diff --git a/sandboxed_api/sandbox2/BUILD.bazel b/sandboxed_api/sandbox2/BUILD.bazel
index 70532cc..6cdeb16 100644
--- a/sandboxed_api/sandbox2/BUILD.bazel
+++ b/sandboxed_api/sandbox2/BUILD.bazel
@@ -1094,3 +1094,21 @@ cc_test(
         "@com_google_googletest//:gtest_main",
     ],
 )
+
+cc_test(
+    name = "network_proxy_test",
+    srcs = ["network_proxy_test.cc"],
+    copts = sapi_platform_copts(),
+    data = [
+        "//sandboxed_api/sandbox2/testcases:network_proxy",
+    ],
+    tags = ["no_qemu_user_mode"],
+    deps = [
+        ":sandbox2",
+        "//sandboxed_api:testing",
+        "//sandboxed_api/sandbox2/network_proxy:testing",
+        "//sandboxed_api/util:status_matchers",
+        "@com_google_absl//absl/strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
diff --git a/sandboxed_api/sandbox2/CMakeLists.txt b/sandboxed_api/sandbox2/CMakeLists.txt
index feed59e..10218e0 100644
--- a/sandboxed_api/sandbox2/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/CMakeLists.txt
@@ -1197,6 +1197,27 @@ if(BUILD_TESTING AND SAPI_BUILD_TESTING)
     ENVIRONMENT "TEST_TMPDIR=/tmp"
     ENVIRONMENT "TEST_SRCDIR=${PROJECT_BINARY_DIR}"
   )
+
+  # sandboxed_api/sandbox2:network_proxy_test
+  add_executable(sandbox2_network_proxy_test
+    network_proxy_test.cc
+  )
+  set_target_properties(sandbox2_network_proxy_test PROPERTIES
+    OUTPUT_NAME network_proxy_test
+  )
+  target_link_libraries(sandbox2_network_proxy_test
+    PRIVATE absl::strings
+            sandbox2::sandbox2
+            sandbox2::network_proxy_testing
+            sapi::status_matchers
+            sapi::testing
+            sapi::test_main
+  )
+  gtest_discover_tests_xcompile(sandbox2_bpfdisassembler_test PROPERTIES
+    ENVIRONMENT "TEST_TMPDIR=/tmp"
+    ENVIRONMENT "TEST_SRCDIR=${PROJECT_BINARY_DIR}"
+  )
+
 endif()
 
 configure_file(
diff --git a/sandboxed_api/sandbox2/examples/network/BUILD.bazel b/sandboxed_api/sandbox2/examples/network/BUILD.bazel
index 82ccef6..11baced 100644
--- a/sandboxed_api/sandbox2/examples/network/BUILD.bazel
+++ b/sandboxed_api/sandbox2/examples/network/BUILD.bazel
@@ -36,14 +36,14 @@ cc_binary(
         "//sandboxed_api:config",
         "//sandboxed_api/sandbox2",
         "//sandboxed_api/sandbox2:comms",
-        "//sandboxed_api/sandbox2/util:bpf_helper",
-        "//sandboxed_api/util:fileops",
+        "//sandboxed_api/sandbox2/network_proxy:testing",
         "//sandboxed_api/util:runfiles",
         "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/flags:parse",
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:globals",
         "@com_google_absl//absl/log:initialize",
+        "@com_google_absl//absl/status:statusor",
         "@com_google_absl//absl/strings:string_view",
         "@com_google_absl//absl/time",
     ],
diff --git a/sandboxed_api/sandbox2/examples/network/CMakeLists.txt b/sandboxed_api/sandbox2/examples/network/CMakeLists.txt
index acbef87..f443b98 100644
--- a/sandboxed_api/sandbox2/examples/network/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/examples/network/CMakeLists.txt
@@ -27,11 +27,12 @@ target_link_libraries(sandbox2_network_sandbox PRIVATE
   absl::log_globals
   absl::log_initialize
   absl::log_severity
+  absl::statusor
   absl::strings
   absl::time
   sandbox2::bpf_helper
   sandbox2::comms
-  sapi::fileops
+  sandbox2::network_proxy_testing
   sapi::runfiles
   sandbox2::sandbox2
   sapi::base
diff --git a/sandboxed_api/sandbox2/examples/network/network_sandbox.cc b/sandboxed_api/sandbox2/examples/network/network_sandbox.cc
index 896faef..8ad392c 100644
--- a/sandboxed_api/sandbox2/examples/network/network_sandbox.cc
+++ b/sandboxed_api/sandbox2/examples/network/network_sandbox.cc
@@ -26,22 +26,22 @@
 #include <utility>
 #include <vector>
 
