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NAME

       http - Client-side implementation of the HTTP/1.1 protocol

SYNOPSIS

       package require http ?2.7?

       ::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::meta 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/1.1 protocol, as defined in RFC
       2616.  The package implements the GET, POST, and HEAD operations of HTTP/1.1.   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
       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 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  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  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 during ::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 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 specified by RFC 2718.  Prior
                     to http 2.5 this was unspecified, and  that  behavior  can  be  returned  by
                     specifying  the  empty  string  ({}),  although  iso8859-1 is recommended to
                     restore similar behavior but without  the  ::http::formatQuery  throwing  an
                     error processing non-latin-1 characters.

              -useragent string
                     The value of the User-Agent header in the HTTP request.  The default is “Tcl
                     http client package 2.7”.

       ::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  several
              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 procedure 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
                                # For 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.
                     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

              -keepalive boolean
                     If  true,  attempt  to  keep  the  connection  open  for  servicing multiple
                     requests.  Default is 0.

              -method type
                     Force the HTTP request method to type. ::http::geturl will auto-select  GET,
                     POST  or  HEAD  based on other options, but this option enables choices like
                     PUT and DELETE for webdav support.

              -myaddr address
                     Pass an specific local  address  to  the  underlying  socket  call  in  case
                     multiple interfaces are available.

              -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 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
                            }

              -protocol version
                     Select the HTTP protocol version to use. This should  be  1.0  or  1.1  (the
                     default).  Should  only  be  necessary for servers that do not understand or
                     otherwise complain about HTTP/1.1.

              -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).

              -strict boolean
                     Whether to enforce RFC 3986 URL validation on the request.  Default is 1.

              -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 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)  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.  Also, it is  not
              useful  for  the  case  where  ::http::geturl is called without the -command option
              because in this case the  ::http::geturl  call  does  not  return  until  the  HTTP
              transaction is complete, and thus there is 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::meta token
              This  is  a  convenience procedure that returns the meta element of the state array
              which contains the HTTP response headers. See below  for  an  explanation  of  this
              element.

       ::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.   It is strongly recommended that you call this
              function after you are 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 performance 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  previously  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 reading  the  HTTP  reply  headers  or  data.
       Because  ::http::geturl  does  not return a token in these cases, it does all the required
       cleanup and there is no issue of your app having to call ::http::cleanup.

       For asynchronous ::http::geturl calls, all of the above  error  situations  apply,  except
       that  if  there is 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 are
       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 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.

              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/1.1 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  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
                     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.  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 transaction 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(3tcl), socket(3tcl), safesock(3tcl)

KEYWORDS

       security policy, socket