Add back the otlpmetrichttp exporter (#3097)

* Add otlpmetric package doc

* Add Client interface

* Add the Exporter

Have the Exporter ensure synchronous access to all client methods.

* Add race detection test for Exporter

* Expand New godocs

* Fix lint

* Add back the otlpmetrichttp pkg from main

* Restrict to Go 1.18 and above

* Remove integration testing

* Rename client_unit_test.go to client_test.go

* Rename options.go to config.go

* Remove the NewUnstarted func

* Remove Start method from client

* Add no-op ForceFlush method to client

* Update otlpconfig pkg name to oconf

* Rename Stop method to Shutdown

Match the otlpmetric.Client interface.

* Update creation functions to compile

* Remove name field from client

* Remove sync of methods from client

This is handled by the exporter.

* Remove unused generalCfg field from client

* Replace cfg client field with used conf vals

* Use a http request instead of url/header fields

* Remove NewClient and move New into client.go

* Rename client.client field to client.httpClient

* Update client tests

Remove test of a retry config and add functional tests of the client
methods honoring a context.

* Remove deprecated WithMaxAttempts and WithBackoff

* Update option docs

Include info on envvars.

* Fix lint

* Fix lint errors

* Revert New to accept a context

* Add example test

* Update pkg docs

* go mod tidy

* Use url.URL to form HTTP request URL

.github/dependabot.yml

@@ -145,6 +145,15 @@ updates:
     schedule:
       interval: weekly
       day: sunday
+  - package-ecosystem: gomod
+    directory: /exporters/otlp/otlpmetric/otlpmetrichttp
+    labels:
+      - dependencies
+      - go
+      - Skip Changelog
+    schedule:
+      interval: weekly
+      day: sunday
   - package-ecosystem: gomod
     directory: /exporters/otlp/otlptrace
     labels:

