can I work on this? @bradfitz

Sure, if you're familiar with the http code. Note that we already did this for the http2 Transport (during server graceful shutdown in GOAWAY), so be sure to read that code first.

@bradfitz Thanks. I will spend some time this weekend.

Sorry for very late reply.

I started going through the code, to understand the problem correctly.

I noticed like you mentioned, http2 transport already creating the retry Request via Request.GetBody in http2shouldRetryRequest function inside h2_bundle.go

At the same time, in transport.go, the same operation is done via
pconn.shouldRetryRequest()
and
treq := &transportRequest{Request: req, trace: trace}

creating new request every time. Instead we have use to Request.GetBody to achieve that.

@bradfitz

CL https://golang.org/cl/42142 mentions this issue.

To clarify: is this issue specifically about retrying on idempotent-method requests (GET/HEAD/OPTIONS/TRACE) which have non-nil Body but have GetBody set?

In Go 1.12 we now have the fix for #19943 (comment) ....

Change https://golang.org/cl/147457 mentions this issue: net/http: make Transport respect {X-,}Idempotency-Key header