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## net.i2p.client.streaming
Class Packet

    java.lang.Object
      net.i2p.client.streaming.Packet

Direct Known Subclasses:
  PacketLocal

     class Packet

extends Object

Contain a single packet transferred as part of a streaming connection. The data format is as follows:

- `sendStreamId` [4 byte value]
- `receiveStreamId` [4 byte value]
- `sequenceNum` [4 byte unsigned integer]
- `ackThrough` [4 byte unsigned integer]
- number of NACKs [1 byte unsigned integer]
- that many `NACKs`
- `resendDelay` [1 byte integer]
- flags [2 byte value]
- option data size [2 byte integer]
- option data specified by those flags [0 or more bytes]
- payload [remaining packet size]

The flags field above specifies some metadata about the packet, and in turn may require certain additional data to be included. The flags are as follows (with any data structures specified added to the options area in the given order):

1. `FLAG_SYNCHRONIZE`: no option data
2. `FLAG_CLOSE`: no option data
3. `FLAG_RESET`: no option data
4. `FLAG_SIGNATURE_INCLUDED`: `Signature`
5. `FLAG_SIGNATURE_REQUESTED`: no option data
6. `FLAG_FROM_INCLUDED`: `Destination`
7. `FLAG_DELAY_REQUESTED`: 2 byte integer
8. `FLAG_MAX_PACKET_SIZE_INCLUDED`: 2 byte integer
9. `FLAG_PROFILE_INTERACTIVE`: no option data
10. `FLAG_ECHO`: no option data
11. `FLAG_NO_ACK`: no option data - this appears to be unused, we always ack, even for the first packet

If the signature is included, it uses the Destination's DSA key to sign the entire header and payload with the space in the options for the signature being set to all zeroes.

If the sequenceNum is 0 and the SYN is not set, this is a plain ACK packet that should not be ACKed

Field Summary
`static int` | `DEFAULT_MAX_SIZE`
`static int` | `FLAG_CLOSE` The sender of this packet will not be sending any more payload data.
`static int` | `FLAG_DELAY_REQUESTED` This packet includes an explicit request for the recipient to delay sending any packets with data for a given amount of time.
`static int` | `FLAG_ECHO` If set, this packet is a ping (if sendStreamId is set) or a ping reply (if receiveStreamId is set).
`static int` | `FLAG_FROM_INCLUDED` This packet includes the full I2P destination of the packet's sender.
`static int` | `FLAG_MAX_PACKET_SIZE_INCLUDED` This packet includes a request that the recipient not send any subsequent packets with payloads greater than a specific size.
`static int` | `FLAG_NO_ACK` If set, this packet doesn't really want to ack anything
`static int` | `FLAG_PROFILE_INTERACTIVE` If set, this packet is travelling as part of an interactive flow, meaning it is more lag sensitive than throughput sensitive.
`static int` | `FLAG_RESET` This packet is being sent to signify that the socket does not exist (or, if in response to an initial synchronize packet, that the connection was refused).
`static int` | `FLAG_SIGNATURE_INCLUDED` This packet contains a DSA signature from the packet's sender.
`static int` | `FLAG_SIGNATURE_REQUESTED` This packet wants the recipient to include signatures on subsequent packets sent to the creator of this packet.
`static int` | `FLAG_SYNCHRONIZE` This packet is creating a new socket connection (if the receiveStreamId is STREAM_ID_UNKNOWN) or it is acknowledging a request to create a connection and in turn is accepting the socket.
`protected static int` | `MAX_DELAY_REQUEST`
`static int` | `MAX_PAYLOAD_SIZE`
`static long` | `MAX_STREAM_ID`
`static long` | `STREAM_ID_UNKNOWN` The receiveStreamId will be set to this when the packet doesn't know what ID will be assigned by the remote peer (aka this is the initial synchronize packet)

