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


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

       package require http ?2.2?

       ::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

       ::http::cleanup token

       ::http::register proto port command

       ::http::unregister proto

       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. This package can be extened to support additional HTTP transport
       protocols, such as HTTPS, by providing a custom socket command, via

       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 applications, the
       caller can use ::http::wait after calling ::http::geturl to start the
       event loop.

       ::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

              -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 2.2."

       ::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
              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 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
                            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.

              -type mime-type
                     Use mime-type as the Content-Type value, instead of the
                     default value (application/x-www-form-urlencoded) during
                     a POST operation.

              -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.

       ::http::cleanup token
              This procedure cleans up the state associated with the
              connection identified by token.  After this call, the procedures
              like ::http::data cannot be used to get information about the

       ::http::register proto port command
              This procedure allows one to provide custom HTTP transport types
              such as HTTPS, by registering a prefix, the default port, and
              the command to execute to create the Tcl channel. E.g.:
                     package require http
                     package require tls

                     http::register https 443 ::tls::socket

                     set token [http::geturl]

       ::http::unregister proto
              This procedure unregisters a protocol handler that was
              previously registered via http::register.

       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
       Once the data associated with the url is no longer needed, the state
       array should be unset to free up storage.  The http::cleanup procedure
       is provided for that purpose.  The following elements of the array are

              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.

                     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 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

              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

                            The type of the URL contents.  Examples include
                            text/html, image/gif, application/postscript and

                            The advertised size of the contents.  The actual
                            size obtained by ::http::geturl is available as

                            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.

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

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

              url    The requested URL.

       # 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 }

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

       security policy, socket

Tcl                                   8.3                              Http(n)