net,os: set the theoretical unlimited remaining bytes to max int64

Based on https://go-review.googlesource.com/c/go/+/466015/comment/073a63fa_7a9e485f

Change-Id: I3e1b035de6b8217c5fa5695e436f164b3058e33c
Reviewed-on: https://go-review.googlesource.com/c/go/+/471439
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Andy Pan <panjf2000@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/net/sendfile_linux.go

@@ -18,7 +18,7 @@ import (
 //
 // if handled == false, sendFile performed no work.
 func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
-	var remain int64 = 1 << 62 // by default, copy until EOF
+	var remain int64 = 1<<63 - 1 // by default, copy until EOF
 
 	lr, ok := r.(*io.LimitedReader)
 	if ok {

src/net/splice_linux.go

@@ -15,7 +15,7 @@ import (
 //
 // If splice returns handled == false, it has performed no work.
 func splice(c *netFD, r io.Reader) (written int64, err error, handled bool) {
-	var remain int64 = 1 << 62 // by default, copy until EOF
+	var remain int64 = 1<<63 - 1 // by default, copy until EOF
 	lr, ok := r.(*io.LimitedReader)
 	if ok {
 		remain, r = lr.N, lr.R

src/os/readfrom_linux.go

@@ -112,7 +112,7 @@ func (f *File) copyFileRange(r io.Reader) (written int64, handled bool, err erro
 // the underlying io.Reader and the remaining amount of bytes if the assertion succeeds,
 // otherwise it just returns the original io.Reader and the theoretical unlimited remaining amount of bytes.
 func tryLimitedReader(r io.Reader) (*io.LimitedReader, io.Reader, int64) {
-	remain := int64(1 << 62)
+	var remain int64 = 1<<63 - 1 // by default, copy until EOF
 
 	lr, ok := r.(*io.LimitedReader)
 	if !ok {