NAME
Http - Client-side implementation of the HTTP/1.0 proto
col.
SYNOPSIS
package require http ?2.3?
::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 com
patible 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 transac
tion is performed. The return value of ::http::geturl is
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 opera
tion 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 applica
tions, 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 configura
tion is returned. If a single argument is speci
fied, then it should be one of the flags described
below. In this case the current value of that set
ting is returned. Otherwise, the options should be
a set of flags and values that define the configu
ration:
-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 dur
ing ::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 call
back should return a two element list con
taining the proxy server and proxy port.
Otherwise the filter should return an empty
list. The default filter returns the values
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 sec
tion 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 (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 avail
able; 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
return the number of bytes read from the
socket. Here is a template for the call
back:
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 ele
ments that alternate between keys and val
ues. 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 trans
ferred 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).
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 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 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 for
mat 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 time
out 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 opera
tion.
-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)
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 rep
resents 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.
This procedure allows one to provide custom HTTP
transport types such as HTTPS, by registering a
prefix, the default port, and the command to exe
cute 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 fol
lowing 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 head
ers 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 head
ers, ::http::geturl returns, and the rest of the HTTP
transaction occurs in the background. The command call
back 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.
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.
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 com
mand. 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 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 ele
ment 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. Exam
ples include text/html, image/gif,
application/postscript and applica
tion/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 writ
ing 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 com
plete, 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
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(n), socket(n), safesock(n)
KEYWORDS
security policy, socket
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