The body-code (see section 3.1) is
driven by a Request. This request is generated from http_read_request/2
defined in
library(http/http_header).
- http_read_request(+Stream,
-Request)
- Reads an HTTP request from Stream and unify Request
with the parsed request. Request is a list of
Name(Value)
elements. It provides a number of predefined elements for the result of
parsing the first line of the request, followed by the additional
request parameters. The predefined fields are:
- host(Host)
- If the request contains
Host: Host, Host is
unified with the host-name. If Host is of the format <host>:<port>
Host only describes <host> and a field port(Port)
where
Port is an integer is added.
- input(Stream)
- The Stream is passed along, allowing to read more data or
requests from the same stream. This field is always present.
- method(Method)
- Method is the HTTP method represented as a
lower-case atom (i.e.,
delete, get, head,
options, patch, post, put,
trace). This field is present if the header has been parsed
successfully.
- path(Path)
- Path associated to the request. This field is always present.
- peer(Peer)
- Peer is a term
ip(A,B,C,D) containing the IP
address of the contacting host.
- port(Port)
- Port requested. See
host for details.
- request_uri(RequestURI)
- This is the untranslated string that follows the method in the request
header. It is used to construct the path and search fields of the Request.
It is provided because reconstructing this string from the path and
search fields may yield a different value due to different usage of
percent encoding.
- search(ListOfNameValue)
- Search-specification of URI. This is the part after the
?
The URL specification does not demand the query part to be
of the form name=value. If the field is syntactically incorrect,
ListOfNameValue is bound the the empty list ([]).
- http_version(Major-Minor)
- If the first line contains the
HTTP/Major.Minor
version indicator this element indicate the HTTP version of the peer.
Otherwise this field is not present.
- cookie(ListOfNameValue)
- If the header contains a
Cookie line, the value of the
cookie is broken down in Name=Value pairs, where
the
Name is the lowercase version of the cookie name as used for
the HTTP fields.
- set_cookie(set_cookie(Name, Value, Options))
- If the header contains a
SetCookie line, the cookie field
is broken down into the Name of the cookie, the Value
and a list of Name=Value pairs for additional
options such as expire, path, domain
or secure.
If the first line of the request is tagged with
HTTP/Major.Minor, http_read_request/2
reads all input upto the first blank line. This header consists of
Name:Value fields. Each such field appears as a
term
Name(Value) in the Request, where Name
is canonicalised for use with Prolog. Canonisation implies that the
Name is converted to lower case and all occurrences of the
-_. The value
for the
Content-length fields is translated into an integer.
Here is an example:
?- http_read_request(user_input, X).
|: GET /mydb?class=person HTTP/1.0
|: Host: gollem
|:
X = [ input(user),
method(get),
search([ class = person
]),
path('/mydb'),
http_version(1-0),
host(gollem)
].
Where the HTTP GET operation is intended to get a
document, using a path and possibly some additional search
information, the POST operation is intended to hand
potentially large amounts of data to the server for processing.
The Request parameter above contains the term method(post).
The data posted is left on the input stream that is available through
the term input(Stream) from the Request header.
This data can be read using http_read_data/3
from the HTTP client library. Here is a demo implementation simply
returning the parsed posted data as plain text (assuming pp/1
pretty-prints the data).
reply(Request) :-
member(method(post), Request), !,
http_read_data(Request, Data, []),
format('Content-type: text/plain~n~n', []),
pp(Data).
If the POST is initiated from a browser, content-type is generally
either application/x-www-form-urlencoded or
multipart/form-data.
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