Provided by: tcl8.4-doc_8.4.20-8_all 
NAME
http - Client-side implementation of the HTTP/1.0 protocol.
SYNOPSIS
package require http ?2.5?
::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/1.0 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 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 2.4."
::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
...
(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 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).
-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::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'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
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'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 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