-#include "absl/base/macros.h"
 #include "absl/flags/parse.h"
 #include "absl/log/globals.h"
 #include "absl/log/initialize.h"
 #include "absl/log/log.h"
 #include "absl/base/log_severity.h"
+#include "absl/status/statusor.h"
 #include "absl/strings/string_view.h"
 #include "absl/time/time.h"
 #include "sandboxed_api/config.h"
 #include "sandboxed_api/sandbox2/comms.h"
 #include "sandboxed_api/sandbox2/executor.h"
+#include "sandboxed_api/sandbox2/network_proxy/testing.h"
 #include "sandboxed_api/sandbox2/policy.h"
 #include "sandboxed_api/sandbox2/policybuilder.h"
+#include "sandboxed_api/sandbox2/result.h"
 #include "sandboxed_api/sandbox2/sandbox2.h"
-#include "sandboxed_api/sandbox2/util/bpf_helper.h"
-#include "sandboxed_api/util/fileops.h"
 #include "sandboxed_api/util/runfiles.h"
 
 namespace {
@@ -60,58 +60,6 @@ std::unique_ptr<sandbox2::Policy> GetPolicy(absl::string_view sandboxee_path) {
       .BuildOrDie();
 }
 
-void Server(int port) {
-  sapi::file_util::fileops::FDCloser s(
-      socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0));
-  if (s.get() < 0) {
-    PLOG(ERROR) << "socket() failed";
-    return;
-  }
-
-  if (int enable = 1; setsockopt(s.get(), SOL_SOCKET, SO_REUSEADDR, &enable,
-                                 sizeof(enable)) < 0) {
-    PLOG(ERROR) << "setsockopt(SO_REUSEADDR) failed";
-    return;
-  }
-
-  // Listen to localhost only.
-  struct sockaddr_in6 addr = {};
-  addr.sin6_family = AF_INET6;
-  addr.sin6_port = htons(port);
-
-  int err = inet_pton(AF_INET6, "::1", &addr.sin6_addr.s6_addr);
-  if (err == 0) {
-    LOG(ERROR) << "inet_pton() failed";
-    return;
-  }
-  if (err == -1) {
-    PLOG(ERROR) << "inet_pton() failed";
-    return;
-  }
-
-  if (bind(s.get(), reinterpret_cast<struct sockaddr*>(&addr), sizeof(addr)) <
-      0) {
-    PLOG(ERROR) << "bind() failed";
-    return;
-  }
-
-  if (listen(s.get(), 1) < 0) {
-    PLOG(ERROR) << "listen() failed";
-    return;
-  }
-
-  sapi::file_util::fileops::FDCloser client(accept(s.get(), 0, 0));
-  if (client.get() < 0) {
-    PLOG(ERROR) << "accept() failed";
-    return;
-  }
-
-  constexpr char kMsg[] = "Hello World\n";
-  if (write(client.get(), kMsg, ABSL_ARRAYSIZE(kMsg) - 1) < 0) {
-    PLOG(ERROR) << "write() failed";
-  }
-}
-
 int ConnectToServer(int port) {
   int s = socket(AF_INET6, SOCK_STREAM, 0);
   if (s < 0) {
@@ -177,9 +125,12 @@ int main(int argc, char* argv[]) {
   absl::SetStderrThreshold(absl::LogSeverityAtLeast::kInfo);
   absl::ParseCommandLine(argc, argv);
   absl::InitializeLog();
-  int port = 8085;
-  std::thread server_thread{Server,port};
-  server_thread.detach();
+
+  absl::StatusOr<int> port = sandbox2::StartNetworkProxyTestServer();
+  if (!port.ok()) {
+    LOG(ERROR) << port.status();
+    return EXIT_FAILURE;
+  }
 
   // Note: In your own code, use sapi::GetDataDependencyFilePath() instead.
   const std::string path = sapi::internal::GetSapiDataDependencyFilePath(
@@ -214,7 +165,7 @@ int main(int argc, char* argv[]) {
     return 2;
   }
 
