[confighttp] Add support for proxy (open-telemetry#8339)

**Description:**
Adding a feature to support proxy configuration field in all exporters

**Link to tracking Issue:**
open-telemetry#5761

---------

Signed-off-by: Hrittik Roy <[email protected]>
Signed-off-by: Juraci Paixão Kröhling <[email protected]>
Co-authored-by: Juraci Paixão Kröhling <[email protected]>
Co-authored-by: Juraci Paixão Kröhling <[email protected]>
Co-authored-by: Andrzej Stencel <[email protected]>
Co-authored-by: Alex Boten <[email protected]>

.chloggen/proxy.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: Support proxy configuration field in all exporters that support confighttp
+
+# One or more tracking issues or pull requests related to the change
+issues: [5761]
+
+# (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/confighttp.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"net/url"
 	"time"
 
 	"github.com/rs/cors"
@@ -32,6 +33,9 @@ type HTTPClientSettings struct {
 	// The target URL to send data to (e.g.: http://some.url:9411/v1/traces).
 	Endpoint string `mapstructure:"endpoint"`
 
+	// ProxyURL setting for the collector
+	ProxyURL string `mapstructure:"proxy_url"`
+
 	// TLSSetting struct exposes TLS client configuration.
 	TLSSetting configtls.TLSClientSetting `mapstructure:"tls"`
 
@@ -132,6 +136,15 @@ func (hcs *HTTPClientSettings) ToClient(host component.Host, settings component.
 		transport.IdleConnTimeout = *hcs.IdleConnTimeout
 	}
 
+	// Setting the Proxy URL
+	if hcs.ProxyURL != "" {
+		proxyURL, parseErr := url.ParseRequestURI(hcs.ProxyURL)
+		if parseErr != nil {
+			return nil, parseErr
+		}
+		transport.Proxy = http.ProxyURL(proxyURL)
+	}
+
 	transport.DisableKeepAlives = hcs.DisableKeepAlives
 
 	clientTransport := (http.RoundTripper)(transport)

config/confighttp/confighttp_test.go

@@ -208,6 +208,61 @@ func TestDefaultHTTPClientSettings(t *testing.T) {
 	assert.EqualValues(t, 90*time.Second, *httpClientSettings.IdleConnTimeout)
 }
 
+func TestProxyURL(t *testing.T) {
+	testCases := []struct {
+		desc        string
+		proxyURL    string
+		expectedURL *url.URL
+		err         bool
+	}{
+		{
+			desc:        "default config",
+			expectedURL: nil,
+		},
+		{
+			desc:        "proxy is set",
+			proxyURL:    "http://proxy.example.com:8080",
+			expectedURL: &url.URL{Scheme: "http", Host: "proxy.example.com:8080"},
+		},
+		{
+			desc:     "proxy is invalid",
+			proxyURL: "://example.com",
+			err:      true,
+		},
+	}
+	for _, tC := range testCases {
+		t.Run(tC.desc, func(t *testing.T) {
+			s := NewDefaultHTTPClientSettings()
+			s.ProxyURL = tC.proxyURL
+
+			tt := componenttest.NewNopTelemetrySettings()
+			tt.TracerProvider = nil
+			client, err := s.ToClient(componenttest.NewNopHost(), tt)
+
+			if tC.err {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+
+			if err == nil {
+				transport := client.Transport.(*http.Transport)
+				require.NotNil(t, transport.Proxy)
+
+				url, err := transport.Proxy(&http.Request{URL: &url.URL{Scheme: "http", Host: "example.com"}})
+				require.NoError(t, err)
+
+				if tC.expectedURL == nil {
+					assert.Nil(t, url)
+				} else {
+					require.NotNil(t, url)
+					assert.Equal(t, tC.expectedURL, url)
+				}
+			}
+		})
+	}
+}
+
 func TestHTTPClientSettingsError(t *testing.T) {
 	host := &mockHost{
 		ext: map[component.ID]component.Component{},