src/virtualization/tests/fake_netstack.cc - fuchsia - Git at Google

 // Copyright 2019 The Fuchsia Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "fake_netstack.h"

 #include <lib/async/default.h>
 #include <lib/fit/defer.h>
 #include <lib/syslog/cpp/macros.h>
 #include <netinet/icmp6.h>
 #include <netinet/if_ether.h>
 #include <netinet/ip.h>
 #include <netinet/ip6.h>
 #include <zircon/device/ethernet.h>

 static constexpr size_t kMtu = 1500;
 static constexpr size_t kVmoSize = kMtu * 2;

 static constexpr uint8_t kHostMacAddress[ETH_ALEN] = {0x02, 0x1a, 0x11, 0x00, 0x00, 0x00};

 static constexpr uint8_t kHostIpv4Address[4] = {192, 168, 0, 1};
 static constexpr uint8_t kGuestIpv4Address[4] = {192, 168, 0, 10};

 static constexpr uint16_t kProtocolIpv4 = 0x0800;
 static constexpr uint8_t kPacketTypeUdp = 17;
 static constexpr uint16_t kTestPort = 4242;

 zx_status_t Device::Create(fuchsia::hardware::ethernet::DeviceSyncPtr eth_device,
                            std::unique_ptr<Device>* out) {
   std::unique_ptr<fuchsia::hardware::ethernet::Fifos> fifos;
   zx_status_t status;
   eth_device->GetFifos(&status, &fifos);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to get fifos: " << status;
     return status;
   }

   zx::vmo vmo;
   status = zx::vmo::create(kVmoSize, 0, &vmo);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to create vmo: " << status;
     return status;
   }

   zx::vmo vmo_dup;
   status = vmo.duplicate(ZX_RIGHTS_IO | ZX_RIGHT_MAP | ZX_RIGHT_TRANSFER, &vmo_dup);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to duplicate vmo: " << status;
     return status;
   }

   eth_device->SetIOBuffer(std::move(vmo_dup), &status);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to set IO buffer: " << status;
     return status;
   }

   uintptr_t io_addr;
   status = zx::vmar::root_self()->map(
       0, vmo, 0, kVmoSize, ZX_VM_PERM_READ | ZX_VM_PERM_WRITE | ZX_VM_REQUIRE_NON_RESIZABLE,
       &io_addr);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to map vmo: " << status;
     return status;
   }

   eth_fifo_entry_t entry;
   entry.offset = 0;
   entry.length = kMtu;
   entry.flags = 0;
   entry.cookie = 0;
   status = fifos->rx.write(sizeof(eth_fifo_entry_t), &entry, 1, nullptr);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to write to rx fifo: " << status;
     return status;
   }

   eth_device->Start(&status);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to start ethernet device: " << status;
     return status;
   }

   *out = std::unique_ptr<Device>(new Device(std::move(eth_device), std::move(fifos->rx),
                                             std::move(fifos->tx), std::move(vmo), io_addr));
   return ZX_OK;
 }

 zx_status_t Device::Start(async_dispatcher_t* dispatcher) {
   zx_status_t status = rx_wait_.Begin(dispatcher);
   if (status != ZX_OK) {
     return status;
   }
   return tx_wait_.Begin(dispatcher);
 }

 void Device::OnReceive(async_dispatcher_t* dispatcher, async::WaitBase* wait, zx_status_t status,
                        const zx_packet_signal_t* signal) {
   if (status == ZX_ERR_CANCELED) {
     return;
   } else if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Device receive waiter failed " << status;
     return;
   }

   {
     std::lock_guard<std::mutex> lock(mutex_);

     if (signal->observed & ZX_SOCKET_PEER_CLOSED) {
       while (!rx_completers_.empty()) {
         rx_completers_.back().complete_error(ZX_ERR_PEER_CLOSED);
         rx_completers_.pop_back();
       }
       return;
     }

     while (!rx_completers_.empty()) {
       eth_fifo_entry_t entry;
       zx_status_t status = rx_.read(sizeof(eth_fifo_entry_t), &entry, 1, nullptr);
       if (status == ZX_ERR_SHOULD_WAIT) {
         break;
       }

       if (status != ZX_OK) {
         rx_completers_.back().complete_error(status);
         rx_completers_.pop_back();
         break;
         ;
       }
       rx_completers_.back().complete_ok(std::move(entry));
       rx_completers_.pop_back();
     }
   }

   status = wait->Begin(dispatcher);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to wait for device rx fifo " << status;
   }
 }

 void Device::OnTransmit(async_dispatcher_t* dispatcher, async::WaitBase* wait, zx_status_t status,
                         const zx_packet_signal_t* signal) {
   if (status == ZX_ERR_CANCELED) {
     return;
   } else if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Device receive waiter failed " << status;
     return;
   }

