libfyaml ·

A fancy 1.2 YAML and JSON parser/writer.

Fully feature complete YAML parser and emitter, supporting the latest YAML spec and passing the full YAML testsuite.

It is designed to be very efficient, avoiding copies of data, and has no artificial limits like the 1024 character limit for implicit keys.

libfyaml is using https://github.com/yaml/yaml-test-suite as a core part of its testsuite.

Features

• Fully supports YAML version 1.2.
• Attempts to adhere to features coming with YAML version 1.3 so that it will be ready.
• Zero content copy operation, which means that content is never copied to internal structures. On input types that support it (mmap files and constant strings) that means that memory usage is kept low, and arbitrary large content can be manipulated without problem.
• Parser may be used in event mode (like libyaml) or in document generating mode.
• Extensive programmable API capable of manipulating parsed YAML documents or creating them from scratch.
• YAML emitter with programmable options, supporting colored output.
• Extensive testsuite for the API, the full YAML test-suite and correct emitter operation.
• Easy printf/scanf based YAML creation and data extraction API.
• Accurate and descriptive error messages, in standard compiler format that can be parsed by editors and developer GUIs.
• Testsuite supports running under valgrind and checking for memory leaks. No leaks should be possible under normal operation, so it is usable for long- running applications.

Contents

• Features
• Prerequisites
• Building
• Usage and examples
• API documentation
• fy-tool reference
• Missing Features

Prerequisites

libfyaml is primarily developed on Linux based debian distros but Apple MacOS X builds (using homebrew) are supported as well.

On a based debian distro (i.e. ubuntu 19.04 disco) you should install the following dependencies:

• sudo apt-get install gcc autoconf automake libtool git make libltdl-dev pkg-config

To enable the libyaml comparison checker:

• sudo apt-get install libyaml-dev

For the API testsuite libcheck is required:

• sudo apt-get install check

And finally in order to build the sphinx based documentation:

• sudo apt-get install python3 python3-pip python3-setuptools
• pip3 install wheel sphinx git+http://github.com/return42/linuxdoc.git sphinx\_rtd\_theme sphinx-markdown-builder

Note that some older distros (like xenial) do not have a sufficiently recent sphinx in their repos. In that case you can create a virtual environment using scripts/create-virtual-env

Building

libfyaml uses a standard autotools based build scheme so:

• ./bootstrap.sh
• ./configure
• make

Will build the library and fy-tool.

• make check

Will run the test-suite.

Binaries, libraries, header files and pkgconfig files maybe installed with

• make install

By default, the installation prefix will be /usr/local, which you can change with the --prefix <dir> option during configure.

To build the documentation API in HTML format use:

• make doc-html

The documentation for the public API will be found in doc/_build/html

• make doc-latexpdf

Will generate a single pdf containing everything.

Usage and examples

Usage of libfyaml is somewhat similar to libyaml, but with a few notable differences.

1. The objects of the library are opaque, they are pointers that may be used but may not be derefenced via library users. This makes the public API not be dependent of internal changes in the library structures.

2. The object pointers used are guaranteed to not 'move' like libyaml object pointers so you may embed them freely in your own structures.

3. The convenience methods of libyaml allow you to avoid tedious iteration and code duplication. While fully manual YAML document tree manipulation is available, if your application is not performance sensitive when manipulating YAML, you are advised to use the helpers.

Using libfyaml in your projects

Typically you only have to include the single header file libfyaml.h and link against the correct fyaml-\<major>-\<minor> library.

It is recommended to use pkg-config, i.e.

CFLAGS+= `pkg-config --cflags libfyaml`
LDFLAGS+= `pkg-config --libs libfyaml`

For use in an automake based project you may use the following fragment

PKG_CHECK_MODULES(LIBFYAML, [ libfyaml ], HAVE_LIBFYAML=1, HAVE_LIBFYAML=0)

if test "x$HAVE_LIBFYAML" != "x1" ; then
    AC_MSG_ERROR([failed to find libfyaml])
fi

AC_SUBST(HAVE_LIBFYAML)
AC_SUBST(LIBFYAML_CFLAGS)
AC_SUBST(LIBFYAML_LIBS)
AC_DEFINE_UNQUOTED([HAVE_LIBFYAML], [$HAVE_LIBFYAML], [Define to 1 if you have libfyaml available])
AM_CONDITIONAL([HAVE_LIBFYAML], [ test x$HAVE_LIBFYAML = x1 ])

The examples that follow will make things clear.