Constructor Summary
`Packet()`

Method Summary
`ByteArray` | `acquirePayload()`
`protected StringBuilder` | `formatAsString()`
`long` | `getAckThrough()` The highest packet sequence number that received on the receiveStreamId.
`long[]` | `getNacks()` List of packet sequence numbers below the getAckThrough() value have not been received.
`int` | `getOptionalDelay()` How many milliseconds the sender of this packet wants the recipient to wait before sending any more data (only valid if the flag for it is set)
`Destination` | `getOptionalFrom()` the sender of the packet (only included if the flag for it is set)
`int` | `getOptionalMaxSize()` What is the largest payload the sender of this packet wants to receive?
`Signature` | `getOptionalSignature()` the signature on the packet (only included if the flag for it is set)
`ByteArray` | `getPayload()` get the actual payload of the message.
`int` | `getPayloadSize()`
`long` | `getReceiveStreamId()` stream the replies should be sent on.
`int` | `getResendDelay()` How long is the creator of this packet going to wait before resending this packet (if it hasn't yet been ACKed).
`long` | `getSendStreamId()` what stream do we send data to the peer on?
`long` | `getSequenceNum()` 0-indexed sequence number for this Packet in the sendStream
`boolean` | `isFlagSet(int flag)` is a particular flag set on this packet?
`void` | `readPacket(byte[] buffer, int offset, int length)` Read the packet from the buffer (starting at the offset) and return the number of bytes read.
`void` | `releasePayload()`
`void` | `setAckThrough(long id)`
`void` | `setFlag(int flag)`
`void` | `setFlag(int flag, boolean set)`
`void` | `setFlags(int flags)`
`void` | `setNacks(long[] nacks)`
`void` | `setOptionalDelay(int delayMs)`
`void` | `setOptionalFrom(Destination from)`
`void` | `setOptionalMaxSize(int numBytes)`
`void` | `setOptionalSignature(Signature sig)`
`void` | `setPayload(ByteArray payload)`
`void` | `setReceiveStreamId(long id)`
`void` | `setResendDelay(int numSeconds)` Unused.
`void` | `setSendStreamId(long id)`
`void` | `setSequenceNum(long num)`
`(package private) static String` | `toId(long id)`
`String` | `toString()`
`boolean` | `verifySignature(I2PAppContext ctx, Destination from, byte[] buffer)` Determine whether the signature on the data is valid.
`int` | `writePacket(byte[] buffer, int offset)` Write the packet to the buffer (starting at the offset) and return the number of bytes written.
`int` | `writeSignedPacket(byte[] buffer, int offset, I2PAppContext ctx, SigningPrivateKey key)` Sign and write the packet to the buffer (starting at the offset) and return the number of bytes written.
`int` | `writtenSize()` how large would this packet be if we wrote it

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Field Detail

### STREAM_ID_UNKNOWN

    public static final long STREAM_ID_UNKNOWN

  The receiveStreamId will be set to this when the packet doesn't know what ID will be assigned by the remote peer (aka this is the initial synchronize packet)

  See Also:
    Constant Field Values

### MAX_STREAM_ID

    public static final long MAX_STREAM_ID

See Also:
  Constant Field Values

### FLAG_SYNCHRONIZE

    public static final int FLAG_SYNCHRONIZE

  This packet is creating a new socket connection (if the receiveStreamId is STREAM_ID_UNKNOWN) or it is acknowledging a request to create a connection and in turn is accepting the socket.

  See Also:
    Constant Field Values

### FLAG_CLOSE

    public static final int FLAG_CLOSE

  The sender of this packet will not be sending any more payload data.

  See Also:
    Constant Field Values

### FLAG_RESET

    public static final int FLAG_RESET

  This packet is being sent to signify that the socket does not exist (or, if in response to an initial synchronize packet, that the connection was refused).

  See Also:
    Constant Field Values

### FLAG_SIGNATURE_INCLUDED

    public static final int FLAG_SIGNATURE_INCLUDED

  This packet contains a DSA signature from the packet's sender. This signature is within the packet options. All synchronize packets must have this flag set.

