TITLE
HTTP::Headers
SUBTITLE
Tools for working with HTTP message headers
SYNOPSIS
use HTTP::Headers :standard-names;
my $headers = HTTP::Headers.new;
$headers.Content-Type = 'text/html';
$headers.Content-Type.charset = "UTF-8";
$headers.Content-Length = $content.encode.bytes;
my $CRLF = "\x0d\x0a";
print "200 OK$CRLF;
print $headers.as-string(:eol($CRLF));
print $CRLF;
print $content;
DESCRIPTION
This module provides convenient tools for working with HTTP headers. An emphasis has been placed on making it easy to use in a way that helps catch errors early. It has also been built for extensibility.
Methods
method new
method new(HTTP::Headers:U: @headers, Bool:D :$quiet = False --> HTTP::Headers:D)
method new(HTTP::Headers:U: %headers, Bool:D :$quiet = False --> HTTP::Headers:D)
method new(HTTP::Headers:U: Bool:D :$quiet = False, *@headers, *%headers --> HTTP::Headers:D)
Constructs a new object for working with headers. The :$quiet option can be used to suppress all warnings normally generated by this object.
The various %headers and @headers methods can be used to initialize the object from a list of pairs:
my $headers = HTTP::Headers.new:
::(Content-Type) => 'text/html',
::(Content-Length) => 42,
'X-Requested-With' => 'XMLHTTPRequest',
;
multi method headers(HTTP::Headers:D: Pair:D @headers)
multi method headers(HTTP::Headers:D: %headers)
multi method headers(HTTP::Headers:D: *@headers, *%headers)
Sets all the headers given as pairs or named parameters.
multi method header(HTTP::Headers:D: HTTP::Header::Standard::Name $name --> HTTP::Header) is rw
multi method header(HTTP::Headers:D: Str $name --> HTTP::Header) is rw
This method is writable and allows the use of either the values in the HTTP::Header::Standard::Name enumeration or string values. In general, you should not use strings when you can use the enumeration in your code. By using the enumeration, you can discover typos at compile time.
use HTTP::Headers :standard-names;
$headers.header(Content-MIME-Type); # I forgot it's just Content-Type
# Undeclared name:
# Content-MIME-Type used at line 1
The library will remind you of this best practice if you use a string when you could use an enumeration:
$headers.header("Content-Type");
# Calling .header(Content-Type) is preferred to .header("Content-Type") for standard HTTP headers.
If you don't want to see these, you can ask the object or the method to be quiet:
$headers.header("Content-Type", :quiet);
# OR during construction
my $headers = HTTP::Headers.new(:$quiet);
When setting values on a header, you may set either a single or multiples.
$headers.header(Content-Length) = 42;
$headers.header(Accept) = "text/html", "text/*", "*/*";
say $headers.as-string;
# Accept: text/html
# Accept: text/*
# Accept: */*
# Content-Length: 42
By setting with a comma, you will generate multiple headers.
You may also set headers with DateTime, Instant, and Duration objects and it should do the right thing. For example,
$headers.header(Date) = DateTime.now;
$headers.header(Retry-After) = Duration.new(120);
say $headers.as-string;
# Date: Thu, 14 May 2015 09:48:00 GMT
# Retry-After: 120
When you read a header, the value returns is a HTTP::Header object.
my HTTP::Header $ct = $headers.header(Content-Type);
my HTTP::Header $xf = $headers.header("X-Foo-Custom");
This object stringifies to the value of the header (with multiple values being joined together using a comma, safe according to RFC). It also provides a bunch of additional tools for working with and manipulating the header. For example:
$headers.header(Accept).push: "text/css", "text/js";
$headers.header(Content-Type).charset = "UTF-8";
See HTTP::Header for details.
multi method remove-header(HTTP::Header:D: $name --> HTTP::Header)
multi method remove-header(HTTP::Header:D: *@names --> List)
These method will remove headers from the list. The removed HTTP::Header object is returned.
method remove-content-headers(HTTP::Headers:D: --> List)
This method removes all the entity headers:
Allow Content-Encoding Content-Language Content-Length
Content-Location Content-MD5 Content-Range Content-Type
Expires Last-Modified
as well as any that start with "Content-".
method clear
method clear(HTTP::Headers:D:)
This removes all headers.
method clone
method clone(HTTP::Headers:D: --> HTTP::Headers:D)
This performs a deep clone of the object.
method sorted-headers(HTTP::Headers:D: --> Seq)
Returns all HTTP::Header objcts in a sequence sorted by header name.
method list
method list(HTTP::Headers:D: --> List)
This returns all the headers stored in this object, sorted according to the RFC recommendation (general headers first, then request/response headers, then entity/content headers, and finally custom headers).
method map
method map(HTTP::Headers:D: &code --> Seq)
Provides a way to iterate over all the headers in the object.
method as-string
method as-string(HTTP::Headers:D: Str:D :$eol = "\n" --> Str)
Returns the headers for output using the given line separator. If no line separator is given, "\n" is used.
method Str
multi method Str(:$eol = "\n") returns Str
This calls [/method as-string](/method as-string) with the given arguments.
method for-WAPI
method for-WAPI(HTTP::Headers:D: --> List:D)
This returns the headers formatted for output from a RakuWAPI application, as an array of Pairs.
