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.so man.macros

.TH "Http" n 8.0 Tcl "Tcl Built-In Commands"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

Http \- Client-side implementation of the HTTP/1.0 protocol.

.SH SYNOPSIS

\fBpackage require http ?2.0?\fP

.sp

\fB::http::config \fI?options?\fR

.sp

\fB::http::geturl \fIurl ?options?\fR

.sp

\fB::http::formatQuery \fIlist\fR

.sp

\fB::http::reset \fItoken\fR

.sp

\fB::http::wait \fItoken\fR

.sp

\fB::http::status \fItoken\fR

.sp

\fB::http::size \fItoken\fR

.sp

\fB::http::code \fItoken\fR

.sp

\fB::http::data \fItoken\fR

.BE

.SH DESCRIPTION

.PP

The \fBhttp\fR package provides the client side of the HTTP/1.0

protocol.  The package implements the GET, POST, and HEAD operations

of HTTP/1.0.  It allows configuration of a proxy host to get through

firewalls.  The package is compatible with the \fBSafesock\fR security

policy, so it can be used by untrusted applets to do URL fetching from

a restricted set of hosts.

.PP

The \fB::http::geturl\fR procedure does a HTTP transaction.

Its \fIoptions \fR determine whether a GET, POST, or HEAD transaction

is performed.

The return value of \fB::http::geturl\fR is a token for the transaction.

The value is also the name of an array in the ::http namespace

 that contains state

information about the transaction.  The elements of this array are

described in the STATE ARRAY section.

.PP

If the \fB-command\fP option is specified, then

the HTTP operation is done in the background.

\fB::http::geturl\fR returns immediately after generating the

HTTP request and the callback is invoked

when the transaction completes.  For this to work, the Tcl event loop

must be active.  In Tk applications this is always true.  For pure-Tcl

applications, the caller can use \fB::http::wait\fR after calling

\fB::http::geturl\fR to start the event loop.

.SH COMMANDS

.TP

\fB::http::config\fP ?\fIoptions\fR?

The \fB::http::config\fR command is used to set and query the name of the

proxy server and port, and the User-Agent name used in the HTTP

requests.  If no options are specified, then the current configuration

is returned.  If a single argument is specified, then it should be one

of the flags described below.  In this case the current value of

that setting is returned.  Otherwise, the options should be a set of

flags and values that define the configuration:

.RS

.TP

\fB\-accept\fP \fImimetypes\fP

The Accept header of the request.  The default is */*, which means that

all types of documents are accepted.  Otherwise you can supply a

comma separated list of mime type patterns that you are

willing to receive.  For example, "image/gif, image/jpeg, text/*".

.TP

\fB\-proxyhost\fP \fIhostname\fP

The name of the proxy host, if any.  If this value is the

empty string, the URL host is contacted directly.

.TP

\fB\-proxyport\fP \fInumber\fP

The proxy port number.

.TP

\fB\-proxyfilter\fP \fIcommand\fP

The command is a callback that is made during

\fB::http::geturl\fR

to determine if a proxy is required for a given host.  One argument, a

host name, is added to \fIcommand\fR when it is invoked.  If a proxy

is required, the callback should return a two element list containing

the proxy server and proxy port.  Otherwise the filter should return

an empty list.  The default filter returns the values of the

\fB\-proxyhost\fR and \fB\-proxyport\fR settings if they are

non-empty.

.TP

\fB\-useragent\fP \fIstring\fP

The value of the User-Agent header in the HTTP request.  The default

is \fB"Tcl http client package 2.0."\fR

.RE

.TP

\fB::http::geturl\fP \fIurl\fP ?\fIoptions\fP?

The \fB::http::geturl \fR command is the main procedure in the package.

The \fB\-query\fR option causes a POST operation and

the \fB\-validate\fR option causes a HEAD operation;

otherwise, a GET operation is performed.  The \fB::http::geturl\fR command

returns a \fItoken\fR value that can be used to get

information about the transaction.  See the STATE ARRAY section for

details.  The \fB::http::geturl\fR command blocks until the operation

completes, unless the \fB\-command\fR option specifies a callback

that is invoked when the HTTP transaction completes.

\fB::http::geturl\fR takes several options:

.RS

.TP

\fB\-blocksize\fP \fIsize\fP

The blocksize used when reading the URL.

