Package net.i2p.router.tunnel

Class FragmentHandler

  • Direct Known Subclasses:
    RouterFragmentHandler
    class FragmentHandler
extends Object
    Handle fragments at the endpoint of a tunnel, peeling off fully completed I2NPMessages when they arrive, and dropping fragments if they take too long to arrive. From tunnel-alt.html:

    When the gateway wants to deliver data through the tunnel, it first gathers zero or more I2NP messages, selects how much padding will be used, fragments it across the necessary number of 1KB tunnel messages, and decides how each I2NP message should be handled by the tunnel endpoint, encoding that data into the raw tunnel payload:

    • The 4 byte Tunnel ID
    • The 16 byte IV
    • the first 4 bytes of the SHA256 of (the remaining preprocessed data concatenated with the IV), using the IV as will be seen on the tunnel endpoint (for outbound tunnels), or the IV as was seen on the tunnel gateway (for inbound tunnels) (see below for IV processing).
    • 0 or more bytes containing random nonzero integers
    • 1 byte containing 0x00
    • a series of zero or more { instructions, message } pairs

    Note that the padding, if any, must be before the instruction/message pairs. there is no provision for padding at the end.

    The instructions are encoded with a single control byte, followed by any necessary additional information. The first bit in that control byte determines how the remainder of the header is interpreted - if it is not set, the message is either not fragmented or this is the first fragment in the message. If it is set, this is a follow on fragment.

    With the first (leftmost or MSB) bit being 0, the instructions are:

    • 1 byte control byte:
            bit 0: is follow on fragment?  (1 = true, 0 = false, must be 0)
   bits 1-2: delivery type
             (0x0 = LOCAL, 0x01 = TUNNEL, 0x02 = ROUTER)
      bit 3: delay included?  (1 = true, 0 = false) (unimplemented)
      bit 4: fragmented?  (1 = true, 0 = false)
      bit 5: extended options?  (1 = true, 0 = false) (unimplemented)
   bits 6-7: reserved
    • if the delivery type was TUNNEL, a 4 byte tunnel ID
    • if the delivery type was TUNNEL or ROUTER, a 32 byte router hash
    • if the delay included flag is true, a 1 byte value (unimplemented):
            bit 0: type (0 = strict, 1 = randomized)
   bits 1-7: delay exponent (2^value minutes)
    • if the fragmented flag is true, a 4 byte message ID
    • if the extended options flag is true (unimplemented):
         = a 1 byte option size (in bytes)
   = that many bytes
    • 2 byte size of the I2NP message or this fragment

    If the first bit being 1, the instructions are:

    • 1 byte control byte:
            bit 0: is follow on fragment?  (1 = true, 0 = false, must be 1)
   bits 1-6: fragment number
      bit 7: is last? (1 = true, 0 = false)
    • 4 byte message ID (same one defined in the first fragment)
    • 2 byte size of this fragment

    The I2NP message is encoded in its standard form, and the preprocessed payload must be padded to a multiple of 16 bytes. The total size, including the tunnel ID and IV, is 1028 bytes.

    • Field Detail

      • _log

        protected final Log _log

      • MAX_DEFRAGMENT_TIME

        static long MAX_DEFRAGMENT_TIME
        don't wait more than this long to completely receive a fragmented message

      • MASK_IS_SUBSEQUENT

        static final byte MASK_IS_SUBSEQUENT
        is this a follw up byte?
        See Also:
        Constant Field Values

      • MASK_TYPE

        static final byte MASK_TYPE
        how should this be delivered. shift this 5 the right and get TYPE_*
        See Also:
        Constant Field Values

      • MASK_FRAGMENTED

        static final byte MASK_FRAGMENTED
        is this the first of a fragmented message?
        See Also:
        Constant Field Values

      • MASK_EXTENDED

        static final byte MASK_EXTENDED
        are there follow up headers? UNIMPLEMENTED
        See Also:
        Constant Field Values

    • Method Detail

      • receiveTunnelMessage

        public boolean receiveTunnelMessage​(byte[] preprocessed,
                                    int offset,
                                    int length)
        Receive the raw preprocessed message at the endpoint, parsing out each of the fragments, using those to fill various FragmentedMessages, and sending the resulting I2NPMessages where necessary. The received fragments are all verified.
        Returns:
        ok (false if corrupt)

      • getCompleteCount

        public int getCompleteCount()

      • getFailedCount

        public int getFailedCount()

      • noteReception

        protected void noteReception​(long messageId,
                             int fragmentId,
                             Object status)

      • noteCompletion

        protected void noteCompletion​(long messageId)

      • noteFailure

        protected void noteFailure​(long messageId,
                           String status)