-  if (!HandleSandboxee(comms, port)) {
+  if (!HandleSandboxee(comms, *port)) {
     if (!s2.IsTerminated()) {
       // Kill the sandboxee, because failure to receive the data over the Comms
       // channel doesn't automatically mean that the sandboxee itself had
diff --git a/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel b/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel
index 03e2e36..7f94437 100644
--- a/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel
+++ b/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel
@@ -32,7 +32,7 @@ cc_binary(
         "//sandboxed_api:config",
         "//sandboxed_api/sandbox2",
         "//sandboxed_api/sandbox2:comms",
-        "//sandboxed_api/util:fileops",
+        "//sandboxed_api/sandbox2/network_proxy:testing",
         "//sandboxed_api/util:runfiles",
         "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/flags:flag",
@@ -40,6 +40,7 @@ cc_binary(
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:globals",
         "@com_google_absl//absl/log:initialize",
+        "@com_google_absl//absl/status:statusor",
         "@com_google_absl//absl/strings:string_view",
         "@com_google_absl//absl/time",
     ],
diff --git a/sandboxed_api/sandbox2/examples/network_proxy/CMakeLists.txt b/sandboxed_api/sandbox2/examples/network_proxy/CMakeLists.txt
index 73889ff..9f7f649 100644
--- a/sandboxed_api/sandbox2/examples/network_proxy/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/examples/network_proxy/CMakeLists.txt
@@ -27,11 +27,12 @@ target_link_libraries(sandbox2_networkproxy_sandbox PRIVATE
   absl::log_globals
   absl::log_initialize
   absl::log_severity
+  absl::statusor
   absl::strings
   absl::time
   sandbox2::bpf_helper
   sandbox2::comms
-  sapi::fileops
+  sandbox2::network_proxy_testing
   sapi::runfiles
   sandbox2::sandbox2
   sapi::base
diff --git a/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc b/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc
index 4cd9fb5..537a904 100644
--- a/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc
+++ b/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc
@@ -12,22 +12,23 @@
 #include <utility>
 #include <vector>
 
-#include "absl/base/macros.h"
 #include "absl/flags/flag.h"
 #include "absl/flags/parse.h"
 #include "absl/log/globals.h"
 #include "absl/log/initialize.h"
 #include "absl/log/log.h"
 #include "absl/base/log_severity.h"
+#include "absl/status/statusor.h"
 #include "absl/strings/string_view.h"
 #include "absl/time/time.h"
 #include "sandboxed_api/config.h"
 #include "sandboxed_api/sandbox2/comms.h"
 #include "sandboxed_api/sandbox2/executor.h"
+#include "sandboxed_api/sandbox2/network_proxy/testing.h"
 #include "sandboxed_api/sandbox2/policy.h"
 #include "sandboxed_api/sandbox2/policybuilder.h"
+#include "sandboxed_api/sandbox2/result.h"
 #include "sandboxed_api/sandbox2/sandbox2.h"
-#include "sandboxed_api/util/fileops.h"
 #include "sandboxed_api/util/runfiles.h"
 
 ABSL_FLAG(bool, connect_with_handler, true, "Connect using automatic mode.");
@@ -59,59 +60,6 @@ std::unique_ptr<sandbox2::Policy> GetPolicy(absl::string_view sandboxee_path) {
   return builder.AllowIPv6("::1").BuildOrDie();
 }
 
-void Server(int port) {
-  sapi::file_util::fileops::FDCloser s{
-      socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0)};
-  if (s.get() < 0) {
-    PLOG(ERROR) << "socket() failed";
-    return;
-  }
-
-  {
-    int enable = 1;
-    if (setsockopt(s.get(), SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) <
-        0) {
-      PLOG(ERROR) << "setsockopt(SO_REUSEADDR) failed";
-      return;
-    }
-  }
-
-  // Listen to localhost only.
-  struct sockaddr_in6 addr = {};
-  addr.sin6_family = AF_INET6;
-  addr.sin6_port = htons(port);
-
-  int err = inet_pton(AF_INET6, "::1", &addr.sin6_addr.s6_addr);
-  if (err == 0) {
-    LOG(ERROR) << "inet_pton() failed";
-    return;
-  } else if (err == -1) {
-    PLOG(ERROR) << "inet_pton() failed";
-    return;
-  }
-
-  if (bind(s.get(), (struct sockaddr*)&addr, sizeof(addr)) < 0) {
-    PLOG(ERROR) << "bind() failed";
-    return;
-  }
-
-  if (listen(s.get(), 1) < 0) {
-    PLOG(ERROR) << "listen() failed";
-    return;
-  }
-
-  sapi::file_util::fileops::FDCloser client{accept(s.get(), 0, 0)};
-  if (client.get() < 0) {
-    PLOG(ERROR) << "accept() failed";
-    return;
-  }
-
-  constexpr char kMsg[] = "Hello World\n";
-  if (write(client.get(), kMsg, ABSL_ARRAYSIZE(kMsg) - 1) < 0) {
-    PLOG(ERROR) << "write() failed";
-  }
-}
-
 }  // namespace
 
 int main(int argc, char* argv[]) {
@@ -125,9 +73,12 @@ int main(int argc, char* argv[]) {
   absl::SetStderrThreshold(absl::LogSeverityAtLeast::kInfo);
   absl::ParseCommandLine(argc, argv);
   absl::InitializeLog();
-  int port = 8085;
-  std::thread server_thread{Server, port};
-  server_thread.detach();
+
+  absl::StatusOr<int> port = sandbox2::StartNetworkProxyTestServer();
+  if (!port.ok()) {
+    LOG(ERROR) << port.status();
+    return EXIT_FAILURE;
+  }
 
