HTTP/2: empty data-frame without Content-Length generated for requests without request body

[rfc2822]

Let's assume this code for generating an OPTIONS request:

Response response = httpClient.newCall(new Request.Builder()
                .method("OPTIONS", null)
                .url(location)
                .build()).execute();

With HTTP/1.1, it just generates a request without body, which will be accepted and processed by the server.

However, when HTTP/2 is active, okhttp 3.4.1 generates an empty DATA frame without Content-Length:

davdroid.DavResourceFinder: [HttpClient$1] --> OPTIONS https://yourserver/katana/public/server.php/principals/bitfire/ http/1.1
davdroid.DavResourceFinder: [HttpClient$1] --> END OPTIONS
davdroid.dav4android: [dav4android.BasicDigestAuthHandler] Adding Basic authorization header for https://yourserver/katana/public/server.php/principals/bitfire/
okhttp3.internal.framed.Http2$FrameLogger: [okhttp3.internal.framed.Http2$Writer] >> 0x0000001f   218 HEADERS       END_HEADERS
[!!!] okhttp3.internal.framed.Http2$FrameLogger: [okhttp3.internal.framed.Http2$Writer] >> 0x0000001f     0 DATA          END_STREAM
okhttp3.internal.framed.Http2$FrameLogger: [okhttp3.internal.framed.Http2$Reader] << 0x0000001f     7 HEADERS       END_HEADERS

Servers like Apache 2.4 reject this request because the OPTIONS request should either have

1. no body – and thus no data frame, or
2. a body, and thus Content-Length.

Because null is specified as the request body, okhttp shouldn't send a data frame.

For further information, see https://forums.bitfire.at/topic/1124/411-length-error-davdroid-1-0-9-2-owncloud/10. If I can provide more information, please let me know.

[swankjesse]

Can fix!