io: add an Err field to LimitedReader

Fixes #51115

Change-Id: I3c5296e4adc71c1c1b1808a45abd4801ae43465a
GitHub-Last-Rev: 4c197acd51e1cac051302deba57b97da66e004e1
GitHub-Pull-Request: golang/go#51990
Reviewed-on: https://go-review.googlesource.com/c/go/+/396215
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/io/example_test.go b/src/io/example_test.go
index 419e449982..e4b20bd981 100644
--- a/src/io/example_test.go
+++ b/src/io/example_test.go
@@ -6,6 +6,7 @@ package io_test
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"log"
@@ -283,3 +284,16 @@ func ExampleReadAll() {
 	// Output:
 	// Go is a general-purpose language designed with systems programming in mind.
 }
+
+func ExampleLimitedReader() {
+	r := strings.NewReader("some io.Reader stream to be read\n")
+	sentinel := errors.New("reached read limit")
+	lr := &io.LimitedReader{R: r, N: 4, Err: sentinel}
+
+	if _, err := io.Copy(os.Stdout, lr); err != sentinel {
+		log.Fatal(err)
+	}
+
+	// Output:
+	// some
+}