[confighttp] - Expose an option to set ForceAttemptHttp2 setting (#13426)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

We make use golang's `DefaultTransport`, which forces the use of [HTTP/2
by
default](https://cs.opensource.google/go/go/+/refs/tags/go1.24.5:src/net/http/transport.go;l=51).

However, some of our settings are only applicable while using HTTP/1
transport (`MaxConnsPerHost`, `MaxIdleConnsPerHost` and `MaxIdleConns`).
Users wanting to force such settings should have an option to use HTTP/1
by disabling `ForceAttemptHTTP2` to `false`. This PR adds that option.

By default, `ForceAttemptHTTP2` is set to `true` for backward
compatibility.

Author: VihasMakwana

.chloggen/http2.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confighttp
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add option to configure ForceAttemptHTTP2 to support HTTP/1 specific transport settings. 
+
+# One or more tracking issues or pull requests related to the change
+issues: [13426]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: 
+ 
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

config/confighttp/README.md

@@ -56,6 +56,7 @@ README](../configtls/README.md).
 - [`idle_conn_timeout`](https://golang.org/pkg/net/http/#Transport)
 - [`auth`](../configauth/README.md)
 - [`disable_keep_alives`](https://golang.org/pkg/net/http/#Transport)
+- [`force_attempt_http2`](https://golang.org/pkg/net/http/#Transport)
 - [`http2_read_idle_timeout`](https://pkg.go.dev/golang.org/x/net/http2#Transport)
 - [`http2_ping_timeout`](https://pkg.go.dev/golang.org/x/net/http2#Transport)
 - [`cookies`](https://pkg.go.dev/net/http#CookieJar)

config/confighttp/confighttp.go

@@ -119,6 +119,11 @@ type ClientConfig struct {
 	// Cookies configures the cookie management of the HTTP client.
 	Cookies CookiesConfig `mapstructure:"cookies,omitempty"`
 
+	// Enabling ForceAttemptHTTP2 forces the HTTP transport to use the HTTP/2 protocol.
+	// By default, this is set to true.
+	// NOTE: HTTP/2 does not support settings such as MaxConnsPerHost, MaxIdleConnsPerHost and MaxIdleConns.
+	ForceAttemptHTTP2 bool `mapstructure:"force_attempt_http2,omitempty"`
+
 	// Middlewares are used to add custom functionality to the HTTP client.
 	// Middleware handlers are called in the order they appear in this list,
 	// with the first middleware becoming the outermost handler.
@@ -141,9 +146,10 @@ func NewDefaultClientConfig() ClientConfig {
 	defaultTransport := http.DefaultTransport.(*http.Transport)
 
 	return ClientConfig{
-		Headers:         map[string]configopaque.String{},
-		MaxIdleConns:    defaultTransport.MaxIdleConns,
-		IdleConnTimeout: defaultTransport.IdleConnTimeout,
+		Headers:           map[string]configopaque.String{},
+		MaxIdleConns:      defaultTransport.MaxIdleConns,
+		IdleConnTimeout:   defaultTransport.IdleConnTimeout,
+		ForceAttemptHTTP2: true,
 	}
 }
 
@@ -184,6 +190,7 @@ func (hcs *ClientConfig) ToClient(ctx context.Context, host component.Host, sett
 	transport.MaxIdleConnsPerHost = hcs.MaxIdleConnsPerHost
 	transport.MaxConnsPerHost = hcs.MaxConnsPerHost
 	transport.IdleConnTimeout = hcs.IdleConnTimeout
+	transport.ForceAttemptHTTP2 = hcs.ForceAttemptHTTP2
 
 	// Setting the Proxy URL
 	if hcs.ProxyURL != "" {

config/confighttp/confighttp_test.go

@@ -101,6 +101,28 @@ func TestAllHTTPClientSettings(t *testing.T) {
 			},
 			shouldError: false,
 		},
+		{
+			name: "all_valid_settings_http2_enabled",
+			settings: ClientConfig{
+				Endpoint: "localhost:1234",
+				TLS: configtls.ClientConfig{
+					Insecure: false,
+				},
+				ReadBufferSize:       1024,
+				WriteBufferSize:      512,
+				MaxIdleConns:         maxIdleConns,
+				MaxIdleConnsPerHost:  maxIdleConnsPerHost,
+				MaxConnsPerHost:      maxConnsPerHost,
+				ForceAttemptHTTP2:    true,
+				IdleConnTimeout:      idleConnTimeout,
+				Compression:          "",
+				DisableKeepAlives:    true,
+				Cookies:              CookiesConfig{Enabled: true},
+				HTTP2ReadIdleTimeout: idleConnTimeout,
+				HTTP2PingTimeout:     http2PingTimeout,
+			},
+			shouldError: false,
+		},
 		{
 			name: "all_valid_settings_with_none_compression",
 			settings: ClientConfig{
@@ -699,8 +721,9 @@ func TestHttpReception(t *testing.T) {
 			}
 
 			hcs := &ClientConfig{
-				Endpoint: prefix + ln.Addr().String(),
-				TLS:      *tt.tlsClientCreds,
+				Endpoint:          prefix + ln.Addr().String(),
+				TLS:               *tt.tlsClientCreds,
+				ForceAttemptHTTP2: true,
 			}
 
 			client, errClient := hcs.ToClient(context.Background(), componenttest.NewNopHost(), nilProvidersSettings)

exporter/otlphttpexporter/config_test.go

@@ -82,6 +82,7 @@ func TestUnmarshalConfig(t *testing.T) {
 				MaxIdleConnsPerHost: defaultMaxIdleConnsPerHost,
 				MaxConnsPerHost:     defaultMaxConnsPerHost,
 				IdleConnTimeout:     defaultIdleConnTimeout,
+				ForceAttemptHTTP2:   true,
 			},
 		}, cfg)
 }

internal/e2e/confighttp_test.go

@@ -18,9 +18,10 @@ func TestConfmapMarshalConfigHTTP(t *testing.T) {
 	conf := confmap.New()
 	require.NoError(t, conf.Marshal(confighttp.NewDefaultClientConfig()))
 	assert.Equal(t, map[string]any{
-		"headers":           map[string]any{},
-		"idle_conn_timeout": 90 * time.Second,
-		"max_idle_conns":    100,
+		"headers":             map[string]any{},
+		"idle_conn_timeout":   90 * time.Second,
+		"max_idle_conns":      100,
+		"force_attempt_http2": true,
 	}, conf.ToStringMap())
 
 	conf = confmap.New()