man `S HTTP`

Http(n) Tcl Built-In Commands Http(n)

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

SYNOPSIS
package require http ?2.0?

::http::config ?options?

::http::geturl url ?options?

::http::formatQuery list

::http::reset token

::http::wait token

::http::status token

::http::size token

::http::code token

::http::data token
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DESCRIPTION
The http 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 Safesock security policy, so it can be
used by untrusted applets to do URL fetching from a restricted set of
hosts.

The ::http::geturl procedure does a HTTP transaction. Its options de-
termine whether a GET, POST, or HEAD transaction is performed. The re-
turn value of ::http::geturl 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.

If the -command option is specified, then the HTTP operation is done in
the background. ::http::geturl returns immediately after generating
the HTTP request and the callback is invoked when the transaction com-
pletes. 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 ::http::wait after calling ::http::geturl to start the
event loop.

COMMANDS
::http::config ?options?
The ::http::config 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:

-accept mimetypes
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 exam-
ple, "image/gif, image/jpeg, text/*".

-proxyhost hostname
The name of the proxy host, if any. If this value is the
empty string, the URL host is contacted directly.

-proxyport number
The proxy port number.

-proxyfilter command
The command is a callback that is made during
::http::geturl to determine if a proxy is required for a
given host. One argument, a host name, is added to com-
mand 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 -proxyhost and -proxyport settings if they
are non-empty.

-useragent string
The value of the User-Agent header in the HTTP request.
The default is "Tcl http client package 2.0."

::http::geturl url ?options?
The ::http::geturl command is the main procedure in the pack-
age. The -query option causes a POST operation and the -vali-
date option causes a HEAD operation; otherwise, a GET operation
is performed. The ::http::geturl command returns a token value
that can be used to get information about the transaction. See
the STATE ARRAY section for details. The ::http::geturl command
blocks until the operation completes, unless the -command option
specifies a callback that is invoked when the HTTP transaction
completes. ::http::geturl takes several options:

-blocksize size
The blocksize used when reading the URL. At most size
bytes are read at once. After each block, a call to the
-progress callback is made.

-channel name
Copy the URL contents to channel name instead of saving
it in state(body).

-command callback
Invoke callback after the HTTP transaction completes.
This option causes ::http::geturl to return immediately.
The callback gets an additional argument that is the to-
ken returned from ::http::geturl. This token is the name
of an array that is described in the STATE ARRAY section.
Here is a template for the callback:
proc httpCallback {token} {
upvar #0 $token state
# Access state as a Tcl array
}

-handler callback
Invoke callback 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 token returned from
::http::geturl. The token is the name of a global array
that is described in the STATE ARRAY section. The proce-
dure is expected to return the number of bytes read from
the socket. Here is a template for the callback:
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
}

-headers keyvaluelist
This option is used to add extra headers to the HTTP re-
quest. The keyvaluelist 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 cor-
rupted. For example, if keyvaluelist is Pragma no-cache
then the following header is included in the HTTP re-
quest:
Pragma: no-cache

-progress callback
The callback is made after each transfer of data from the
URL. The callback gets three additional arguments: the
token from ::http::geturl, the expected total size of the
contents from the Content-Length meta-data, and the cur-
rent 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:
proc httpProgress {token total current} {
upvar #0 $token state
}

-query query
This flag causes ::http::geturl to do a POST request that
passes the query to the server. The query must be a x-
url-encoding formatted query. The ::http::formatQuery
procedure can be used to do the formatting.

-timeout milliseconds
If milliseconds is non-zero, then ::http::geturl sets up
a timeout to occur after the specified number of mil-
liseconds. A timeout results in a call to ::http::reset
and to the -command callback, if specified. The return
value of ::http::status is timeout after a timeout has
occurred.

-validate boolean
If boolean is non-zero, then ::http::geturl 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 state(meta) vari-
able after the transaction. See the STATE ARRAY section
for details.

::http::formatQuery key value ?key value ...?
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 -query value passed to ::http::geturl.

::http::reset token ?why?
This command resets the HTTP transaction identified by token, if
any. This sets the state(status) value to why, which defaults
to reset, and then calls the registered -command callback.

::http::wait token
This is a convenience procedure that blocks and waits for the
transaction to complete. This only works in trusted code be-
cause it uses vwait.

::http::data token
This is a convenience procedure that returns the body element
(i.e., the URL data) of the state array.

::http::status token
This is a convenience procedure that returns the status element
of the state array.

::http::code token
This is a convenience procedure that returns the http element of
the state array.

::http::size token
This is a convenience procedure that returns the currentsize el-
ement of the state array.

STATE ARRAY
The ::http::geturl procedure returns a token 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:
upvar #0 $token state
The following elements of the array are supported:

body The contents of the URL. This will be empty if the
-channel option has been specified. This value is re-
turned by the ::http::data command.

currentsize
The current number of bytes fetched from the URL. This
value is returned by the ::http::size command.

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

http The HTTP status reply from the server. This value is re-
turned by the ::http::code command. The format of this
value is:
code string
The code 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 redi-
rection errors. In this case the Location meta-data
specifies a new URL that contains the requested informa-
tion.

meta The HTTP protocol returns meta-data that describes the
URL contents. The meta 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 con-
tains the meta-data:
array set meta $state(meta)
Some of the meta-data keys are listed below, but the HTTP
standard defines more, and servers are free to add their
own.

Content-Type
The type of the URL contents. Examples include
text/html, image/gif, application/postscript and
application/x-tcl.

Content-Length
The advertised size of the contents. The actual
size obtained by ::http::geturl is available as
state(size).

Location
An alternate URL that contains the requested data.

status Either ok, for successful completion, reset for user-re-
set, or error for an error condition. During the trans-
action this value is the empty string.

totalsize
A copy of the Content-Length meta-data value.

type A copy of the Content-Type meta-data value.

url The requested URL.

EXAMPLE
# 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 }

SEE ALSO
safe(n), socket(n), safesock(n)

KEYWORDS
security policy, socket

Tcl 8.0 Http(n)

man S HTTP

man `S HTTP`