Hash-like Operations
You can also treat HTTP::Headers like a hash in some ways. These are experimental and might be removed or changed in the future.
method postcircumfix:<{ }>
multi method postcircumfix:<{ }>(HTTP::Headers:D: Str:D $key --> HTTP::Header)
multi method postcircumfix:<{ }>(HTTP::Headers:D: HTTP::Header::Standard::Name:D $key --> HTTP::Header)
This may be used to return or assign a head value.
adverb :delete
This may be used to delete headers.
adverb :exists
This may be used to check to see if a head is set.
Convenience Methods
The following methods are provided as a shortcut for [/method header](/method header) and can be used as an accessor or mutator.
# General Headers
method Cache-Control is rw
method Connection is rw
method Date is rw
method Pragma is rw
method Trailer is rw
method Transfer-Encoding is rw
method Upgrade is rw
method Via is rw
method Warning is rw
# Request Headers
method Accept is rw
method Accept-Charset is rw
method Accept-Encoding is rw
method Accept-Language is rw
method Authorization is rw
method Expect is rw
method From is rw
method Host is rw
method If-Match is rw
method If-Modified-Since is rw
method If-None-Match is rw
method If-Range is rw
method If-Unmodified-Since is rw
method Max-Forwards is rw
method Proxy-Authorization is rw
method Range is rw
method Referer is rw
method TE is rw
method User-Agent is rw
# Response Headers
method Accept-Ranges is rw
method Age is rw
method ETag is rw
method Location is rw
method Proxy-Authenticate is rw
method Retry-After is rw
method Server is rw
method Vary is rw
method WWW-Authenticate is rw
# Entity Headers
method Allow is rw
method Content-Encoding is rw
method Content-Language is rw
method Content-Length is rw
method Content-Location is rw
method Content-MD5 is rw
method Content-Range is rw
method Content-Type is rw
method Expires is rw
method Last-Modified is rw
It is possible to create a sub-class of HTTP::Headers more suited to your application. As a simplistic example, here's a customization that provides two new custom headers named "X-Foo" and "X-Bar" which have a default column setting of 42 when used.
class MyApp::CustomHeaders is HTTP::Headers {
enum MyAppHeader < X-Foo X-Bar >;
method build-header($name, *@values) {
if $name ~~ MyAppHeader {
HTTP::Header::Custom.new(:name($name.Str), :42values);
}
else {
nextsame;
}
}
multi method header(MyAppHeader $name) is rw {
self.header-proxy($name);
}
method X-Foo is rw { self.header(MyAppHeader::X-Foo) }
method X-Bar is rw { self.header(MyAppHeader::X-Bar) }
}
Here is a description of the methods you'll need to consider in doing this.
multi method build-header(HTTP::Headers:D: Str:D $name, *@values --> HTTP::Header:D)
multi method build-header(HTTP::Headers:D: HTTP::Header::Standard::Name:D $name, *@values --> HTTP::Header:D)
This is a factory method used to decide how to build the headers being stored. Here is the place where you'll want to add custom roles to your headers, instantiate any custom implementations of HTTP::Header, etc.
It is recommended that you define it to build what you need and then use nextsame to handle all the remaining cases.
multi method header-proxy(HTTP::Headers:D: Str:D $name --> HTTP::Header) is rw
multi method header-proxy(HTTP::Headers:D: HTTP::Header::Standard::Name:D $name --> HTTP::Header) is rw
This is a handy helper that allows you to easily build your own custom version of [/method header](/method header). It returns a Proxy useful for building is rw methods similar to those in HTTP::Headers.
CAVEATS
This module provides a mutator style that is not considered ideal, possibly even un-Perlish. It pretty much completely overuses Proxy objects and such to make mutators that perform complex operations during seemingly straightforward assignment operations. This is probably not wise, but it seemed like a good idea at the time of first writing.
For a detailed write-up of why this is not preferable, see this blog post by Jonathan Worthington: [https://6guts.wordpress.com/2016/11/25/perl-6-is-biased-towards-mutators-being-really-simple-thats-a-good-thing/](Perl 6 is biased towards mutators being really simple. That’s a good thing.)