http -
Client-side implementation of the HTTP/1.1 protocol
package require http ?2.7?
::http::config ?-option value ...?
::http::geturl url ?-option value ...?
::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
The http package provides the client side of the HTTP/1.1
protocol, as defined in RFC 2616.
The package implements the GET, POST, and HEAD operations
of HTTP/1.1. 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.
-
::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 2.7".
-
::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
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
# 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 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
-
-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 interfaces 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
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).
-
-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) 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 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 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::register.
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.
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/1.1 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, 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(currentsize).
- 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.
This example creates a procedure to copy a URL to a file while printing a
progress meter, and prints the meta-data associated with the URL.
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
}
safe(n), socket(n), safesock(n)
internet, security policy, socket, www