vi/simple_cbor_stream_parse

Simple low-level streamed callback-based CBOR push parser in C and C++

scsp - simple_cbor_stream_parse

A simple low-level streamed callback-based CBOR push parser in C.

License = MIT or Apache 2.0

Features

• No memory allocations, embedded-friendly.
• Should work with 32-bit or 16-bit registers. Float support is also opt-out.
• No buffering at all in low-level mode. You are in charge for buffering. Parse function expects write(2) semantics and process less bytes than you have pushed into it (including 0 bytes if there is not enough data).
• Helper function to parse from a FD (with buffering) or from memory.
• There is C++ binding. istream version has unavoidable buffering, low-level version requires allocation.

Concerns/Notes:

• Nesting depth is statically limited
• Unsigned numbers are represented as signed => can't handle access some extreme values
• Not validating. Bytestrings and strings are handled similarly.
• Strings and bytestrings are delivered in chunks which depend on how you push the data to the parser. String chunks may split UTF-8 characters in pieces.
• There is no CBOR generator here, only parser
• Not entire "Appenfix A" testsuite passes due to forced signed numbers

How to use

C

1. Copy source files (scsp.c and scsp.h) into your project
2. Define your callback functions (copy from some example). Note that strings may arrive in arbitrary chunks.
3. Fill in scsp_callbacks structure (copy from some example)
4. If you need to parse from entire file or from memory buffer, use scsp_parse_from_fd or scsp_parse_from_memory.
5. If you need flexible parsing, create scsp_state structure, initialize it with zeroes and call scsp_parse_lowlevel in a loop. It will consume data bit by bit. One call corresponds to a few callbacks.

C++

1. Copy source files scsp.c, scsp_cpp.cpp, scsp.h and scsp_cpp.hpp into your project
2. Inherit from scsp::Callbacks interface or scsp::CallbacksEmpty class
3. Override events you need to listen to
4. For simple mode, use parse_from_istream / parse_from_memory / parse_from_fd functions. Note that istream version does buffering inside.
5. For flexible mode, create scsp::State object with new_state, use parse_lowlevel (see fifth point in "C" version of "How to use") in a loop, then delete state object with delete_state.

Examples

• cbor_to_jsonesque - read cbor from a file or stdin and dump something similar to JSON or CBOR diagnostic.
• dump_scsp_events - dump each event in a separate line
• simple_example - parse from memory and assert it works
• extract_strings - a C++ example. Prints all encountered strings.
• roundtrip - a C++ example of copying a cbor file. Resulting CBOR is uncanonical.

Configurable parameters

• SCSP_MAXDEPTH - maximum nesting depth of CBOR objects or strings. Should probably be 2-3 more than you plan to do. Defaults to 16.
• SCSP_DEBUG, SCSP_DEBUG_STDERR - enable debugging output
• SCSP_USERDATA - data passed to each callback. Defaults to void*
• SCSP_EXPORT - just resides in signature of user-facing functions
• SCSP_INT - primary data type for integers, lengths and return values. Defaults to int64_t.
• SCSP_ENABLE_HELPERS - Enable some helper functions.
• SCSP_ENABLE_FLOAT
• SCSP_ENABLE_32BIT
• SCSP_ENABLE_64BIT
• SCSP_ENABLE_IOSTREAM - Enable additional features in C++ binding

Example of an scsp event stream

{"bytes": h'0102030405', 4: -6, true: 23.45, "array": [1, 1, 1]}

00000000  a4 65 62 79 74 65 73 45  01 02 03 04 05 04 25 f5  |.ebytesE......%.|
00000010  fb 40 37 73 33 33 33 33  33 65 61 72 72 61 79 83  |.@7s33333earray.|
00000020  01 01 01                                          |...|
00000023

map_opened(4)
map_key
string_open(5)
string_chunk("\x62\x79\x74\x65\x73")
string_close
map_value
bytestring_open(5)
bytestring_chunk("\x01\x02\x03\x04\x05")
bytestring_close
map_key
integer(4)
map_value
integer(-6)
map_key
simple(T)
map_value
noninteger(23.45)
map_key
string_open(5)
string_chunk("\x61\x72\x72\x61\x79")
string_close
map_value
array_opened(3)
array_item
integer(1)
array_item
integer(1)
array_item
integer(1)
array_closed
map_closed