   {
     std::lock_guard<std::mutex> lock(mutex_);

     if (signal->observed & ZX_SOCKET_PEER_CLOSED) {
       while (!tx_completers_.empty()) {
         tx_completers_.back().complete_error(ZX_ERR_PEER_CLOSED);
         tx_completers_.pop_back();
       }
       return;
     }

     while (!tx_completers_.empty()) {
       eth_fifo_entry_t entry;
       zx_status_t status = tx_.read(sizeof(eth_fifo_entry_t), &entry, 1, nullptr);
       if (status == ZX_ERR_SHOULD_WAIT) {
         break;
       }

       if (status != ZX_OK) {
         tx_completers_.back().complete_error(status);
         tx_completers_.pop_back();
         break;
         ;
       }
       tx_completers_.back().complete_ok(std::move(entry));
       tx_completers_.pop_back();
     }
   }

   status = wait->Begin(dispatcher);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to wait for device tx fifo " << status;
   }
 }

 fit::promise<eth_fifo_entry_t, zx_status_t> Device::GetRxEntry() {
   fit::bridge<eth_fifo_entry_t, zx_status_t> bridge;
   std::lock_guard<std::mutex> lock(mutex_);
   rx_completers_.push_back(std::move(bridge.completer));
   return bridge.consumer.promise();
 }

 fit::promise<eth_fifo_entry_t, zx_status_t> Device::GetTxEntry() {
   fit::bridge<eth_fifo_entry_t, zx_status_t> bridge;
   std::lock_guard<std::mutex> lock(mutex_);
   tx_completers_.push_back(std::move(bridge.completer));
   return bridge.consumer.promise();
 }

 fit::promise<std::vector<uint8_t>, zx_status_t> Device::ReadPacket() {
   return GetRxEntry().and_then(
       [this](const eth_fifo_entry_t& entry) -> fit::result<std::vector<uint8_t>, zx_status_t> {
         if (entry.flags != ETH_FIFO_RX_OK) {
           return fit::error(ZX_ERR_IO);
         }
         if (entry.length > kMtu) {
           return fit::error(ZX_ERR_INTERNAL);
         }
         std::vector<uint8_t> packet(entry.length);
         memcpy(packet.data(), reinterpret_cast<void*>(io_addr_ + entry.offset), packet.size());

         memset(reinterpret_cast<void*>(io_addr_), 0, kMtu);
         eth_fifo_entry_t new_entry;
         new_entry.offset = 0;
         new_entry.length = kMtu;
         new_entry.flags = 0;
         new_entry.cookie = 0;
         zx_status_t status = rx_.write(sizeof(eth_fifo_entry_t), &new_entry, 1, nullptr);
         if (status != ZX_OK) {
           FX_LOGS(ERROR) << "Failed to write to rx fifo: " << status;
           return fit::error(status);
         }

         return fit::ok(std::move(packet));
       });
 }

 fit::promise<void, zx_status_t> Device::WritePacket(std::vector<uint8_t> packet) {
   eth_fifo_entry_t entry;
   entry.offset = kMtu;
   entry.length = packet.size();
   entry.flags = 0;
   entry.cookie = 0;

   memcpy(reinterpret_cast<void*>(io_addr_ + entry.offset), packet.data(), packet.size());

   size_t count;
   zx_status_t status = tx_.write(sizeof(eth_fifo_entry_t), &entry, 1, &count);
   if (status != ZX_OK) {
     return fit::make_error_promise(status);
   }
   if (count != 1) {
     return fit::make_error_promise(ZX_ERR_INTERNAL);
   }

   return GetTxEntry().and_then([](const eth_fifo_entry_t& entry) -> fit::result<void, zx_status_t> {
     if (entry.flags != ETH_FIFO_TX_OK) {
       return fit::error(ZX_ERR_IO);
     }
     return fit::ok();
   });
 }

