HTTP - gzip vs deflate compression algorithms (Accept-Encoding header)

In the HTTP protocol, the Accept-Encoding header located in client request informs the server about the compression formats that the client can handle. The two most commonly used compression methods are gzip and deflate.

Here's how they differ:

1. Gzip:

   • Format: Gzip is compression based on the DEFLATE algorithm, but with additional headers and footers that are part of the Gzip format.
   • Usage: Most commonly used in HTTP compression. It is widely accepted and supported by servers and browsers.
   • Advantage: Gzip includes more detailed metadata, which can be useful in certain scenarios, such as file storage.
   • How it works: It compresses data using the DEFLATE algorithm but adds extra information about the file, such as checksums, which allow for easier validation.

2. Deflate:

   • Format: Deflate refers to the raw DEFLATE compression algorithm, without the additional headers and footers. It contains only the compressed data.
   • Usage: Less commonly used in HTTP than gzip, although supported by most browsers and servers.
   • Advantage: Deflate produces slightly smaller files because it does not include the extra headers like gzip.
   • How it works: Deflate compresses data using a combination of the LZ77 algorithm and Huffman coding, allowing for efficient data size reduction.

Key differences:

• Data structure: Gzip adds additional headers and footers, which slightly increase the size of the compressed data but offer more functionality (e.g., validation).
• Usage: Gzip is more popular and widely used in HTTP. Deflate is used less frequently, though it produces smaller sizes.
• Compatibility: Most browsers and servers support both formats, but gzip is generally preferred.

In practice, gzip is usually favored because it provides better compatibility and more reliable compression results for HTTP transmission.