Build

Install the openvcdiff packages. Configure nginx like this:

./configure --add-module=/path/to/sdch_module

Directives

sdch

syntax: sdch (on|off);

default: off

context: location

on – Enable module

off – Disable module

sdch_group

syntax: sdch_group <group>

default: default

context: location, server, if

Set group of the query (see sdch_dict). group can contain variables (i.e. it is a script).

sdch_dict

syntax: sdch_dict <filename> [<group> [<priority>]]

context: location, server, if

Specify the file with the dictionary. It is possible to configure several dictionaries by specifying the directive per dictionary. If a client have several configured dictionaries, the dictionary for use is selected like this:

1. A dictionary with group that equal to sdch_group of the query is preferred over a dictionary those group is not equal to the sdch_group of the query.
2. If the group is equally good, lower priority is preferred over high priority.

sdch_url

syntax: sdch_url <url>

context: location, server, if

Url to suggest to the client (in the Get-Dictionary header) if it does not have the best possible dictionary. Variables allowed.

sdch_disablecv

syntax: sdch_disablecv <script>

Disable SDCH if the value is non-empty and is not equal to 0.

sdch_min_length

syntax: sdch_min_length <length>

Minimal size of response to encode.

sdch_types

syntax: sdch_types <types>

Enable encoding responses with list of mime/types. Default is text/html, text/css, application/javascript, and application/x-sdch-dictionary.

sdch_nodict_types

syntax: sdch_nodict_types <types>

Don't announce a dictionary (with the Get-Dictionary header) if the response has Content-Type listed here. The default is application/x-sdch-dictionary, i.e. an SDCH dictionary.

sdch_fastdict

syntax: sdch_fastdict (on|off);

context: location, server, if

default: off

Enable quasi dictionaries. I.e., if client support quasi-dictionaries, store the reply in memory and allow client to use the reply as a dictionary.

If a client announces several quasi-dictionaries to the server, the one with the group that match the group of the current query is preferred. Configured dictionaries, if any, is preferred over all quasi-dictionaries.

sdch_stor_size

syntax: sdch_stor_size <memsize>

context: main

default: 10 000 000

The memory limit for quasi-dictionaries.

sdch_vary

syntax: sdch_vary (on|off)

context: main, location, server

default: on

Add Vary header

The FastDict protocol extension

To announce FastDict support, the client sends Sdch-Features: fastdict header.

If the client support FastDicts, and server suggest that the current reply will be used as the quasi-dictionary, it add X-Sdch-Use-As-Dictionary header to the reply.

Then, the client may use the reply as a dictionary, i.e. announce it in the Avail-Dictionary header etc.

(There is no headers in the quasi-dictionaries.)