 void FakeNetstack::AddEthernetDevice(
     std::string topological_path, fuchsia::netstack::InterfaceConfig interfaceConfig,
     fidl::InterfaceHandle<::fuchsia::hardware::ethernet::Device> eth_device,
     AddEthernetDeviceCallback callback) {
   auto deferred = fit::defer([this, callback = std::move(callback)]() {
     callback(nic_counter_);
     nic_counter_++;
   });

   auto device_sync_ptr = eth_device.BindSync();

   fuchsia::hardware::ethernet::Info device_info;
   zx_status_t status = device_sync_ptr->GetInfo(&device_info);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to get device info: " << status;
     return;
   }

   std::unique_ptr<Device> device;
   status = Device::Create(std::move(device_sync_ptr), &device);
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to create device " << status;
     return;
   }

   status = device->Start(loop_.dispatcher());
   if (status != ZX_OK) {
     FX_LOGS(ERROR) << "Failed to start device " << status;
     return;
   }

   std::lock_guard<std::mutex> lock(mutex_);
   auto [itr, success] = devices_.insert(std::make_pair(device_info.mac, std::move(device)));
   if (!success) {
     FX_LOGS(ERROR) << "Device already exists";
     return;
   }

   auto completers_itr = completers_.find(device_info.mac);
   if (completers_itr == completers_.end()) {
     return;
   }
   while (!completers_itr->second.empty()) {
     completers_itr->second.back().complete_ok(itr->second.get());
     completers_itr->second.pop_back();
   }
 }

 void FakeNetstack::SetInterfaceAddress(uint32_t nicid, fuchsia::net::IpAddress addr,
                                        uint8_t prefixLen, SetInterfaceAddressCallback callback) {
   fuchsia::netstack::NetErr err;

   if (nicid >= nic_counter_) {
     err.status = fuchsia::netstack::Status::UNKNOWN_INTERFACE;
     err.message = "No such interface.";
   } else {
     err.status = fuchsia::netstack::Status::OK;
     err.message = "";
   }

   callback(std::move(err));
 }

 static uint16_t checksum(const void* _data, size_t len, uint16_t _sum) {
   uint32_t sum = _sum;
   auto data = static_cast<const uint16_t*>(_data);
   for (; len > 1; len -= 2) {
     sum += *data++;
   }
   if (len) {
     sum += (*data & UINT8_MAX);
   }
   while (sum > UINT16_MAX) {
     sum = (sum & UINT16_MAX) + (sum >> 16);
   }
   return ~sum;
 }

 static size_t make_ip_header(const uint8_t guest_mac[ETH_ALEN], uint8_t packet_type, size_t length,
                              uint8_t* data) {
   // First construct the ethernet header.
   ethhdr* eth = reinterpret_cast<ethhdr*>(data);
   memcpy(eth->h_dest, guest_mac, ETH_ALEN);
   memcpy(eth->h_source, kHostMacAddress, ETH_ALEN);
   eth->h_proto = htons(kProtocolIpv4);

   // Now construct the IPv4 header.
   auto ip = reinterpret_cast<iphdr*>(data + sizeof(ethhdr));
   ip->version = 4;
   ip->ihl = sizeof(iphdr) >> 2;  // Header length in 32-bit words.
   ip->tos = 0;
   ip->tot_len = htons(sizeof(iphdr) + length);
   ip->id = 0;
   ip->frag_off = 0;
   ip->ttl = UINT8_MAX;
   ip->protocol = packet_type;
   memcpy(&ip->saddr, kHostIpv4Address, sizeof(kHostIpv4Address));
   memcpy(&ip->daddr, kGuestIpv4Address, sizeof(kGuestIpv4Address));
   ip->check = 0;
   ip->check = checksum(ip, sizeof(iphdr), 0);

   return sizeof(ethhdr) + sizeof(iphdr);
 }

 fit::promise<void, zx_status_t> FakeNetstack::SendUdpPacket(
     const fuchsia::hardware::ethernet::MacAddress& mac_addr, std::vector<uint8_t> packet) {
   struct udp_hdr_t {
     uint16_t src_port;
     uint16_t dst_port;
     uint16_t length;
     uint16_t checksum;
   } __PACKED;

   size_t packet_length = sizeof(udp_hdr_t) + packet.size();
   size_t total_length = sizeof(ethhdr) + sizeof(iphdr) + packet_length;
   if (total_length > kMtu) {
     return fit::make_error_promise(ZX_ERR_BUFFER_TOO_SMALL);
   }

