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


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

       package require http ?2.4?

       ::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

       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 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
       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 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 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   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:

              -binary boolean
                     Specifies  whether  to force interpreting the url data as
                     binary.  Normally this  is  auto-detected  (anything  not
                     beginning  with  a  text  content  type  or whose content
                     encoding is gzip or compress is considered binary  data).

              -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.  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

       ::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]

       ::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, 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

       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.

       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 value of the charset attribute from the  Content-Type
                     meta-data value.  If none was specified, this defaults to
                     the   RFC   standard   iso8859-1,   or   the   value   of
                     $::http::defaultCharset.   Incoming  text  data  will  be
                     automatically converted from this charset to utf-8.

              coding A copy of the Content-Encoding meta-data value.

                     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

                     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.

                     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)