Create basic othttp.Transport for simple client instrumentation (#678)

* Create basic othttp.Transport for simple client instrumentation

* change props to propagators for clarity

* Add othttp.Transport usage example

Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>

plugin/othttp/common.go

@@ -0,0 +1,54 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package othttp
+
+import (
+	"net/http"
+
+	"go.opentelemetry.io/otel/api/core"
+	"go.opentelemetry.io/otel/api/trace"
+)
+
+// Attribute keys that can be added to a span.
+const (
+	HostKey       = core.Key("http.host")        // the HTTP host (http.Request.Host)
+	MethodKey     = core.Key("http.method")      // the HTTP method (http.Request.Method)
+	PathKey       = core.Key("http.path")        // the HTTP path (http.Request.URL.Path)
+	URLKey        = core.Key("http.url")         // the HTTP URL (http.Request.URL.String())
+	UserAgentKey  = core.Key("http.user_agent")  // the HTTP user agent (http.Request.UserAgent())
+	RouteKey      = core.Key("http.route")       // the HTTP route (ex: /users/:id)
+	RemoteAddrKey = core.Key("http.remote_addr") // the network address of the client that sent the HTTP request (http.Request.RemoteAddr)
+	StatusCodeKey = core.Key("http.status_code") // if set, the HTTP status
+	ReadBytesKey  = core.Key("http.read_bytes")  // if anything was read from the request body, the total number of bytes read
+	ReadErrorKey  = core.Key("http.read_error")  // If an error occurred while reading a request, the string of the error (io.EOF is not recorded)
+	WroteBytesKey = core.Key("http.wrote_bytes") // if anything was written to the response writer, the total number of bytes written
+	WriteErrorKey = core.Key("http.write_error") // if an error occurred while writing a reply, the string of the error (io.EOF is not recorded)
+)
+
+// Filter is a predicate used to determine whether a given http.request should
+// be traced. A Filter must return true if the request should be traced.
+type Filter func(*http.Request) bool
+
+// Setup basic span attributes before so that they
+// are available to be mutated if needed.
+func setBasicAttributes(span trace.Span, r *http.Request) {
+	span.SetAttributes(
+		HostKey.String(r.Host),
+		MethodKey.String(r.Method),
+		PathKey.String(r.URL.Path),
+		URLKey.String(r.URL.String()),
+		UserAgentKey.String(r.UserAgent()),
+	)
+}