Display libfyaml version example

This is the minimal example that checks that you've compiled against the correct libfyaml.

/*
 * fy-version.c - libfyaml version example
 *
 * Copyright (c) 2019 Pantelis Antoniou <pantelis.antoniou@konsulko.com>
 *
 * SPDX-License-Identifier: MIT
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>
#include <stdio.h>

#include <libfyaml.h>

int main(int argc, char *argv[])
{
    printf("%s\n", fy_library_version());
    return EXIT_SUCCESS;
}

libfyaml example using simplified inprogram YAML generation

This example simply parses an in-program YAML string and displays a string.

The standard header plus variables definition.

/*
 * inprogram.c - libfyaml inprogram YAML example
 *
 * Copyright (c) 2019 Pantelis Antoniou <pantelis.antoniou@konsulko.com>
 *
 * SPDX-License-Identifier: MIT
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>
#include <stdio.h>
#include <assert.h>

#include <libfyaml.h>

int main(int argc, char *argv[])
{
    static const char *yaml = 
        "invoice: 34843\n"
        "date   : !!str 2001-01-23\n"
        "bill-to: &id001\n"
        "    given  : Chris\n"
        "    family : Dumars\n"
        "    address:\n"
        "        lines: |\n"
        "            458 Walkman Dr.\n"
        "            Suite #292\n";
    struct fy_document *fyd = NULL;
    int rc, count, ret = EXIT_FAILURE;
    unsigned int invoice_nr;
    char given[256 + 1];

Parsing and creating a YAML document from either the built-in YAML, or an invoice file given on the command line:

    if (argc == 1)
        fyd = fy_document_build_from_string(NULL, yaml, FY_NT);
    else
        fyd = fy_document_build_from_file(NULL, argv[1]);
    if (!fyd) {
        fprintf(stderr, "failed to build document");
        goto fail;
    }

Get the invoice number and the given name using a single call.

    /* get the invoice number and the given name */
    count = fy_document_scanf(fyd,
            "/invoice %u "
            "/bill-to/given %256s",
            &invoice_nr, given);
    if (count != 2) {
        fprintf(stderr, "Failed to retreive the two items\n");
        goto fail;
    }

    /* print them as comments in the emitted YAML */
    printf("# invoice number was %u\n", invoice_nr);
    printf("# given name is %s\n", given);

In sequence, increase the invoice number, add a spouse and a secondary address.

    rc =
        /* set increased invoice number (modify existing node) */
        fy_document_insert_at(fyd, "/invoice", FY_NT,
            fy_node_buildf(fyd, "%u", invoice_nr + 1)) ||
        /* add spouse (create new mapping pair) */
        fy_document_insert_at(fyd, "/bill-to", FY_NT,
            fy_node_buildf(fyd, "spouse: %s", "Doris")) ||
        /* add a second address */
        fy_document_insert_at(fyd, "/bill-to", FY_NT,
            fy_node_buildf(fyd, "delivery-address:\n"
                            "  lines: |\n"
                        "    1226 Windward Ave.\n"));
    if (rc) {
        fprintf(stderr, "failed to insert to document\n");
        goto fail;
    }

Emit the document to standard output (while sorting the keys)

    /* emit the document to stdout (but sorted) */
    rc = fy_emit_document_to_fp(fyd, FYECF_DEFAULT | FYECF_SORT_KEYS, stdout);
    if (rc) {
        fprintf(stderr, "failed to emit document to stdout");
        goto fail;
    }

Finally exit and report condition.

    ret = EXIT_SUCCESS;
fail:
    fy_document_destroy(fyd);   /* NULL is OK */

    return ret;
}

API documentation

For complete documentation of libfyaml API, visit https://pantoniou.github.io/libfyaml/

fy-tool reference

A YAML manipulation tool is included in libfyaml, aptly name fy-tool. It's a multi tool application, acting differently according to the name it has when it's invoked. There are four tool modes, namely:

• fy-testsuite: Used for outputing a test-suite specific event stream which is used for comparison with the expected output of the suite.
• fy-dump: General purpose YAML parser and dumper, with syntax coloring support, visible whitespace options, and a number of output modes.
• fy-filter: YAML filtering tool allows to extract information out of a YAML document.
• fy-join: YAML flexible join tool.

fy-testsuite usage

A number of options are common in every fy-tool invocation:

Usage : fy-tool [options] [args]

Options:

