NAME

       Log::Fmt - a little parser and emitter of structured log lines

VERSION

       version 3.013

OVERVIEW

       This library primarily exists to service Log::Dispatchouli's "log_event" methods.  It converts an
       arrayref of key/value pairs to a string that a human can scan tolerably well, and which a machine can
       parse about as well.  It can also do that tolerably-okay parsing for you.

PERL VERSION

       This library should run on perls released even a long time ago.  It should work on any version of perl
       released in the last five years.

       Although it may work on older versions of perl, no guarantee is made that the minimum required version
       will not be increased.  The version may be increased for any reason, and there is no promise that patches
       will be accepted to lower the minimum required perl.

METHODS

   format_event_string
         my $octets = Log::Fmt->format_event_string([
           key1 => $value1,
           key2 => $value2,
         ]);

       Note especially that if any value to encode is a reference to a reference, then String::Flogger is used
       to encode the referenced value.  This means you can embed, in your logfmt, a JSON dump of a structure by
       passing a reference to the structure, instead of passing the structure itself.

       String values are assumed to be character strings, and will be UTF-8 encoded as part of the formatting
       process.

   parse_event_string
         my $kv_pairs = Log::Fmt->parse_event_string($octets);

       Given the kind of (byte) string emitted by "format_event_string", this method returns a reference to an
       array of key/value pairs.  After being unquoted, value strings will be UTF-8 decoded into character
       strings.

       This isn't exactly a round trip.  First off, the formatting can change illegal keys by replacing
       characters with question marks, or replacing empty strings with tildes.  Secondly, the formatter will
       expand some values like arrayrefs and hashrefs into multiple keys, but the parser will not recombined
       those keys into structures.  Also, there might be other asymmetric conversions.  That said, the string
       escaping done by the formatter should correctly reverse.

       If the input string is badly formed, hunks that don't appear to be value key/value pairs will be
       presented as values for the key "junk".

   parse_event_string_as_hash
           my $hashref = Log::Fmt->parse_event_string_as_hash($line);

       This parses the given line as logfmt, then puts the key/value pairs into a hash and returns a reference
       to it.

       Because nothing prevents a single key from appearing more than once, you should use this with the
       understanding that data could be lost.  No guarantee is made of which value will be preserved.

SPECIFICATION

   The logfmt text format
       Although quite a few tools exist for managing "logfmt", there is no spec-like document for it.  Because
       you may require multiple implementations, a specification can be helpful.

       Every logfmt event is a sequence of pairs in the form "key=value".  Pairs are separated by a single
       space.

           event = pair *(WSP pair)
           pair  = key "=" value
           okchr = %x21 / %x23-3c / %x3e-5b / %x5d-7e ; VCHAR minus \ and " and =
           key   = 1*(okchr)
           value = key / quoted

           quoted = DQUOTE *( escaped / quoted-ok / okchr / eightbit ) DQUOTE
           escaped         = escaped-special / escaped-hex
           escaped-special = "\\" / "\n" / "\r" / "\t" / ("\" DQUOTE)
           escaped-hex     = "\x{" 2HEXDIG "}" ; lowercase forms okay also
           quoted-ok       = SP / "="
           eightbit        = %x80-ff

       When formatting a value, if a value is already a valid "key" token, use it without further quoting.

   Quoting a Unicode string
       It is preferable to build quoted values from a Unicode string, because it's possible to know whether a
       given codepoint is a non-ASCII unsafe character, like "LINE SEPARATOR".  Safe non-ASCII characters can be
       directly UTF-8 encoded, rather than quoted with "\x{...}".  In that way, viewing logfmt events with a
       standard terminal can show something like:

           user.name="Jürgen"

       To generate a "quoted" from a Unicode string, for each codepoint:

       •   convert "\" to "\\"

       •   convert """ to "\""

       •   convert a newline (U+000A) to "\n"

       •   convert a carriage return (U+000D) to "\r"

       •   convert a character tabulation (U+0009) to "\t"

       •   for any control character (by general category) or vertical newline:

           •   encode the character into a UTF-8 bytestring

           •   convert each byte in the bytestring into "\x{...}" form

           •   use that sequence of "\x{...}" codes in place of the replaced character

       Finally, UTF-8 encode the entire string and wrap it in double qoutes.

       This Perl implementation assumes that all string values to be encoded are character strings!

       Quoting a bytestring

       Encoding  a  Unicode string is preferable, but may not be practical.  In those cases when you have only a
       byte sequence, apply these steps.

       For each byte (using ASCII conventions):

       •   convert "\" to "\\"

       •   convert """ to "\""

       •   convert a newline (%0a) to "\n"

       •   convert a carriage return (%0d) to "\r"

       •   convert a character tabulation (%x09) to "\t"

       •   convert any control character ("%x00-1f / %x7f") to the "\x{...}" form

       •   convert any non-ASCII byte ("%x80-ff") to the "\x{...}" form

       Finally, wrap the string in double quotes.

AUTHOR

       Ricardo SIGNES <cpan@semiotic.systems>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2025 by Ricardo SIGNES.

       This is free software; you can redistribute it and/or modify it under  the  same  terms  as  the  Perl  5
       programming language system itself.

perl v5.40.1                                       2025-10-21                                      Log::Fmt(3pm)