plugin/othttp/config.go

@@ -0,0 +1,140 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package othttp
+
+import (
+	"net/http"
+
+	"go.opentelemetry.io/otel/api/propagation"
+	"go.opentelemetry.io/otel/api/trace"
+)
+
+// Config represents the configuration options available for the othttp.Handler
+// and othttp.Transport types.
+type Config struct {
+	Tracer            trace.Tracer
+	Propagators       propagation.Propagators
+	SpanStartOptions  []trace.StartOption
+	ReadEvent         bool
+	WriteEvent        bool
+	Filters           []Filter
+	SpanNameFormatter func(string, *http.Request) string
+}
+
+// Option Interface used for setting *optional* Config properties
+type Option interface {
+	Apply(*Config)
+}
+
+// OptionFunc provides a convenience wrapper for simple Options
+// that can be represented as functions.
+type OptionFunc func(*Config)
+
+func (o OptionFunc) Apply(c *Config) {
+	o(c)
+}
+
+// NewConfig creates a new Config struct and applies opts to it.
+func NewConfig(opts ...Option) *Config {
+	c := &Config{}
+	for _, opt := range opts {
+		opt.Apply(c)
+	}
+	return c
+}
+
+// WithTracer configures a specific tracer. If this option
+// isn't specified then the global tracer is used.
+func WithTracer(tracer trace.Tracer) Option {
+	return OptionFunc(func(c *Config) {
+		c.Tracer = tracer
+	})
+}
+
+// WithPublicEndpoint configures the Handler to link the span with an incoming
+// span context. If this option is not provided, then the association is a child
+// association instead of a link.
+func WithPublicEndpoint() Option {
+	return OptionFunc(func(c *Config) {
+		c.SpanStartOptions = append(c.SpanStartOptions, trace.WithNewRoot())
+	})
+}
+
+// WithPropagators configures specific propagators. If this
+// option isn't specified then
+// go.opentelemetry.io/otel/api/global.Propagators are used.
+func WithPropagators(ps propagation.Propagators) Option {
+	return OptionFunc(func(c *Config) {
+		c.Propagators = ps
+	})
+}
+
+// WithSpanOptions configures an additional set of
+// trace.StartOptions, which are applied to each new span.
+func WithSpanOptions(opts ...trace.StartOption) Option {
+	return OptionFunc(func(c *Config) {
+		c.SpanStartOptions = append(c.SpanStartOptions, opts...)
+	})
+}
+
+// WithFilter adds a filter to the list of filters used by the handler.
+// If any filter indicates to exclude a request then the request will not be
+// traced. All filters must allow a request to be traced for a Span to be created.
+// If no filters are provided then all requests are traced.
+// Filters will be invoked for each processed request, it is advised to make them
+// simple and fast.
+func WithFilter(f Filter) Option {
+	return OptionFunc(func(c *Config) {
+		c.Filters = append(c.Filters, f)
+	})
+}
+
+type event int
+
+// Different types of events that can be recorded, see WithMessageEvents
+const (
+	ReadEvents event = iota
+	WriteEvents
+)
+
+// WithMessageEvents configures the Handler to record the specified events
+// (span.AddEvent) on spans. By default only summary attributes are added at the
+// end of the request.
+//
+// Valid events are:
+//     * ReadEvents: Record the number of bytes read after every http.Request.Body.Read
+//       using the ReadBytesKey
+//     * WriteEvents: Record the number of bytes written after every http.ResponeWriter.Write
+//       using the WriteBytesKey
+func WithMessageEvents(events ...event) Option {
+	return OptionFunc(func(c *Config) {
+		for _, e := range events {
+			switch e {
+			case ReadEvents:
+				c.ReadEvent = true
+			case WriteEvents:
+				c.WriteEvent = true
+			}
+		}
+	})
+}
+
+// WithSpanNameFormatter takes a function that will be called on every
+// request and the returned string will become the Span Name
+func WithSpanNameFormatter(f func(operation string, r *http.Request) string) Option {
+	return OptionFunc(func(c *Config) {
+		c.SpanNameFormatter = f
+	})
+}