   // Note: In your own code, use sapi::GetDataDependencyFilePath() instead.
   const std::string path =
@@ -157,7 +108,7 @@ int main(int argc, char* argv[]) {
 
   auto policy = GetPolicy(path);
   sandbox2::Sandbox2 s2(std::move(executor), std::move(policy));
-  auto* comms = s2.comms();
+  sandbox2::Comms* comms = s2.comms();
 
   // Let the sandboxee run.
   if (!s2.RunAsync()) {
@@ -167,7 +118,7 @@ int main(int argc, char* argv[]) {
   }
 
   // Send the port number via comms
-  if (!comms->SendInt32(port)) {
+  if (!comms->SendInt32(*port)) {
     LOG(ERROR) << "sandboxee_comms->SendInt32() failed";
     return 3;
   }
diff --git a/sandboxed_api/sandbox2/network_proxy/BUILD.bazel b/sandboxed_api/sandbox2/network_proxy/BUILD.bazel
index 296910e..40df1fd 100644
--- a/sandboxed_api/sandbox2/network_proxy/BUILD.bazel
+++ b/sandboxed_api/sandbox2/network_proxy/BUILD.bazel
@@ -77,3 +77,16 @@ cc_test(
         "@com_google_googletest//:gtest_main",
     ],
 )
+
+cc_library(
+    name = "testing",
+    srcs = ["testing.cc"],
+    hdrs = ["testing.h"],
+    deps = [
+        "//sandboxed_api/util:fileops",
+        "@com_google_absl//absl/log",
+        "@com_google_absl//absl/status",
+        "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/strings",
+    ],
+)
diff --git a/sandboxed_api/sandbox2/network_proxy/CMakeLists.txt b/sandboxed_api/sandbox2/network_proxy/CMakeLists.txt
index f74dd03..16ed82e 100644
--- a/sandboxed_api/sandbox2/network_proxy/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/network_proxy/CMakeLists.txt
@@ -60,6 +60,21 @@ target_link_libraries(sandbox2_network_proxy_client PRIVATE
   sapi::status
 )
 
