Module org.jnetpcap

Package org.jnetpcap.windows

Class PcapSendQueue

java.lang.Object

org.jnetpcap.windows.PcapSendQueue

All Implemented Interfaces:

AutoCloseable

public class PcapSendQueue
extends Object
implements AutoCloseable

Represents a queue of raw packets for efficient batch transmission on Microsoft Windows platforms. This class provides functionality to queue multiple packets and transmit them either as quickly as possible or with precise timing synchronization.

Native Structure

Maps to the native pcap_send_queue structure:

 struct pcap_send_queue {
     u_int maxlen;  // Maximum size of the queue buffer in bytes
     u_int len;     // Current size of the queue in bytes
     char *buffer;  // Buffer containing queued packets
 };
 

Usage Example

 try (PcapSendQueue queue = new PcapSendQueue(65536)) { // 64KB queue
 	// Queue multiple packets
 	queue.queue(header1, packet1);
 	queue.queue(header2, packet2);
 
 	// Transmit all queued packets with timing synchronization
 	int bytesSent = queue.transmit(pcapHandle, true);
 }
 

Performance Considerations

• Using a send queue is more efficient than multiple pcap_sendpacket() calls due to reduced context switching
• Synchronized transmission (sync=true) provides microsecond precision but requires more CPU resources
• The CRC is automatically calculated by the network interface

Platform Support

This functionality is only available on Microsoft Windows platforms through WinPcap/Npcap.

Since:

WinPcap 1.0

See Also:

• PcapHeader

Constructor Summary

Constructors

Constructor	Description
PcapSendQueue(int capacity)	Creates a new send queue with specified capacity.

Method Summary

Modifier and Type	Method	Description
void	close()	Closes and deallocates the send queue.
int	len()	Returns the current size of the queue in bytes.
int	maxlen()	Returns the maximum capacity of the send queue in bytes.
int	queue(MemorySegment header, MemorySegment packet)	Adds a packet to the end of the send queue using native memory segments.
int	queue(PcapHeader header, byte[] packet, int offset)	Adds a packet to the end of the send queue using Java byte array.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

PcapSendQueue

public PcapSendQueue(int capacity)

Creates a new send queue with specified capacity. The capacity determines the maximum amount of packet data that can be queued.

Parameters:

capacity - Maximum size of the queue in bytes

Throws:

OutOfMemoryError - if native memory allocation fails

Method Details

close

public void close()

Closes and deallocates the send queue. This method must be called to prevent memory leaks.

Specified by:

close in interface AutoCloseable

Throws:

IllegalStateException - if the queue has already been closed

queue

public int queue(MemorySegment header,
 MemorySegment packet)

Adds a packet to the end of the send queue using native memory segments. Both packet header and data must be properly formatted in native memory.

Parameters:

header - The pcap_pkthdr structure containing timestamp and length

packet - The packet data buffer

Returns:

0 on success, -1 on failure (queue full)

queue

public int queue(PcapHeader header,
 byte[] packet,
 int offset)

Adds a packet to the end of the send queue using Java byte array. Automatically handles conversion to native memory format.

Parameters:

header - The pcap header containing timestamp and length

packet - The packet data as byte array

offset - Starting offset in the packet array

Returns:

0 on success, -1 on failure

Throws:

IllegalArgumentException - if offset is outside packet array bounds

maxlen

public int maxlen()

Returns the maximum capacity of the send queue in bytes.

Returns:

The maximum number of bytes that can be queued

len

public int len()

Returns the current size of the queue in bytes.

Returns:

The number of bytes currently queued