Add dedicated tests for base85 decoding

These are fairly basic as the decoder is also exercised by the fragment
parsing tests, but they cover some errror cases that may not be covered
otherwise.

Author: bluekeyes

gitdiff/base85.go

@@ -4,21 +4,17 @@ import (
 	"fmt"
 )
 
-const (
-	base85Alphabet = "0123456789" +
-		"ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
-		"abcdefghijklmnopqrstuvwxyz" +
-		"!#$%&()*+-;<=>?@^_`{|}~"
-)
-
 var (
-	de85 map[byte]byte
+	b85Table map[byte]byte
+	b85Alpha = []byte(
+		"0123456789" + "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "abcdefghijklmnopqrstuvwxyz" + "!#$%&()*+-;<=>?@^_`{|}~",
+	)
 )
 
 func init() {
-	de85 = make(map[byte]byte)
-	for i, c := range base85Alphabet {
-		de85[byte(c)] = byte(i)
+	b85Table = make(map[byte]byte)
+	for i, c := range b85Alpha {
+		b85Table[c] = byte(i)
 	}
 }
 
@@ -29,7 +25,7 @@ func base85Decode(dst, src []byte) error {
 	var v uint32
 	var n, ndst int
 	for i, b := range src {
-		if b, ok := de85[b]; ok {
+		if b, ok := b85Table[b]; ok {
 			v = 85*v + uint32(b)
 			n++
 		} else {
@@ -50,7 +46,7 @@ func base85Decode(dst, src []byte) error {
 		return fmt.Errorf("base85 data terminated by underpadded sequence")
 	}
 	if ndst < len(dst) {
-		return fmt.Errorf("base85 data is too short: %d < %d", ndst, len(dst))
+		return fmt.Errorf("base85 data underrun: %d < %d", ndst, len(dst))
 	}
 	return nil
 }

gitdiff/base85_test.go

@@ -0,0 +1,60 @@
+package gitdiff
+
+import (
+	"testing"
+)
+
+func TestBase85Decode(t *testing.T) {
+	tests := map[string]struct {
+		Input  string
+		Output []byte
+		Err    bool
+	}{
+		"twoBytes": {
+			Input:  "%KiWV",
+			Output: []byte{0xCA, 0xFE},
+		},
+		"fourBytes": {
+			Input:  "007GV",
+			Output: []byte{0x0, 0x0, 0xCA, 0xFE},
+		},
+		"sixBytes": {
+			Input:  "007GV%KiWV",
+			Output: []byte{0x0, 0x0, 0xCA, 0xFE, 0xCA, 0xFE},
+		},
+		"invalidCharacter": {
+			Input: "00'GV",
+			Err:   true,
+		},
+		"underpaddedSequence": {
+			Input: "007G",
+			Err:   true,
+		},
+		"dataUnderrun": {
+			Input:  "007GV",
+			Output: make([]byte, 8),
+			Err:    true,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			dst := make([]byte, len(test.Output))
+			err := base85Decode(dst, []byte(test.Input))
+			if test.Err {
+				if err == nil {
+					t.Fatalf("expected error decoding base85 data, but got nil")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error decoding base85 data: %v", err)
+			}
+			for i, b := range test.Output {
+				if dst[i] != b {
+					t.Errorf("incorrect byte at index %d: expected 0x%X, actual 0x%X", i, b, dst[i])
+				}
+			}
+		})
+	}
+}