fix empty SERVER_ADDRESS config loading

After bumping packages, envconfig behaviour has changed. If a struct contains a pointer, and no value is being loaded, it will now generate the zero value for the pointed type rather than nil.

This prevented the proxy from being started if no SERVER_ADDRESS was specified, as ConfigureProxy checks for no server address being specified by comparing it to url.URL{}, which because of the pointer is no longer equal.

The fix is a simple config change for envconfig so that it will use nil rather than the zero value for the pointer when no value is specified.

Author: joshkeegan-form3

internal/app/configuration/proxyconfig.go

@@ -4,16 +4,20 @@ import (
 	"context"
 	"net/url"
 
-	"github.com/form3tech-oss/pact-proxy/internal/app/pactproxy"
 	"github.com/pkg/errors"
 	"github.com/sethvargo/go-envconfig"
+
+	"github.com/form3tech-oss/pact-proxy/internal/app/pactproxy"
 )
 
 func NewFromEnv() (pactproxy.Config, error) {
 	ctx := context.Background()
 
 	var config pactproxy.Config
-	err := envconfig.Process(ctx, &config)
+	err := envconfig.ProcessWith(ctx, &envconfig.Config{
+		Target:        &config,
+		DefaultNoInit: true,
+	})
 	if err != nil {
 		return config, errors.Wrap(err, "process env config")
 	}

internal/app/configuration/proxyconfig_test.go

@@ -21,9 +21,10 @@ import (
 	"testing"
 	"time"
 
-	"github.com/form3tech-oss/pact-proxy/internal/app/pactproxy"
 	"github.com/pact-foundation/pact-go/utils"
 	"github.com/stretchr/testify/require"
+
+	"github.com/form3tech-oss/pact-proxy/internal/app/pactproxy"
 )
 
 const (
@@ -183,6 +184,16 @@ func TestConfigureProxy_MTLS(t *testing.T) {
 	}
 }
 
+// When no server address env var is specified, config.ServerAddress should be the zero value.
+// This is used during ConfigureProxy logic, but is no longer the default behaviour of envconfig.Process due to url.URL
+// containing a pointer.
+func TestProxyConfig_NewFromEnv_EmptyServerAddress(t *testing.T) {
+	os.Clearenv()
+	config, err := NewFromEnv()
+	require.NoError(t, err)
+	require.Equal(t, url.URL{}, config.ServerAddress)
+}
+
 func TestProxyConfig_ForwardUnrecognisedRequests(t *testing.T) {
 	os.Clearenv()
 	config, err := NewFromEnv()