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http(n) - http, http - Client-side implementation of the HTTP/1.0 protocol - man n http

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http(n)                      Tcl Bundled Packages                      http(n)



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

SYNOPSIS
       package require http ?2.4?

       ::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(1,5) 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(7,n,1 builtins) of
       hosts. This package can be extended to support additional  HTTP  trans-
       port  protocols,  such  as HTTPS, by providing a custom socket(2,7,n) 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(1,8) the ::http namespace that con-
       tains state information about the transaction.  The  elements  of  this
       array are described in(1,8) the STATE ARRAY section.

       If the -command option is specified, then the HTTP operation is done in(1,8)
       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(7,n,1 builtins) and query the name of
              the proxy server and port, and the User-Agent name used  in(1,8)  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(7,n,1 builtins) 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(1,5), if(3,n) any.  If this value is the
                     empty string(3,n), the URL host(1,5) 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(3,n) a proxy is required for  a
                     given  host.  One argument, a host(1,5) 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(1,3x,3x curs_util) should
                     return  an  empty  list.   The default filter(1,3x,3x curs_util) returns the
                     values of the -proxyhost and -proxyport settings if(3,n)  they
                     are non-empty.

              -useragent string(3,n)
                     The  value  of the User-Agent header in(1,8) 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(1,8) 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(3,n) is gzip or compress is considered binary  data).

              -blocksize size
                     The  blocksize  used  when reading the URL.  At most size
                     bytes are read(2,n,1 builtins) at once.  After each block, a call to  the
                     -progress callback is made (if(3,n) that option is specified).

              -channel name
                     Copy the URL contents to channel name instead  of  saving
                     it in(1,8) state(body).

              -command callback
                     Invoke  callback  after  the  HTTP transaction completes.
                     This option causes ::http::geturl to return  immediately.
                     The  callback  gets(3,n)  an  additional  argument that is the
                     token returned from ::http::geturl.  This  token  is  the
                     name  of  an  array  that is described in(1,8) the STATE ARRAY
                     section.  Here is a template for the callback:
                     proc(5,n) httpCallback {token} {
                         upvar #0 $token state
                         # Access state as a Tcl array }

              -handler callback
                     Invoke callback  whenever  HTTP  data  is  available;  if(3,n)
                     present,  nothing  else  will be done with the HTTP data.
                     This procedure gets(3,n) two additional arguments: the  socket(2,7,n)
                     for   the   HTTP   data   and  the  token  returned  from
                     ::http::geturl.  The token is the name of a global  array
                     that is described in(1,8) the STATE ARRAY section.  The proce-
                     dure is expected to return the number of bytes read(2,n,1 builtins)  from
                     the socket.  Here is a template for the callback:
                     proc(5,n) httpHandlerCallback {socket(2,7,n) token} {
                         upvar #0 $token state
                         # Access socket(2,7,n), and state as a Tcl array
                         ...
                         (example:  set(7,n,1 builtins)  data  [read(2,n,1 builtins)  $socket(2,7,n) 1000];set(7,n,1 builtins) nbytes
                     [string(3,n) 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(3,n) keyvaluelist is Pragma no-
                     cache then the following header is included in(1,8)  the  HTTP
                     request: Pragma: no-cache

              -progress callback
                     The callback is made after each transfer of data from the
                     URL.  The callback gets(3,n) 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(1,8) which case zero  is  passed
                     to  the  callback.   Here  is a template for the progress
                     callback:
                     proc(5,n) 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(3,n)
                     that option is specified).

