all: report detailed fingerprint mismatch only in debug mode

api/stun1.txt

@@ -175,7 +175,6 @@ pkg github.com/gortc/stun, method (AttrType) Required() bool
 pkg github.com/gortc/stun, method (AttrType) String() string
 pkg github.com/gortc/stun, method (AttrType) Value() uint16
 pkg github.com/gortc/stun, method (Attributes) Get(AttrType) (RawAttribute, bool)
-pkg github.com/gortc/stun, method (CRCMismatch) Error() string
 pkg github.com/gortc/stun, method (CloseErr) Error() string
 pkg github.com/gortc/stun, method (DecodeErr) Error() string
 pkg github.com/gortc/stun, method (DecodeErr) IsInvalidCookie() bool
@@ -231,9 +230,6 @@ pkg github.com/gortc/stun, type AttrOverflowErr struct, Max int
 pkg github.com/gortc/stun, type AttrOverflowErr struct, Type AttrType
 pkg github.com/gortc/stun, type AttrType uint16
 pkg github.com/gortc/stun, type Attributes []RawAttribute
-pkg github.com/gortc/stun, type CRCMismatch struct
-pkg github.com/gortc/stun, type CRCMismatch struct, Actual uint32
-pkg github.com/gortc/stun, type CRCMismatch struct, Expected uint32
 pkg github.com/gortc/stun, type Checker interface { Check }
 pkg github.com/gortc/stun, type Checker interface, Check(*Message) error
 pkg github.com/gortc/stun, type Client struct
@@ -318,6 +314,7 @@ pkg github.com/gortc/stun, var ErrClientClosed error
 pkg github.com/gortc/stun, var ErrClientNotInitialized error
 pkg github.com/gortc/stun, var ErrDecodeToNil error
 pkg github.com/gortc/stun, var ErrFingerprintBeforeIntegrity error
+pkg github.com/gortc/stun, var ErrFingerprintMismatch error
 pkg github.com/gortc/stun, var ErrIntegrityMismatch error
 pkg github.com/gortc/stun, var ErrNoConnection error
 pkg github.com/gortc/stun, var ErrNoDefaultReason error

checks.go

@@ -18,3 +18,10 @@ func checkHMAC(got, expected []byte) error {
 	}
 	return ErrIntegrityMismatch
 }
+
+func checkFingerprint(got, expected uint32) error {
+	if got == expected {
+		return nil
+	}
+	return ErrFingerprintMismatch
+}

checks_debug.go

@@ -25,3 +25,13 @@ func checkHMAC(got, expected []byte) error {
 		Actual:   got,
 	}
 }
+
+func checkFingerprint(got, expected uint32) error {
+	if got == expected {
+		return nil
+	}
+	return &CRCMismatch{
+		Actual:   got,
+		Expected: expected,
+	}
+}

fingerprint.go

@@ -1,7 +1,7 @@
 package stun
 
 import (
-	"fmt"
+	"errors"
 	"hash/crc32"
 )
 
@@ -10,18 +10,8 @@ import (
 // RFC 5389 Section 15.5
 type FingerprintAttr struct{}
 
-// CRCMismatch represents CRC check error.
+// ErrFingerprintMismatch means that computed fingerprint differs from expected.
-type CRCMismatch struct {
+var ErrFingerprintMismatch = errors.New("fingerprint check failed")
-	Expected uint32
-	Actual   uint32
-}
-
-func (m CRCMismatch) Error() string {
-	return fmt.Sprintf("CRC mismatch: %x (expected) != %x (actual)",
-		m.Expected,
-		m.Actual,
-	)
-}
 
 // Fingerprint is shorthand for FingerprintAttr.
 //
@@ -73,8 +63,5 @@ func (FingerprintAttr) Check(m *Message) error {
 	val := bin.Uint32(b)
 	attrStart := len(m.Raw) - (fingerprintSize + attributeHeaderSize)
 	expected := FingerprintValue(m.Raw[:attrStart])
-	if expected != val {
+	return checkFingerprint(val, expected)
-		return &CRCMismatch{Expected: expected, Actual: val}
-	}
-	return nil
 }

fingerprint_debug.go

@@ -0,0 +1,18 @@
+// +build debug
+
+package stun
+
+import "fmt"
+
+// CRCMismatch represents CRC check error.
+type CRCMismatch struct {
+	Expected uint32
+	Actual   uint32
+}
+
+func (m CRCMismatch) Error() string {
+	return fmt.Sprintf("CRC mismatch: %x (expected) != %x (actual)",
+		m.Expected,
+		m.Actual,
+	)
+}

fingerprint_test.go

@@ -34,8 +34,8 @@ func TestFingerprint_Check(t *testing.T) {
 		t.Error(err)
 	}
 	m.Raw[3] = m.Raw[3] + 1
-	if err, ok := Fingerprint.Check(m).(*CRCMismatch); !ok {
+	if err := Fingerprint.Check(m); err == nil {
-		t.Error(err, "should be *CRCMissmatch")
+		t.Error("should error")
 	}
 }
 

message_test.go

@@ -706,7 +706,11 @@ func ExampleMessage() {
 	}
 	fmt.Println("for corrupted message:")
 	decoded.Raw[22] = 33
-	fmt.Println("fingerprint:", Fingerprint.Check(decoded))
+	if Fingerprint.Check(decoded) == nil {
+		fmt.Println("fingerprint: ok")
+	} else {
+		fmt.Println("fingerprint: failed")
+	}
 
 	// Output:
 	// binding request l=48 attrs=3 id=AQIDBAUGBwgJAAEA buff length: 68
@@ -717,7 +721,7 @@ func ExampleMessage() {
 	// fingerprint is correct
 	// integrity ok
 	// for corrupted message:
-	// fingerprint: CRC mismatch: b36d2c38 (expected) != 8ef13141 (actual)
+	// fingerprint: failed
 }
 
 func TestAllocations(t *testing.T) {