encoding: add AppendEncode and AppendDecode

Implement append-like equivalent of Encode and Decode functions.

Fixes #53693

Change-Id: I79d8d834e3c8f77fad32be2fd391e33d4d1527ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/504884
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/encoding/hex/hex_test.go b/src/encoding/hex/hex_test.go
index a820fe7a15..03331eaae5 100644
--- a/src/encoding/hex/hex_test.go
+++ b/src/encoding/hex/hex_test.go
@@ -37,6 +37,11 @@ func TestEncode(t *testing.T) {
 		if string(dst) != test.enc {
 			t.Errorf("#%d: got: %#v want: %#v", i, dst, test.enc)
 		}
+		dst = []byte("lead")
+		dst = AppendEncode(dst, test.dec)
+		if string(dst) != "lead"+test.enc {
+			t.Errorf("#%d: got: %#v want: %#v", i, dst, "lead"+test.enc)
+		}
 	}
 }
 
@@ -52,6 +57,13 @@ func TestDecode(t *testing.T) {
 		} else if !bytes.Equal(dst, test.dec) {
 			t.Errorf("#%d: got: %#v want: %#v", i, dst, test.dec)
 		}
+		dst = []byte("lead")
+		dst, err = AppendDecode(dst, []byte(test.enc))
+		if err != nil {
+			t.Errorf("#%d: AppendDecode error: %v", i, err)
+		} else if string(dst) != "lead"+string(test.dec) {
+			t.Errorf("#%d: got: %#v want: %#v", i, dst, "lead"+string(test.dec))
+		}
 	}
 }