+# sandboxed_api/sandbox2/network_proxy:testing
+add_library(sandbox2_network_proxy_testing ${SAPI_LIB_TYPE}
+  testing.cc
+  testing.h
+)
+add_library(sandbox2::network_proxy_testing ALIAS sandbox2_network_proxy_testing)
+target_link_libraries(sandbox2_network_proxy_testing PRIVATE
+  absl::log
+  absl::status
+  absl::statusor
+  absl::strings
+  sapi::fileops
+  sapi::base
+)
+
 if(BUILD_TESTING AND SAPI_BUILD_TESTING)
   # sandboxed_api/sandbox2/network_proxy:filtering_test
   add_executable(sandbox2_filtering_test
diff --git a/sandboxed_api/sandbox2/network_proxy/testing.cc b/sandboxed_api/sandbox2/network_proxy/testing.cc
new file mode 100644
index 0000000..7af2fa7
--- /dev/null
+++ b/sandboxed_api/sandbox2/network_proxy/testing.cc
@@ -0,0 +1,91 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "sandboxed_api/sandbox2/network_proxy/testing.h"
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+#include <thread>
+
+#include "absl/log/log.h"
+#include "absl/status/status.h"
+#include "absl/strings/string_view.h"
+#include "sandboxed_api/util/fileops.h"
+
+namespace sandbox2 {
+namespace {
+void ServerThread(int port) {
+  sapi::file_util::fileops::FDCloser s{
+      socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0)};
+  if (s.get() < 0) {
+    PLOG(ERROR) << "socket() failed";
+    return;
+  }
+
+  {
+    int enable = 1;
+    if (setsockopt(s.get(), SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) <
+        0) {
+      PLOG(ERROR) << "setsockopt(SO_REUSEADDR) failed";
+      return;
+    }
+  }
+
+  // Listen to localhost only.
+  struct sockaddr_in6 addr = {};
+  addr.sin6_family = AF_INET6;
+  addr.sin6_port = htons(port);
+
+  int err = inet_pton(AF_INET6, "::1", &addr.sin6_addr.s6_addr);
+  if (err == 0) {
+    LOG(ERROR) << "inet_pton() failed";
+    return;
+  } else if (err == -1) {
+    PLOG(ERROR) << "inet_pton() failed";
+    return;
+  }
+
+  if (bind(s.get(), (struct sockaddr*)&addr, sizeof(addr)) < 0) {
+    PLOG(ERROR) << "bind() failed";
+    return;
+  }
+
+  if (listen(s.get(), 1) < 0) {
+    PLOG(ERROR) << "listen() failed";
+    return;
+  }
+
+  sapi::file_util::fileops::FDCloser client{accept(s.get(), 0, 0)};
+  if (client.get() < 0) {
+    PLOG(ERROR) << "accept() failed";
+    return;
+  }
+
+  constexpr absl::string_view kMsg = "Hello World\n";
+  if (write(client.get(), kMsg.data(), kMsg.size()) < 0) {
+    PLOG(ERROR) << "write() failed";
+  }
+}
+}  // namespace
+
+absl::StatusOr<int> StartNetworkProxyTestServer() {
+  static int port = 8085;
+  std::thread server_thread([] { ServerThread(++port); });
+  server_thread.detach();
+  return port;
+}
+
+}  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/network_proxy/testing.h b/sandboxed_api/sandbox2/network_proxy/testing.h
new file mode 100644
index 0000000..5689f7e
--- /dev/null
+++ b/sandboxed_api/sandbox2/network_proxy/testing.h
@@ -0,0 +1,27 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SANDBOXED_API_SANDBOX2_EXAMPLES_NETWORK_PROXY_NETWORKPROXY_LIB_H_
+#define SANDBOXED_API_SANDBOX2_EXAMPLES_NETWORK_PROXY_NETWORKPROXY_LIB_H_
+
+#include "absl/status/statusor.h"
+
+namespace sandbox2 {
+
+// Returns the port the server was started on.
+absl::StatusOr<int> StartNetworkProxyTestServer();
+
+}  // namespace sandbox2
+
+#endif  // SANDBOXED_API_SANDBOX2_EXAMPLES_NETWORK_PROXY_NETWORKPROXY_LIB_H_
diff --git a/sandboxed_api/sandbox2/network_proxy_test.cc b/sandboxed_api/sandbox2/network_proxy_test.cc
new file mode 100644
index 0000000..0055026
--- /dev/null
+++ b/sandboxed_api/sandbox2/network_proxy_test.cc
@@ -0,0 +1,135 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <syscall.h>
+
+#include <cstdlib>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "sandboxed_api/sandbox2/executor.h"
