Add Transport Option to allow egress proxies (#217)

This commit adds a `Transport` to the `Options` struct when constructing
a new instance of the Go SDK. If set it allows the end user to pass in
their own `http.RoundTripper` instead of using `http.DefaultTransport`.

The reasoning for this change it to allow users to provide a transport
which is capabile of acting as middleware for the outbound requests made
by the SDK (such as allowing routing via an authenticated egress proxy).

Co-authored-by: Dominic Black <[email protected]>

statsig.go

@@ -25,8 +25,9 @@ func Initialize(sdkKey string) {
 type Options struct {
 	API                   string       `json:"api"`
 	APIOverrides          APIOverrides `json:"api_overrides"`
-	Environment           Environment  `json:"environment"`
-	LocalMode             bool         `json:"localMode"`
+	Transport             http.RoundTripper
+	Environment           Environment `json:"environment"`
+	LocalMode             bool        `json:"localMode"`
 	ConfigSyncInterval    time.Duration
 	IDListSyncInterval    time.Duration
 	LoggingInterval       time.Duration

transport.go

@@ -62,8 +62,11 @@ func newTransport(secret string, options *Options) *transport {
 		api:      api,
 		metadata: getStatsigMetadata(),
 		sdkKey:   secret,
-		client:   &http.Client{Timeout: time.Second * 3},
-		options:  options,
+		client: &http.Client{
+			Timeout:   time.Second * 3,
+			Transport: options.Transport,
+		},
+		options: options,
 	}
 }
 

transport_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"testing"
 )
 
@@ -85,3 +86,23 @@ func TestRetries(t *testing.T) {
 		t.Errorf("Expected successful request but got error")
 	}
 }
+
+func TestProxy(t *testing.T) {
+	testServerHit := false
+	testServer := httptest.NewServer(http.HandlerFunc(func(res http.ResponseWriter, req *http.Request) {
+		res.WriteHeader(http.StatusOK)
+		testServerHit = true
+	}))
+	defer testServer.Close()
+	in := Empty{}
+	var out ServerResponse
+	url, _ := url.Parse(testServer.URL)
+	opt := &Options{
+		Transport: &http.Transport{Proxy: http.ProxyURL(url)},
+	}
+	n := newTransport("secret-123", opt)
+	_, _ = n.post("/123", in, &out, RequestOptions{})
+	if !testServerHit {
+		t.Errorf("Expected request to hit proxy server")
+	}
+}