exporters/otlp/otlpmetric/otlpmetrichttp/client.go

@@ -0,0 +1,290 @@
+// 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.
+
+//go:build go1.18
+// +build go1.18
+
+package otlpmetrichttp // import "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
+
+import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"strconv"
+	"sync"
+	"time"
+
+	"google.golang.org/protobuf/proto"
+
+	"go.opentelemetry.io/otel/exporters/otlp/internal/retry"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/internal/oconf"
+	"go.opentelemetry.io/otel/sdk/metric"
+	colmetricpb "go.opentelemetry.io/proto/otlp/collector/metrics/v1"
+	metricpb "go.opentelemetry.io/proto/otlp/metrics/v1"
+)
+
+// New returns an OpenTelemetry metric Exporter. The Exporter can be used with
+// a PeriodicReader to export OpenTelemetry metric data to an OTLP receiving
+// endpoint using protobufs over HTTP.
+func New(_ context.Context, opts ...Option) (metric.Exporter, error) {
+	c, err := newClient(opts...)
+	if err != nil {
+		return nil, err
+	}
+	return otlpmetric.New(c), nil
+}
+
+type client struct {
+	// req is cloned for every upload the client makes.
+	req         *http.Request
+	compression Compression
+	requestFunc retry.RequestFunc
+	httpClient  *http.Client
+}
+
+// Keep it in sync with golang's DefaultTransport from net/http! We
+// have our own copy to avoid handling a situation where the
+// DefaultTransport is overwritten with some different implementation
+// of http.RoundTripper or it's modified by another package.
+var ourTransport = &http.Transport{
+	Proxy: http.ProxyFromEnvironment,
+	DialContext: (&net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+	}).DialContext,
+	ForceAttemptHTTP2:     true,
+	MaxIdleConns:          100,
+	IdleConnTimeout:       90 * time.Second,
+	TLSHandshakeTimeout:   10 * time.Second,
+	ExpectContinueTimeout: 1 * time.Second,
+}
+
+// newClient creates a new HTTP metric client.
+func newClient(opts ...Option) (otlpmetric.Client, error) {
+	cfg := oconf.NewHTTPConfig(asHTTPOptions(opts)...)
+
+	httpClient := &http.Client{
+		Transport: ourTransport,
+		Timeout:   cfg.Metrics.Timeout,
+	}
+	if cfg.Metrics.TLSCfg != nil {
+		transport := ourTransport.Clone()
+		transport.TLSClientConfig = cfg.Metrics.TLSCfg
+		httpClient.Transport = transport
+	}
+
+	u := &url.URL{
+		Scheme: "https",
+		Host:   cfg.Metrics.Endpoint,
+		Path:   cfg.Metrics.URLPath,
+	}
+	if cfg.Metrics.Insecure {
+		u.Scheme = "http"
+	}
+	// Body is set when this is cloned during upload.
+	req, err := http.NewRequest(http.MethodPost, u.String(), http.NoBody)
+	if err != nil {
+		return nil, err
+	}
+
+	if n := len(cfg.Metrics.Headers); n > 0 {
+		for k, v := range cfg.Metrics.Headers {
+			req.Header.Set(k, v)
+		}
+	}
+	req.Header.Set("Content-Type", "application/x-protobuf")
+
+	return &client{
+		compression: Compression(cfg.Metrics.Compression),
+		req:         req,
+		requestFunc: cfg.RetryConfig.RequestFunc(evaluate),
+		httpClient:  httpClient,
+	}, nil
+}
+
+// ForceFlush does nothing, the client holds no state.
+func (c *client) ForceFlush(ctx context.Context) error { return ctx.Err() }
+
+// Shutdown shuts down the client, freeing all resources.
+func (c *client) Shutdown(ctx context.Context) error {
+	// The otlpmetric.Exporter synchronizes access to client methods and
+	// ensures this is called only once. The only thing that needs to be done
+	// here is to release any computational resources the client holds.
+
+	c.requestFunc = nil
+	c.httpClient = nil
+	return ctx.Err()
+}
+
+// UploadMetrics sends protoMetrics to the connected endpoint.
+//
+// Retryable errors from the server will be handled according to any
+// RetryConfig the client was created with.
+func (c *client) UploadMetrics(ctx context.Context, protoMetrics *metricpb.ResourceMetrics) error {
+	// The otlpmetric.Exporter synchronizes access to client methods, and
+	// ensures this is not called after the Exporter is shutdown. Only thing
+	// to do here is send data.
+
+	pbRequest := &colmetricpb.ExportMetricsServiceRequest{
+		ResourceMetrics: []*metricpb.ResourceMetrics{protoMetrics},
+	}
+	body, err := proto.Marshal(pbRequest)
+	if err != nil {
+		return err
+	}
+	request, err := c.newRequest(ctx, body)
+	if err != nil {
+		return err
+	}
+
+	return c.requestFunc(ctx, func(iCtx context.Context) error {
+		select {
+		case <-iCtx.Done():
+			return iCtx.Err()
+		default:
+		}
+
+		request.reset(iCtx)
+		resp, err := c.httpClient.Do(request.Request)
+		if err != nil {
+			return err
+		}
+
+		var rErr error
+		switch resp.StatusCode {
+		case http.StatusOK:
+			// Success, do not retry.
+		case http.StatusTooManyRequests,
+			http.StatusServiceUnavailable:
+			// Retry-able failure.
+			rErr = newResponseError(resp.Header)
+
+			// Going to retry, drain the body to reuse the connection.
+			if _, err := io.Copy(io.Discard, resp.Body); err != nil {
+				_ = resp.Body.Close()
+				return err
+			}
+		default:
+			rErr = fmt.Errorf("failed to send metrics to %s: %s", request.URL, resp.Status)
+		}
+
+		if err := resp.Body.Close(); err != nil {
+			return err
+		}
+		return rErr
+	})
+}
+
+var gzPool = sync.Pool{
+	New: func() interface{} {
+		w := gzip.NewWriter(io.Discard)
+		return w
+	},
+}
+
+func (c *client) newRequest(ctx context.Context, body []byte) (request, error) {
+	r := c.req.Clone(ctx)
+	req := request{Request: r}
+
+	switch c.compression {
+	case NoCompression:
+		r.ContentLength = (int64)(len(body))
+		req.bodyReader = bodyReader(body)
+	case GzipCompression:
+		// Ensure the content length is not used.
+		r.ContentLength = -1
+		r.Header.Set("Content-Encoding", "gzip")
+
+		gz := gzPool.Get().(*gzip.Writer)
+		defer gzPool.Put(gz)
+
+		var b bytes.Buffer
+		gz.Reset(&b)
+
+		if _, err := gz.Write(body); err != nil {
+			return req, err
+		}
+		// Close needs to be called to ensure body if fully written.
+		if err := gz.Close(); err != nil {
+			return req, err
+		}
+
+		req.bodyReader = bodyReader(b.Bytes())
+	}
+
+	return req, nil
+}
+
+// bodyReader returns a closure returning a new reader for buf.
+func bodyReader(buf []byte) func() io.ReadCloser {
+	return func() io.ReadCloser {
+		return io.NopCloser(bytes.NewReader(buf))
+	}
+}
+
+// request wraps an http.Request with a resettable body reader.
+type request struct {
+	*http.Request
+
+	// bodyReader allows the same body to be used for multiple requests.
+	bodyReader func() io.ReadCloser
+}
+
+// reset reinitializes the request Body and uses ctx for the request.
+func (r *request) reset(ctx context.Context) {
+	r.Body = r.bodyReader()
+	r.Request = r.Request.WithContext(ctx)
+}
+
+// retryableError represents a request failure that can be retried.
+type retryableError struct {
+	throttle int64
+}
+
+// newResponseError returns a retryableError and will extract any explicit
+// throttle delay contained in headers.
+func newResponseError(header http.Header) error {
+	var rErr retryableError
+	if s, ok := header["Retry-After"]; ok {
+		if t, err := strconv.ParseInt(s[0], 10, 64); err == nil {
+			rErr.throttle = t
+		}
+	}
+	return rErr
+}
+
+func (e retryableError) Error() string {
+	return "retry-able request failure"
+}
+
+// evaluate returns if err is retry-able. If it is and it includes an explicit
+// throttling delay, that delay is also returned.
+func evaluate(err error) (bool, time.Duration) {
+	if err == nil {
+		return false, 0
+	}
+
+	rErr, ok := err.(retryableError)
+	if !ok {
+		return false, 0
+	}
+
+	return true, time.Duration(rErr.throttle)
+}

