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

SYNOPSIS
       package require http ?2.5?

       ::http::config ?options?

       ::http::geturl url ?options?

       ::http::formatQuery key value ?key value ...?

       ::http::reset token ?why?

       ::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 extended to support additional  HTTP  trans-
       port  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
       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
              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.

              -urlencoding encoding
                     The  encoding  used  for  creating the x-url-encoded URLs
                     with ::http::formatQuery.  The default is utf-8, as spec-
                     ified  by  RFC 2718.  Prior to http 2.5 this was unspeci-
                     fied, and that behavior can be returned by specifying the
                     empty  string  ({}), although iso8859-1 is recommended to
                     restore similar behavior but without the  ::http::format-
                     Query  throwing  an  error processing non-latin-1 charac-
                     ters.

              -useragent string
                     The value of the User-Agent header in the  HTTP  request.
                     The default is "Tcl http client package 2.4."

       ::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 block size 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 an x-
                     url-encoding formatted  query.   The  ::http::formatQuery
                     procedure can be used to do the formatting.

              -queryblocksize size
                     The  block  size 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  an  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 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 its 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
              procedure 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  proce-
       dure 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.

              charset
                     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.

              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 httpcopy { url file {chunk 4096} } {
                 set out [open $file w]
                 set token [::http::geturl $url -channel $out \
                        -progress httpCopyProgress -blocksize $chunk]
                 close $out

                 # This ends the line started by httpCopyProgress
                 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 [httpcopy [string trim $value] $file $chunk]
                    }
                 }
                 incr max
                 foreach {name value} $state(meta) {
                    puts [format "%-*s %s" $max $name: $value]
                 }

                 return $token
              }
              proc httpCopyProgress {args} {
                 puts -nonewline stderr .
                 flush stderr
              }


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


KEYWORDS
