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

SYNOPSIS
       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


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. 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  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
       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  appli-
       cations,  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 2.2."

       ::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 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.

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

              -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 operation.
       ::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  exe-
              cute 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 previously registered via http::register.


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 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
              }



SEE ALSO
       safe(n), socket(n), safesock(n)

KEYWORDS
       security policy, socket
