ddtrace

Documentation

Overview

Package ddtrace contains the interfaces that specify the implementations of Datadog's tracing library, as well as a set of sub-packages containing various implementations: our native implementation ("tracer"), a wrapper that can be used with Opentracing ("opentracer") and a mock tracer to be used for testing ("mocktracer"). Additionally, package "ext" provides a set of tag names and values specific to Datadog's APM product.

To get started, visit the documentation for any of the packages you'd like to begin with by accessing the subdirectories of this package: https://godoc.org/gopkg.in/DataDog/dd-trace-go.v1/ddtrace#pkg-subdirectories.

Example (Datadog)

The below example illustrates a simple use case using the "tracer" package, our native Datadog APM tracing client integration. For thorough documentation and further examples, visit its own godoc page.

package main

import (
	"io/ioutil"
	"log"

	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
)

func main() {
	// Start the tracer and defer the Stop method.
	tracer.Start(tracer.WithAgentAddr("host:port"))
	defer tracer.Stop()

	// Start a root span.
	span := tracer.StartSpan("get.data")
	defer span.Finish()

	// Create a child of it, computing the time needed to read a file.
	child := tracer.StartSpan("read.file", tracer.ChildOf(span.Context()))
	child.SetTag(ext.ResourceName, "test.json")

	// Perform an operation.
	_, err := ioutil.ReadFile("~/test.json")

	// We may finish the child span using the returned error. If it's
	// nil, it will be disregarded.
	child.Finish(tracer.WithError(err))
	if err != nil {
		log.Fatal(err)
	}
}

Example (Mocking)

The code below illustrates a scenario of how one could use a mock tracer in tests to assert that spans are created correctly.

package main

import (
	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/mocktracer"
	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
)

func main() {
	// Setup the test environment: start the mock tracer.
	mt := mocktracer.Start()
	defer mt.Stop()

	// Run test code: in this example we will simply create a span to illustrate.
	tracer.StartSpan("test.span").Finish()

	// Assert the results: query the mock tracer for finished spans.
	spans := mt.FinishedSpans()
	if len(spans) != 1 {
		// fail
	}
	if spans[0].OperationName() != "test.span" {
		// fail
	}
}

Example (Opentracing)

The below example illustrates how to set up an opentracing.Tracer using Datadog's tracer.

package main

import (
	opentracing "github.com/opentracing/opentracing-go"

	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/opentracer"
	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
)

func main() {
	// Start a Datadog tracer, optionally providing a set of options,
	// returning an opentracing.Tracer which wraps it.
	t := opentracer.New(tracer.WithAgentAddr("host:port"))
	defer tracer.Stop() // important for data integrity (flushes any leftovers)

	// Use it with the Opentracing API. The (already started) Datadog tracer
	// may be used in parallel with the Opentracing API if desired.
	opentracing.SetGlobalTracer(t)
}

Index

• type FinishConfig
• type FinishOption
• type Span
• type SpanContext
• type StartSpanConfig
• type StartSpanOption
• type Tracer

Examples

• Package (Datadog)
• Package (Mocking)
• Package (Opentracing)

Types

type FinishConfig

type FinishConfig struct {
	// FinishTime represents the time that should be set as finishing time for the
	// span. Implementations should use the current time when FinishTime.IsZero().
	FinishTime time.Time

	// Error holds an optional error that should be set on the span before
	// finishing.
	Error error
}

FinishConfig holds the configuration for finishing a span. It is usually passed around by reference to one or more FinishOption functions which shape it into its final form.

type FinishOption

type FinishOption func(cfg *FinishConfig)

FinishOption is a configuration option that can be used with a Span's Finish method.

type Span

type Span interface {
	// SetTag sets a key/value pair as metadata on the span.
	SetTag(key string, value interface{})

	// SetOperationName sets the operation name for this span. An operation name should be
	// a representative name for a group of spans (e.g. "grpc.server" or "http.request").
	SetOperationName(operationName string)

	// BaggageItem returns the baggage item held by the given key.
	BaggageItem(key string) string

	// SetBaggageItem sets a new baggage item at the given key. The baggage
	// item should propagate to all descendant spans, both in- and cross-process.
	SetBaggageItem(key, val string)

	// Finish finishes the current span with the given options. Finish calls should be idempotent.
	Finish(opts ...FinishOption)

	// Context returns the SpanContext of this Span.
	Context() SpanContext
}

Span represents a chunk of computation time. Spans have names, durations, timestamps and other metadata. A Tracer is used to create hierarchies of spans in a request, buffer and submit them to the server.

type SpanContext

type SpanContext interface {
	// SpanID returns the span ID that this context is carrying.
	SpanID() uint64

	// TraceID returns the trace ID that this context is carrying.
	TraceID() uint64

	// ForeachBaggageItem provides an iterator over the key/value pairs set as
	// baggage within this context. Iteration stops when the handler returns
	// false.
	ForeachBaggageItem(handler func(k, v string) bool)
}

SpanContext represents a span state that can propagate to descendant spans and across process boundaries. It contains all the information needed to spawn a direct descendant of the span that it belongs to. It can be used to create distributed tracing by propagating it using the provided interfaces.

type StartSpanConfig

type StartSpanConfig struct {
	// Parent holds the SpanContext that should be used as a parent for the
	// new span. If nil, implementations should return a root span.
	Parent SpanContext

	// StartTime holds the time that should be used as the start time of the span.
	// Implementations should use the current time when StartTime.IsZero().
	StartTime time.Time

	// Tags holds a set of key/value pairs that should be set as metadata on the
	// new span.
	Tags map[string]interface{}
}

StartSpanConfig holds the configuration for starting a new span. It is usually passed around by reference to one or more StartSpanOption functions which shape it into its final form.

type StartSpanOption

type StartSpanOption func(cfg *StartSpanConfig)

StartSpanOption is a configuration option that can be used with a Tracer's StartSpan method.

type Tracer

type Tracer interface {
	// StartSpan starts a span with the given operation name and options.
	StartSpan(operationName string, opts ...StartSpanOption) Span

	// Extract extracts a span context from a given carrier. Note that baggage item
	// keys will always be lower-cased to maintain consistency. It is impossible to
	// maintain the original casing due to MIME header canonicalization standards.
	Extract(carrier interface{}) (SpanContext, error)

	// Inject injects a span context into the given carrier.
	Inject(context SpanContext, carrier interface{}) error

	// Stop stops the active tracer and sets the global tracer to a no-op. Calls to
	// Stop should be idempotent.
	Stop()
}

Tracer specifies an implementation of the Datadog tracer which allows starting and propagating spans. The official implementation if exposed as functions within the "tracer" package.