guile/doc/ref/web.texi

@c -*-texinfo-*-
@c This is part of the GNU Guile Reference Manual.
@c Copyright (C) 2010 Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.

@node Web
@section @acronym{HTTP}, the Web, and All That
@cindex Web
@cindex WWW
@cindex HTTP

When Guile started back in the mid-nineties, the GNU system was still
focused on producing a good POSIX implementation.  This is why Guile's
POSIX support is good, and has been so for a while.

But times change, and in a way these days the web is the new POSIX: a
standard and a motley set of implementations on which much computing is
done.  So today's Guile also supports the web at the programming
language level, by defining common data types and operations for the
technologies underpinning the web: URIs, HTTP, and XML.

It is particularly important to define native web data types.  Though
the web is text in motion, programming the web in text is like
programming with @code{goto}: muddy, and error-prone.  Most current
security problems on the web are due to treating the web as text instead
of as instances of the proper data types.

In addition, common web data types help programmers to share code.

Well.  That's all very nice and opinionated and such, but how do I use
the thing?  Read on!

@menu
* URIs::                        Universal Resource Identifiers.
* HTTP::                        The Hyper-Text Transfer Protocol.
* Requests::                    HTTP requests.
* Responses::                   HTTP responses.
* Web Handlers::                A simple web application interface.
* Web Server::                  Serving HTTP to the internet.
@end menu

@node URIs
@subsection Universal Resource Identifiers

Guile provides a standard data type for Universal Resource Identifiers
(URIs), as defined in RFC 3986.

The generic URI syntax is as follows:

@example
URI := scheme ":" ["//" [userinfo "@@"] host [":" port]] path \
       [ "?" query ] [ "#" fragment ]
@end example

So, all URIs have a scheme and a path. Some URIs have a host, and some
of those have ports and userinfo. Any URI might have a query part or a
fragment.

Userinfo is something of an abstraction, as some legacy URI schemes
allowed userinfo of the form @code{@var{username}:@var{passwd}}.
Passwords don't belong in URIs, so the RFC does not want to condone
this, but neither can it say that what is before the @code{@@} sign is
just a username, so the RFC punts on the issue and calls it
@dfn{userinfo}.

Also, strictly speaking, a URI with a fragment is a @dfn{URI
reference}.  A fragment is typically not serialized when sending a URI
over the wire; that is, it is not part of the identifier of a resource.
It only identifies a part of a given resource.  But it's useful to have
a field for it in the URI record itself, so we hope you will forgive the
inconsistency.

@example
(use-modules (web uri))
@end example

The following procedures can be found in the @code{(web uri)}
module. Load it into your Guile, using a form like the above, to have
access to them.

@defun build-uri scheme [#:userinfo] [#:host] [#:port] [#:path] [#:query] [#:fragment] [#:validate?]
Construct a URI object. If @var{validate?} is true, also run some
consistency checks to make sure that the constructed URI is valid.
@end defun

@defun uri? x
@defunx uri-scheme uri
@defunx uri-userinfo uri
@defunx uri-host uri
@defunx uri-port uri
@defunx uri-path uri
@defunx uri-query uri
@defunx uri-fragment uri
A predicate and field accessors for the URI record type.
@end defun

@defun declare-default-port! scheme port
Declare a default port for the given URI scheme.

Default ports are for printing URI objects: a default port is not
printed.
@end defun

@defun parse-uri string
Parse @var{string} into a URI object. Returns @code{#f} if the string
could not be parsed.
@end defun

@defun unparse-uri uri
Serialize @var{uri} to a string.
@end defun

@defun uri-decode str [#:charset]
Percent-decode the given @var{str}, according to @var{charset}.

Note that this function should not generally be applied to a full URI
string. For paths, use split-and-decode-uri-path instead. For query
strings, split the query on @code{&} and @code{=} boundaries, and decode
the components separately.

Note that percent-encoded strings encode @emph{bytes}, not characters.
There is no guarantee that a given byte sequence is a valid string
encoding. Therefore this routine may signal an error if the decoded
bytes are not valid for the given encoding. Pass @code{#f} for
@var{charset} if you want decoded bytes as a bytevector directly.
@end defun

@defun uri-encode str [#:charset] [#:unescaped-chars]
Percent-encode any character not in @var{unescaped-chars}.

