The Cro::HTTP::Message role is done by both Cro::HTTP::Request and Cro::HTTP::Response. It factors out the many aspects that requests and responses have in common, including handling of headers and bodies. Cro uses the same request and response classes for both client and server use cases, which besides giving less to learn also eases the writing of HTTP intermediaries.


Retrieving headers

The headers method gets a List of Cro::HTTP::Header objects. This gets the headers in the order they were originally received. If multiple headers with the same name were sent, they will have multiple entries in the list. This is both the most precise and least convenient way to access headers.

my @links = $resp.headers.grep(* eq 'link').map(*.value);

When expecting a single header with a particular name, use the header method to retrieve its value. If there are multiple headers of the same name, their values will be joined by commas. The header name is matched case-insensitively. If there is no such header, then Nil will be returned.

my $content-type = $resp.header('Content-type');

To get a list of header values matching a particular name (case-insensitive), use header-list. This will return an empty list if there is no header with the specified name.

my @links = $resp.header-list('link');

The has-header method is useful for checking if a header is present in the request without caring about its value; again, matching is case-insensitive.

if $resp.has-header('expires') {

Setting headers

Headers can be added to the response object using the append-header method. This can take either a Cro::HTTP::Header object:

    name => 'ETag',
    value => '"737060cd8c284d8af7ad3082f209582d"'

Or the header in string format, which will be parsed into name and value (this is the slowest way due to the need for parsing):

$resp.append-header('ETag: "737060cd8c284d8af7ad3082f209582d"');

Or by specifying the header name, which must be a Str, and the header value, which can be any Cool type and will be coerced to a Str:

$resp.append-header('ETag', '"737060cd8c284d8af7ad3082f209582d"');

Removing headers

The remove-header method can be used to remove one or more headers. There are a number of overloads. The simplest takes a Str containing the header name to remove. All headers with this name, matched case-insensitively, will be removed. The number of headers removed will be returned.


Alternatively, a predicate may be passed; all headers that match it will be removed. Again, the number of headers removed will be returned.

$resp.remove-header(* eq 'link');

Finally, a Cro::HTTP::Header object may be passed to remove that specific header.

my $header = $resp.headers.pick; # Pick a random header to remove
$resp.remove-header($header);    # And remove it

Content type

The content-type method obtains the Content-type header, if any, and parses it into a Cro::MediaType instance. If there is no Content-type header, then Nil is returned. If for some reason the header value is not a valid media type then an exception will be thrown.


Retrieving the body

Cro provides access to the message body at a range of abstraction levels, from low-level ("give me bytes as they arrived") to high level ("automatically parse application/json and give me an object"). Note that each of these will "sink" the body bytes, meaning that only one of them may be used on a given HTTP message.

As a byte stream

The body-byte-stream method returns a Supply containing the bytes making up the message, as they are received over the network. Transfer encoding (such as "chunked") will already have been applied, as will handling of known length content (marked by the presence of the Content-length header). When the body has been full received, then a done will be emitted on the Supply.

react {
    whenever $resp.body-stream -> $blob {
        say "Got bytes: " ~ $blob.gist;

As a binary Blob

The body-blob method returns a Promise that is kept with all of the data emitted on body-byte-stream joined into a single Blob.

my Blob $bytes = await $resp.body-blob();

As a text Str

The body-text method returns a Promise that is kept when all of the data emitted on the body-body-stream has been received and then decoded to a Str.

my Str $text = await $resp.body-text();

This uses the charset on Content-type as its primary means of knowing what encoding to use. If that is missing, but the content starts with a recognized [BOM](, then this will be taken as the encoding to use. Failing that, the default-enc named parameter will be used, if passed:

my Str $text = await $resp.body-text(:default-enc<latin-1>);

If it is not passed, the a heuristic will be used: if the body can be decoded as utf-8 then it will be deemed to be utf-8, and failing that it will be decoded as latin-1 (which can never fail as all bytes are valid, although the result may not be meaningful).

As an object

Implementations of the Cro::HTTP::BodyParser role are used to parse a HTTP message body into an appropriate object. Examples of what a body parser might do include:

Cro provides a number of body parsers, which it enables by default. They can also be provided externally.

A Cro::HTTP::Message has a Cro::HTTP::BodyParserSelector, which picks the appropriate Cro::HTTP::BodyParser implementation to use. This may be changed at any point before body is called. Body parser selectors can come from a range of places:

The following body parsers are provided by default for requests:

The final 3 body parsers are in the default set for parsing responses:

Setting the Body

The set-body method can be used to set the body. The Cro::HTTP::Message will typically then reach either a Cro::HTTP::ResponseSerializer (servers) or Cro::HTTP::RequestSerializer (clients), which call body-byte-stream. At this point, an instance of Cro::HTTP::BodySerializerSelector will be used to pick a Cro::HTTP::BodySerializer to use. Applications can change the selector in order to add extra body serializers at any point before the message is serialized to be sent over the network.

The following body serializers are in the default set for serializing requests:

All of these will set a Content-length header.

The default set of serializers for a response are: