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Updated: Wednesday, February 9, 2022

http (1t)


http - side implementation of the HTTP/1.1 protocol


package require http ?2.7?

::http::config ?-option value ...?

::http::geturl url ?-option value ...?

::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


http(1t)                     Tcl Bundled Packages                     http(1t)


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

       package require http ?2.7?

       ::http::config ?-option value ...?

       ::http::geturl url ?-option value ...?

       ::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

       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  secu-
       rity  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 cus-
       tom 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 call-
       er can use ::http::wait after calling ::http::geturl to start the event

       ::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

              -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-

              -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 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
                                # For example...
                                set data [read $socket 1000]
                                set nbytes [string length $data]
                                return $nbytes

              -headers keyvaluelist
                     This option is used to add headers not already  specified
                     by  ::http::config 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  val-
                     ues  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 servic-
                     ing 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 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

                            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

              -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  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

              -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 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  noth-
              ing 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

       ::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 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 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 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, returning a two-item list
              of the default port and  handler  command  that  was  previously
              installed  (via  ::http::register)  if there was such a handler,
              and an error if there was no such handler.

       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 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 situa-
       tions 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

       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.

       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.

                     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.

                     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 redi-
                     rection errors.  In  this  case  the  Location  meta-data
                     specifies  a new URL that contains the requested informa-

              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

                            The type of the URL  contents.   Examples  include
                            text/html,  image/gif,  application/postscript and

                            The advertised size of the contents.   The  actual
                            size  obtained  by  ::http::geturl is available as

                            An alternate URL that contains the requested data.

                     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.

                     A copy of the Content-Length meta-data value.

              type   A copy of the Content-Type meta-data value.

              url    The requested URL.

       This example creates a procedure to copy a URL to a file while printing
       a progress meter, and prints the meta-data associated with the URL.

              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 attributes(7) for descriptions of the following attributes:

       |Availability   | runtime/tcl-8    |
       |Stability      | Uncommitted      |

       safe(n), socket(n), safesock(n)

       internet, security policy, socket, www

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.

http                                  2.7                             http(1t)