At most

\fIsize\fR

bytes are read at once.  After each block, a call to the

\fB\-progress\fR

callback is made.

.TP

\fB\-channel\fP \fIname\fP

Copy the URL contents to channel \fIname\fR instead of saving it in

\fBstate(body)\fR.

.TP

\fB\-command\fP \fIcallback\fP

Invoke \fIcallback\fP after the HTTP transaction completes.

This option causes \fB::http::geturl\fP to return immediately.

The \fIcallback\fP gets an additional argument that is the \fItoken\fR returned

from \fB::http::geturl\fR. This token is the name of an array that is

described in the STATE ARRAY section.  Here is a template for the

callback:

.RS

.CS

proc httpCallback {token} {

    upvar #0 $token state

    # Access state as a Tcl array

}

.CE

.RE

.TP

\fB\-handler\fP \fIcallback\fP

Invoke \fIcallback\fP whenever HTTP data is available; if present, nothing

else will be done with the HTTP data.  This procedure gets two additional

arguments: the socket for the HTTP data and the \fItoken\fR returned from

\fB::http::geturl\fR.  The token is the name of a global array that is described

in the STATE ARRAY section.  The procedure is expected to return the number

of bytes read from the socket.  Here is a template for the callback:

.RS

.CS

proc httpHandlerCallback {socket token} {

    upvar #0 $token state

    # Access socket, and state as a Tcl array

    ...

    (example: set data [read $socket 1000];set nbytes [string length $data])

    ...

    return nbytes

}

.CE

.RE

.TP

\fB\-headers\fP \fIkeyvaluelist\fP

This option is used to add extra headers to the HTTP request.  The

\fIkeyvaluelist\fR argument must be a list with an even number of

elements that alternate between keys and values.  The keys become

header field names.  Newlines are stripped from the values so the

header cannot be corrupted.  For example, if \fIkeyvaluelist\fR is

\fBPragma no-cache\fR then the following header is included in the

HTTP request:

.CS

Pragma: no-cache

.CE

.TP

\fB\-progress\fP \fIcallback\fP

The \fIcallback\fR is made after each transfer of data from the URL.

The callback gets three additional arguments: the \fItoken\fR from

\fB::http::geturl\fR, the expected total size of the contents from the

\fBContent-Length\fR meta-data, and the current number of bytes

transferred so far.  The expected total size may be unknown, in which

case zero is passed to the callback.  Here is a template for the

progress callback:

.RS

.CS

proc httpProgress {token total current} {

    upvar #0 $token state

}

.CE

.RE

.TP

\fB\-query\fP \fIquery\fP

This flag causes \fB::http::geturl\fR to do a POST request that passes the

\fIquery\fR to the server. The \fIquery\fR must be a x-url-encoding

formatted query.  The \fB::http::formatQuery\fR procedure can be used to

do the formatting.

.TP

\fB\-timeout\fP \fImilliseconds\fP

If \fImilliseconds\fR is non-zero, then \fB::http::geturl\fR sets up a timeout

to occur after the specified number of milliseconds.

A timeout results in a call to \fB::http::reset\fP and to

the \fB-command\fP callback, if specified.

The return value of \fB::http::status\fP is \fBtimeout\fP

after a timeout has occurred.

.TP

\fB\-validate\fP \fIboolean\fP

If \fIboolean\fR is non-zero, then \fB::http::geturl\fR does an HTTP HEAD

request.  This request returns meta information about the URL, but the

contents are not returned.  The meta information is available in the

\fBstate(meta) \fR variable after the transaction.  See the STATE

ARRAY section for details.

.RE

.TP

\fB::http::formatQuery\fP \fIkey value\fP ?\fIkey value\fP ...?

This procedure does x-url-encoding of query data.  It takes an even

number of arguments that are the keys and values of the query.  It

encodes the keys and values, and generates one string that has the

proper & and = separators.  The result is suitable for the

\fB\-query\fR value passed to \fB::http::geturl\fR.

.TP

\fB::http::reset\fP \fItoken\fP ?\fIwhy\fP?

This command resets the HTTP transaction identified by \fItoken\fR, if

any.  This sets the \fBstate(status)\fP value to \fIwhy\fP, which defaults to \fBreset\fR, and then calls the registered \fB\-command\fR callback.

