Skip to content

Runtime architecture

Gossipper intentionally separates concerns that are tightly coupled inside SIPp.

Binary entry (cmd/gossip)

The main binary parses -version early, routes reserved subcommands (tui, shell, server, auth, pcap2scenario, …) and optional gossipper sipp (SIPp-style flag tail only), then runs internal/cli.Parse and internal/launcher. See cli.md.

Main components

  • internal/scenario
  • parses XML into a neutral command list

  • resolves labels and scenario mode

  • internal/template

  • renders SIPp-style keywords without network side effects
  • computes Content-Length in a dedicated second pass

  • now fails explicitly on unsupported scenario keywords instead of silently emitting empty strings

  • internal/sip

  • parses SIP start line and headers

  • provides Call-ID extraction and recv matching helpers

  • internal/transport

  • owns UDP, TCP, and TLS transport implementations

  • supports shared/per-call client modes plus server-side UDP aliases

  • internal/engine

  • orchestrates calls, branching, retransmits, timeouts, auth, XML actions, and stats

  • keeps runtime state per call instead of using globals

  • internal/hep

  • encodes HEP3 packets and manages UDP export to Homer-compatible collectors

  • mirrors SIP send/recv traffic when HEP is enabled

  • internal/scheduler

  • abstracts time and rate pacing

  • keeps room for future deterministic test clocks

  • internal/stats

  • aggregates success/failure, failure classes, latency distributions, retransmits, and timeouts

  • internal/media

  • isolated RTP helpers based on Pion
  • SRTP (SDES + DTLS-SRTP), ICE, and TURN integration for scenario media when -media_srtp (see docs/srtp.md)

  • intentionally decoupled from SIP call execution

  • internal/api

  • HTTP /api/v1/* management surface: stats, scenario get/put/apply, control, transports, dynamic clients, /live WebSocket, optional /auth/* when internal auth is enabled

  • optional embedded Control UI (go:embed webdist) at GET /

  • internal/settingsauth

  • SQLite user store, bcrypt passwords, JWT issuance for auth.type: internal

  • internal/launcher

  • builds engines from CLI and flat JSON (gossipper server -config): composite server + clients[], hybrid multi-listener profiles, LoadCoordinator for POST /api/v1/clients

  • web/control-ui

  • Vite/React panel for the management API (see web/control-ui/README.md); production assets go to internal/api/webdist/

Execution flow

  1. CLI loads XML or a built-in scenario and builds runtime config
  2. Engine starts trace sinks, optional HEP export, and optional command peers
  3. Engine selects client or server mode
  4. Transport creates shared or per-call UDP/TCP/TLS sockets as needed
  5. Each call renders a step through the template layer
  6. XML actions execute against per-call/global/user variable scopes
  7. Sent and received SIP messages are parsed through internal/sip
  8. HEP export observes SIP send/recv traffic without duplicating scenario logic
  9. Stats collector aggregates final results and optional CSV trace snapshots