plugin/othttp/config_test.go

@@ -0,0 +1,131 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package othttp
+
+import (
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	mocktrace "go.opentelemetry.io/otel/internal/trace"
+)
+
+func TestBasicFilter(t *testing.T) {
+	rr := httptest.NewRecorder()
+
+	var id uint64
+	tracer := mocktrace.MockTracer{StartSpanID: &id}
+
+	h := NewHandler(
+		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if _, err := io.WriteString(w, "hello world"); err != nil {
+				t.Fatal(err)
+			}
+		}), "test_handler",
+		WithTracer(&tracer),
+		WithFilter(func(r *http.Request) bool {
+			return false
+		}),
+	)
+
+	r, err := http.NewRequest(http.MethodGet, "http://localhost/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	h.ServeHTTP(rr, r)
+	if got, expected := rr.Result().StatusCode, http.StatusOK; got != expected {
+		t.Fatalf("got %d, expected %d", got, expected)
+	}
+	if got := rr.Header().Get("Traceparent"); got != "" {
+		t.Fatal("expected empty trace header")
+	}
+	if got, expected := id, uint64(0); got != expected {
+		t.Fatalf("got %d, expected %d", got, expected)
+	}
+	d, err := ioutil.ReadAll(rr.Result().Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, expected := string(d), "hello world"; got != expected {
+		t.Fatalf("got %q, expected %q", got, expected)
+	}
+}
+
+func TestSpanNameFormatter(t *testing.T) {
+	var testCases = []struct {
+		name      string
+		formatter func(s string, r *http.Request) string
+		operation string
+		expected  string
+	}{
+		{
+			name:      "default handler formatter",
+			formatter: defaultHandlerFormatter,
+			operation: "test_operation",
+			expected:  "test_operation",
+		},
+		{
+			name:      "default transport formatter",
+			formatter: defaultTransportFormatter,
+			expected:  http.MethodGet,
+		},
+		{
+			name: "custom formatter",
+			formatter: func(s string, r *http.Request) string {
+				return r.URL.Path
+			},
+			operation: "",
+			expected:  "/hello",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			rr := httptest.NewRecorder()
+			var id uint64
+			var spanName string
+			tracer := mocktrace.MockTracer{
+				StartSpanID: &id,
+				OnSpanStarted: func(span *mocktrace.MockSpan) {
+					spanName = span.Name
+				},
+			}
+			handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if _, err := io.WriteString(w, "hello world"); err != nil {
+					t.Fatal(err)
+				}
+			})
+			h := NewHandler(
+				handler,
+				tc.operation,
+				WithTracer(&tracer),
+				WithSpanNameFormatter(tc.formatter),
+			)
+			r, err := http.NewRequest(http.MethodGet, "http://localhost/hello", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			h.ServeHTTP(rr, r)
+			if got, expected := rr.Result().StatusCode, http.StatusOK; got != expected {
+				t.Fatalf("got %d, expected %d", got, expected)
+			}
+			if got, expected := spanName, tc.expected; got != expected {
+				t.Fatalf("got %q, expected %q", got, expected)
+			}
+		})
+	}
+}

plugin/othttp/handler.go

@@ -26,26 +26,6 @@ import (
 
 var _ http.Handler = &Handler{}
 
-// Attribute keys that the Handler can add to a span.
-const (
-	HostKey       = core.Key("http.host")        // the HTTP host (http.Request.Host)
-	MethodKey     = core.Key("http.method")      // the HTTP method (http.Request.Method)
-	PathKey       = core.Key("http.path")        // the HTTP path (http.Request.URL.Path)
-	URLKey        = core.Key("http.url")         // the HTTP URL (http.Request.URL.String())
-	UserAgentKey  = core.Key("http.user_agent")  // the HTTP user agent (http.Request.UserAgent())
-	RouteKey      = core.Key("http.route")       // the HTTP route (ex: /users/:id)
-	RemoteAddrKey = core.Key("http.remote_addr") // the network address of the client that sent the HTTP request (http.Request.RemoteAddr)
-	StatusCodeKey = core.Key("http.status_code") // if set, the HTTP status
-	ReadBytesKey  = core.Key("http.read_bytes")  // if anything was read from the request body, the total number of bytes read
-	ReadErrorKey  = core.Key("http.read_error")  // If an error occurred while reading a request, the string of the error (io.EOF is not recorded)
-	WroteBytesKey = core.Key("http.wrote_bytes") // if anything was written to the response writer, the total number of bytes written
-	WriteErrorKey = core.Key("http.write_error") // if an error occurred while writing a reply, the string of the error (io.EOF is not recorded)
-)
-
-// Filter is a predicate used to determine whether a given http.request should
-// be traced. A Filter must return true if the request should be traced.
-type Filter func(*http.Request) bool
-
 // Handler is http middleware that corresponds to the http.Handler interface and
 // is designed to wrap a http.Mux (or equivalent), while individual routes on
 // the mux are wrapped with WithRouteTag. A Handler will add various attributes
@@ -55,7 +35,7 @@ type Handler struct {
 	handler   http.Handler
 
 	tracer            trace.Tracer
-	props             propagation.Propagators
+	propagators       propagation.Propagators
 	spanStartOptions  []trace.StartOption
 	readEvent         bool
 	writeEvent        bool
@@ -63,118 +43,41 @@ type Handler struct {
 	spanNameFormatter func(string, *http.Request) string
 }
 
