CODEWITHSUNDEEP
httpgo
jonhadfield
jonhadfield

Reputation: 165

Go net/http Transport Accept-Encoding: gzip not prompting encoded response

Possibly related to Go: Detect gzip encoding to manually decompress response, but 'Content-Encoding' header missing

I understand that net/http Transport will add Accept-Encoding: gzip to a request unless DisableCompression is set to True, and that is required if I want it to automatically decompress a gzipped response. That being the case, the following code does not receive a Content-Encoding: gzip header:
https://play.golang.org/p/FWs5uG9pZEL (note: will not run in the playground due to network constraints)

If I run a local server and run the above code with it I can see the expected header being sent:

GET / HTTP/1.1
Host: localhost:5555
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip

Is there something else about the connection go creates that is causing the server not to return a gzipped response?

Upvotes: 0

Views: 2068

Answers (1)

Steffen Ullrich
Steffen Ullrich

Reputation: 123280

Accept-Encoding: gzip only means that the client is able and willing to handle gzip compressed content. It does not mean that the server must actually compress the content. In fact, for example with images it would not make any sense to compress the content with gzip because these are already compressed data (but not with gzip) and adding gzip on top might actually increase the size of the payload.

If you want your server to return compressed content you actually have to configure your server to do this. See for example here on how to do this with nginx.

Note that http.Response will transparently decompress the response and update the header accordingly, i.e. remove Content-Encoding. This means you will not get the original response header when checking with resp.Header.Get("Content-Encoding"). If the response was automatically decompressed can be seen in the Uncompressed field:

fmt.Println("was compressed ", resp.Uncompressed)

For more see go doc http.Response:

// Uncompressed reports whether the response was sent compressed but
// was decompressed by the http package. When true, reading from
// Body yields the uncompressed content instead of the compressed
// content actually set from the server, ContentLength is set to -1,
// and the "Content-Length" and "Content-Encoding" fields are deleted
// from the responseHeader. To get the original response from
// the server, set Transport.DisableCompression to true.
Uncompressed bool

Upvotes: 2

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