Percent-encoding first writes out the given character to a bytevector
within the given @var{charset}, then encodes each byte as
@code{%@var{HH}}, where @var{HH} is the hexadecimal representation of
the byte.
@end defun

@defun split-and-decode-uri-path path
Split @var{path} into its components, and decode each component,
removing empty components.

For example, @code{"/foo/bar/"} decodes to the two-element list,
@code{("foo" "bar")}.
@end defun

@defun encode-and-join-uri-path parts
URI-encode each element of @var{parts}, which should be a list of
strings, and join the parts together with @code{/} as a delimiter.
@end defun

@node HTTP
@subsection The Hyper-Text Transfer Protocol

The initial motivation for including web functionality in Guile, rather
than rely on an external package, was to establish a standard base on
which people can share code.  To that end, we continue the focus on data
types by providing a number of low-level parsers and unparsers for
elements of the HTTP protocol.

If you are want to skip the low-level details for now and move on to web
pages, @pxref{Web Server}.  Otherwise, load the HTTP module, and read
on.

@example
(use-modules (web http))
@end example

The focus of the @code{(web http)} module is to parse and unparse
standard HTTP headers, representing them to Guile as native data
structures.  For example, a @code{Date:} header will be represented as a
SRFI-19 date record (@pxref{SRFI-19}), rather than as a string.

Guile tries to follow RFCs fairly strictly---the road to perdition being
paved with compatibility hacks---though some allowances are made for
not-too-divergent texts.

The first bit is to define a registry of parsers, validators, and
unparsers, keyed by header name.  That is the function of the
@code{<header-decl>} object.

@defun make-header-decl sym name multiple? parser validator writer
@defunx header-decl? x
@defunx header-decl-sym decl
@defunx header-decl-name decl
@defunx header-decl-multiple? decl
@defunx header-decl-parser decl
@defunx header-decl-validator decl
@defunx header-decl-writer decl.
A constructor, predicate, and field accessors for the
@code{<header-decl>} type. The fields are as follows:

@table @code
@item sym
The symbol name for this header field, always in lower-case.  For
example, @code{"Content-Length"} has a symbolic name of
@code{content-length}.
@item name
The string name of the header, in its preferred capitalization.
@item multiple?
@code{#t} iff this header may appear multiple times in a message.
@item parser
A procedure which takes a string and returns a parsed value.
@item validator
A predicate, returning @code{#t} iff the value is valid for this header.
@item writer
A writer, which writes a value to the port given in the second argument.
@end table
@end defun

@defun declare-header! sym name [#:multiple?] [#:parser] [#:validator] [#:writer]
Make a header declaration, as above, and register it by symbol and by
name.
@end defun

@defun lookup-header-decl name
Return the @var{header-decl} object registered for the given @var{name}.

@var{name} may be a symbol or a string. Strings are mapped to headers in
a case-insensitive fashion.
@end defun

@defun valid-header? sym val
Returns a true value iff @var{val} is a valid Scheme value for the
header with name @var{sym}.
@end defun

Now that we have a generic interface for reading and writing headers, we
do just that.

@defun read-header port
Reads one HTTP header from @var{port}. Returns two values: the header
name and the parsed Scheme value. May raise an exception if the header
was known but the value was invalid.

Returns @var{#f} for both values if the end of the message body was
reached (i.e., a blank line).
@end defun

@defun parse-header name val
Parse @var{val}, a string, with the parser for the header named
@var{name}.

Returns two values, the header name and parsed value. If a parser was
found, the header name will be returned as a symbol. If a parser was not
found, both the header name and the value are returned as strings.
@end defun

@defun write-header name val port
Writes the given header name and value to @var{port}. If @var{name} is a
symbol, looks up a declared header and uses that writer. Otherwise the
value is written using @var{display}.
@end defun

@defun read-headers port
Read an HTTP message from @var{port}, returning the headers as an
ordered alist.
@end defun

@defun write-headers headers port
Write the given header alist to @var{port}. Doesn't write the final
\r\n, as the user might want to add another header.
@end defun

The @code{(web http)} module also has some utility procedures to read
and write request and response lines.