  See Also:
    Constant Field Values

### FLAG_SIGNATURE_REQUESTED

    public static final int FLAG_SIGNATURE_REQUESTED

  This packet wants the recipient to include signatures on subsequent packets sent to the creator of this packet.

  See Also:
    Constant Field Values

### FLAG_FROM_INCLUDED

    public static final int FLAG_FROM_INCLUDED

  This packet includes the full I2P destination of the packet's sender. The initial synchronize packet must have this flag set.

  See Also:
    Constant Field Values

### FLAG_DELAY_REQUESTED

    public static final int FLAG_DELAY_REQUESTED

  This packet includes an explicit request for the recipient to delay sending any packets with data for a given amount of time.

  See Also:
    Constant Field Values

### FLAG_MAX_PACKET_SIZE_INCLUDED

    public static final int FLAG_MAX_PACKET_SIZE_INCLUDED

  This packet includes a request that the recipient not send any subsequent packets with payloads greater than a specific size. If not set and no prior value was delivered, the maximum value will be assumed (approximately 32KB).

  See Also:
    Constant Field Values

### FLAG_PROFILE_INTERACTIVE

    public static final int FLAG_PROFILE_INTERACTIVE

  If set, this packet is travelling as part of an interactive flow, meaning it is more lag sensitive than throughput sensitive. aka send data ASAP rather than waiting around to send full packets.

  See Also:
    Constant Field Values

### FLAG_ECHO

    public static final int FLAG_ECHO

  If set, this packet is a ping (if sendStreamId is set) or a ping reply (if receiveStreamId is set).

  See Also:
    Constant Field Values

### FLAG_NO_ACK

    public static final int FLAG_NO_ACK

  If set, this packet doesn't really want to ack anything

  See Also:
    Constant Field Values

### DEFAULT_MAX_SIZE

    public static final int DEFAULT_MAX_SIZE

See Also:
  Constant Field Values

### MAX_DELAY_REQUEST

    protected static final int MAX_DELAY_REQUEST

See Also:
  Constant Field Values

### MAX_PAYLOAD_SIZE

    public static final int MAX_PAYLOAD_SIZE

See Also:
  Constant Field Values

Constructor Detail

### Packet

    public Packet()

Method Detail

### getSendStreamId

    public long getSendStreamId()

  what stream do we send data to the peer on?

  Returns:
    stream ID we use to send data

### setSendStreamId

    public void setSendStreamId(long id)

### getReceiveStreamId

    public long getReceiveStreamId()

  stream the replies should be sent on. this should be 0 if the connection is still being built.

  Returns:
    stream ID we use to get data, zero if the connection is still being built.

### setReceiveStreamId

    public void setReceiveStreamId(long id)

### getSequenceNum

    public long getSequenceNum()

  0-indexed sequence number for this Packet in the sendStream

  Returns:
    0-indexed sequence number for current Packet in current sendStream

### setSequenceNum

    public void setSequenceNum(long num)

### getAckThrough

    public long getAckThrough()

  The highest packet sequence number that received on the receiveStreamId. This field is ignored on the initial connection packet (where receiveStreamId is the unknown id) or if FLAG_NO_ACK is set.

  Returns:
    The highest packet sequence number received on receiveStreamId

### setAckThrough

    public void setAckThrough(long id)

### getNacks

    public long[] getNacks()

  List of packet sequence numbers below the getAckThrough() value have not been received. this may be null.

  Returns:
    List of packet sequence numbers not ACKed, or null if there are none.

### setNacks

    public void setNacks(long[] nacks)

### getResendDelay

    public int getResendDelay()

  How long is the creator of this packet going to wait before resending this packet (if it hasn't yet been ACKed). The value is seconds since the packet was created. Unused. Broken before release 0.7.8 Not to be used without sanitizing for huge values. Setters from options did not divide by 1000, and the options default is 1000, so the value sent in the 1-byte field was always 1000 & 0xff = 0xe8 = 232

  Returns:
    Delay before resending a packet in seconds.