-// Option function used for setting *optional* Handler properties
-type Option func(*Handler)
-
-// WithTracer configures the Handler with a specific tracer. If this option
-// isn't specified then the global tracer is used.
-func WithTracer(tracer trace.Tracer) Option {
-	return func(h *Handler) {
-		h.tracer = tracer
-	}
-}
-
-// WithPublicEndpoint configures the Handler to link the span with an incoming
-// span context. If this option is not provided, then the association is a child
-// association instead of a link.
-func WithPublicEndpoint() Option {
-	return func(h *Handler) {
-		h.spanStartOptions = append(h.spanStartOptions, trace.WithNewRoot())
-	}
-}
-
-// WithPropagators configures the Handler with specific propagators. If this
-// option isn't specified then
-// go.opentelemetry.io/otel/api/global.Propagators are used.
-func WithPropagators(ps propagation.Propagators) Option {
-	return func(h *Handler) {
-		h.props = ps
-	}
-}
-
-// WithSpanOptions configures the Handler with an additional set of
-// trace.StartOptions, which are applied to each new span.
-func WithSpanOptions(opts ...trace.StartOption) Option {
-	return func(h *Handler) {
-		h.spanStartOptions = append(h.spanStartOptions, opts...)
-	}
-}
-
-// WithFilter adds a filter to the list of filters used by the handler.
-// If any filter indicates to exclude a request then the request will not be
-// traced. All filters must allow a request to be traced for a Span to be created.
-// If no filters are provided then all requests are traced.
-// Filters will be invoked for each processed request, it is advised to make them
-// simple and fast.
-func WithFilter(f Filter) Option {
-	return func(h *Handler) {
-		h.filters = append(h.filters, f)
-	}
-}
-
-type event int
-
-// Different types of events that can be recorded, see WithMessageEvents
-const (
-	ReadEvents event = iota
-	WriteEvents
-)
-
-// WithMessageEvents configures the Handler to record the specified events
-// (span.AddEvent) on spans. By default only summary attributes are added at the
-// end of the request.
-//
-// Valid events are:
-//     * ReadEvents: Record the number of bytes read after every http.Request.Body.Read
-//       using the ReadBytesKey
-//     * WriteEvents: Record the number of bytes written after every http.ResponeWriter.Write
-//       using the WriteBytesKey
-func WithMessageEvents(events ...event) Option {
-	return func(h *Handler) {
-		for _, e := range events {
-			switch e {
-			case ReadEvents:
-				h.readEvent = true
-			case WriteEvents:
-				h.writeEvent = true
-			}
-		}
-	}
-}
-
-// WithSpanNameFormatter takes a function that will be called on every
-// incoming request and the returned string will become the Span Name
-func WithSpanNameFormatter(f func(operation string, r *http.Request) string) Option {
-	return func(h *Handler) {
-		h.spanNameFormatter = f
-	}
-}
-
-func defaultFormatter(operation string, _ *http.Request) string {
+func defaultHandlerFormatter(operation string, _ *http.Request) string {
 	return operation
 }
 
 // NewHandler wraps the passed handler, functioning like middleware, in a span
-// named after the operation and with any provided HandlerOptions.
+// named after the operation and with any provided Options.
 func NewHandler(handler http.Handler, operation string, opts ...Option) http.Handler {
 	h := Handler{
 		handler:   handler,
 		operation: operation,
-		spanNameFormatter: defaultFormatter,
 	}
 
 	defaultOpts := []Option{
 		WithTracer(global.Tracer("go.opentelemetry.io/plugin/othttp")),
 		WithPropagators(global.Propagators()),
 		WithSpanOptions(trace.WithSpanKind(trace.SpanKindServer)),
+		WithSpanNameFormatter(defaultHandlerFormatter),
 	}
 
-	for _, opt := range append(defaultOpts, opts...) {
-		opt(&h)
-	}
+	c := NewConfig(append(defaultOpts, opts...)...)
+	h.configure(c)
+
 	return &h
 }
 
