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http(n) Tcl Bundled Packages http(n)
____________________________________________________________________________________________________________
NAME
http - Client-side implementation of the HTTP/1.1 protocol
SYNOPSIS
package require http ?2.7?
::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/1.1 protocol. The package implements the GET,
POST, and HEAD operations of HTTP/1.1. It allows configuration of a proxy host to get through fire-walls. firewalls.
walls. 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. Other-wise, Otherwise,
wise, 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 con-taining containing
taining 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::format-Query ::http::formatQuery
Query 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 2.7".
::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 informa-tion information
tion 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 speci-fies specifies
fies 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 autodetected
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 call-back: callback:
back:
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 extra headers to the HTTP request. The keyvaluelist argu-ment argument
ment 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
-keepalive boolean
If true, attempt to keep the connection open for servicing 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 inter-faces interfaces
faces 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 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
}
-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 for-matted formatted
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 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 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) (application/xwww-form-urlencoded)
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 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 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 con-tains contains
tains 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 opera-tion. operation.
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 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::reg-ister. ::http::register.
ister.
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 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 situations 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 does.
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.
STATE ARRAY
The ::http::geturl procedure returns a token that can be used to get to the state of the HTTP trans-action transaction
action 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 com-mand. command.
mand. 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 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, applica-tion/postscript application/postscript
tion/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. Dur-ing During
ing 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(n), socket(n), safesock(n)
KEYWORDS
security policy, socket
http 2.7 http(n)
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