+#include "sandboxed_api/sandbox2/network_proxy/testing.h"
+#include "sandboxed_api/sandbox2/policybuilder.h"
+#include "sandboxed_api/sandbox2/result.h"
+#include "sandboxed_api/sandbox2/sandbox2.h"
+#include "sandboxed_api/testing.h"
+#include "sandboxed_api/util/status_matchers.h"
+
+namespace sandbox2 {
+namespace {
+
+using ::sapi::GetTestSourcePath;
+using ::testing::Eq;
+
+TEST(NetworkProxy, ProxyWithHandlerAllowed) {
+  SKIP_SANITIZERS;
+  const std::string path =
+      GetTestSourcePath("sandbox2/testcases/network_proxy");
+  std::vector<std::string> args = {"network_proxy"};
+  auto executor = std::make_unique<Executor>(path, args);
+
+  PolicyBuilder builder;
+  builder.AllowDynamicStartup()
+      .AllowWrite()
+      .AllowRead()
+      .AllowExit()
+      .AllowSyscall(__NR_sendto)
+      .AllowTcMalloc()
+      .AddNetworkProxyHandlerPolicy()
+      .AllowLlvmCoverage()
+      .AllowIPv6("::1")
+      .AddLibrariesForBinary(path);
+
+  SAPI_ASSERT_OK_AND_ASSIGN(auto policy, builder.TryBuild());
+
+  Sandbox2 s2(std::move(executor), std::move(policy));
+  ASSERT_TRUE(s2.RunAsync());
+
+  SAPI_ASSERT_OK_AND_ASSIGN(int port, StartNetworkProxyTestServer());
+  ASSERT_TRUE(s2.comms()->SendInt32(port));
+
+  sandbox2::Result result = s2.AwaitResult();
+  ASSERT_THAT(result.final_status(), Eq(Result::OK));
+  EXPECT_THAT(result.reason_code(), Eq(EXIT_SUCCESS));
+}
+
+TEST(NetworkProxy, ProxyWithHandlerNotAllowed) {
+  SKIP_SANITIZERS;
+  const std::string path =
+      GetTestSourcePath("sandbox2/testcases/network_proxy");
+  std::vector<std::string> args = {"network_proxy"};
+  auto executor = std::make_unique<Executor>(path, args);
+
+  PolicyBuilder builder;
+  builder.AllowDynamicStartup()
+      .AllowWrite()
+      .AllowRead()
+      .AllowExit()
+      .AllowSyscall(__NR_sendto)
+      .AllowTcMalloc()
+      .AddNetworkProxyHandlerPolicy()
+      .AllowLlvmCoverage()
+      .AddLibrariesForBinary(path);
+
+  SAPI_ASSERT_OK_AND_ASSIGN(auto policy, builder.TryBuild());
+
+  Sandbox2 s2(std::move(executor), std::move(policy));
+  ASSERT_TRUE(s2.RunAsync());
+
+  SAPI_ASSERT_OK_AND_ASSIGN(int port, StartNetworkProxyTestServer());
+  ASSERT_TRUE(s2.comms()->SendInt32(port));
+
+  sandbox2::Result result = s2.AwaitResult();
+  ASSERT_THAT(result.final_status(), Eq(Result::VIOLATION));
+  EXPECT_THAT(result.reason_code(), Eq(Result::VIOLATION_NETWORK));
+}
+
+TEST(NetworkProxy, ProxyWithoutHandlerAllowed) {
+  SKIP_SANITIZERS;
+  const std::string path =
+      GetTestSourcePath("sandbox2/testcases/network_proxy");
+  std::vector<std::string> args = {"network_proxy", "--noconnect_with_handler"};
+  auto executor = std::make_unique<Executor>(path, args);
+
+  PolicyBuilder builder;
+  builder.AllowDynamicStartup()
+      .AllowExit()
+      .AllowWrite()
+      .AllowRead()
+      .AllowSyscall(__NR_sendto)
+      .AllowTcMalloc()
+      .AddNetworkProxyHandlerPolicy()
+      .AllowLlvmCoverage()
+      .AllowIPv6("::1")
+      .AddLibrariesForBinary(path);
+
+  SAPI_ASSERT_OK_AND_ASSIGN(auto policy, builder.TryBuild());
+
+  Sandbox2 s2(std::move(executor), std::move(policy));
+  ASSERT_TRUE(s2.RunAsync());
+
+  SAPI_ASSERT_OK_AND_ASSIGN(int port, StartNetworkProxyTestServer());
+  ASSERT_TRUE(s2.comms()->SendInt32(port));
+
+  sandbox2::Result result = s2.AwaitResult();
+  ASSERT_THAT(result.final_status(), Eq(Result::OK));
+  EXPECT_THAT(result.reason_code(), Eq(EXIT_SUCCESS));
+}
+
+}  // namespace
+}  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/policy_test.cc b/sandboxed_api/sandbox2/policy_test.cc
index 422d658..4b02137 100644
--- a/sandboxed_api/sandbox2/policy_test.cc
+++ b/sandboxed_api/sandbox2/policy_test.cc
@@ -137,7 +137,7 @@ TEST(PolicyTest, BpfPtracePermissionDenied) {
 
