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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  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 call‐
       er can use ::http::wait after calling ::http::geturl to start the event

       ::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 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 2.2."

       ::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	 and  ERRORS   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 (if that option is specified).

	      -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 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
		     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.	  New‐
		     lines  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
		     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
			    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.

	      -queryblocksize size
		     The blocksize used when posting query data	 to  the  URL.
		     At	 most  size  bytes  are	 written  at once.  After each
		     block, a call to the -queryprogress callback is made  (if
		     that option is specified).

	      -querychannel channelID
		     This flag causes ::http::geturl to do a POST request that
		     passes the data contained in channelID to the server. The
		     data contained in channelID must be a x-url-encoding for‐
		     matted query unless the -type option below is used.  If a
		     Content-Length  header  is not specified via the -headers
		     options, ::http::geturl attempts to determine the size of
		     the  post	data in order to create that header.  If it is
		     unable to determine the size, it returns an error.

	      -queryprogress callback
		     The callback is made after each transfer of data  to  the
		     URL  (i.e.	 POST)	and  acts  exactly  like the -progress
		     option (the callback format is the same).

	      -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

	      -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)	 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
	      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  connec‐
	      tion  identified by token.  After this call, the procedures like
	      ::http::data cannot be used to get information about the	opera‐

       ::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 previ‐
	      ously registered via http::register.

       The http::geturl procedure will raise errors in	the  following	cases:
       invalid	command	 line options, an invalid URL, or a URL on a non-exis‐
       tent host, These errors mean that it  cannot  even  start  the  network
       transaction.  It will also raise an error if it gets an I/O error while
       writing out the HTTP request header.

       The http::wait procedure will raise errors if an I/O error occurs while
       reading	the  HTTP  reply headers or data.  If the -command flag is not
       passed to http::geturl, then it	will  call  http::wait	and  so	 these
       errors	will  occur  in	 http::geturl.	 If  you  get  an  error  from
       http::wait, you must still  call	 http::cleanup	to  delete  the	 state

       There  are other possible results of the HTTP transaction determined by
       examining the status from http::status.	These are described below.

       ok     If the HTTP transaction completes entirely, then status will  be
	      ok.  However, you should still check the http::code value to get
	      the HTTP status.	The http::ncode procedure  provides  just  the
	      numeric  error (e.g., 200, 404 or 500) while the http::code pro‐
	      cedure returns a value like "HTTP 404 File not found".

       eof    If the server closes the socket without replying, then no	 error
	      is rasied, but the status of the transaction will be eof.

       error  In  this case http::wait should have raised an error.  The error
	      message will also be stored in the error status array element.

       Another error possibility is that http::geturl is unable to  write  all
       the post query data to the server before the server responds and closes
       the socket.  The error message is saved in the posterror	 status	 array
       element	and  then   http::geturl attempts to complete the transaction.
       If it can read the server's response it will end up with an ok  status,
       otherwise it will have an eof status.

       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:
			    HTTP/1.0 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‐

	      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

			    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.

		     The  error,  if any, that occurred while writing the post
		     query data to the server.

	      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)

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