+func (h *Handler) configure(c *Config) {
+	h.tracer = c.Tracer
+	h.propagators = c.Propagators
+	h.spanStartOptions = c.SpanStartOptions
+	h.readEvent = c.ReadEvent
+	h.writeEvent = c.WriteEvent
+	h.filters = c.Filters
+	h.spanNameFormatter = c.SpanNameFormatter
+}
+
 // ServeHTTP serves HTTP requests (http.Handler)
 func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	for _, f := range h.filters {
@@ -187,7 +90,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	opts := append([]trace.StartOption{}, h.spanStartOptions...) // start with the configured options
 
-	ctx := propagation.ExtractHTTP(r.Context(), h.props, r.Header)
+	ctx := propagation.ExtractHTTP(r.Context(), h.propagators, r.Header)
 	ctx, span := h.tracer.Start(ctx, h.spanNameFormatter(h.operation, r), opts...)
 	defer span.End()
 
@@ -207,18 +110,10 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	rww := &respWriterWrapper{ResponseWriter: w, record: writeRecordFunc, ctx: ctx, props: h.props}
+	rww := &respWriterWrapper{ResponseWriter: w, record: writeRecordFunc, ctx: ctx, props: h.propagators}
 
-	// Setup basic span attributes before calling handler.ServeHTTP so that they
-	// are available to be mutated by the handler if needed.
-	span.SetAttributes(
-		HostKey.String(r.Host),
-		MethodKey.String(r.Method),
-		PathKey.String(r.URL.Path),
-		URLKey.String(r.URL.String()),
-		UserAgentKey.String(r.UserAgent()),
-		RemoteAddrKey.String(r.RemoteAddr),
-	)
+	setBasicAttributes(span, r)
+	span.SetAttributes(RemoteAddrKey.String(r.RemoteAddr))
 
 	h.handler.ServeHTTP(rww, r.WithContext(ctx))
 

plugin/othttp/handler_test.go

@@ -23,7 +23,7 @@ import (
 	mocktrace "go.opentelemetry.io/otel/internal/trace"
 )
 
-func TestBasics(t *testing.T) {
+func TestHandlerBasics(t *testing.T) {
 	rr := httptest.NewRecorder()
 
 	var id uint64
@@ -59,104 +59,3 @@ func TestBasics(t *testing.T) {
 		t.Fatalf("got %q, expected %q", got, expected)
 	}
 }
-
-func TestBasicFilter(t *testing.T) {
-	rr := httptest.NewRecorder()
-
-	var id uint64
-	tracer := mocktrace.MockTracer{StartSpanID: &id}
-
-	h := NewHandler(
-		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if _, err := io.WriteString(w, "hello world"); err != nil {
-				t.Fatal(err)
-			}
-		}), "test_handler",
-		WithTracer(&tracer),
-		WithFilter(func(r *http.Request) bool {
-			return false
-		}),
-	)
-
-	r, err := http.NewRequest(http.MethodGet, "http://localhost/", nil)
-	if err != nil {
-		t.Fatal(err)
-	}
-	h.ServeHTTP(rr, r)
-	if got, expected := rr.Result().StatusCode, http.StatusOK; got != expected {
-		t.Fatalf("got %d, expected %d", got, expected)
-	}
-	if got := rr.Header().Get("Traceparent"); got != "" {
-		t.Fatal("expected empty trace header")
-	}
-	if got, expected := id, uint64(0); got != expected {
-		t.Fatalf("got %d, expected %d", got, expected)
-	}
-	d, err := ioutil.ReadAll(rr.Result().Body)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got, expected := string(d), "hello world"; got != expected {
-		t.Fatalf("got %q, expected %q", got, expected)
-	}
-}
-
-func TestSpanNameFormatter(t *testing.T) {
-	var testCases = []struct {
-		name      string
-		formatter func(s string, r *http.Request) string
-		operation string
-		expected  string
-	}{
-		{
-			name:      "default formatter",
-			formatter: defaultFormatter,
-			operation: "test_operation",
-			expected:  "test_operation",
-		},
-		{
-			name: "custom formatter",
-			formatter: func(s string, r *http.Request) string {
-				return r.URL.Path
-			},
-			operation: "",
-			expected:  "/hello",
-		},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			rr := httptest.NewRecorder()
-			var id uint64
-			var spanName string
-			tracer := mocktrace.MockTracer{
-				StartSpanID: &id,
-				OnSpanStarted: func(span *mocktrace.MockSpan) {
-					spanName = span.Name
-				},
-			}
-			handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-				if _, err := io.WriteString(w, "hello world"); err != nil {
-					t.Fatal(err)
-				}
-			})
-			h := NewHandler(
-				handler,
-				tc.operation,
-				WithTracer(&tracer),
-				WithSpanNameFormatter(tc.formatter),
-			)
-			r, err := http.NewRequest(http.MethodGet, "http://localhost/hello", nil)
-			if err != nil {
-				t.Fatal(err)
-			}
-			h.ServeHTTP(rr, r)
-			if got, expected := rr.Result().StatusCode, http.StatusOK; got != expected {
-				t.Fatalf("got %d, expected %d", got, expected)
-			}
-			if got, expected := spanName, tc.expected; got != expected {
-				t.Fatalf("got %q, expected %q", got, expected)
-			}
-		})
-	}
-}