 TEST(PolicyTest, IsattyAllowed) {
   SKIP_SANITIZERS;
-  sandbox2::PolicyBuilder builder;
+  PolicyBuilder builder;
   if constexpr (sapi::host_os::IsAndroid()) {
     builder.DisableNamespaces().AllowDynamicStartup();
   }
@@ -157,7 +157,7 @@ TEST(PolicyTest, IsattyAllowed) {
 }
 
 std::unique_ptr<Policy> MinimalTestcasePolicy(absl::string_view path = "") {
-  sandbox2::PolicyBuilder builder;
+  PolicyBuilder builder;
 
   if constexpr (sapi::host_os::IsAndroid()) {
     builder.AllowDynamicStartup();
@@ -191,7 +191,7 @@ TEST(MinimalTest, MinimalSharedBinaryWorks) {
       GetTestSourcePath("sandbox2/testcases/minimal_dynamic");
   std::vector<std::string> args = {path};
 
-  sandbox2::PolicyBuilder builder;
+  PolicyBuilder builder;
 
   if constexpr (sapi::host_os::IsAndroid()) {
     builder.DisableNamespaces();
@@ -216,7 +216,7 @@ TEST(MallocTest, SystemMallocWorks) {
       GetTestSourcePath("sandbox2/testcases/malloc_system");
   std::vector<std::string> args = {path};
 