   std::vector<uint8_t> udp_packet(total_length);
   size_t header_len =
       make_ip_header(mac_addr.octets.data(), kPacketTypeUdp, packet_length, udp_packet.data());

   uintptr_t off = header_len;
   auto udp = reinterpret_cast<udp_hdr_t*>(udp_packet.data() + off);
   udp->src_port = htons(kTestPort);
   udp->dst_port = htons(kTestPort);
   udp->length = htons(sizeof(udp_hdr_t) + packet.size());
   // The checksum is optional for IPv4.
   udp->checksum = 0;

   off += sizeof(udp_hdr_t);
   memcpy(udp_packet.data() + off, packet.data(), packet.size());

   return SendPacket(mac_addr, std::move(udp_packet));
 }

 fit::promise<Device*> FakeNetstack::GetDevice(
     const fuchsia::hardware::ethernet::MacAddress& mac_addr) {
   std::lock_guard<std::mutex> lock(mutex_);

   // If the device is already connected the the netstack then just return a pointer to it.
   auto itr = devices_.find(mac_addr);
   if (itr != devices_.end()) {
     return fit::make_promise([device = &itr->second] { return fit::ok(device->get()); });
   }

   // Otherwise, add to the list of completers for this MAC address. The promise will complete when
   // the devices calls AddEthernetDevice.
   fit::bridge<Device*> bridge;
   auto completers_itr = completers_.find(mac_addr);
   if (completers_itr == completers_.end()) {
     std::vector<fit::completer<Device*>> vec;
     vec.push_back(std::move(bridge.completer));
     completers_.insert(std::make_pair(mac_addr, std::move(vec)));
   } else {
     completers_itr->second.push_back(std::move(bridge.completer));
   }

   return bridge.consumer.promise();
 }

 fit::promise<void, zx_status_t> FakeNetstack::SendPacket(
     const fuchsia::hardware::ethernet::MacAddress& mac_addr, std::vector<uint8_t> packet) {
   if (packet.size() > kMtu) {
     return fit::make_error_promise(ZX_ERR_INVALID_ARGS);
   }

   return GetDevice(mac_addr).then(
       [packet = std::move(packet)](
           const fit::result<Device*>& result) mutable -> fit::promise<void, zx_status_t> {
         if (!result.is_ok()) {
           return fit::make_error_promise(ZX_ERR_INTERNAL);
         }
         Device* device = result.value();
         return device->WritePacket(std::move(packet));
       });
 }

 fit::promise<std::vector<uint8_t>, zx_status_t> FakeNetstack::ReceivePacket(
     const fuchsia::hardware::ethernet::MacAddress& mac_addr) {
   return GetDevice(mac_addr).then(
       [](const fit::result<Device*>& result) -> fit::promise<std::vector<uint8_t>, zx_status_t> {
         if (!result.is_ok()) {
           return fit::make_result_promise<std::vector<uint8_t>, zx_status_t>(
               fit::error(ZX_ERR_INTERNAL));
         }
         Device* device = result.value();
         return device->ReadPacket();
       });
 }
	// Copyright 2019 The Fuchsia Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "fake_netstack.h"

	#include <lib/async/default.h>
	#include <lib/fit/defer.h>
	#include <lib/syslog/cpp/macros.h>
	#include <netinet/icmp6.h>
	#include <netinet/if_ether.h>
	#include <netinet/ip.h>
	#include <netinet/ip6.h>
	#include <zircon/device/ethernet.h>

	static constexpr size_t kMtu = 1500;
	static constexpr size_t kVmoSize = kMtu * 2;

	static constexpr uint8_t kHostMacAddress[ETH_ALEN] = {0x02, 0x1a, 0x11, 0x00, 0x00, 0x00};

	static constexpr uint8_t kHostIpv4Address[4] = {192, 168, 0, 1};
	static constexpr uint8_t kGuestIpv4Address[4] = {192, 168, 0, 10};

	static constexpr uint16_t kProtocolIpv4 = 0x0800;
	static constexpr uint8_t kPacketTypeUdp = 17;
	static constexpr uint16_t kTestPort = 4242;

	zx_status_t Device::Create(fuchsia::hardware::ethernet::DeviceSyncPtr eth_device,
	std::unique_ptr<Device>* out) {
	std::unique_ptr<fuchsia::hardware::ethernet::Fifos> fifos;
	zx_status_t status;
	eth_device->GetFifos(&status, &fifos);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to get fifos: " << status;
	return status;
	}

