Revert "hex: fix panic in Decode when len(src) > 2*len(dst)"

This reverts CL 461958 and CL 465855.

Reason for revert: This introduced an irreconcilable inconsistency with Encode

Fixes #58391.

Change-Id: Ifd01a04d433b24c092b73e627b8149a5851c2bca
Reviewed-on: https://go-review.googlesource.com/c/go/+/469615
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Run-TryBot: Joseph Tsai <[email protected]>
Auto-Submit: Joseph Tsai <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: dsnet

src/encoding/hex/hex.go

@@ -88,9 +88,6 @@ func Decode(dst, src []byte) (int, error) {
 		if b > 0x0f {
 			return i, InvalidByteError(q)
 		}
-		if i >= len(dst) {
-			return i, errors.New("encoding/hex: output buffer too small")
-		}
 		dst[i] = (a << 4) | b
 		i++
 	}

src/encoding/hex/hex_test.go

@@ -55,18 +55,6 @@ func TestDecode(t *testing.T) {
 	}
 }
 
-func TestDecodeDstTooSmall(t *testing.T) {
-	dst := make([]byte, 1)
-	src := []byte{'0', '1', '2', '3'}
-	n, err := Decode(dst, src)
-	if err == nil {
-		t.Errorf("expected Decode to return an error, but it returned none")
-	}
-	if !bytes.Equal(dst[:n], []byte{0x01}) {
-		t.Errorf("output mismatch: got %x, want 01", dst[:n])
-	}
-}
-
 func TestEncodeToString(t *testing.T) {
 	for i, test := range encDecTests {
 		s := EncodeToString(test.dec)