http_config: Add host

config/http_config.go

@@ -309,6 +309,9 @@ type HTTPClientConfig struct {
 	// The omitempty flag is not set, because it would be hidden from the
 	// marshalled configuration when set to false.
 	EnableHTTP2 bool `yaml:"enable_http2" json:"enable_http2"`
+	// Host optionally overrides the Host header to send.
+	// If empty, the host from the URL will be used.
+	Host string `yaml:"host,omitempty" json:"host,omitempty"`
 	// Proxy configuration.
 	ProxyConfig `yaml:",inline"`
 }
@@ -430,6 +433,7 @@ type httpClientOptions struct {
 	http2Enabled      bool
 	idleConnTimeout   time.Duration
 	userAgent         string
+	host              string
 }
 
 // HTTPClientOption defines an option that can be applied to the HTTP client.
@@ -470,6 +474,13 @@ func WithUserAgent(ua string) HTTPClientOption {
 	}
 }
 
+// WithHost allows setting the host header.
+func WithHost(host string) HTTPClientOption {
+	return func(opts *httpClientOptions) {
+		opts.host = host
+	}
+}
+
 // NewClient returns a http.Client using the specified http.RoundTripper.
 func newClient(rt http.RoundTripper) *http.Client {
 	return &http.Client{Transport: rt}
@@ -571,6 +582,10 @@ func NewRoundTripperFromConfig(cfg HTTPClientConfig, name string, optFuncs ...HT
 			rt = NewUserAgentRoundTripper(opts.userAgent, rt)
 		}
 
+		if opts.host != "" {
+			rt = NewHostRoundTripper(opts.host, rt)
+		}
+
 		// Return a new configured RoundTripper.
 		return rt, nil
 	}
@@ -1168,11 +1183,21 @@ type userAgentRoundTripper struct {
 	rt        http.RoundTripper
 }
 
+type hostRoundTripper struct {
+	host string
+	rt   http.RoundTripper
+}
+
 // NewUserAgentRoundTripper adds the user agent every request header.
 func NewUserAgentRoundTripper(userAgent string, rt http.RoundTripper) http.RoundTripper {
 	return &userAgentRoundTripper{userAgent, rt}
 }
 
+// NewHostRoundTripper sets the [http.Request.Host] of every request.
+func NewHostRoundTripper(host string, rt http.RoundTripper) http.RoundTripper {
+	return &hostRoundTripper{host, rt}
+}
+
 func (rt *userAgentRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
 	req = cloneRequest(req)
 	req.Header.Set("User-Agent", rt.userAgent)
@@ -1185,6 +1210,19 @@ func (rt *userAgentRoundTripper) CloseIdleConnections() {
 	}
 }
 
+func (rt *hostRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	req = cloneRequest(req)
+	req.Host = rt.host
+	req.Header.Set("Host", rt.host)
+	return rt.rt.RoundTrip(req)
+}
+
+func (rt *hostRoundTripper) CloseIdleConnections() {
+	if ci, ok := rt.rt.(closeIdler); ok {
+		ci.CloseIdleConnections()
+	}
+}
+
 func (c HTTPClientConfig) String() string {
 	b, err := yaml.Marshal(c)
 	if err != nil {

config/http_config_test.go

@@ -35,7 +35,7 @@ import (
 	"testing"
 	"time"
 
-	yaml "gopkg.in/yaml.v2"
+	"gopkg.in/yaml.v2"
 )
 
 const (
@@ -1501,6 +1501,32 @@ func TestOAuth2UserAgent(t *testing.T) {
 	}
 }
 
+func TestHost(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Host != "localhost.localdomain" {
+			t.Fatalf("Expected Host header in request to be 'localhost.localdomain', got '%s'", r.Host)
+		}
+
+		w.Header().Add("Content-Type", "application/json")
+	}))
+	defer ts.Close()
+
+	config := DefaultHTTPClientConfig
+
+	rt, err := NewRoundTripperFromConfig(config, "test_host", WithHost("localhost.localdomain"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	client := http.Client{
+		Transport: rt,
+	}
+	_, err = client.Get(ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestOAuth2WithFile(t *testing.T) {
 	var expectedAuth *string
 	var previousAuth string