Räägi mulle snifferside tööpõhimõttest ja nende kasutamisest testimisel.

Sniffers (or network traffic analyzers) intercept, record, and analyze data packets transmitted over a network. They operate at the network layer (or below) and "listen" to all traffic accessible to the network interface. The principle is based on putting the network card into "promiscuous mode," allowing it to accept all packets passing through the network segment, not just those addressed to it.

Main stages of operation:

1. Capture: Collecting network packets from the interface.
2. Filtering: Selecting packets based on specified criteria (port, protocol, IP address, etc.).
3. Analysis: Decoding packet contents according to protocol standards (TCP, UDP, HTTP, DNS, etc.).
4. Presentation: Displaying data in a user-friendly format.

Application in testing:

• Network interaction debugging: Identifying issues with data transfer between client and server, verifying correctness of requests and responses.
• Security testing: Finding vulnerabilities related to the transmission of unencrypted data (e.g., logins and passwords).
• Performance analysis: Measuring latency, throughput, identifying "bottlenecks" in the network.
• Protocol compliance checking: Ensuring correct packet formation and adherence to network protocols.
• Integration testing: Verifying correct interaction between different system components using network communication.

Examples of popular tools: Wireshark, tcpdump, Fiddler.