Http(n) Tcl (8.0) 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 determine whether a GET, POST, or HEAD transaction
is performed. The return 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 completes. For
this to work, the Tcl event loop must be active. In Tk
applications this is always true. For pure-Tcl
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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 example, "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 command 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 package. The -query option causes a POST operation
and the -validate option causes a HEAD operation;
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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 token 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 procedure 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
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HTTP request. 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 corrupted.
For example, if keyvaluelist is Pragma no-cache
then the following header is included in the HTTP
request:
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 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:
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 milliseconds. 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) variable 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
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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 because 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 element 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 returned 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.
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Http(n) Tcl (8.0) Http(n)http The HTTP status reply from the server. This value
is returned 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 redirection errors. In this
case the Location meta-data specifies a new URL
that contains the requested information.
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 contains 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-reset, or error for an error condition.
During the transaction 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} } {
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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
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