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.\" ========================================================================
.\"
.IX Title "HTTP::Headers::Util 3"
.TH HTTP::Headers::Util 3 2023-10-03 "perl v5.38.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&  use HTTP::Headers::Util qw(split_header_words);
\&  @values = split_header_words($h\->header("Content\-Type"));
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This module provides a few functions that helps parsing and
construction of valid HTTP header values.  None of the functions are
exported by default.
.PP
The following functions are available:
.ie n .IP "split_header_words( @header_values )" 4
.el .IP "split_header_words( \f(CW@header_values\fR )" 4
.IX Item "split_header_words( @header_values )"
This function will parse the header values given as argument into a
list of anonymous arrays containing key/value pairs.  The function
knows how to deal with ",", ";" and "=" as well as quoted values after
"=".  A list of space separated tokens are parsed as if they were
separated by ";".
.Sp
If the \f(CW@header_values\fR passed as argument contains multiple values,
then they are treated as if they were a single value separated by
comma ",".
.Sp
This means that this function is useful for parsing header fields that
follow this syntax (BNF as from the HTTP/1.1 specification, but we relax
the requirement for tokens).
.Sp
.Vb 2
\&  headers           = #header
\&  header            = (token | parameter) *( [";"] (token | parameter))
\&
\&  token             = 1*<any CHAR except CTLs or separators>
\&  separators        = "(" | ")" | "<" | ">" | "@"
\&                    | "," | ";" | ":" | "\e" | <">
\&                    | "/" | "[" | "]" | "?" | "="
\&                    | "{" | "}" | SP | HT
\&
\&  quoted\-string     = ( <"> *(qdtext | quoted\-pair ) <"> )
\&  qdtext            = <any TEXT except <">>
\&  quoted\-pair       = "\e" CHAR
\&
\&  parameter         = attribute "=" value
\&  attribute         = token
\&  value             = token | quoted\-string
.Ve
.Sp
Each \fIheader\fR is represented by an anonymous array of key/value
pairs.  The keys will be all be forced to lower case.
The value for a simple token (not part of a parameter) is \f(CW\*(C`undef\*(C'\fR.
Syntactically incorrect headers will not necessarily be parsed as you
would want.
.Sp
This is easier to describe with some examples:
.Sp
.Vb 3
\&   split_header_words(\*(Aqfoo="bar"; port="80,81"; DISCARD, BAR=baz\*(Aq);
\&   split_header_words(\*(Aqtext/html; charset="iso\-8859\-1"\*(Aq);
\&   split_header_words(\*(AqBasic realm="\e\e"foo\e\e\e\ebar\e\e""\*(Aq);
.Ve
.Sp
will return
.Sp
.Vb 3
\&   [foo=>\*(Aqbar\*(Aq, port=>\*(Aq80,81\*(Aq, discard=> undef], [bar=>\*(Aqbaz\*(Aq ]
\&   [\*(Aqtext/html\*(Aq => undef, charset => \*(Aqiso\-8859\-1\*(Aq]
\&   [basic => undef, realm => "\e"foo\e\ebar\e""]
.Ve
.Sp
If you don't want the function to convert tokens and attribute keys to
lower case you can call it as \f(CW\*(C`_split_header_words\*(C'\fR instead (with a
leading underscore).
.ie n .IP "join_header_words( @arrays )" 4
.el .IP "join_header_words( \f(CW@arrays\fR )" 4
.IX Item "join_header_words( @arrays )"
This will do the opposite of the conversion done by \fBsplit_header_words()\fR.
It takes a list of anonymous arrays as arguments (or a list of
key/value pairs) and produces a single header value.  Attribute values
are quoted if needed.
.Sp
Example:
.Sp
.Vb 2
\&   join_header_words(["text/plain" => undef, charset => "iso\-8859/1"]);
\&   join_header_words("text/plain" => undef, charset => "iso\-8859/1");
.Ve
.Sp
will both return the string:
.Sp
.Vb 1
\&   text/plain; charset="iso\-8859/1"
.Ve