[exporter/otlphttpexporter] Remove unnecessary nil assignment in default client config (open-telemetry#11299)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
This is a follow up to open-telemetry#11273 in which I had set fields `MaxIdleConns`,
`MaxIdleConnsPerHost`, `MaxConnsPerHost`, `IdleConnTimeout` to nil
manually to keep backwards compatibility.

However, in the call to
[ToClient](https://github.com/open-telemetry/opentelemetry-collector/blob/main/config/confighttp/confighttp.go#L141-L166)
the `http.Transport` defaults are used. The call to
`NewDefaultClientConfig` also uses the `http.Transport` defaults.

Thus, not setting to nil will maintain the same behaviour/ is
unnecessary.

<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #

<!--Describe what testing was performed and which tests were added.-->
#### Testing

<!--Describe the documentation added.-->
#### Documentation

<!--Please delete paragraphs that you did not use before submitting.-->

Author: mackjmr

exporter/otlphttpexporter/config_test.go

@@ -4,6 +4,7 @@
 package otlphttpexporter
 
 import (
+	"net/http"
 	"path/filepath"
 	"testing"
 	"time"
@@ -31,6 +32,11 @@ func TestUnmarshalDefaultConfig(t *testing.T) {
 }
 
 func TestUnmarshalConfig(t *testing.T) {
+	defaultMaxIdleConns := http.DefaultTransport.(*http.Transport).MaxIdleConns
+	defaultMaxIdleConnsPerHost := http.DefaultTransport.(*http.Transport).MaxIdleConnsPerHost
+	defaultMaxConnsPerHost := http.DefaultTransport.(*http.Transport).MaxConnsPerHost
+	defaultIdleConnTimeout := http.DefaultTransport.(*http.Transport).IdleConnTimeout
+
 	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "config.yaml"))
 	require.NoError(t, err)
 	factory := NewFactory()
@@ -67,10 +73,14 @@ func TestUnmarshalConfig(t *testing.T) {
 					},
 					Insecure: true,
 				},
-				ReadBufferSize:  123,
-				WriteBufferSize: 345,
-				Timeout:         time.Second * 10,
-				Compression:     "gzip",
+				ReadBufferSize:      123,
+				WriteBufferSize:     345,
+				Timeout:             time.Second * 10,
+				Compression:         "gzip",
+				MaxIdleConns:        &defaultMaxIdleConns,
+				MaxIdleConnsPerHost: &defaultMaxIdleConnsPerHost,
+				MaxConnsPerHost:     &defaultMaxConnsPerHost,
+				IdleConnTimeout:     &defaultIdleConnTimeout,
 			},
 		}, cfg)
 }

exporter/otlphttpexporter/factory.go

@@ -38,10 +38,6 @@ func createDefaultConfig() component.Config {
 	clientConfig.Compression = configcompression.TypeGzip
 	// We almost read 0 bytes, so no need to tune ReadBufferSize.
 	clientConfig.WriteBufferSize = 512 * 1024
-	clientConfig.MaxIdleConns = nil
-	clientConfig.MaxIdleConnsPerHost = nil
-	clientConfig.MaxConnsPerHost = nil
-	clientConfig.IdleConnTimeout = nil
 
 	return &Config{
 		RetryConfig:  configretry.NewDefaultBackOffConfig(),

exporter/otlphttpexporter/factory_test.go

@@ -50,7 +50,21 @@ func TestCreateMetricsExporter(t *testing.T) {
 	require.NotNil(t, oexp)
 }
 
+func clientConfig(endpoint string, headers map[string]configopaque.String, tlsSetting configtls.ClientConfig, compression configcompression.Type) confighttp.ClientConfig {
+	clientConfig := confighttp.NewDefaultClientConfig()
+	clientConfig.TLSSetting = tlsSetting
+	clientConfig.Compression = compression
+	if endpoint != "" {
+		clientConfig.Endpoint = endpoint
+	}
+	if headers != nil {
+		clientConfig.Headers = headers
+	}
+	return clientConfig
+}
+
 func TestCreateTracesExporter(t *testing.T) {
+	var configCompression configcompression.Type
 	endpoint := "http://" + testutil.GetAvailableLocalAddress(t)
 
 	tests := []struct {
@@ -62,111 +76,86 @@ func TestCreateTracesExporter(t *testing.T) {
 		{
 			name: "NoEndpoint",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint: "",
-				},
+				ClientConfig: clientConfig("", nil, configtls.ClientConfig{}, configCompression),
 			},
 			mustFailOnCreate: true,
 		},
 		{
 			name: "UseSecure",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint: endpoint,
-					TLSSetting: configtls.ClientConfig{
-						Insecure: false,
-					},
-				},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{
+					Insecure: false,
+				}, configCompression),
 			},
 		},
 		{
 			name: "Headers",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint: endpoint,
-					Headers: map[string]configopaque.String{
-						"hdr1": "val1",
-						"hdr2": "val2",
-					},
-				},
+				ClientConfig: clientConfig(endpoint, map[string]configopaque.String{
+					"hdr1": "val1",
+					"hdr2": "val2",
+				}, configtls.ClientConfig{}, configCompression),
 			},
 		},
 		{
 			name: "CaCert",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint: endpoint,
-					TLSSetting: configtls.ClientConfig{
-						Config: configtls.Config{
-							CAFile: filepath.Join("testdata", "test_cert.pem"),
-						},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{
+					Config: configtls.Config{
+						CAFile: filepath.Join("testdata", "test_cert.pem"),
 					},
-				},
+				}, configCompression),
 			},
 		},
 		{
 			name: "CertPemFileError",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint: endpoint,
-					TLSSetting: configtls.ClientConfig{
-						Config: configtls.Config{
-							CAFile: "nosuchfile",
-						},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{
+					Config: configtls.Config{
+						CAFile: "nosuchfile",
 					},
 				},
+					configCompression),
 			},
 			mustFailOnCreate: false,
 			mustFailOnStart:  true,
 		},
 		{
 			name: "NoneCompression",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint:    endpoint,
-					Compression: "none",
-				},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{}, "none"),
 			},
 		},
 		{
 			name: "GzipCompression",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint:    endpoint,
-					Compression: configcompression.TypeGzip,
-				},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{}, configcompression.TypeGzip),
 			},
 		},
 		{
 			name: "SnappyCompression",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint:    endpoint,
-					Compression: configcompression.TypeSnappy,
-				},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{}, configcompression.TypeSnappy),
 			},
 		},
 		{
 			name: "ZstdCompression",
 			config: &Config{
-				ClientConfig: confighttp.ClientConfig{
-					Endpoint:    endpoint,
-					Compression: configcompression.TypeZstd,
-				},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{}, configcompression.TypeZstd),
 			},
 		},
 		{
 			name: "ProtoEncoding",
 			config: &Config{
 				Encoding:     EncodingProto,
-				ClientConfig: confighttp.ClientConfig{Endpoint: endpoint},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{}, configCompression),
 			},
 		},
 		{
 			name: "JSONEncoding",
 			config: &Config{
 				Encoding:     EncodingJSON,
-				ClientConfig: confighttp.ClientConfig{Endpoint: endpoint},
+				ClientConfig: clientConfig(endpoint, nil, configtls.ClientConfig{}, configCompression),
 			},
 		},
 	}