-  sandbox2::PolicyBuilder builder;
+  PolicyBuilder builder;
 
   if constexpr (sapi::host_os::IsAndroid()) {
     builder.DisableNamespaces();
@@ -250,7 +250,7 @@ TEST(MultipleSyscalls, AddPolicyOnSyscallsWorks) {
       GetTestSourcePath("sandbox2/testcases/add_policy_on_syscalls");
   std::vector<std::string> args = {path};
 
-  sandbox2::PolicyBuilder builder;
+  PolicyBuilder builder;
   if constexpr (sapi::host_os::IsAndroid()) {
     builder.DisableNamespaces();
     builder.AllowDynamicStartup();
diff --git a/sandboxed_api/sandbox2/testcases/BUILD.bazel b/sandboxed_api/sandbox2/testcases/BUILD.bazel
index e4e8cf4..f872a64 100644
--- a/sandboxed_api/sandbox2/testcases/BUILD.bazel
+++ b/sandboxed_api/sandbox2/testcases/BUILD.bazel
@@ -236,3 +236,27 @@ cc_binary(
         "@com_google_absl//absl/strings",
     ],
 )
+
+cc_binary(
+    name = "network_proxy",
+    testonly = True,
+    srcs = ["network_proxy.cc"],
+    copts = sapi_platform_copts(),
+    deps = [
+        "//sandboxed_api/sandbox2:client",
+        "//sandboxed_api/sandbox2:comms",
+        "//sandboxed_api/sandbox2/network_proxy:client",
+        "//sandboxed_api/util:fileops",
+        "//sandboxed_api/util:status",
+        "@com_google_absl//absl/base:log_severity",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+        "@com_google_absl//absl/log",
+        "@com_google_absl//absl/log:globals",
+        "@com_google_absl//absl/log:initialize",
+        "@com_google_absl//absl/status",
+        "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/strings:str_format",
+        "@com_google_absl//absl/strings:string_view",
+    ],
+)
diff --git a/sandboxed_api/sandbox2/testcases/CMakeLists.txt b/sandboxed_api/sandbox2/testcases/CMakeLists.txt
index b865336..6298e43 100644
--- a/sandboxed_api/sandbox2/testcases/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/testcases/CMakeLists.txt
@@ -292,3 +292,32 @@ target_link_libraries(sandbox2_testcase_namespace PRIVATE
   sapi::file_base
   sapi::fileops
 )
+
+# sandboxed_api/sandbox2/testcases:network_proxy
+add_executable(sandbox2_testcase_network_proxy
+  network_proxy.cc
+)
+add_executable(sandbox2::testcase_network_proxy ALIAS sandbox2_testcase_network_proxy)
+set_target_properties(sandbox2_testcase_network_proxy PROPERTIES
+  OUTPUT_NAME network_proxy
+)
+target_link_libraries(sandbox2_testcase_network_proxy PRIVATE
+  absl::flags
+  absl::flags_parse
+  absl::log
+  absl::log_globals
+  absl::log_initialize
+  absl::log_severity
+  absl::status
+  absl::statusor
+  absl::strings
+  absl::str_format
+  sandbox2::client
+  sandbox2::comms
+  sandbox2::network_proxy_client
+  sapi::base
+  sapi::file_base
+  sapi::fileops
+  sapi::status
+)
+
diff --git a/sandboxed_api/sandbox2/testcases/network_proxy.cc b/sandboxed_api/sandbox2/testcases/network_proxy.cc
new file mode 100644
index 0000000..f6ab922
--- /dev/null
+++ b/sandboxed_api/sandbox2/testcases/network_proxy.cc
@@ -0,0 +1,168 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// A binary doing various malloc calls to check that the malloc policy works as
+// expected.
+// This file is an example of a network sandboxed binary inside a network
+// namespace. It can't connect with the server directly, but the executor can
+// establish a connection and pass the connected socket to the sandboxee.
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <cerrno>
+#include <cstdint>
+#include <cstring>
+
+#include "absl/base/log_severity.h"
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+#include "absl/log/globals.h"
+#include "absl/log/initialize.h"
+#include "absl/log/log.h"
+#include "absl/status/status.h"
+#include "absl/status/statusor.h"
+#include "absl/strings/str_format.h"
+#include "absl/strings/string_view.h"
+#include "sandboxed_api/sandbox2/client.h"
+#include "sandboxed_api/sandbox2/comms.h"
+#include "sandboxed_api/sandbox2/network_proxy/client.h"
+#include "sandboxed_api/util/fileops.h"
+#include "sandboxed_api/util/status_macros.h"
+
+ABSL_FLAG(bool, connect_with_handler, true, "Connect using automatic mode.");
+
+namespace {
+
+using ::sapi::file_util::fileops::FDCloser;
+
+static sandbox2::NetworkProxyClient* g_proxy_client;
+
+ssize_t ReadFromFd(int fd, uint8_t* buf, size_t size) {
+  ssize_t received = 0;
+  while (received < size) {
+    ssize_t read_status =
+        TEMP_FAILURE_RETRY(read(fd, &buf[received], size - received));
+    if (read_status == 0) {
+      break;
+    }
+    if (read_status < 0) {
+      return -1;
+    }
+    received += read_status;
+  }
+  return received;
+}
+
+absl::Status CommunicationTest(int sock) {
+  char received[1025] = {0};
+
+  if (ReadFromFd(sock, reinterpret_cast<uint8_t*>(received),
+                 sizeof(received) - 1) <= 0) {
+    return absl::InternalError("Data receiving error");
+  }
+  absl::PrintF("Sandboxee received data from the server:\n\n%s\n", received);
+  if (strcmp(received, "Hello World\n")) {
+    return absl::InternalError("Data receiving error");
+  }
+  return absl::OkStatus();
+}
+
+absl::StatusOr<struct sockaddr_in6> CreateAddres(int port) {
+  static struct sockaddr_in6 saddr {};
+  saddr.sin6_family = AF_INET6;
+  saddr.sin6_port = htons(port);
+
+  if (int err = inet_pton(AF_INET6, "::1", &saddr.sin6_addr); err <= 0) {
+    return absl::ErrnoToStatus(errno, "socket()");
+  }
+  return saddr;
+}
+
+absl::Status ConnectWithoutHandler(int s, const struct sockaddr_in6& saddr) {
+  return g_proxy_client->Connect(
+      s, reinterpret_cast<const struct sockaddr*>(&saddr), sizeof(saddr));
+}
+
+absl::Status ConnectWithHandler(int s, const struct sockaddr_in6& saddr) {
+  int err = connect(s, reinterpret_cast<const struct sockaddr*>(&saddr),
+                    sizeof(saddr));
+  if (err != 0) {
+    return absl::InternalError("connect() failed");
+  }
+
+  return absl::OkStatus();
+}
+
+absl::StatusOr<FDCloser> ConnectToServer(int port) {
+  SAPI_ASSIGN_OR_RETURN(struct sockaddr_in6 saddr, CreateAddres(port));
+
+  FDCloser s(socket(AF_INET6, SOCK_STREAM, 0));
+  if (s.get() < 0) {
+    return absl::ErrnoToStatus(errno, "socket()");
+  }
+
+  if (absl::GetFlag(FLAGS_connect_with_handler)) {
+    SAPI_RETURN_IF_ERROR(ConnectWithHandler(s.get(), saddr));
+  } else {
+    SAPI_RETURN_IF_ERROR(ConnectWithoutHandler(s.get(), saddr));
+  }
+
+  LOG(INFO) << "Connected to the server";
+  return s;
+}
+
+}  // namespace
+
+int main(int argc, char* argv[]) {
+  absl::SetStderrThreshold(absl::LogSeverityAtLeast::kInfo);
+  absl::ParseCommandLine(argc, argv);
+  absl::InitializeLog();
+
+  // Set-up the sandbox2::Client object, using a file descriptor (1023).
+  sandbox2::Comms comms(sandbox2::Comms::kDefaultConnection);
+  sandbox2::Client sandbox2_client(&comms);
+
+  if (absl::GetFlag(FLAGS_connect_with_handler)) {
+    if (auto status = sandbox2_client.InstallNetworkProxyHandler();
+        !status.ok()) {
+      LOG(ERROR) << "InstallNetworkProxyHandler() failed: " << status;
+      return 1;
+    }
+  } else {
+    g_proxy_client = sandbox2_client.GetNetworkProxyClient();
+  }
+
+  // Receive port number of the server
+  int port;
+  if (!comms.RecvInt32(&port)) {
+    LOG(ERROR) << "Failed to receive port number";
+    return 2;
+  }
+
+  absl::StatusOr<FDCloser> client = ConnectToServer(port);
+  if (!client.ok()) {
+    LOG(ERROR) << client.status();
+    return 3;
+  }
+
+  if (auto status = CommunicationTest(client->get()); !status.ok()) {
+    LOG(ERROR) << status;
+    return 4;
+  }
+  return 0;
+}