a secret key";
bool key_found = false;

void find_string(void * _ctx, cbor_data buffer, size_t len)
{
    if (key_found) {
        printf("Found the value: %*s\n", (int) len, buffer);
        key_found = false;
    } else if (len == strlen(key)) {
        key_found = (memcmp(key, buffer, len) == 0);
    }
}

int main(int argc, char * argv[])
{
    FILE * f = fopen(argv[1], "rb");
    fseek(f, 0, SEEK_END);
    size_t length = (size_t)ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char * buffer = malloc(length);
    fread(buffer, length, 1, f);

    struct cbor_callbacks callbacks = cbor_empty_callbacks;
    struct cbor_decoder_result decode_result;
    size_t bytes_read = 0;
    callbacks.string = find_string;
    while (bytes_read < length) {
        decode_result = cbor_stream_decode(buffer + bytes_read,
                                           length - bytes_read,
                                           &callbacks, NULL);
        bytes_read += decode_result.read;
    }

    free(buffer);
    fclose(f);
}

The callbacks are defined by

struct

Callback bundle passed to the decoder.

Public Members

cbor_int8_callback cbor_callbacks::uint8¶: Unsigned int.

cbor_int16_callback cbor_callbacks::uint16¶: Unsigned int.

cbor_int32_callback cbor_callbacks::uint32¶: Unsigned int.

cbor_int64_callback cbor_callbacks::uint64¶: Unsigned int.

cbor_int64_callback cbor_callbacks::negint64¶: Negative int.

cbor_int32_callback cbor_callbacks::negint32¶: Negative int.

cbor_int16_callback cbor_callbacks::negint16¶: Negative int.

cbor_int8_callback cbor_callbacks::negint8¶: Negative int.

cbor_simple_callback cbor_callbacks::byte_string_start¶: Definite byte string.

cbor_string_callback cbor_callbacks::byte_string¶: Indefinite byte string start.

cbor_string_callback cbor_callbacks::string¶: Definite string.

cbor_simple_callback cbor_callbacks::string_start¶: Indefinite string start.

cbor_simple_callback cbor_callbacks::indef_array_start¶: Definite array.

cbor_collection_callback cbor_callbacks::array_start¶: Indefinite array.

cbor_simple_callback cbor_callbacks::indef_map_start¶: Definite map.

cbor_collection_callback cbor_callbacks::map_start¶: Indefinite map.

cbor_int64_callback cbor_callbacks::tag¶: Tags.

cbor_float_callback cbor_callbacks::float2¶: Half float.

cbor_double_callback cbor_callbacks::float8¶: Single float.

cbor_float_callback cbor_callbacks::float4¶: Double float.

cbor_simple_callback cbor_callbacks::undefined¶: Undef.

cbor_simple_callback cbor_callbacks::null¶: Null.

cbor_bool_callback cbor_callbacks::boolean¶: Bool.

cbor_simple_callback cbor_callbacks::indef_break¶: Indefinite item break.

When building custom sets of callbacks, feel free to start from

const struct cbor_callbacks cbor_empty_callbacks¶: Dummy callback bundle - does nothing.

Callback types definition¶

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

typedef: Callback prototype.

Encoding¶

TODO

Tests¶

Unit tests¶

There is a comprehensive test suite employing CMocka. You can run all of them using ctest in the build directory. Individual tests are themselves runnable. Please refer to CTest documentation for detailed information on how to specify particular subset of tests.

Testing for memory leaks¶

Every release is tested for memory correctness. You can run these tests by passing the -T memcheck flag to ctest. [1]

[1]	Project should be configured with `-DCMAKE_BUILD_TYPE=Debug` to obtain meaningful description of location of the leak. You might also need `--dsymutil=yes` on OS X.

Code coverage¶

Every release is inspected using GCOV/LCOV. Platform-independent code should be fully covered by the test suite. Simply run

make coverage

or alternatively run lcov by hand using

lcov --capture --directory . --output-file coverage.info
genhtml coverage.info --output-directory out

Fuzz testing¶

Every release is tested using a fuzz test. In this test, a huge buffer filled with random data is passed to the decoder. We require that it either succeeds or fail with a sensible error, without leaking any memory. This is intended to simulate real-world situations where data received from the network are CBOR-decoded before any further processing.