@defun parse-http-method str [start] [end]
Parse an HTTP method from @var{str}. The result is an upper-case symbol,
like @code{GET}.
@end defun

@defun parse-http-version str [start] [end]
Parse an HTTP version from @var{str}, returning it as a major-minor
pair. For example, @code{HTTP/1.1} parses as the pair of integers,
@code{(1 . 1)}.
@end defun

@defun parse-request-uri str [start] [end]
Parse a URI from an HTTP request line. Note that URIs in requests do not
have to have a scheme or host name. The result is a URI object.
@end defun

@defun read-request-line port
Read the first line of an HTTP request from @var{port}, returning three
values: the method, the URI, and the version.
@end defun

@defun write-request-line method uri version port
Write the first line of an HTTP request to @var{port}.
@end defun

@defun read-response-line port
Read the first line of an HTTP response from @var{port}, returning three
values: the HTTP version, the response code, and the "reason phrase".
@end defun

@defun write-response-line version code reason-phrase port
Write the first line of an HTTP response to @var{port}.
@end defun


@node Requests
@subsection HTTP Requests

@example
(use-modules (web request))
@end example

@defun request? 
@end defun

@defun request-method 
@end defun

@defun request-uri 
@end defun

@defun request-version 
@end defun

@defun request-headers 
@end defun

@defun request-meta 
@end defun

@defun request-port 
@end defun

@defun read-request port [meta]
Read an HTTP request from @var{port}, optionally attaching the given
metadata, @var{meta}.

As a side effect, sets the encoding on @var{port} to ISO-8859-1
(latin-1), so that reading one character reads one byte. See the
discussion of character sets in "HTTP Requests" in the manual, for more
information.
@end defun

@defun build-request [#:method] [#:uri] [#:version] [#:headers] [#:port] [#:meta] [#:validate-headers?]
Construct an HTTP request object. If @var{validate-headers?} is true,
the headers are each run through their respective validators.
@end defun

@defun write-request r port
Write the given HTTP request to @var{port}.

Returns a new request, whose @code{request-port} will continue writing
on @var{port}, perhaps using some transfer encoding.
@end defun

@defun read-request-body/latin-1 r
Reads the request body from @var{r}, as a string.

Assumes that the request port has ISO-8859-1 encoding, so that the
number of characters to read is the same as the
@code{request-content-length}. Returns @code{#f} if there was no request
body.
@end defun

@defun write-request-body/latin-1 r body
Write @var{body}, a string encodable in ISO-8859-1, to the port
corresponding to the HTTP request @var{r}.
@end defun

@defun read-request-body/bytevector r
Reads the request body from @var{r}, as a bytevector. Returns @code{#f}
if there was no request body.
@end defun

@defun write-request-body/bytevector r bv
Write @var{body}, a bytevector, to the port corresponding to the HTTP
request @var{r}.
@end defun

@defun request-accept request [default='()]
@defunx request-accept-charset request [default='()]
@defunx request-accept-encoding request [default='()]
@defunx request-accept-language request [default='()]
@defunx request-allow request [default='()]
@defunx request-authorization request [default=#f]
@defunx request-cache-control request [default='()]
@defunx request-connection request [default='()]
@defunx request-content-encoding request [default='()]
@defunx request-content-language request [default='()]
@defunx request-content-length request [default=#f]
@defunx request-content-location request [default=#f]
@defunx request-content-md5 request [default=#f]
@defunx request-content-range request [default=#f]
@defunx request-content-type request [default=#f]
@defunx request-date request [default=#f]
@defunx request-expect request [default='()]
@defunx request-expires request [default=#f]
@defunx request-from request [default=#f]
@defunx request-host request [default=#f]
@defunx request-if-match request [default=#f]
@defunx request-if-modified-since request [default=#f]
@defunx request-if-none-match request [default=#f]
@defunx request-if-range request [default=#f]
@defunx request-if-unmodified-since request [default=#f]
@defunx request-last-modified request [default=#f]
@defunx request-max-forwards request [default=#f]
@defunx request-pragma request [default='()]
@defunx request-proxy-authorization request [default=#f]
@defunx request-range request [default=#f]
@defunx request-referer request [default=#f]
@defunx request-te request [default=#f]
@defunx request-trailer request [default='()]
@defunx request-transfer-encoding request [default='()]
@defunx request-upgrade request [default='()]
@defunx request-user-agent request [default=#f]
@defunx request-via request [default='()]
@defunx request-warning request [default='()]
@end defun

@defun request-absolute-uri r [default-host] [default-port]
@end defun



@node Responses
@subsection HTTP Responses

@example
(use-modules (web response))
@end example


@defun response? 
@end defun

@defun response-version 
@end defun

@defun response-code 
@end defun

@defun response-reason-phrase response
Return the reason phrase given in @var{response}, or the standard reason
phrase for the response's code.
@end defun

@defun response-headers 
@end defun

@defun response-port 
@end defun

@defun read-response port
Read an HTTP response from @var{port}, optionally attaching the given
metadata, @var{meta}.

