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package opentracing
import "time"
// Tracer is a simple, thin interface for Span creation and SpanContext
// propagation.
type Tracer interface {
// Create, start, and return a new Span with the given `operationName` and
// incorporate the given StartSpanOption `opts`. (Note that `opts` borrows
// from the "functional options" pattern, per
// http://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis)
//
// A Span with no SpanReference options (e.g., opentracing.ChildOf() or
// opentracing.FollowsFrom()) becomes the root of its own trace.
//
// Examples:
//
// var tracer opentracing.Tracer = ...
//
// // The root-span case:
// sp := tracer.StartSpan("GetFeed")
//
// // The vanilla child span case:
// sp := tracer.StartSpan(
// "GetFeed",
// opentracing.ChildOf(parentSpan.Context()))
//
// // All the bells and whistles:
// sp := tracer.StartSpan(
// "GetFeed",
// opentracing.ChildOf(parentSpan.Context()),
// opentracing.Tag("user_agent", loggedReq.UserAgent),
// opentracing.StartTime(loggedReq.Timestamp),
// )
//
StartSpan(operationName string, opts ...StartSpanOption) Span
// Inject() takes the `sm` SpanContext instance and injects it for
// propagation within `carrier`. The actual type of `carrier` depends on
// the value of `format`.
//
// OpenTracing defines a common set of `format` values (see BuiltinFormat),
// and each has an expected carrier type.
//
// Other packages may declare their own `format` values, much like the keys
// used by `context.Context` (see
// https://godoc.org/golang.org/x/net/context#WithValue).
//
// Example usage (sans error handling):
//
// carrier := opentracing.HTTPHeadersCarrier(httpReq.Header)
// err := tracer.Inject(
// span.Context(),
// opentracing.HttpHeaders,
// carrier)
//
// NOTE: All opentracing.Tracer implementations MUST support all
// BuiltinFormats.
//
// Implementations may return opentracing.ErrUnsupportedFormat if `format`
// is not supported by (or not known by) the implementation.
//
// Implementations may return opentracing.ErrInvalidCarrier or any other
// implementation-specific error if the format is supported but injection
// fails anyway.
//
// See Tracer.Extract().
Inject(sm SpanContext, format interface{}, carrier interface{}) error
// Extract() returns a SpanContext instance given `format` and `carrier`.
//
// OpenTracing defines a common set of `format` values (see BuiltinFormat),
// and each has an expected carrier type.
//
// Other packages may declare their own `format` values, much like the keys
// used by `context.Context` (see
// https://godoc.org/golang.org/x/net/context#WithValue).
//
// Example usage (with StartSpan):
//
//
// carrier := opentracing.HttpHeadersCarrier(httpReq.Header)
// clientContext, err := tracer.Extract(opentracing.HttpHeaders, carrier)
//
// // ... assuming the ultimate goal here is to resume the trace with a
// // server-side Span:
// var serverSpan opentracing.Span
// if err == nil {
// span = tracer.StartSpan(
// rpcMethodName, ext.RPCServerOption(clientContext))
// } else {
// span = tracer.StartSpan(rpcMethodName)
// }
//
//
// NOTE: All opentracing.Tracer implementations MUST support all
// BuiltinFormats.
//
// Return values:
// - A successful Extract returns a SpanContext instance and a nil error
// - If there was simply no SpanContext to extract in `carrier`, Extract()
// returns (nil, opentracing.ErrSpanContextNotFound)
// - If `format` is unsupported or unrecognized, Extract() returns (nil,
// opentracing.ErrUnsupportedFormat)
// - If there are more fundamental problems with the `carrier` object,
// Extract() may return opentracing.ErrInvalidCarrier,
// opentracing.ErrSpanContextCorrupted, or implementation-specific
// errors.
//
// See Tracer.Inject().
Extract(format interface{}, carrier interface{}) (SpanContext, error)
}
// StartSpanOptions allows Tracer.StartSpan() callers and implementors a
// mechanism to override the start timestamp, specify Span References, and make
// a single Tag or multiple Tags available at Span start time.
//
// StartSpan() callers should look at the StartSpanOption interface and
// implementations available in this package.
//
// Tracer implementations can convert a slice of `StartSpanOption` instances
// into a `StartSpanOptions` struct like so:
//
// func StartSpan(opName string, opts ...opentracing.StartSpanOption) {
// sso := opentracing.StartSpanOptions{}
// for _, o := range opts {
// o.Apply(&sso)
// }
// ...
// }
//
type StartSpanOptions struct {
// Zero or more causal references to other Spans (via their SpanContext).
// If empty, start a "root" Span (i.e., start a new trace).
References []SpanReference
// StartTime overrides the Span's start time, or implicitly becomes
// time.Now() if StartTime.IsZero().
StartTime time.Time
// Tags may have zero or more entries; the restrictions on map values are
// identical to those for Span.SetTag(). May be nil.