RFC conformance¶

libcbor is, generally speaking, very faithful implementation of RFC 7049. There are, however, some limitations imposed by technical constraints.

Bytestring length¶

There is no explicit limitation of indefinite length byte strings. [1] libcbor will not handle byte strings with more chunks than the maximum value of size_t. On any sane platform, such string would not fit in the memory anyway. It is, however, possible to process arbitrarily long strings and byte strings using the streaming decoder.

[1]	http://tools.ietf.org/html/rfc7049#section-2.2.2

“Half-precision” IEEE 754 floats¶

As of C99 and even C11, there is no standard implementation for 2 bytes floats. libcbor packs them as a double. When encoding, libcbor selects the appropriate wire representation based on metadata and the actual value. This applies both to canonical and normal mode.

Internal mechanics¶

Internal workings of libcbor are mostly derived from the specification. The purpose of this document is to describe technical choices made during design & implementation and to explicate the reasoning behind those choices.

Terminology¶

MTB

Major Type Byte

http://tools.ietf.org/html/rfc7049#section-2.1

DST

Dynamically Sized Type

Type whose storage requirements cannot be determined

during compilation (originated in the Rust community)

Conventions¶

API symbols start with cbor_ or CBOR_ prefix, internal symbols have _cbor_ or _CBOR_ prefix.

General notes on the API design¶

The API design has two main driving priciples:

Let the client manage the memory as much as possible

Behave exactly as specified by the standard

Combining these two principles in practice turns out to be quite difficult. Indefinite-length strings, arrays, and maps require client to handle every fixed-size chunk explicitly in order to

ensure the client never runs out of memory due to libcbor

use realloc() sparsely and predictably [1]

provide strong guarantees about its usage (to prevent latency spikes)

provide APIs to avoid realloc() altogether

allow proper handling of (streamed) data bigger than available memory

[1] Reasonable handling of DSTs requires reallocation if the API is to remain sane.

Coding style¶

This code loosely follows the Linux kernel coding style. Tabs are tabs, and they are 4 characters wide.

Memory layout¶

CBOR is very dynamic in the sense that it contains many data elements of variable length, sometimes even indefinite length. This section describes internal representation of all CBOR data types.

Generally speaking, data items consist of three parts:

a generic handle,

the associated metadata,

and the actual data

type cbor_item_t¶

Represents the item. Used as an opaque type

cbor_type type¶: Type discriminator

size_t refcount¶: Reference counter. Used by cbor_decref(), cbor_incref()

union cbor_item_metadata metadata¶: Union discriminated by cbor_item_t.type. Contains type-specific metadata

unsigned char *data¶

Contains pointer to the actual data. Small, fixed size items (Types 0 & 1 – Positive and negative integers, Type 6 – Semantic tags, Type 7 – Floats & control tokens) are allocated as a single memory block.

Consider the following snippet

cbor_item_t * item = cbor_new_int8();

then the memory is laid out as follows

+-----------+---------------+---------------+-----------------------------------++-----------+
|           |               |               |                                   ||           |
|   type    |   refcount    |   metadata    |              data                 ||  uint8_t  |
|           |               |               |   (= item + sizeof(cbor_item_t))  ||           |
+-----------+---------------+---------------+-----------------------------------++-----------+
^                                                                                ^
|                                                                                |
+--- item                                                                        +--- item->data

Dynamically sized types (Type 2 – Byte strings, Type 3 – UTF-8 strings, Type 4 – Arrays, Type 5 – Maps) may store handle and data in separate locations. This enables creating large items (e.g byte strings) without realloc() or copying large blocks of memory. One simply attaches the correct pointer to the handle.

union cbor_item_metadata

struct _cbor_int_metadata int_metadata;: Used both by both Types 0 & 1 – Positive and negative integers

struct _cbor_bytestring_metadata bytestring_metadata;

struct _cbor_string_metadata string_metadata;

struct _cbor_array_metadata array_metadata;

struct _cbor_map_metadata map_metadata;

struct _cbor_tag_metadata tag_metadata;

struct _cbor_float_ctrl_metadata float_ctrl_metadata;

Decoding¶

As outlined in API, there decoding is based on the streaming decoder Essentially, the decoder is a custom set of callbacks for the streaming decoder.