plugin/othttp/transport.go

@@ -0,0 +1,132 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package othttp
+
+import (
+	"context"
+	"io"
+	"net/http"
+
+	"go.opentelemetry.io/otel/api/global"
+	"go.opentelemetry.io/otel/api/propagation"
+	"go.opentelemetry.io/otel/api/trace"
+
+	"google.golang.org/grpc/codes"
+)
+
+// Transport implements the http.RoundTripper interface and wraps
+// outbound HTTP(S) requests with a span.
+type Transport struct {
+	rt http.RoundTripper
+
+	tracer            trace.Tracer
+	propagators       propagation.Propagators
+	spanStartOptions  []trace.StartOption
+	filters           []Filter
+	spanNameFormatter func(string, *http.Request) string
+}
+
+var _ http.RoundTripper = &Transport{}
+
+// NewTransport wraps the provided http.RoundTripper with one that
+// starts a span and injects the span context into the outbound request headers.
+func NewTransport(base http.RoundTripper, opts ...Option) *Transport {
+	t := Transport{
+		rt: base,
+	}
+
+	defaultOpts := []Option{
+		WithTracer(global.Tracer("go.opentelemetry.io/plugin/othttp")),
+		WithPropagators(global.Propagators()),
+		WithSpanOptions(trace.WithSpanKind(trace.SpanKindClient)),
+		WithSpanNameFormatter(defaultTransportFormatter),
+	}
+
+	c := NewConfig(append(defaultOpts, opts...)...)
+	t.configure(c)
+
+	return &t
+}
+
+func (t *Transport) configure(c *Config) {
+	t.tracer = c.Tracer
+	t.propagators = c.Propagators
+	t.spanStartOptions = c.SpanStartOptions
+	t.filters = c.Filters
+	t.spanNameFormatter = c.SpanNameFormatter
+}
+
+func defaultTransportFormatter(_ string, r *http.Request) string {
+	return r.Method
+}
+
+// RoundTrip creates a Span and propagates its context via the provided request's headers
+// before handing the request to the configured base RoundTripper. The created span will
+// end when the response body is closed or when a read from the body returns io.EOF.
+func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
+	for _, f := range t.filters {
+		if !f(r) {
+			// Simply pass through to the base RoundTripper if a filter rejects the request
+			return t.rt.RoundTrip(r)
+		}
+	}
+
+	opts := append([]trace.StartOption{}, t.spanStartOptions...) // start with the configured options
+
+	ctx, span := t.tracer.Start(r.Context(), t.spanNameFormatter("", r), opts...)
+
+	r = r.WithContext(ctx)
+	setBasicAttributes(span, r)
+	propagation.InjectHTTP(ctx, t.propagators, r.Header)
+
+	res, err := t.rt.RoundTrip(r)
+	if err != nil {
+		span.RecordError(ctx, err, trace.WithErrorStatus(codes.Internal))
+		span.End()
+		return res, err
+	}
+
+	span.SetAttributes(StatusCodeKey.Int(res.StatusCode))
+	res.Body = &wrappedBody{ctx: ctx, span: span, body: res.Body}
+
+	return res, err
+}
+
+type wrappedBody struct {
+	ctx  context.Context
+	span trace.Span
+	body io.ReadCloser
+}
+
+var _ io.ReadCloser = &wrappedBody{}
+
+func (wb *wrappedBody) Read(b []byte) (int, error) {
+	n, err := wb.body.Read(b)
+
+	switch err {
+	case nil:
+		// nothing to do here but fall through to the return
+	case io.EOF:
+		wb.span.End()
+	default:
+		wb.span.RecordError(wb.ctx, err, trace.WithErrorStatus(codes.Internal))
+	}
+	return n, err
+}
+
+func (wb *wrappedBody) Close() error {
+	wb.span.End()
+	return wb.body.Close()
+}