### setResendDelay

    public void setResendDelay(int numSeconds)

  Unused. Broken before release 0.7.8 See above

### getPayload

    public ByteArray getPayload()

  get the actual payload of the message. may be null

  Returns:
    the payload of the message, null if none.

### setPayload

    public void setPayload(ByteArray payload)

### getPayloadSize

    public int getPayloadSize()

### releasePayload

    public void releasePayload()

### acquirePayload

    public ByteArray acquirePayload()

### isFlagSet

    public boolean isFlagSet(int flag)

  is a particular flag set on this packet?

  Parameters:
    `flag` - bitmask of any flag(s)
  Returns:
    true if set, false if not.

### setFlag

    public void setFlag(int flag)

### setFlag

    public void setFlag(int flag,
                        boolean set)

### setFlags

    public void setFlags(int flags)

### getOptionalSignature

    public Signature getOptionalSignature()

  the signature on the packet (only included if the flag for it is set)

  Returns:
    signature on the packet if the flag for signatures is set

### setOptionalSignature

    public void setOptionalSignature(Signature sig)

### getOptionalFrom

    public Destination getOptionalFrom()

  the sender of the packet (only included if the flag for it is set)

  Returns:
    the sending Destination

### setOptionalFrom

    public void setOptionalFrom(Destination from)

### getOptionalDelay

    public int getOptionalDelay()

  How many milliseconds the sender of this packet wants the recipient to wait before sending any more data (only valid if the flag for it is set)

  Returns:
    How long the sender wants the recipient to wait before sending any more data in ms.

### setOptionalDelay

    public void setOptionalDelay(int delayMs)

### getOptionalMaxSize

    public int getOptionalMaxSize()

  What is the largest payload the sender of this packet wants to receive?

  Returns:
    Maximum payload size sender can receive (MRU)

### setOptionalMaxSize

    public void setOptionalMaxSize(int numBytes)

### writePacket

    public int writePacket(byte[] buffer,
                           int offset)
                    throws IllegalStateException

  Write the packet to the buffer (starting at the offset) and return the number of bytes written.

  Parameters:
    `buffer` - bytes to write to a destination
    `offset` - starting point in the buffer to send
  Returns:
    Count actually written
  Throws:
    `IllegalStateException` - if there is data missing or otherwise b0rked

### writtenSize

    public int writtenSize()
                    throws IllegalStateException

  how large would this packet be if we wrote it

  Returns:
    How large the current packet would be
  Throws:
    `IllegalStateException`

### readPacket

    public void readPacket(byte[] buffer,
                           int offset,
                           int length)
                    throws IllegalArgumentException

  Read the packet from the buffer (starting at the offset) and return the number of bytes read.

  Parameters:
    `buffer` - packet buffer containing the data
    `offset` - index into the buffer to start readign
    `length` - how many bytes within the buffer past the offset are part of the packet?
  Throws:
    `IllegalArgumentException` - if the data is b0rked

### verifySignature

    public boolean verifySignature(I2PAppContext ctx,
                                   Destination from,
                                   byte[] buffer)

  Determine whether the signature on the data is valid.

  Parameters:
    `ctx` - Application context
    `from` - the Destination the data came from
    `buffer` - data to validate with signature
  Returns:
    true if the signature exists and validates against the data, false otherwise.

### writeSignedPacket

    public int writeSignedPacket(byte[] buffer,
                                 int offset,
                                 I2PAppContext ctx,
                                 SigningPrivateKey key)
                          throws IllegalStateException

  Sign and write the packet to the buffer (starting at the offset) and return the number of bytes written.

  Parameters:
    `buffer` - data to be written
    `offset` - starting point in the buffer
    `ctx` - Application Context
    `key` - signing key
  Returns:
    Count of bytes written
  Throws:
    `IllegalStateException` - if there is data missing or otherwise b0rked

### toString

    public String toString()

  Overrides:
    `toString` in class `Object`

### formatAsString

    protected StringBuilder formatAsString()

### toId

    static final String toId(long id)

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