Http

Http(3tcl)                   Tcl Built-In Commands                  Http(3tcl)



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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 list

       ::http::reset token

       ::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 extened to support additional HTTP transport
       protocols, such as HTTPS, by providing a custom socket command, via
       http::register.

       The ::http::geturl procedure does a HTTP transaction.  Its options
       determine whether a GET, POST, or HEAD 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.

              -useragent string
                     The value of the User-Agent header in the HTTP request.
                     The default is "Tcl http client package 2.2."

       ::http::geturl url ?options?
              The ::http::geturl command is the main procedure in the package.
              The -query option causes a POST operation and the -validate
              option causes a HEAD operation; otherwise, a GET operation is
              performed.  The ::http::geturl command returns a token value
              that can be used to get information about the transaction.  See
              the STATE ARRAY and ERRORS 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 blocksize used when reading the URL.  At most size
                     bytes are read at once.  After each block, a call to the
                     -progress callback is made (if that option is specified).

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

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

              -handler callback
                     Invoke callback whenever HTTP data is 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
                                ...
                                (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

              -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
                            }

              -query query
                     This flag causes ::http::geturl to do a POST request that
                     passes the query to the server. The query must be a x-
                     url-encoding formatted query.  The ::http::formatQuery
                     procedure can be used to do the formatting.

              -queryblocksize size
                     The blocksize used when posting query data to the URL.
                     At most size bytes are written at once.  After each
                     block, a call to the -queryprogress callback is made (if
                     that option is specified).

              -querychannel channelID
                     This flag causes ::http::geturl to do a POST request that
                     passes the data contained in channelID to the server. The
                     data contained in channelID must be a x-url-encoding
                     formatted query unless the -type option below is used.
                     If a Content-Length header is not specified via the
                     -headers options, ::http::geturl attempts to determine
                     the size of the post data in order to create that header.
                     If it is unable to determine the size, it returns an
                     error.

              -queryprogress callback
                     The callback is made after each transfer of data to the
                     URL (i.e. POST) and acts exactly like the -progress
                     option (the callback 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
                     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'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
              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'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
              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 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
       situations 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 it's 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 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/1.0 code string
                     The code is a three-digit number defined in the HTTP
                     standard.  A code of 200 is OK.  Codes beginning with 4
                     or 5 indicate errors.  Codes beginning with 3 are
                     redirection errors.  In this case the Location meta-data
                     specifies a new URL that contains the requested
                     information.

              meta   The HTTP protocol returns meta-data that describes the
                     URL contents.  The meta 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 ::http::copy { url file
       {chunk 4096} } {
           set out [open $file w]
           set token [geturl $url -channel $out -progress ::http::Progress \
         -blocksize $chunk]
           close $out
           # This ends the line started by http::Progress
           puts stderr ""
           upvar #0 $token state
           set max 0
           foreach {name value} $state(meta) {   if {[string length $name] >
       $max} {       set max [string length $name]   }   if {[regexp -nocase
       ^location$ $name]} {       # Handle URL redirects       puts stderr
       "Location:$value"       return [copy [string trim $value] $file $chunk]
         }
           }
           incr max
           foreach {name value} $state(meta) {   puts [format "%-*s %s" $max
       $name: $value]
           }

           return $token } proc ::http::Progress {args} {
           puts -nonewline stderr . ; flush stderr }


SEE ALSO
       safe(3tcl), socket(3tcl), safesock(3tcl)


KEYWORDS
       security policy, socket



Tcl                                   8.3                           Http(3tcl)