encoding/base32: support custom and disabled padding when decoding

CL 38634 added support for custom (and disabled) padding characters
when encoding, but didn't update the decoding paths. This adds
decoding support.

Fixes #20854

Change-Id: I9fb1a0aaebb27f1204c9f726a780d5784eb71024
Reviewed-on: https://go-review.googlesource.com/47341
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/src/encoding/base32/base32_test.go b/src/encoding/base32/base32_test.go
index ee7525c997..6fe292b476 100644
--- a/src/encoding/base32/base32_test.go
+++ b/src/encoding/base32/base32_test.go
@@ -490,3 +490,91 @@ func TestWithoutPadding(t *testing.T) {
 		}
 	}
 }
+
+func TestDecodeWithPadding(t *testing.T) {
+	encodings := []*Encoding{
+		StdEncoding,
+		StdEncoding.WithPadding('-'),
+		StdEncoding.WithPadding(NoPadding),
+	}
+
+	for i, enc := range encodings {
+		for _, pair := range pairs {
+
+			input := pair.decoded
+			encoded := enc.EncodeToString([]byte(input))
+
+			decoded, err := enc.DecodeString(encoded)
+			if err != nil {
+				t.Errorf("DecodeString Error for encoding %d (%q): %v", i, input, err)
+			}
+
+			if input != string(decoded) {
+				t.Errorf("Unexpected result for encoding %d: got %q; want %q", i, decoded, input)
+			}
+		}
+	}
+}
+
+func TestDecodeWithWrongPadding(t *testing.T) {
+	encoded := StdEncoding.EncodeToString([]byte("foobar"))
+
+	_, err := StdEncoding.WithPadding('-').DecodeString(encoded)
+	if err == nil {
+		t.Error("expected error")
+	}
+
+	_, err = StdEncoding.WithPadding(NoPadding).DecodeString(encoded)
+	if err == nil {
+		t.Error("expected error")
+	}
+}
+
+func TestEncodedDecodedLen(t *testing.T) {
+	type test struct {
+		in      int
+		wantEnc int
+		wantDec int
+	}
+	data := bytes.Repeat([]byte("x"), 100)
+	for _, test := range []struct {
+		name  string
+		enc   *Encoding
+		cases []test
+	}{
+		{"StdEncoding", StdEncoding, []test{
+			{0, 0, 0},
+			{1, 8, 5},
+			{5, 8, 5},
+			{6, 16, 10},
+			{10, 16, 10},
+		}},
+		{"NoPadding", StdEncoding.WithPadding(NoPadding), []test{
+			{0, 0, 0},
+			{1, 2, 5},
+			{2, 4, 5},
+			{5, 8, 5},
+			{6, 10, 10},
+			{7, 12, 10},
+			{10, 16, 10},
+			{11, 18, 15},
+		}},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			for _, tc := range test.cases {
+				encLen := test.enc.EncodedLen(tc.in)
+				decLen := test.enc.DecodedLen(encLen)
+				enc := test.enc.EncodeToString(data[:tc.in])
+				if len(enc) != encLen {
+					t.Fatalf("EncodedLen(%d) = %d but encoded to %q (%d)", tc.in, encLen, enc, len(enc))
+				}
+				if encLen != tc.wantEnc {
+					t.Fatalf("EncodedLen(%d) = %d; want %d", tc.in, encLen, tc.wantEnc)
+				}
+				if decLen != tc.wantDec {
+					t.Fatalf("DecodedLen(%d) = %d; want %d", encLen, decLen, tc.wantDec)
+				}
+			}
+		})
+	}
+}