As a side effect, sets the encoding on @var{port} to ISO-8859-1
(latin-1), so that reading one character reads one byte. See the
discussion of character sets in "HTTP Responses" in the manual, for more
information.
@end defun

@defun build-response [#:version] [#:code] [#:reason-phrase] [#:headers] [#:port]
Construct an HTTP response object. If @var{validate-headers?} is true,
the headers are each run through their respective validators.
@end defun

@defun extend-response r k v . additional
Extend an HTTP response by setting additional HTTP headers @var{k},
@var{v}. Returns a new HTTP response.
@end defun

@defun adapt-response-version response version
Adapt the given response to a different HTTP version. Returns a new HTTP
response.

The idea is that many applications might just build a response for the
default HTTP version, and this method could handle a number of
programmatic transformations to respond to older HTTP versions (0.9 and
1.0). But currently this function is a bit heavy-handed, just updating
the version field.
@end defun

@defun write-response r port
Write the given HTTP response to @var{port}.

Returns a new response, whose @code{response-port} will continue writing
on @var{port}, perhaps using some transfer encoding.
@end defun

@defun read-response-body/latin-1 r
Reads the response body from @var{r}, as a string.

Assumes that the response port has ISO-8859-1 encoding, so that the
number of characters to read is the same as the
@code{response-content-length}. Returns @code{#f} if there was no
response body.
@end defun

@defun write-response-body/latin-1 r body
Write @var{body}, a string encodable in ISO-8859-1, to the port
corresponding to the HTTP response @var{r}.
@end defun

@defun read-response-body/bytevector r
Reads the response body from @var{r}, as a bytevector. Returns @code{#f}
if there was no response body.
@end defun

@defun write-response-body/bytevector r bv
Write @var{body}, a bytevector, to the port corresponding to the HTTP
response @var{r}.
@end defun

@defun response-accept-ranges response [default=#f]
@defunx response-age response [default='()]
@defunx response-allow response [default='()]
@defunx response-cache-control response [default='()]
@defunx response-connection response [default='()]
@defunx response-content-encoding response [default='()]
@defunx response-content-language response [default='()]
@defunx response-content-length response [default=#f]
@defunx response-content-location response [default=#f]
@defunx response-content-md5 response [default=#f]
@defunx response-content-range response [default=#f]
@defunx response-content-type response [default=#f]
@defunx response-date response [default=#f]
@defunx response-etag response [default=#f]
@defunx response-expires response [default=#f]
@defunx response-last-modified response [default=#f]
@defunx response-location response [default=#f]
@defunx response-pragma response [default='()]
@defunx response-proxy-authenticate response [default=#f]
@defunx response-retry-after response [default=#f]
@defunx response-server response [default=#f]
@defunx response-trailer response [default='()]
@defunx response-transfer-encoding response [default='()]
@defunx response-upgrade response [default='()]
@defunx response-vary response [default='()]
@defunx response-via response [default='()]
@defunx response-warning response [default='()]
@defunx response-www-authenticate response [default=#f]
@end defun


@node Web Handlers
@subsection Web Handlers

from request to response

@node Web Server
@subsection Web Server

@code{(web server)} is a generic web server interface, along with a main
loop implementation for web servers controlled by Guile.

The lowest layer is the <server-impl> object, which defines a set of
hooks to open a server, read a request from a client, write a
response to a client, and close a server.  These hooks -- open,
read, write, and close, respectively -- are bound together in a
<server-impl> object.  Procedures in this module take a
<server-impl> object, if needed.

A <server-impl> may also be looked up by name.  If you pass the
@code{http} symbol to @code{run-server}, Guile looks for a variable named
@code{http} in the @code{(web server http)} module, which should be bound to a
<server-impl> object.  Such a binding is made by instantiation of
the @code{define-server-impl} syntax.  In this way the run-server loop can
automatically load other backends if available.

The life cycle of a server goes as follows:

@enumerate
@item
The @code{open} hook is called, to open the server. @code{open} takes 0 or
more arguments, depending on the backend, and returns an opaque
server socket object, or signals an error.

