Syntax

Transfer-Encoding: chunked
Transfer-Encoding: compress
Transfer-Encoding: deflate
Transfer-Encoding: gzip

// Several values can be listed, separated by a comma
Transfer-Encoding: gzip, chunked

Directives

chunked

Data is sent in a series of chunks. Content can be sent in streams of unknown size to be transferred as a sequence of length-delimited buffers, so the sender can keep a connection open, and let the recipient know when it has received the entire message. The Content-Length header must be omitted, and at the beginning of each chunk, a string of hex digits indicate the size of the chunk-data in octets, followed by \r\n and then the chunk itself, followed by another \r\n. The terminating chunk is a zero-length chunk.

compress

A format using the Lempel-Ziv-Welch (LZW) algorithm. The value name was taken from the UNIX compress program, which implemented this algorithm. Like the compress program, which has disappeared from most UNIX distributions, this content-encoding is used by almost no browsers today, partly because of a patent issue (which expired in 2003).

deflate

Using the zlib structure (defined in RFC 1950), with the deflate compression algorithm (defined in RFC 1951).

gzip

A format using the Lempel-Ziv coding (LZ77), with a 32-bit CRC. This is originally the format of the UNIX gzip program. The HTTP/1.1 standard also recommends that the servers supporting this content-encoding should recognize x-gzip as an alias, for compatibility purposes.

Examples

Response with chunked encoding

Chunked encoding is useful when larger amounts of data are sent to the client and the total size of the response may not be known until the request has been fully processed. For example, when generating a large HTML table resulting from a database query or when transmitting large images. A chunked response looks like this:

HTTP/1.1 200 OK
Content-Type: text/plain
Transfer-Encoding: chunked

7\r\n
Welcome\r\n
1c\r\n
to Mozilla Developer Network\r\n
0\r\n
\r\n

Specifications

Browser compatibility

See also

• Accept-Encoding
• Content-Encoding
• Content-Length
• Chunked transfer encoding