              -querychannel channelID
                     This flag causes ::http::geturl to do a POST request that
                     passes the data contained in(1,8) channelID to the server. The
                     data contained in(1,8) 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(1,8) 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(1,3x,3x cbreak) to occur after the  specified  number  of  mil-
                     liseconds.   A timeout(1,3x,3x cbreak) results in(1,8) a call to ::http::reset
                     and to the -command callback, if(3,n) specified.   The  return
                     value  of  ::http::status  is timeout(1,3x,3x cbreak) after a timeout(1,3x,3x cbreak) 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(1,8) 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(3,n)
              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(3,n)
              any.  This sets the state(status) value to why,  which  defaults
              to reset(1,7,1 tput), 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(1,8)  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(1,8)
              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(8,n) 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(1,8) 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(1,8)  memory  not  being  freed,  and  if(3,n)  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(7,n,1 builtins) 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(3,n) errors in(1,8)  the  following  cases:
       invalid  command  line options, an invalid URL, a URL on a non-existent
       host(1,5), 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(3,n)
       an error(8,n) if(3,n) it gets(3,n) an I/O error(8,n) while writing  out  the  HTTP  request
       header.   For  synchronous  ::http::geturl calls (where -command is not
       specified), it will raise(3,n) an error(8,n) if(3,n) it gets(3,n) an I/O error(8,n) while  read-
       ing  the  HTTP  reply  headers or data.  Because ::http::geturl doesn't
       return a token in(1,8) 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(8,n) situa-
       tions apply, except that if(3,n) there's any error(8,n) 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(1,8) the background.  The command callback can
       check if(3,n) any error(8,n) occurred during the read(2,n,1 builtins) by  calling  ::http::status
       to  check the status and if(3,n) its error(8,n), calling ::http::error to get the
       error(8,n) message.

       Alternatively, if(3,n) 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(8,n),  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(8,n) (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(2,7,n) without replying, then no error(8,n)
              is raised, but the status of the transaction will be eof.

       error(8,n)  The error(8,n) message will also be stored in(1,8) the error(8,n) status  array
              element, accessible via ::http::error.

       Another  error(8,n)  possibility is that http::geturl is unable to write(1,2) all
       the post query data to the server before the server responds and closes
       the  socket.   The error(8,n) message is saved in(1,8) the posterror status array
       element and then  http::geturl attempts to  complete  the  transaction.
       If  it can read(2,n,1 builtins) 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(1,8) 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 pro-
       cedure  is  provided  for  that purpose.  The following elements of the
       array are supported:

              body   The contents of the URL.   This  will  be  empty  if(3,n)  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(8,n)  If  defined,  this is the error(8,n) string(3,n) 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(3,n) The code  is  a  three-digit  number
                     defined  in(1,8)  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(1,8)
                     a format useful for initializing an array that just  con-
                     tains the meta-data:
                     array  set(7,n,1 builtins)  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(8,n), if(3,n) any, that occurred while writing  the  post
                     query data to the server.

              status Either  ok,  for  successful  completion, reset(1,7,1 tput) for user-
                     reset(1,7,1 tput), timeout(1,3x,3x cbreak) if(3,n) a timeout(1,3x,3x cbreak) occurred before the  transac-
                     tion  could  complete,  or  error(8,n) for an error(8,n) 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(1,n) and print meta-data proc(5,n) ::http::copy { url file(1,n)
       {chunk 4096} } {
           set(7,n,1 builtins) out [open(2,3,n) $file(1,n) w]
           set(7,n,1 builtins)  token  [geturl $url -channel $out -progress ::http::Progress \
            -blocksize $chunk]
           close(2,7,n) $out
           # This ends the line started by http::Progress
           puts(3,n) stderr ""
           upvar #0 $token state
           set(7,n,1 builtins) max 0
           foreach {name value} $state(meta) {      if(3,n) {[string(3,n) length  $name]
       >  $max} {          set(7,n,1 builtins) max [string(3,n) length $name]      }      if(3,n) {[reg-
       exp -nocase ^location$ $name]} {          # Handle URL redirects
       puts(3,n)  stderr  "Location:$value"            return  [copy  [string(3,n)  trim
       $value] $file(1,n) $chunk]      }
           }
           incr max
           foreach {name value} $state(meta) {       puts(3,n)  [format  "%-*s  %s"
       $max $name: $value]
           }

           return $token } proc(5,n) ::http::Progress {args} {
           puts(3,n) -nonewline stderr . ; flush(8,n) stderr }


SEE ALSO
       safe(n), socket(2,7,n)(n), safesock(n)


KEYWORDS
       security policy, socket(2,7,n)



http                                  2.4                              http(n)

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