    --include, -I <path>     : Add directory to include path (default path "")
    --debug-level, -d <lvl>  : Set debug level to <lvl>(default level 3)
    --indent, -i <indent>    : Set dump indent to <indent> (default indent 2)
    --width, -w <width>      : Set dump width to <width> (default width 80)
    --resolve, -r            : Perform anchor and merge key resolution (default false)
    --color, -C <mode>       : Color output can be one of on, off, auto (default auto)
    --visible, -V            : Make all whitespace and linebreaks visible (default false)
    --follow, -l             : Follow aliases when using paths (default false)
    --strip-labels           : Strip labels when emitting (default false)
    --strip-tags             : Strip tags when emitting (default false)
    --strip-doc              : Strip document headers and indicators when emitting (default false)
    --quiet, -q              : Quiet operation, do not output messages (default false)
    --version, -v            : Display libfyaml version
    --help, -h               : Display  help message

Usage: fy-testsuite [options] [args]

    [common options]

    Parse and dump test-suite event format
    $ fy-testsuite input.yaml
    ...

    Parse and dump of event example
    $ echo "foo: bar" | fy-testsuite -
    +STR
    +DOC
    +MAP
    =VAL :foo
    =VAL :bar
    -MAP
    -DOC
    -STR

fy-dump usage

Usage: fy-dump [options] [args]

Options:

    [common options]

    --sort, -s               : Perform mapping key sort (valid for dump) (default false)
    --comment, -c            : Output comments (experimental) (default false)
    --mode, -m <mode>        : Output mode can be one of original, block, flow, flow-oneline, json, json-tp, json-oneline (default original)
    --streaming              : Use streaming output mode (default false)

    [common options]

    Parse and dump generated YAML document tree in the original YAML form
    $ fy-dump input.yaml
    ...

    Parse and dump generated YAML document tree in block YAML form (and make whitespace visible)
    $ fy-dump -V -mblock input.yaml
    ...

    Parse and dump generated YAML document from the input string
    $ fy-dump -mjson ">foo: bar"
    {
      "foo": "bar"
    }

    Parse and dump generated YAML document from the input string (using streaming mode)
    $ fy-dump --streaming ">foo: bar"
    foo: bar

    Note that streaming mode can not perform document validity checks, like duplicate keys nor
        support the sort keys option.

fy-filter usage

Usage: fy-filter [options] [args]

Options:

    [common options]

    --sort, -s               : Perform mapping key sort (valid for dump) (default false)
    --comment, -c            : Output comments (experimental) (default false)
    --mode, -m <mode>        : Output mode can be one of original, block, flow, flow-oneline, json, json-tp, json-oneline (default original)
    --file, -f <file>        : Use given file instead of <stdin>
                               Note that using a string with a leading '>' is equivalent to a file with the trailing content
                               --file ">foo: bar" is as --file file.yaml with file.yaml "foo: bar"

    Parse and filter YAML document tree starting from the '/foo' path followed by the '/bar' path
    $ fy-filter --file input.yaml /foo /bar
    ...

    Parse and filter for two paths (note how a multi-document stream is produced)
    $ fy-filter --file -mblock --filter --file ">{ foo: bar, baz: [ frooz, whee ] }" /foo /baz
    bar
    ---
    - frooz
    - whee

    Parse and filter YAML document in stdin (note how the key may be complex)
    $ echo "{ foo: bar }: baz" | fy-filter "/{foo: bar}/"
    baz

fy-join usage

Usage: fy-join [options] [args]

Options:

    [common options]

    --sort, -s               : Perform mapping key sort (valid for dump) (default false)
    --comment, -c            : Output comments (experimental) (default false)
    --mode, -m <mode>        : Output mode can be one of original, block, flow, flow-oneline, json, json-tp, json-oneline (default original)
    --file, -f <file>        : Use given file instead of <stdin>
                               Note that using a string with a leading '>' is equivalent to a file with the trailing content
                               --file ">foo: bar" is as --file file.yaml with file.yaml "foo: bar"
    --to, -T <path>          : Join to <path> (default /)
    --from, -F <path>        : Join from <path> (default /)
    --trim, -t <path>        : Output given path (default /)

    Parse and join two YAML files
    $ fy-join file1.yaml file2.yaml
    ...

    Parse and join two YAML maps
    $ fy-join ">foo: bar" ">baz: frooz"
    foo: bar
    baz: frooz

Missing features and omissions

1. Windows - libfyaml is not supporting windows yet.
2. Unicode - libfyaml only supports UTF8 and has no support for wide character input.

Development and contributing

Feel free to send pull requests and raise issues.