func newTransferWriter()

in garbage/nethttp.go [5647:5722]
70 lines of code
22 McCabe index (conditional complexity)

func newTransferWriter(r interface{}) (t *transferWriter, err error) {
	t = &transferWriter{}

	atLeastHTTP11 := false
	switch rr := r.(type) {
	case *Request:
		if rr.ContentLength != 0 && rr.Body == nil {
			return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
		}
		t.Method = rr.Method
		t.Body = rr.Body
		t.BodyCloser = rr.Body
		t.ContentLength = rr.ContentLength
		t.Close = rr.Close
		t.TransferEncoding = rr.TransferEncoding
		t.Trailer = rr.Trailer
		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
		if t.Body != nil && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
			if t.ContentLength == 0 {
				// Test to see if it's actually zero or just unset.
				var buf [1]byte
				n, rerr := io.ReadFull(t.Body, buf[:])
				if rerr != nil && rerr != io.EOF {
					t.ContentLength = -1
					t.Body = errorReader{rerr}
				} else if n == 1 {

					t.ContentLength = -1
					t.Body = io.MultiReader(bytes.NewReader(buf[:]), t.Body)
				} else {

					t.Body = nil
					t.BodyCloser = nil
				}
			}
			if t.ContentLength < 0 {
				t.TransferEncoding = []string{"chunked"}
			}
		}
	case *Response:
		t.IsResponse = true
		if rr.Request != nil {
			t.Method = rr.Request.Method
		}
		t.Body = rr.Body
		t.BodyCloser = rr.Body
		t.ContentLength = rr.ContentLength
		t.Close = rr.Close
		t.TransferEncoding = rr.TransferEncoding
		t.Trailer = rr.Trailer
		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
		t.ResponseToHEAD = noBodyExpected(t.Method)
	}

	if t.ResponseToHEAD {
		t.Body = nil
		if chunked(t.TransferEncoding) {
			t.ContentLength = -1
		}
	} else {
		if !atLeastHTTP11 || t.Body == nil {
			t.TransferEncoding = nil
		}
		if chunked(t.TransferEncoding) {
			t.ContentLength = -1
		} else if t.Body == nil {
			t.ContentLength = 0
		}
	}

	if !chunked(t.TransferEncoding) {
		t.Trailer = nil
	}

	return t, nil
}