HTTP::Headers::Util(3) User Contributed Perl Documentation HTTP::Headers::Util(3)

# [SYNOPSIS](#SYNOPSIS)

```
  use HTTP::Headers::Util qw(split_header_words);
  @values = split_header_words($h->header("Content-Type"));
```

# [DESCRIPTION](#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.

The following functions are available:

[split\_header\_words( @header\_values )](#split_header_words%28)

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 ";".

If the @header\_values passed as argument contains multiple values, then they are treated as if they were a single value separated by comma ",".

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).

```
  headers           = #header
  header            = (token | parameter) *( [";"] (token | parameter))
  token             = 1*<any CHAR except CTLs or separators>
  separators        = "(" | ")" | "<" | ">" | "@"
                    | "," | ";" | ":" | "\" | <">
                    | "/" | "[" | "]" | "?" | "="
                    | "{" | "}" | SP | HT
  quoted-string     = ( <"> *(qdtext | quoted-pair ) <"> )
  qdtext            = <any TEXT except <">>
  quoted-pair       = "\" CHAR
  parameter         = attribute "=" value
  attribute         = token
  value             = token | quoted-string
    
```

Each *header* 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 "undef". Syntactically incorrect headers will not necessarily be parsed as you would want.

This is easier to describe with some examples:

```
   split_header_words('foo="bar"; port="80,81"; DISCARD, BAR=baz');
   split_header_words('text/html; charset="iso-8859-1"');
   split_header_words('Basic realm="\\"foo\\\\bar\\""');
    
```

will return

```
   [foo=>'bar', port=>'80,81', discard=> undef], [bar=>'baz' ]
   ['text/html' => undef, charset => 'iso-8859-1']
   [basic => undef, realm => "\"foo\\bar\""]
    
```

If you don't want the function to convert tokens and attribute keys to lower case you can call it as "\_split\_header\_words" instead (with a leading underscore).

[join\_header\_words( @arrays )](#join_header_words%28)

This will do the opposite of the conversion done by **split\_header\_words()**. 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.

Example:

```
   join_header_words(["text/plain" => undef, charset => "iso-8859/1"]);
   join_header_words("text/plain" => undef, charset => "iso-8859/1");
    
```

will both return the string:

```
   text/plain; charset="iso-8859/1"
    
```

2026-10-25 perl v5.44.0

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Document: HTTP::Headers::Util(3pm) from perl-http-message 7.04-r1 (Chainguard OS)
Source: https://github.com/libwww-perl/HTTP-Message.git