added PrefixEndBytes (#186)

* added PrefixToBytes

* added test

* added comment

common/byteslice.go

@@ -45,3 +45,29 @@ func TrimmedString(b []byte) string {
 	return string(bytes.TrimLeft(b, trimSet))
 
 }
+
+// PrefixEndBytes returns the end byteslice for a noninclusive range
+// that would include all byte slices for which the input is the prefix
+func PrefixEndBytes(prefix []byte) []byte {
+	if prefix == nil {
+		return nil
+	}
+
+	end := make([]byte, len(prefix))
+	copy(end, prefix)
+	finished := false
+
+	for !finished {
+		if end[len(end)-1] != byte(255) {
+			end[len(end)-1]++
+			finished = true
+		} else {
+			end = end[:len(end)-1]
+			if len(end) == 0 {
+				end = nil
+				finished = true
+			}
+		}
+	}
+	return end
+}

common/byteslice_test.go

@@ -0,0 +1,28 @@
+package common
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPrefixEndBytes(t *testing.T) {
+	assert := assert.New(t)
+
+	var testCases = []struct {
+		prefix   []byte
+		expected []byte
+	}{
+		{[]byte{byte(55), byte(255), byte(255), byte(0)}, []byte{byte(55), byte(255), byte(255), byte(1)}},
+		{[]byte{byte(55), byte(255), byte(255), byte(15)}, []byte{byte(55), byte(255), byte(255), byte(16)}},
+		{[]byte{byte(55), byte(200), byte(255)}, []byte{byte(55), byte(201)}},
+		{[]byte{byte(55), byte(255), byte(255)}, []byte{byte(56)}},
+		{[]byte{byte(255), byte(255), byte(255)}, nil},
+		{nil, nil},
+	}
+
+	for _, test := range testCases {
+		end := PrefixEndBytes(test.prefix)
+		assert.Equal(test.expected, end)
+	}
+}