net/http: client.Do should mask EOF as ErrUnexpectedEOF

[dsnet]

func Test(t *testing.T) {
	server := httptest.NewServer(
		http.HandlerFunc(
			func(w http.ResponseWriter, r *http.Request) {
				rwc, _, _ := w.(http.Hijacker).Hijack()
				defer rwc.Close()
			},
		),
	)
	defer server.Close()

	_, err := http.Get(server.URL)
	if err != nil {
		t.Fatalf("GET returned error: %v", err)
	}
}

The preceding test prints GET returned error: EOF, which is strange since io.EOF is often an "error" signaling normal termination of some stream. Instead, Do should mask the error as io.ErrUnexpectedEOF, which is more indicative of an abrupt termination.

[bradfitz]

We tried to fix this once and had to revert it. There's a testing locking in this behavior. :-/

But maybe we can revisit.

[ibrasho]

@bradfitz Can you link the old fix for reference?

[bradfitz]

@ibrasho, you can probably find it in git history as quickly as I could. (which might not be super quick)