The
Transfer-Encoding header specifies the form of encoding used to safely transfer the payload body to the user.Transfer-Encoding is a hop-by-hop header, that is applied to a message between two nodes, not to a resource itself. Each segment of a multi-node connection can use different Transfer-Encoding values. If you want to compress data over the whole connection, use the end-to-end Content-Encoding header instead.When present on a response to a
HEAD request that has no body, it indicates the value that would have applied to the corresponding GET message.| Header type | Response header |
|---|---|
| Forbidden header name | yes |
Syntax
Transfer-Encoding: chunked Transfer-Encoding: compress Transfer-Encoding: deflate Transfer-Encoding: gzip Transfer-Encoding: identity // Several values can be listed, separated by a comma Transfer-Encoding: gzip, chunked
Directives
chunked- Data is sent in a series of chunks. The
Content-Lengthheader is omitted in this case and at the beginning of each chunk you need to add the length of the current chunk in hexadecimal format, followed by '\r\n' and then the chunk itself, followed by another '\r\n'. The terminating chunk is a regular chunk, with the exception that its length is zero. It is followed by the trailer, which consists of a (possibly empty) sequence of entity header fields. 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-gzipas an alias, for compatibility purposes. identity- Indicates the identity function (i.e. no compression, nor modification). This token, except if explicitly specified, is always deemed acceptable.
Examples
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
Mozilla\r\n
9\r\n
Developer\r\n
7\r\n
Network\r\n
0\r\n
\r\nSpecifications
| Specification | Title |
|---|---|
| RFC 7230, section 3.3.1: Transfer-Encoding | Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing |
Browser compatibility
Update compatibility data on GitHub
| Yes | 12 | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
Legend
- Full support
See also
Accept-EncodingContent-EncodingContent-Length- Header fields that regulate the use of trailers:
TE(requests) andTrailer(responses).