Make sure that Interface() is not called on private values.

equal.go

@@ -147,6 +147,18 @@ func (t *T) isNil(obj interface{}) bool {
 	return v.IsNil()
 }
 
+// Returns a string representation of a Value that is sanitized based on what
+// we are allowed to see. Private fields can not be exposed via a call to
+// Interface() and trying will cause a panic, so we must use String()
+// in that case.
+func stringValue(v reflect.Value) string {
+	if v.CanInterface() {
+		return fmt.Sprintf("%#v", v.Interface())
+	} else {
+		return v.String()
+	}
+}
+
 // Deep comparison. This is based on golang 1.2's reflect.Equal functionality.
 func (t *T) deepEqual(
 	desc string, have, want reflect.Value, ignores []string,
@@ -206,13 +218,13 @@ func (t *T) deepEqual(
 	checkNil := func() bool {
 		if want.IsNil() && !have.IsNil() {
 			diffs = append(diffs, fmt.Sprintf("%s: not equal.", desc))
-			diffs = append(diffs, fmt.Sprintf("  have: %#v", have.Interface()))
+			diffs = append(diffs, fmt.Sprintf("  have: %s", stringValue(have)))
 			diffs = append(diffs, "  want: nil")
 			return true
 		} else if !want.IsNil() && have.IsNil() {
 			diffs = append(diffs, fmt.Sprintf("%s: not equal.", desc))
 			diffs = append(diffs, "  have: nil")
-			diffs = append(diffs, fmt.Sprintf("  want: %#v", want.Interface()))
+			diffs = append(diffs, fmt.Sprintf("  want: %s", stringValue(want)))
 			return true
 		}
 		return false
@@ -224,8 +236,8 @@ func (t *T) deepEqual(
 			diffs = append(diffs, fmt.Sprintf(
 				"%s: (len(have): %d, len(want): %d)",
 				desc, have.Len(), want.Len()))
-			diffs = append(diffs, fmt.Sprintf("  have: %#v", have.Interface()))
-			diffs = append(diffs, fmt.Sprintf("  want: %#v", want.Interface()))
+			diffs = append(diffs, fmt.Sprintf("  have: %s", stringValue(have)))
+			diffs = append(diffs, fmt.Sprintf("  want: %s", stringValue(want)))
 			return true
 		}
 		return false

equal_test.go

@@ -15,6 +15,7 @@
 package testlib
 
 import (
+	"bytes"
 	"fmt"
 	"math/rand"
 	"os"
@@ -259,6 +260,15 @@ func TestT_EqualAndNotEqual(t *testing.T) {
 		[]interface{}{sCust1, sCust2},
 		[]interface{}{dCust1})
 
+	// Structures with private, unexported fields.
+	sBuff1 := bytes.NewBuffer([]byte{1, 2, 3})
+	sBuff2 := bytes.NewBuffer([]byte{1, 2, 3})
+	dBuff1 := bytes.NewBuffer([]byte{1, 2, 3, 4})
+	dBuff2 := bytes.NewBuffer([]byte{1})
+	runTest(
+		[]interface{}{sBuff1, sBuff2},
+		[]interface{}{dBuff1, dBuff2})
+
 	// Structures in a slice.
 	sCustSlice1 := []testEqualCustomStruct{sCust1, sCust2}
 	sCustSlice2 := []testEqualCustomStruct{sCust1, sCust2}