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

______________________________________________________________________________

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

SYNOPSIS
       package require http ?2.3?

       ::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::ncode token

       ::http::data token

       ::http::error token

       ::http::cleanup token

       ::http::register proto port command

       ::http::unregister proto
_________________________________________________________________

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

       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 con‐
       tains 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
       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 2.2."

       ::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
		     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  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.

	      -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
		     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)	 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.  Also, it's not useful for the case where
	      ::http::geturl is called without the -command option because  in
	      this  case the ::http::geturl call doesn't return until the HTTP
	      transaction is complete, and thus there's nothing to wait for.

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

       ::http::error token
	      This  is	a convenience procedure that returns the error element
	      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::ncode token
	      This is a convenience procedure that returns  just  the  numeric
	      return  code (200, 404, etc.) from the http element of the state
	      array.

       ::http::size token
	      This is a convenience procedure  that  returns  the  currentsize
	      element of the state array, which represents the number of bytes
	      received from the URL in the ::http::geturl call.

       ::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‐
	      tion.   It  is  strongly recommended that you call this function
	      after you're done with a given HTTP request.  Not doing so  will
	      result  in  memory  not  being  freed,  and  if  your  app calls
	      ::http::geturl enough times, the memory leak could cause a  per‐
	      formance hit...or worse.

       ::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 https://my.secure.site/]

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

ERRORS
       The http::geturl procedure will raise errors in	the  following	cases:
       invalid	command	 line options, an invalid URL, a URL on a non-existent
       host, or a URL at a bad port on an existing 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.	 For  synchronous  ::http::geturl calls (where -command is not
       specified), it will raise an error if it gets an I/O error while	 read‐
       ing  the	 HTTP  reply  headers or data.	Because ::http::geturl doesn't
       return a token in these cases, it does all  the	required  cleanup  and
       there's no issue of your app having to call ::http::cleanup.

       For  asynchronous  ::http::geturl  calls, all of the above error situa‐
       tions apply, except that if there's any error while  reading  the  HTTP
       reply  headers  or data, no exception is thrown.	 This is because after
       writing the HTTP headers, ::http::geturl returns, and the rest  of  the
       HTTP  transaction  occurs  in the background.  The command callback can
       check if any error occurred during the read by  calling	::http::status
       to check the status and if it's error, calling ::http::error to get the
       error message.

       Alternatively, if the main program flow reaches a point where it	 needs
       to  know	 the  result  of  the  asynchronous  HTTP request, it can call
       ::http::wait and then check status and  error,  just  as	 the  callback
       does.

       In  any	case,  you  must  still call http::cleanup to delete the state
       array when you're done.

       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 raised, but the status of the transaction will be eof.

       error  The error message will also be stored in the error status	 array
	      element, accessible via ::http::error.

       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.

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
       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
       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 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‐
		     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.

	      posterror
		     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, timeout if a timeout occurred before the  transac‐
		     tion  could  complete,  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} } {
	   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

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌────────────────────┬─────────────────┐
       │  ATTRIBUTE TYPE    │ ATTRIBUTE VALUE │
       ├────────────────────┼─────────────────┤
       │Availability	    │ SUNWTcl	      │
       ├────────────────────┼─────────────────┤
       │Interface Stability │ External	      │
       └────────────────────┴─────────────────┘
NOTES
       Source for Tcl is available in the SUNWTclS package.

Tcl				      8.3			       Http(n)
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