Changelog¶

Next¶

0.4.0 (2015-12-25)¶

Breaks build & header compatibility due to: - Improved build configuration and feature check macros - Endianess configuration fixes (by Erwin Kroon (@ekroon) and David Grigsby (@dgrigsby)) - pkg-config compatibility (by Vincent Bernat) - enable use of versioned SONAME (by Vincent Bernat) - better fuzzer (wasn’t random until now, ooops)

0.3.1 (2015-05-21)¶

documentation and comments improvements, mostly for the API reference

0.3.0 (2015-05-21)¶

Fixes, polishing, niceties across the code base
Updated examples
cbor_copy
cbor_build_negint8, 16, 32, 64, matching asserts
cbor_build_stringn
cbor_build_tag
cbor_build_float2, ...

0.2.1 (2015-05-17)¶

C99 support

0.2.0 (2015-05-17)¶

cbor_ctrl_bool -> cbor_ctrl_is_bool
Added cbor_array_allocated & map equivalent
Overhauled endianess conversion - ARM now works as expected
‘sort.c’ example added
Significantly improved and doxyfied documentation

0.1.0 (2015-05-06)¶

The initial release, yay!

Development¶

Development dependencies¶

CMocka (testing)
Python and pip (Sphinx platform)
Doxygen
Sphinx (documentation)
There are some Ruby scripts in misc
Valgrind (memory correctness & profiling)
GCOV/LCOV (test coverage)

Building cmocka¶

# Starting from libcbor source directory
git submodule update --init test/cmocka
cd test
mkdir cmocka_build && cd cmocka_build
cmake ../cmocka
make -j 4
make install

Installing sphinx¶

pip install sphinx
pip install sphinx_rtd_theme
pip install https://github.com/lepture/python-livereload/archive/master.zip
pip install sphinx-autobuild

Further instructions on configuring advanced features can be found at http://read-the-docs.readthedocs.org/en/latest/install.html.

Live preview of docs¶

cd doc
make livehtml

Testing and code coverage¶

Please refer to Tests

libcbor¶

Overview¶

Contents¶

Getting started¶

Building & installing libcbor¶

Linking with libcbor¶

MinGW build instructions¶

Troubleshooting¶

Usage & preliminaries¶

Version information¶

Headers to include¶

Using libcbor¶

API¶

Types of items¶

Binary queries¶

Logical queries¶

Memory management and reference counting¶

Using custom allocator¶

Reference counting¶

Decoding¶

Associated data structures¶

Encoding¶

Type-specific serializers¶

Types 0 & 1 – Positive and negative integers¶

Type 0 - positive integers¶

Type 1 - negative integers¶

Type 0 & 1¶

Building new items¶

Retrieving values¶

Setting values¶

Dealing with width¶

Dealing with signedness¶

Creating new items¶

Type 2 – Byte strings¶

Streaming indefinite byte strings¶

Getting metadata¶

Reading data¶

Creating new items¶

Building items¶

Manipulating existing items¶

Type 3 – UTF-8 strings¶

Streaming indefinite strings¶

UTF-8 encoding validation¶

Getting metadata¶

Reading data¶

Creating new items¶

Building items¶

Manipulating existing items¶

Type 4 – Arrays¶

Examples¶

Streaming indefinite arrays¶

Getting metadata¶

Reading data¶

Creating new items¶

Modifying items¶

Type 5 – Maps¶

Streaming maps¶

Getting metadata¶

Reading data¶

Creating new items¶

Modifying items¶

Type 6 – Semantic tags¶

Type 7 – Floats & control tokens¶

Getting metadata¶

Reading data¶

Creating new items¶

Building items¶

Manipulating existing items¶

Streaming & indefinite items¶

Decoding¶

Related structures¶

Callback types definition¶

Encoding¶

Tests¶

Unit tests¶

Testing for memory leaks¶

Code coverage¶

Fuzz testing¶

RFC conformance¶

Bytestring length¶