autoproxy(3tcl) HTTP protocol helper modules autoproxy(3tcl)
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NAME
autoproxy - Automatic HTTP proxy usage and authentication
SYNOPSIS
package require Tcl 8.5
package require http ?2.0?
package require autoproxy ?1.7?
::autoproxy::init
::autoproxy::cget -option
::autoproxy::configure ?-option value?
::autoproxy::tls_connect args
::autoproxy::tunnel_connect args
::autoproxy::tls_socket args
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DESCRIPTION
This package attempts to automate the use of HTTP proxy servers in Tcl
HTTP client code. It tries to initialize the web access settings from
system standard locations and can be configured to negotiate authenti-
cation with the proxy if required.
On Unix the standard for identifying the local HTTP proxy server seems
to be to use the environment variable http_proxy or ftp_proxy and
no_proxy to list those domains to be excluded from proxying. On Win-
dows we can retrieve the Internet Settings values from the registry to
obtain pretty much the same information. With this information we can
setup a suitable filter procedure for the Tcl http package and arrange
for automatic use of the proxy.
There seem to be a number of ways that the http_proxy environment vari-
able may be set up. Either a plain host:port or more commonly a URL and
sometimes the URL may contain authentication parameters or these may be
requested from the user or provided via http_proxy_user and
http_proxy_pass. This package attempts to deal with all these schemes.
It will do it's best to get the required parameters from the environ-
ment or registry and if it fails can be reconfigured.
TLS SECURITY CONSIDERATIONS
Note This section only applies if TLS support is provided by the TLS
package. It does not apply when autoproxy was configured to use some
other package which can provide the same (i.e twapi), via the
-tls_package configuration option.
This package uses the TLS package to handle the security for https urls
and other socket connections.
Policy decisions like the set of protocols to support and what ciphers
to use are not the responsibility of TLS, nor of this package itself
however. Such decisions are the responsibility of whichever applica-
tion is using the package, and are likely influenced by the set of
servers the application will talk to as well.
For example, in light of the recent POODLE attack [http://googleonli-
nesecurity.blogspot.co.uk/2014/10/this-poodle-bites-exploiting-
ssl-30.html] discovered by Google many servers will disable support for
the SSLv3 protocol. To handle this change the applications using TLS
must be patched, and not this package, nor TLS itself. Such a patch
may be as simple as generally activating tls1 support, as shown in the
example below.
package require tls
tls::init -tls1 1 ;# forcibly activate support for the TLS1 protocol
... your own application code ...
COMMANDS
::autoproxy::init
Initialize the autoproxy package from system resources. Under
unix this means we look for environment variables. Under windows
we look for the same environment variables but also look at the
registry settings used by Internet Explorer.
::autoproxy::cget -option
Retrieve individual package configuration options. See OPTIONS.
::autoproxy::configure ?-option value?
Configure the autoproxy package. Calling configure with no op-
tions will return a list of all option names and values. See
OPTIONS.
::autoproxy::tls_connect args
Connect to a secure socket through a proxy. HTTP proxy servers
permit the use of the CONNECT HTTP command to open a link
through the proxy to the target machine. This function hides the
details. For use with the http package see tls_socket.
The args list may contain any of the options supported by the
specific TLS package that is in use but must end with the host
and port as the last two items.
::autoproxy::tunnel_connect args
Connect to a target host throught a proxy. This uses the same
CONNECT HTTP command as the tls_connect but does not promote the
link security once the connection is established.
The args list may contain any of the options supported by the
specific TLS package that is in use but must end with the host
and port as the last two items.
Note that many proxy servers will permit CONNECT calls to a lim-
ited set of ports - typically only port 443 (the secure HTTP
port).
::autoproxy::tls_socket args
This function is to be used to register a proxy-aware secure
socket handler for the https protocol. It may only be used with
the Tcl http package and should be registered using the
http::register command (see the examples below). The job of ac-
tually creating the tunnelled connection is done by the tls_con-
nect command and this may be used when not registering with the
http package.
OPTIONS
-host hostname
-proxy_host hostname
Set the proxy hostname. This is normally set up by init but may
be configured here as well.
-port number
-proxy_port number
Set the proxy port number. This is normally set up by init.
e.g. configure -port 3128
-no_proxy list
You may manipulate the no_proxy list that was setup by init. The
value of this option is a tcl list of strings that are matched
against the http request host using the tcl string match com-
mand. Therefore glob patterns are permitted. For instance, con-
figure -no_proxy *.localdomain
-authProc procedure
This option may be used to set an application defined procedure
to be called when configure -basic is called with either no or
insufficient authentication details. This can be used to present
a dialog to the user to request the additional information.
-basic Following options are for configuring the Basic authentication
scheme parameters. See Basic Authentication. To unset the proxy
authentication information retained from a previous call of this
function either "--" or no additional parameters can be sup-
plied. This will remove the existing authentication information.
-tls_package packagename
This option may be used to configure the Tcl package to use for
TLS support. Valid package names are tls (default) and twapi.
BASIC AUTHENTICATION
Basic is the simplest and most commonly use HTTP proxy authentication
scheme. It is described in (1 section 11) and also in (2). It offers no
privacy whatsoever and its use should be discouraged in favour of more
secure alternatives like Digest. To perform Basic authentication the
client base64 encodes the username and plaintext password separated by
a colon. This encoded text is prefixed with the word "Basic" and a
space.
The following options exists for this scheme:
-username name
The username required to authenticate with the configured proxy.
-password password
The password required for the username specified.
-realm realm
This option is not used by this package but may be used in re-
questing authentication details from the user.
-- The end-of-options indicator may be used alone to unset any au-
thentication details currently enabled.
EXAMPLES
package require autoproxy
autoproxy::init
autoproxy::configure -basic -username ME -password SEKRET
set tok [http::geturl http://wiki.tcl.tk/]
http::data $tok
package require http
package require tls
package require autoproxy
autoproxy::init
http::register https 443 autoproxy::tls_socket
set tok [http::geturl https://www.example.com/]
REFERENCES
[1] Berners-Lee, T., Fielding R. and Frystyk, H. "Hypertext Trans-
fer Protocol -- HTTP/1.0", RFC 1945, May 1996, (http://www.rfc-
editor.org/rfc/rfc1945.txt)
[2] Franks, J. et al. "HTTP Authentication: Basic and Digest Access
Authentication", RFC 2617, June 1999 (http://www.rfc-edi-
tor.org/rfc/rfc2617.txt)
BUGS
At this time only Basic authentication (1) (2) is supported. It is
planned to add support for Digest (2) and NTLM in the future.
AUTHORS
Pat Thoyts
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain
bugs and other problems. Please report such in the category http ::
autoproxy of the Tcllib Trackers [http://core.tcl.tk/tcllib/re-
portlist]. Please also report any ideas for enhancements you may have
for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the out-
put of diff -u.
Note further that attachments are strongly preferred over inlined
patches. Attachments can be made by going to the Edit form of the
ticket immediately after its creation, and then using the left-most
button in the secondary navigation bar.
SEE ALSO
http(3tcl)
KEYWORDS
authentication, http, proxy
CATEGORY
Networking
tcllib 1.7 autoproxy(3tcl)