Http(n)

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

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 com-
patible 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 transac-
tion 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 opera-
tion 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 applica-
tions, 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 configura-
tion is returned. If a single argument is speci-
fied, then it should be one of the flags described
below. In this case the current value of that set-
ting is returned. Otherwise, the options should be
a set of flags and values that define the configu-
ration:
-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 dur-
ing ::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 call-
back should return a two element list con-
taining 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; 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 sev-
eral 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 avail-
able; 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 call-
back:
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 request. The keyvaluelist argument
must be a list with an even number of ele-
ments that alternate between keys and val-
ues. 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 trans-
ferred 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 time-
out 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 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.
http The HTTP status reply from the server. This
value is returned by the ::http::code com-
mand. 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 ele-
ment 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. Exam-
ples include text/html, image/gif,
application/postscript and applica-
tion/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 condi-
tion. 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} } {
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
}