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67 lines
2 KiB
Go
67 lines
2 KiB
Go
package stun
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import (
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"errors"
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"hash/crc32"
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)
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// FingerprintAttr represents FINGERPRINT attribute.
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//
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// RFC 5389 Section 15.5
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type FingerprintAttr struct{}
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// ErrFingerprintMismatch means that computed fingerprint differs from expected.
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var ErrFingerprintMismatch = errors.New("fingerprint check failed")
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// Fingerprint is shorthand for FingerprintAttr.
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//
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// Example:
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//
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// m := New()
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// Fingerprint.AddTo(m)
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var Fingerprint FingerprintAttr
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const (
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fingerprintXORValue uint32 = 0x5354554e //nolint:staticcheck
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fingerprintSize = 4 // 32 bit
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)
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// FingerprintValue returns CRC-32 of b XOR-ed by 0x5354554e.
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//
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// The value of the attribute is computed as the CRC-32 of the STUN message
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// up to (but excluding) the FINGERPRINT attribute itself, XOR'ed with
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// the 32-bit value 0x5354554e (the XOR helps in cases where an
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// application packet is also using CRC-32 in it).
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func FingerprintValue(b []byte) uint32 {
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return crc32.ChecksumIEEE(b) ^ fingerprintXORValue // XOR
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}
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// AddTo adds fingerprint to message.
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func (FingerprintAttr) AddTo(m *Message) error {
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l := m.Length
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// length in header should include size of fingerprint attribute
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m.Length += fingerprintSize + attributeHeaderSize // increasing length
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m.WriteLength() // writing Length to Raw
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b := make([]byte, fingerprintSize)
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val := FingerprintValue(m.Raw)
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bin.PutUint32(b, val)
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m.Length = l
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m.Add(AttrFingerprint, b)
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return nil
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}
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// Check reads fingerprint value from m and checks it, returning error if any.
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// Can return *AttrLengthErr, ErrAttributeNotFound, and *CRCMismatch.
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func (FingerprintAttr) Check(m *Message) error {
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b, err := m.Get(AttrFingerprint)
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if err != nil {
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return err
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}
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if err = CheckSize(AttrFingerprint, len(b), fingerprintSize); err != nil {
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return err
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}
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val := bin.Uint32(b)
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attrStart := len(m.Raw) - (fingerprintSize + attributeHeaderSize)
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expected := FingerprintValue(m.Raw[:attrStart])
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return checkFingerprint(val, expected)
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}
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