test(e2e): add resolver module e2e test suite

Verifies that a configured resolver drives the proxy's outbound DNS
resolution. A gost HTTP proxy uses a resolver whose only nameserver is a
test responder answering echo.test with the real echo server IP and
NXDOMAIN for everything else. A request to echo.test is resolved by the
custom resolver and reaches the echo server; an unmapped host fails to
resolve. Adds a parametrized DNS responder script and container helper.

tests/e2e/resolver_test.go

@@ -0,0 +1,91 @@
+package e2e
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+	"github.com/testcontainers/testcontainers-go"
+)
+
+// ResolverSuite verifies that a configured resolver drives the proxy's
+// outbound DNS resolution. A gost HTTP proxy uses a resolver whose only
+// nameserver is a test responder: it answers echo.test with the real echo
+// server IP and NXDOMAIN for everything else. A request to echo.test is
+// resolved by the custom resolver and reaches the echo server; a request to an
+// unmapped host fails to resolve.
+type ResolverSuite struct {
+	suite.Suite
+	ctx     context.Context
+	echoC   testcontainers.Container
+	echoIP  string
+	dnsC    testcontainers.Container
+	proxyC  testcontainers.Container
+}
+
+func (s *ResolverSuite) SetupSuite() {
+	s.ctx = context.Background()
+
+	echoC, err := RunEchoContainer(s.ctx, SharedNetworkName)
+	s.Require().NoError(err)
+	s.echoC = echoC
+
+	echoIP, err := echoC.ContainerIP(s.ctx)
+	s.Require().NoError(err)
+	s.echoIP = echoIP
+
+	dnsC, err := RunResolverResponderContainer(s.ctx, SharedNetworkName, s.echoIP)
+	s.Require().NoError(err)
+	s.dnsC = dnsC
+
+	proxyC, err := RunGostContainerWithOptions(s.ctx, SharedNetworkName,
+		"testdata/resolver/server.yaml", []string{"gost-proxy"}, []string{"8080/tcp"})
+	s.Require().NoError(err)
+	s.proxyC = proxyC
+}
+
+func (s *ResolverSuite) TearDownSuite() {
+	for _, c := range []testcontainers.Container{s.proxyC, s.dnsC, s.echoC} {
+		if c != nil {
+			c.Terminate(s.ctx)
+		}
+	}
+}
+
+// proxyRequest sends an HTTP GET to the given host through the gost proxy. When
+// waitResolve is true it retries until the resolver/responder is ready (the
+// resolved-host happy path); otherwise it makes a single attempt. Returns the
+// response body.
+func (s *ResolverSuite) proxyRequest(host string, waitResolve bool) string {
+	loop := "for i in $(seq 1 30); do "
+	if !waitResolve {
+		loop = "for i in 1; do "
+	}
+	cmd := []string{
+		"sh", "-c",
+		fmt.Sprintf("%sbody=$(curl -s -x http://gost-proxy:8080 http://%s:5678/); echo \"$body\" | grep -q hello-gost && { echo \"$body\"; exit 0; }; sleep 1; done; echo \"$body\"", loop, host),
+	}
+	_, out, err := s.echoC.Exec(s.ctx, cmd)
+	s.Require().NoError(err)
+	body, err := io.ReadAll(out)
+	s.Require().NoError(err)
+	return string(body)
+}
+
+// TestResolvedHostname verifies that the custom resolver resolves echo.test to
+// the echo server IP, so the proxied request reaches the echo server.
+func (s *ResolverSuite) TestResolvedHostname() {
+	s.Require().Contains(s.proxyRequest("echo.test", true), "hello-gost")
+}
+
+// TestUnresolvedHostname verifies that a host absent from the resolver gets
+// NXDOMAIN and never reaches the echo server.
+func (s *ResolverSuite) TestUnresolvedHostname() {
+	s.Require().NotContains(s.proxyRequest("nomapped.test", false), "hello-gost")
+}
+
+func TestResolverSuite(t *testing.T) {
+	suite.Run(t, new(ResolverSuite))
+}