SDCH (Shared Dictionary Compression for HTTP) is a
data compression
In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...
algorithm created by
Google
Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...
, based on
VCDIFF
VCDIFF is a format and an algorithm for delta encoding, described in IETF'RFC 3284 The algorithm is based on Jon Bentley and Douglas McIlroy's paper "Data Compression Using Long Common Strings" written in 1999. VCDIFF is used as one of the delta e ...
(RFC 3284).
SDCH achieves its effectiveness by using pre-negotiated dictionaries to "warm up" its internal state prior to encoding or decoding. These may either be already stored locally, or uploaded from a source and then cached.
It was supported natively in
Google Chrome
Google Chrome is a cross-platform web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macO ...
, Chromium, and Android, as well as on Google websites.
SDCH compression was removed from Google Chrome, and other Chromium products, in version 59 (2017-06-05).
See also
*
Brotli
Brotli is a lossless data compression algorithm developed by Google. It uses a combination of the general-purpose LZ77 lossless compression algorithm, Huffman coding and 2nd-order context modelling.
Brotli is primarily used by web servers and ...
*
HTTP compression
HTTP compression is a capability that can be built into web servers and web clients to improve transfer speed and bandwidth utilization.
HTTP data is compressed before it is sent from the server: compliant browsers will announce what methods ar ...
*
SPDY
SPDY (pronounced "speedy") is an obsolete open-specification communication protocol developed for transporting web content. SPDY became the basis for HTTP/2 specification. However, HTTP/2 diverged from SPDY and eventually HTTP/2 subsumed all us ...
References
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Data compression