.TP

\fB::http::wait\fP \fItoken\fP

This is a convenience procedure that blocks and waits for the

transaction to complete.  This only works in trusted code because it

uses \fBvwait\fR.

.TP

\fB::http::data\fP \fItoken\fP

This is a convenience procedure that returns the \fBbody\fP element

(i.e., the URL data) of the state array.

.TP

\fB::http::status\fP \fItoken\fP

This is a convenience procedure that returns the \fBstatus\fP element of

the state array.

.TP

\fB::http::code\fP \fItoken\fP

This is a convenience procedure that returns the \fBhttp\fP element of the

state array.

.TP

\fB::http::size\fP \fItoken\fP

This is a convenience procedure that returns the \fBcurrentsize\fP

element of the state array.

.SH "STATE ARRAY"

The \fB::http::geturl\fR procedure returns a \fItoken\fR that can be used to

get to the state of the HTTP transaction in the form of a Tcl array.

Use this construct to create an easy-to-use array variable:

.CS

upvar #0 $token state

.CE

The following elements of the array are supported:

.RS

.TP

\fBbody\fR

The contents of the URL.  This will be empty if the \fB\-channel\fR

option has been specified.  This value is returned by the \fB::http::data\fP command.

.TP

\fBcurrentsize\fR

The current number of bytes fetched from the URL.

This value is returned by the \fB::http::size\fP command.

.TP

\fBerror\fR

If defined, this is the error string seen when the HTTP transaction

was aborted.

.TP

\fBhttp\fR

The HTTP status reply from the server.  This value

is returned by the \fB::http::code\fP command.  The format of this value is:

.RS

.CS

\fIcode string\fP

.CE

The \fIcode\fR is a three-digit number defined in the HTTP standard.

A code of 200 is OK.  Codes beginning with 4 or 5 indicate errors.

Codes beginning with 3 are redirection errors.  In this case the

\fBLocation\fR meta-data specifies a new URL that contains the

requested information.

.RE

.TP

\fBmeta\fR

The HTTP protocol returns meta-data that describes the URL contents.

The \fBmeta\fR element of the state array is a list of the keys and

values of the meta-data.  This is in a format useful for initializing

an array that just contains the meta-data:

.RS

.CS

array set meta $state(meta)

.CE

Some of the meta-data keys are listed below, but the HTTP standard defines

more, and servers are free to add their own.

.TP

\fBContent-Type\fR

The type of the URL contents.  Examples include \fBtext/html\fR,

\fBimage/gif,\fR \fBapplication/postscript\fR and

\fBapplication/x-tcl\fR.

.TP

\fBContent-Length\fR

The advertised size of the contents.  The actual size obtained by

\fB::http::geturl\fR is available as \fBstate(size)\fR.

.TP

\fBLocation\fR

An alternate URL that contains the requested data.

.RE

.TP

\fBstatus\fR

Either \fBok\fR, for successful completion, \fBreset\fR for

user-reset, or \fBerror\fR for an error condition.  During the

transaction this value is the empty string.

.TP

\fBtotalsize\fR

A copy of the \fBContent-Length\fR meta-data value.

.TP

\fBtype\fR

A copy of the \fBContent-Type\fR meta-data value.

.TP

\fBurl\fR

The requested URL.

.RE

.SH EXAMPLE

.DS

# Copy a URL to a file and print meta-data

proc ::http::copy { url file {chunk 4096} } {

    set out [open $file w]

    set token [geturl $url -channel $out -progress ::http::Progress \\

        -blocksize $chunk]

    close $out

    # This ends the line started by http::Progress

    puts stderr ""

    upvar #0 $token state

    set max 0

    foreach {name value} $state(meta) {

        if {[string length $name] > $max} {

            set max [string length $name]

        }

        if {[regexp -nocase ^location$ $name]} {

            # Handle URL redirects

            puts stderr "Location:$value"

            return [copy [string trim $value] $file $chunk]

        }

    }

    incr max

    foreach {name value} $state(meta) {

        puts [format "%-*s %s" $max $name: $value]

    }

    return $token

}

proc ::http::Progress {args} {

    puts -nonewline stderr . ; flush stderr

}

.DE

.SH "SEE ALSO"

safe(n), socket(n), safesock(n)

.SH KEYWORDS

security policy, socket