	zx::vmo vmo;
	status = zx::vmo::create(kVmoSize, 0, &vmo);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to create vmo: " << status;
	return status;
	}

	zx::vmo vmo_dup;
	status = vmo.duplicate(ZX_RIGHTS_IO \| ZX_RIGHT_MAP \| ZX_RIGHT_TRANSFER, &vmo_dup);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to duplicate vmo: " << status;
	return status;
	}

	eth_device->SetIOBuffer(std::move(vmo_dup), &status);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to set IO buffer: " << status;
	return status;
	}

	uintptr_t io_addr;
	status = zx::vmar::root_self()->map(
	0, vmo, 0, kVmoSize, ZX_VM_PERM_READ \| ZX_VM_PERM_WRITE \| ZX_VM_REQUIRE_NON_RESIZABLE,
	&io_addr);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to map vmo: " << status;
	return status;
	}

	eth_fifo_entry_t entry;
	entry.offset = 0;
	entry.length = kMtu;
	entry.flags = 0;
	entry.cookie = 0;
	status = fifos->rx.write(sizeof(eth_fifo_entry_t), &entry, 1, nullptr);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to write to rx fifo: " << status;
	return status;
	}

	eth_device->Start(&status);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to start ethernet device: " << status;
	return status;
	}

	*out = std::unique_ptr<Device>(new Device(std::move(eth_device), std::move(fifos->rx),
	std::move(fifos->tx), std::move(vmo), io_addr));
	return ZX_OK;
	}

	zx_status_t Device::Start(async_dispatcher_t* dispatcher) {
	zx_status_t status = rx_wait_.Begin(dispatcher);
	if (status != ZX_OK) {
	return status;
	}
	return tx_wait_.Begin(dispatcher);
	}

	void Device::OnReceive(async_dispatcher_t* dispatcher, async::WaitBase* wait, zx_status_t status,
	const zx_packet_signal_t* signal) {
	if (status == ZX_ERR_CANCELED) {
	return;
	} else if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Device receive waiter failed " << status;
	return;
	}

	{
	std::lock_guard<std::mutex> lock(mutex_);

	if (signal->observed & ZX_SOCKET_PEER_CLOSED) {
	while (!rx_completers_.empty()) {
	rx_completers_.back().complete_error(ZX_ERR_PEER_CLOSED);
	rx_completers_.pop_back();
	}
	return;
	}

	while (!rx_completers_.empty()) {
	eth_fifo_entry_t entry;
	zx_status_t status = rx_.read(sizeof(eth_fifo_entry_t), &entry, 1, nullptr);
	if (status == ZX_ERR_SHOULD_WAIT) {
	break;
	}

	if (status != ZX_OK) {
	rx_completers_.back().complete_error(status);
	rx_completers_.pop_back();
	break;
	;
	}
	rx_completers_.back().complete_ok(std::move(entry));
	rx_completers_.pop_back();
	}
	}

	status = wait->Begin(dispatcher);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to wait for device rx fifo " << status;
	}
	}

	void Device::OnTransmit(async_dispatcher_t* dispatcher, async::WaitBase* wait, zx_status_t status,
	const zx_packet_signal_t* signal) {
	if (status == ZX_ERR_CANCELED) {
	return;
	} else if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Device receive waiter failed " << status;
	return;
	}

	{
	std::lock_guard<std::mutex> lock(mutex_);

	if (signal->observed & ZX_SOCKET_PEER_CLOSED) {
	while (!tx_completers_.empty()) {
	tx_completers_.back().complete_error(ZX_ERR_PEER_CLOSED);
	tx_completers_.pop_back();
	}
	return;
	}

	while (!tx_completers_.empty()) {
	eth_fifo_entry_t entry;
	zx_status_t status = tx_.read(sizeof(eth_fifo_entry_t), &entry, 1, nullptr);
	if (status == ZX_ERR_SHOULD_WAIT) {
	break;
	}

	if (status != ZX_OK) {
	tx_completers_.back().complete_error(status);
	tx_completers_.pop_back();
	break;
	;
	}
	tx_completers_.back().complete_ok(std::move(entry));
	tx_completers_.pop_back();
	}
	}

	status = wait->Begin(dispatcher);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to wait for device tx fifo " << status;
	}
	}