plugin/othttp/transport_example_test.go

@@ -0,0 +1,59 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package othttp
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+
+	"go.opentelemetry.io/otel/api/global"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+)
+
+func ExampleNewTransport() {
+	// Start with a working trace provider
+	tp, err := sdktrace.NewProvider(sdktrace.WithConfig(sdktrace.Config{DefaultSampler: sdktrace.AlwaysSample()}))
+	if err != nil {
+		log.Fatal(err)
+	}
+	global.SetTraceProvider(tp)
+
+	// Create an http.Client that uses the othttp.Transport
+	// wrapped around the http.DefaultTransport
+	client := http.Client{
+		Transport: NewTransport(http.DefaultTransport),
+	}
+
+	// Make a request with our tracing client
+	response, err := client.Get("https://postman-echo.com/get")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Read the whole body and close it. The span created by the
+	// othttp.Transport does not end until a read from the response
+	// body returns io.EOF or the response body is closed.
+	body, err := ioutil.ReadAll(response.Body)
+	response.Body.Close()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("%s", body)
+	// body should look like this, with a different "traceparent" value:
+	// {"args":{},"headers":{"x-forwarded-proto":"https","host":"postman-echo.com","accept-encoding":"gzip","traceparent":"00-fb1d6775b94db561d9b51adbb3640de5-919c41073ec08f50-01","user-agent":"Go-http-client/1.1","x-forwarded-port":"443"},"url":"https://postman-echo.com/get"}
+}

plugin/othttp/transport_test.go

@@ -0,0 +1,77 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package othttp
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"go.opentelemetry.io/otel/api/core"
+	"go.opentelemetry.io/otel/api/global"
+	"go.opentelemetry.io/otel/api/propagation"
+	"go.opentelemetry.io/otel/api/trace"
+	mocktrace "go.opentelemetry.io/otel/internal/trace"
+)
+
+func TestTransportBasics(t *testing.T) {
+	var id uint64
+	tracer := mocktrace.MockTracer{StartSpanID: &id}
+	content := []byte("Hello, world!")
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ctx := propagation.ExtractHTTP(r.Context(), global.Propagators(), r.Header)
+		span := trace.RemoteSpanContextFromContext(ctx)
+		tgtID, err := core.SpanIDFromHex(fmt.Sprintf("%016x", id))
+		if err != nil {
+			t.Fatalf("Error converting id to SpanID: %s", err.Error())
+		}
+		if span.SpanID != tgtID {
+			t.Fatalf("testing remote SpanID: got %s, expected %s", span.SpanID, tgtID)
+		}
+		if _, err := w.Write(content); err != nil {
+			t.Fatal(err)
+		}
+	}))
+	defer ts.Close()
+
+	r, err := http.NewRequest(http.MethodGet, ts.URL, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tr := NewTransport(
+		http.DefaultTransport,
+		WithTracer(&tracer),
+	)
+
+	c := http.Client{Transport: tr}
+	res, err := c.Do(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(body, content) {
+		t.Fatalf("unexpected content: got %s, expected %s", body, content)
+	}
+}