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 and ERRORS sec-
              tion  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 (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 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.

              -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
                     formatted  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 for-
                     mat is the same).

              -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.


ERRORS
       The  http::geturl  procedure will raise errors in the fol-
       lowing cases: invalid command  line  options,  an  invalid
       URL,  or  a  URL on a non-existent 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 array.

       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
              procedure 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.


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:
                             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   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.

              posterror
                     The error, if any, that occurred while writ-
                     ing the post query data to the server.

              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