//
// If specified, the caller hands off ownership of Tags at
// StartSpan() invocation time.
Tags map[string]interface{}
}
// StartSpanOption instances (zero or more) may be passed to Tracer.StartSpan.
//
// StartSpanOption borrows from the "functional options" pattern, per
// http://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis
type StartSpanOption interface {
Apply(*StartSpanOptions)
}
// SpanReferenceType is an enum type describing different categories of
// relationships between two Spans. If Span-2 refers to Span-1, the
// SpanReferenceType describes Span-1 from Span-2's perspective. For example,
// ChildOfRef means that Span-1 created Span-2.
//
// NOTE: Span-1 and Span-2 do *not* necessarily depend on each other for
// completion; e.g., Span-2 may be part of a background job enqueued by Span-1,
// or Span-2 may be sitting in a distributed queue behind Span-1.
type SpanReferenceType int
const (
// ChildOfRef refers to a parent Span that caused *and* somehow depends
// upon the new child Span. Often (but not always), the parent Span cannot
// finish until the child Span does.
//
// An timing diagram for a ChildOfRef that's blocked on the new Span:
//
// [-Parent Span---------]
// [-Child Span----]
//
// See http://opentracing.io/spec/
//
// See opentracing.ChildOf()
ChildOfRef SpanReferenceType = iota
// FollowsFromRef refers to a parent Span that does not depend in any way
// on the result of the new child Span. For instance, one might use
// FollowsFromRefs to describe pipeline stages separated by queues,
// or a fire-and-forget cache insert at the tail end of a web request.
//
// A FollowsFromRef Span is part of the same logical trace as the new Span:
// i.e., the new Span is somehow caused by the work of its FollowsFromRef.
//
// All of the following could be valid timing diagrams for children that
// "FollowFrom" a parent.
//
// [-Parent Span-] [-Child Span-]
//
//
// [-Parent Span--]
// [-Child Span-]
//
//
// [-Parent Span-]
// [-Child Span-]
//
// See http://opentracing.io/spec/
//
// See opentracing.FollowsFrom()
FollowsFromRef
)
// SpanReference is a StartSpanOption that pairs a SpanReferenceType and a
// referenced SpanContext. See the SpanReferenceType documentation for
// supported relationships. If SpanReference is created with
// ReferencedContext==nil, it has no effect. Thus it allows for a more concise
// syntax for starting spans:
//
// sc, _ := tracer.Extract(someFormat, someCarrier)
// span := tracer.StartSpan("operation", opentracing.ChildOf(sc))
//
// The `ChildOf(sc)` option above will not panic if sc == nil, it will just
// not add the parent span reference to the options.
type SpanReference struct {
Type SpanReferenceType
ReferencedContext SpanContext
}
// Apply satisfies the StartSpanOption interface.
func (r SpanReference) Apply(o *StartSpanOptions) {
if r.ReferencedContext != nil {
o.References = append(o.References, r)
}
}
// ChildOf returns a StartSpanOption pointing to a dependent parent span.
// If sc == nil, the option has no effect.
//
// See ChildOfRef, SpanReference
func ChildOf(sc SpanContext) SpanReference {
return SpanReference{
Type: ChildOfRef,
ReferencedContext: sc,
}
}
// FollowsFrom returns a StartSpanOption pointing to a parent Span that caused
// the child Span but does not directly depend on its result in any way.
// If sc == nil, the option has no effect.
//
// See FollowsFromRef, SpanReference
func FollowsFrom(sc SpanContext) SpanReference {
return SpanReference{
Type: FollowsFromRef,
ReferencedContext: sc,
}
}
// StartTime is a StartSpanOption that sets an explicit start timestamp for the
// new Span.
type StartTime time.Time
// Apply satisfies the StartSpanOption interface.
func (t StartTime) Apply(o *StartSpanOptions) {
o.StartTime = time.Time(t)
}
// Tags are a generic map from an arbitrary string key to an opaque value type.
// The underlying tracing system is responsible for interpreting and
// serializing the values.
type Tags map[string]interface{}
// Apply satisfies the StartSpanOption interface.
func (t Tags) Apply(o *StartSpanOptions) {
if o.Tags == nil {
o.Tags = make(map[string]interface{})
}
for k, v := range t {
o.Tags[k] = v
}
}
// Tag may be passed as a StartSpanOption to add a tag to new spans,
// or its Set method may be used to apply the tag to an existing Span,
// for example:
//
// tracer.StartSpan("opName", Tag{"Key", value})
//
// or
//
// Tag{"key", value}.Set(span)
type Tag struct {
Key string
Value interface{}
}
// Apply satisfies the StartSpanOption interface.
func (t Tag) Apply(o *StartSpanOptions) {
if o.Tags == nil {
o.Tags = make(map[string]interface{})
}
o.Tags[t.Key] = t.Value
}
// Set applies the tag to an existing Span.
func (t Tag) Set(s Span) {
s.SetTag(t.Key, t.Value)
}