@item
The @code{read} hook is called, to read a request from a new client.
The @code{read} hook takes one arguments, the server socket.  It
should return three values: an opaque client socket, the
request, and the request body. The request should be a
@code{<request>} object, from @code{(web request)}.  The body should be a
string or a bytevector, or @code{#f} if there is no body.

If the read failed, the @code{read} hook may return #f for the client
socket, request, and body.

@item
A user-provided handler procedure is called, with the request
and body as its arguments.  The handler should return two
values: the response, as a @code{<response>} record from @code{(web
response)}, and the response body as a string, bytevector, or
@code{#f} if not present.  We also allow the reponse to be simply an
alist of headers, in which case a default response object is
constructed with those headers.

@item
The @code{write} hook is called with three arguments: the client
socket, the response, and the body.  The @code{write} hook returns no
values.

@item
At this point the request handling is complete. For a loop, we
loop back and try to read a new request.

@item
If the user interrupts the loop, the @code{close} hook is called on
the server socket.
@end enumerate

@defun define-server-impl name open read write close
@end defun

@defun lookup-server-impl impl
Look up a server implementation. If @var{impl} is a server
implementation already, it is returned directly. If it is a symbol, the
binding named @var{impl} in the @code{(web server @var{impl})} module is
looked up. Otherwise an error is signaled.

Currently a server implementation is a somewhat opaque type, useful only
for passing to other procedures in this module, like @code{read-client}.
@end defun

@defun open-server impl open-params
Open a server for the given implementation. Returns one value, the new
server object. The implementation's @code{open} procedure is applied to
@var{open-params}, which should be a list.
@end defun

@defun read-client impl server
Read a new client from @var{server}, by applying the implementation's
@code{read} procedure to the server. If successful, returns three
values: an object corresponding to the client, a request object, and the
request body. If any exception occurs, returns @code{#f} for all three
values.
@end defun

@defun handle-request handler request body state
Handle a given request, returning the response and body.

The response and response body are produced by calling the given
@var{handler} with @var{request} and @var{body} as arguments.

The elements of @var{state} are also passed to @var{handler} as
arguments, and may be returned as additional values. The new
@var{state}, collected from the @var{handler}'s return values, is then
returned as a list. The idea is that a server loop receives a handler
from the user, along with whatever state values the user is interested
in, allowing the user's handler to explicitly manage its state.
@end defun

@defun sanitize-response request response body
"Sanitize" the given response and body, making them appropriate for the
given request.

As a convenience to web handler authors, @var{response} may be given as
an alist of headers, in which case it is used to construct a default
response. Ensures that the response version corresponds to the request
version. If @var{body} is a string, encodes the string to a bytevector,
in an encoding appropriate for @var{response}. Adds a
@code{content-length} and @code{content-type} header, as necessary.

If @var{body} is a procedure, it is called with a port as an argument,
and the output collected as a bytevector. In the future we might try to
instead use a compressing, chunk-encoded port, and call this procedure
later, in the write-client procedure. Authors are advised not to rely on
the procedure being called at any particular time.
@end defun

@defun write-client impl server client response body
Write an HTTP response and body to @var{client}. If the server and
client support persistent connections, it is the implementation's
responsibility to keep track of the client thereafter, presumably by
attaching it to the @var{server} argument somehow.
@end defun

@defun close-server impl server
Release resources allocated by a previous invocation of
@code{open-server}.
@end defun

@defun serve-one-client handler impl server state
Read one request from @var{server}, call @var{handler} on the request
and body, and write the response to the client. Returns the new state
produced by the handler procedure.
@end defun

@defun run-server handler [impl] [open-params] . state
Run Guile's built-in web server.

@var{handler} should be a procedure that takes two or more arguments,
the HTTP request and request body, and returns two or more values, the
response and response body.

For example, here is a simple "Hello, World!" server:

@example 
 (define (handler request body)
   (values '((content-type . ("text/plain")))
           "Hello, World!"))
 (run-server handler)
@end example

The response and body will be run through @code{sanitize-response}
before sending back to the client.

Additional arguments to @var{handler} are taken from @var{state}.
Additional return values are accumulated into a new @var{state}, which
will be used for subsequent requests. In this way a handler can
explicitly manage its state.

The default server implementation is @code{http}, which accepts
@var{open-params} like @code{(#:port 8081)}, among others. See "Web
Server" in the manual, for more information.
@end defun

@example
(use-modules (web server))
@end example


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