socketcap

Socketcap is a software utility designed to capture and analyze the network socket activity of a running application. It records the sequence of socket API calls made by the process, including creation of sockets, connections, data transmission, reception, and closure, along with metadata such as timestamps, process IDs, socket descriptors, IP addresses, ports, and protocol types. This provides visibility into how an application interacts with the network stack.

Most implementations achieve this through user-space instrumentation or dynamic interposition. Common techniques include function interposition via loaders (for example, LD_PRELOAD on Unix-like systems) or API hooking, and, in some environments, kernel tracing or eBPF-based approaches. Output is typically logged to a file or stream and may be formatted for analysis or live inspection. Some tools also attempt to reconstruct higher-level sessions or streams to aid understanding.

Socketcap is platform- and implementation-specific; different projects may support Linux, Windows, or macOS, with varying levels of detail and performance overhead. It is commonly used by developers for debugging network clients, by security researchers to study application behavior, and by performance engineers to understand socket usage patterns. Limitations include potential performance impact, incomplete data for encrypted or obfuscated traffic, and the need for appropriate privileges or compatibility with the target binary.

See also: socket tracing, strace and ltrace, DTrace, and eBPF-based tracing tools.