exporters/otlp/otlpmetric/otlpmetrichttp/client_test.go

@@ -0,0 +1,74 @@
+// 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.
+
+//go:build go1.18
+// +build go1.18
+
+package otlpmetrichttp
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClientHonorsContextErrors(t *testing.T) {
+	t.Run("Shutdown", testCtxErr(func(t *testing.T) func(context.Context) error {
+		c, err := newClient()
+		require.NoError(t, err)
+		return c.Shutdown
+	}))
+
+	t.Run("ForceFlush", testCtxErr(func(t *testing.T) func(context.Context) error {
+		c, err := newClient()
+		require.NoError(t, err)
+		return c.ForceFlush
+	}))
+
+	t.Run("UploadMetrics", testCtxErr(func(t *testing.T) func(context.Context) error {
+		c, err := newClient()
+		require.NoError(t, err)
+		return func(ctx context.Context) error {
+			return c.UploadMetrics(ctx, nil)
+		}
+	}))
+}
+
+func testCtxErr(factory func(*testing.T) func(context.Context) error) func(t *testing.T) {
+	return func(t *testing.T) {
+		t.Helper()
+		ctx, cancel := context.WithCancel(context.Background())
+		t.Cleanup(cancel)
+
+		t.Run("DeadlineExceeded", func(t *testing.T) {
+			innerCtx, innerCancel := context.WithTimeout(ctx, time.Nanosecond)
+			t.Cleanup(innerCancel)
+			<-innerCtx.Done()
+
+			f := factory(t)
+			assert.ErrorIs(t, f(innerCtx), context.DeadlineExceeded)
+		})
+
+		t.Run("Canceled", func(t *testing.T) {
+			innerCtx, innerCancel := context.WithCancel(ctx)
+			innerCancel()
+
+			f := factory(t)
+			assert.ErrorIs(t, f(innerCtx), context.Canceled)
+		})
+	}
+}