Http

NAME

SYNOPSIS

::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::data token

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.

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 2.0."

::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 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:

-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.

-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.

-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.

-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.

::http::data token

This is a convenience procedure that returns the body element (i.e., the URL data) 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::size token

This is a convenience procedure that returns the currentsize element of the state array.

STATE ARRAY

upvar #0 $token state

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.

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:

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.

status

Either ok, for successful completion, reset for user-reset, 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

KEYWORDS

Index

NAME

SYNOPSIS

DESCRIPTION

COMMANDS

STATE ARRAY

EXAMPLE

SEE ALSO

KEYWORDS