Opentracing support

vendor/github.com/opentracing/opentracing-go/propagation.go

@@ -0,0 +1,176 @@
+package opentracing
+
+import (
+	"errors"
+	"net/http"
+)
+
+///////////////////////////////////////////////////////////////////////////////
+// CORE PROPAGATION INTERFACES:
+///////////////////////////////////////////////////////////////////////////////
+
+var (
+	// ErrUnsupportedFormat occurs when the `format` passed to Tracer.Inject() or
+	// Tracer.Extract() is not recognized by the Tracer implementation.
+	ErrUnsupportedFormat = errors.New("opentracing: Unknown or unsupported Inject/Extract format")
+
+	// ErrSpanContextNotFound occurs when the `carrier` passed to
+	// Tracer.Extract() is valid and uncorrupted but has insufficient
+	// information to extract a SpanContext.
+	ErrSpanContextNotFound = errors.New("opentracing: SpanContext not found in Extract carrier")
+
+	// ErrInvalidSpanContext errors occur when Tracer.Inject() is asked to
+	// operate on a SpanContext which it is not prepared to handle (for
+	// example, since it was created by a different tracer implementation).
+	ErrInvalidSpanContext = errors.New("opentracing: SpanContext type incompatible with tracer")
+
+	// ErrInvalidCarrier errors occur when Tracer.Inject() or Tracer.Extract()
+	// implementations expect a different type of `carrier` than they are
+	// given.
+	ErrInvalidCarrier = errors.New("opentracing: Invalid Inject/Extract carrier")
+
+	// ErrSpanContextCorrupted occurs when the `carrier` passed to
+	// Tracer.Extract() is of the expected type but is corrupted.
+	ErrSpanContextCorrupted = errors.New("opentracing: SpanContext data corrupted in Extract carrier")
+)
+
+///////////////////////////////////////////////////////////////////////////////
+// BUILTIN PROPAGATION FORMATS:
+///////////////////////////////////////////////////////////////////////////////
+
+// BuiltinFormat is used to demarcate the values within package `opentracing`
+// that are intended for use with the Tracer.Inject() and Tracer.Extract()
+// methods.
+type BuiltinFormat byte
+
+const (
+	// Binary represents SpanContexts as opaque binary data.
+	//
+	// For Tracer.Inject(): the carrier must be an `io.Writer`.
+	//
+	// For Tracer.Extract(): the carrier must be an `io.Reader`.
+	Binary BuiltinFormat = iota
+
+	// TextMap represents SpanContexts as key:value string pairs.
+	//
+	// Unlike HTTPHeaders, the TextMap format does not restrict the key or
+	// value character sets in any way.
+	//
+	// For Tracer.Inject(): the carrier must be a `TextMapWriter`.
+	//
+	// For Tracer.Extract(): the carrier must be a `TextMapReader`.
+	TextMap
+
+	// HTTPHeaders represents SpanContexts as HTTP header string pairs.
+	//
+	// Unlike TextMap, the HTTPHeaders format requires that the keys and values
+	// be valid as HTTP headers as-is (i.e., character casing may be unstable
+	// and special characters are disallowed in keys, values should be
+	// URL-escaped, etc).
+	//
+	// For Tracer.Inject(): the carrier must be a `TextMapWriter`.
+	//
+	// For Tracer.Extract(): the carrier must be a `TextMapReader`.
+	//
+	// See HTTPHeaderCarrier for an implementation of both TextMapWriter
+	// and TextMapReader that defers to an http.Header instance for storage.
+	// For example, Inject():
+	//
+	//    carrier := opentracing.HTTPHeadersCarrier(httpReq.Header)
+	//    err := span.Tracer().Inject(
+	//        span, opentracing.HTTPHeaders, carrier)
+	//
+	// Or Extract():
+	//
+	//    carrier := opentracing.HTTPHeadersCarrier(httpReq.Header)
+	//    span, err := tracer.Extract(
+	//        opentracing.HTTPHeaders, carrier)
+	//
+	HTTPHeaders
+)
+
+// TextMapWriter is the Inject() carrier for the TextMap builtin format. With
+// it, the caller can encode a SpanContext for propagation as entries in a map
+// of unicode strings.
+type TextMapWriter interface {
+	// Set a key:value pair to the carrier. Multiple calls to Set() for the
+	// same key leads to undefined behavior.
+	//
+	// NOTE: The backing store for the TextMapWriter may contain data unrelated
+	// to SpanContext. As such, Inject() and Extract() implementations that
+	// call the TextMapWriter and TextMapReader interfaces must agree on a
+	// prefix or other convention to distinguish their own key:value pairs.
+	Set(key, val string)
+}
+
+// TextMapReader is the Extract() carrier for the TextMap builtin format. With it,
+// the caller can decode a propagated SpanContext as entries in a map of
+// unicode strings.
+type TextMapReader interface {
+	// ForeachKey returns TextMap contents via repeated calls to the `handler`
+	// function. If any call to `handler` returns a non-nil error, ForeachKey
+	// terminates and returns that error.
+	//
+	// NOTE: The backing store for the TextMapReader may contain data unrelated
+	// to SpanContext. As such, Inject() and Extract() implementations that
+	// call the TextMapWriter and TextMapReader interfaces must agree on a
+	// prefix or other convention to distinguish their own key:value pairs.
+	//
+	// The "foreach" callback pattern reduces unnecessary copying in some cases
+	// and also allows implementations to hold locks while the map is read.
+	ForeachKey(handler func(key, val string) error) error
+}
+
+// TextMapCarrier allows the use of regular map[string]string
+// as both TextMapWriter and TextMapReader.
+type TextMapCarrier map[string]string
+
+// ForeachKey conforms to the TextMapReader interface.
+func (c TextMapCarrier) ForeachKey(handler func(key, val string) error) error {
+	for k, v := range c {
+		if err := handler(k, v); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Set implements Set() of opentracing.TextMapWriter
+func (c TextMapCarrier) Set(key, val string) {
+	c[key] = val
+}
+
+// HTTPHeadersCarrier satisfies both TextMapWriter and TextMapReader.
+//
+// Example usage for server side:
+//
+//     carrier := opentracing.HttpHeadersCarrier(httpReq.Header)
+//     spanContext, err := tracer.Extract(opentracing.HttpHeaders, carrier)
+//
+// Example usage for client side:
+//
+//     carrier := opentracing.HTTPHeadersCarrier(httpReq.Header)
+//     err := tracer.Inject(
+//         span.Context(),
+//         opentracing.HttpHeaders,
+//         carrier)
+//
+type HTTPHeadersCarrier http.Header
+
+// Set conforms to the TextMapWriter interface.
+func (c HTTPHeadersCarrier) Set(key, val string) {
+	h := http.Header(c)
+	h.Add(key, val)
+}
+
+// ForeachKey conforms to the TextMapReader interface.
+func (c HTTPHeadersCarrier) ForeachKey(handler func(key, val string) error) error {
+	for k, vals := range c {
+		for _, v := range vals {
+			if err := handler(k, v); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}