Module skywalking 

Distributed tracing with Apache SkyWalking — a start/end node pair wrapped around the upstream node.

Ported from APISIX’s skywalking.lua. The wire propagation format is the SkyWalking sw8 header (see crate::plugins::util::trace).

• The start node (phase: start, placed before upstream) extracts an incoming sw8 header to continue an existing trace, or begins a new one and makes the sampling decision. It creates this hop’s SpanContext, stores it in context.message, and injects a fresh downstream sw8 header so the upstream service joins the trace.
• The end node (phase: end, placed after upstream) loads the span, and — when sampled — fire-and-forget POSTs a SkyWalking trace segment to <endpoint_addr>/v3/segments on a detached task. The request path is never blocked by the export.

Both nodes always continue through the success port; neither ever routes to the error port.

Wiring

... -> skywalking(start) -> upstream -> skywalking(end) -> ...

Deviations / simplifications from APISIX

Full SkyWalking correlation (segment references, multi-span segments, the ngx.ctx entry/exit span pair, the background report timer) is intentionally reduced to a faithful subset:

• Each request exports a single-span segment (spanId: 0, parentSpanId: -1, spanType: "Entry", spanLayer: "Http"). The incoming sw8’s parent segment/service are honored for propagation (trace id + sampling flag are continued) but are not emitted as a formal refs segment-reference on the exported span.
• Export is per-request and immediate (a detached tokio::spawn), not buffered on APISIX’s report_interval timer.
• The segment is POSTed as a single JSON object to /v3/segments; the real OAP endpoint also accepts a batch array — the single-object form is the documented subset here.
• componentId is reported as 49 (generic HTTP) rather than APISIX’s 6002.

Structs

SkywalkingPlugin

SkyWalking tracing node (a start or end half, selected by phase).

Enums

Phase 🔒

Which node of the start/end pair this instance is.

Constants

COMPONENT_ID_HTTP 🔒

SkyWalking componentId reported for the entry span (49 = generic HTTP).

Functions

build_segment 🔒

Builds the SkyWalking trace segment JSON for a finished span (pure; does no I/O). A single Entry/Http span mirroring the OAP HTTP segment protocol.

build_sw8 🔒

Builds a downstream sw8 header value for span (8 hyphen-separated fields, matching the SkyWalking cross-process propagation header): sample-traceId-parentSegmentId-parentSpanId-service-instance-endpoint-peer. All fields except the sample flag and the plain-integer parent span id are base64-encoded.

roll_fraction 🔒

Draws a pseudo-random fraction in [0.0, 1.0) for sampling — the same cheap, non-cryptographic source proxy-mirror/fault-injection use.