test(e2e): add hosts module e2e test suite

Verify the static hosts mapping (HostMapper) overrides DNS: a mapped
hostname resolves to the configured IP and reaches the echo server,
while an unmapped hostname fails to resolve.

tests/e2e/hosts_test.go

@@ -0,0 +1,85 @@
+package e2e
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+	"github.com/testcontainers/testcontainers-go"
+)
+
+// HostsSuite verifies the static hosts mapping (HostMapper), which overrides
+// DNS for matched hostnames. A mapped hostname resolves to the configured IP
+// and reaches the echo server; an unmapped hostname fails to resolve.
+type HostsSuite struct {
+	suite.Suite
+	ctx    context.Context
+	echoC  testcontainers.Container
+	echoIP string
+	gostC  testcontainers.Container
+}
+
+func (s *HostsSuite) 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
+
+	cfg, err := RenderConfig("testdata/hosts/hosts.yaml", ConfigData{ServerAddr: s.echoIP})
+	s.Require().NoError(err)
+	defer os.Remove(cfg)
+
+	gostC, err := RunGostContainerWithPorts(s.ctx, SharedNetworkName, cfg, "8080/tcp")
+	s.Require().NoError(err)
+	s.gostC = gostC
+}
+
+func (s *HostsSuite) TearDownSuite() {
+	if s.gostC != nil {
+		s.gostC.Terminate(s.ctx)
+	}
+	if s.echoC != nil {
+		s.echoC.Terminate(s.ctx)
+	}
+}
+
+// proxyRequest sends a request to the given hostname through the gost proxy and
+// returns the response body. A resolvable host that reaches the echo server
+// returns "hello-gost"; an unresolvable host returns an empty body.
+func (s *HostsSuite) proxyRequest(host string) string {
+	cmd := []string{
+		"curl", "-s",
+		"-x", "http://127.0.0.1:8080",
+		fmt.Sprintf("http://%s:5678", host),
+	}
+	_, out, err := s.gostC.Exec(s.ctx, cmd)
+	s.Require().NoError(err)
+
+	body, err := io.ReadAll(out)
+	s.Require().NoError(err)
+	return string(body)
+}
+
+// TestMappedHostname verifies that a hostname in the hosts mapping resolves to
+// the configured IP and reaches the echo server.
+func (s *HostsSuite) TestMappedHostname() {
+	s.Require().Contains(s.proxyRequest("echo.internal"), "hello-gost")
+}
+
+// TestUnmappedHostname verifies that a hostname absent from the mapping fails to
+// resolve, so the request never reaches the echo server.
+func (s *HostsSuite) TestUnmappedHostname() {
+	s.Require().NotContains(s.proxyRequest("nomap.internal"), "hello-gost")
+}
+
+func TestHostsSuite(t *testing.T) {
+	suite.Run(t, new(HostsSuite))
+}

tests/e2e/testdata/hosts/hosts.yaml

@@ -0,0 +1,18 @@
+# HTTP proxy with a static hosts mapping. The made-up hostname echo.internal is
+# mapped to the echo server's real IP, overriding DNS. A request to
+# echo.internal resolves via the mapping and reaches the echo server; a request
+# to an unmapped hostname fails to resolve and never connects.
+services:
+  - name: proxy
+    addr: ":8080"
+    hosts: hosts-0
+    handler:
+      type: http
+    listener:
+      type: tcp
+
+hosts:
+  - name: hosts-0
+    mappings:
+      - ip: {{.ServerAddr}}
+        hostname: echo.internal