	fit::promise<eth_fifo_entry_t, zx_status_t> Device::GetRxEntry() {
	fit::bridge<eth_fifo_entry_t, zx_status_t> bridge;
	std::lock_guard<std::mutex> lock(mutex_);
	rx_completers_.push_back(std::move(bridge.completer));
	return bridge.consumer.promise();
	}

	fit::promise<eth_fifo_entry_t, zx_status_t> Device::GetTxEntry() {
	fit::bridge<eth_fifo_entry_t, zx_status_t> bridge;
	std::lock_guard<std::mutex> lock(mutex_);
	tx_completers_.push_back(std::move(bridge.completer));
	return bridge.consumer.promise();
	}

	fit::promise<std::vector<uint8_t>, zx_status_t> Device::ReadPacket() {
	return GetRxEntry().and_then(
	[this](const eth_fifo_entry_t& entry) -> fit::result<std::vector<uint8_t>, zx_status_t> {
	if (entry.flags != ETH_FIFO_RX_OK) {
	return fit::error(ZX_ERR_IO);
	}
	if (entry.length > kMtu) {
	return fit::error(ZX_ERR_INTERNAL);
	}
	std::vector<uint8_t> packet(entry.length);
	memcpy(packet.data(), reinterpret_cast<void*>(io_addr_ + entry.offset), packet.size());

	memset(reinterpret_cast<void*>(io_addr_), 0, kMtu);
	eth_fifo_entry_t new_entry;
	new_entry.offset = 0;
	new_entry.length = kMtu;
	new_entry.flags = 0;
	new_entry.cookie = 0;
	zx_status_t status = rx_.write(sizeof(eth_fifo_entry_t), &new_entry, 1, nullptr);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to write to rx fifo: " << status;
	return fit::error(status);
	}

	return fit::ok(std::move(packet));
	});
	}

	fit::promise<void, zx_status_t> Device::WritePacket(std::vector<uint8_t> packet) {
	eth_fifo_entry_t entry;
	entry.offset = kMtu;
	entry.length = packet.size();
	entry.flags = 0;
	entry.cookie = 0;

	memcpy(reinterpret_cast<void*>(io_addr_ + entry.offset), packet.data(), packet.size());

	size_t count;
	zx_status_t status = tx_.write(sizeof(eth_fifo_entry_t), &entry, 1, &count);
	if (status != ZX_OK) {
	return fit::make_error_promise(status);
	}
	if (count != 1) {
	return fit::make_error_promise(ZX_ERR_INTERNAL);
	}

	return GetTxEntry().and_then([](const eth_fifo_entry_t& entry) -> fit::result<void, zx_status_t> {
	if (entry.flags != ETH_FIFO_TX_OK) {
	return fit::error(ZX_ERR_IO);
	}
	return fit::ok();
	});
	}

	void FakeNetstack::AddEthernetDevice(
	std::string topological_path, fuchsia::netstack::InterfaceConfig interfaceConfig,
	fidl::InterfaceHandle<::fuchsia::hardware::ethernet::Device> eth_device,
	AddEthernetDeviceCallback callback) {
	auto deferred = fit::defer([this, callback = std::move(callback)]() {
	callback(nic_counter_);
	nic_counter_++;
	});

	auto device_sync_ptr = eth_device.BindSync();

	fuchsia::hardware::ethernet::Info device_info;
	zx_status_t status = device_sync_ptr->GetInfo(&device_info);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to get device info: " << status;
	return;
	}

	std::unique_ptr<Device> device;
	status = Device::Create(std::move(device_sync_ptr), &device);
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to create device " << status;
	return;
	}

	status = device->Start(loop_.dispatcher());
	if (status != ZX_OK) {
	FX_LOGS(ERROR) << "Failed to start device " << status;
	return;
	}

	std::lock_guard<std::mutex> lock(mutex_);
	auto [itr, success] = devices_.insert(std::make_pair(device_info.mac, std::move(device)));
	if (!success) {
	FX_LOGS(ERROR) << "Device already exists";
	return;
	}

	auto completers_itr = completers_.find(device_info.mac);
	if (completers_itr == completers_.end()) {
	return;
	}
	while (!completers_itr->second.empty()) {
	completers_itr->second.back().complete_ok(itr->second.get());
	completers_itr->second.pop_back();
	}
	}

	void FakeNetstack::SetInterfaceAddress(uint32_t nicid, fuchsia::net::IpAddress addr,
	uint8_t prefixLen, SetInterfaceAddressCallback callback) {
	fuchsia::netstack::NetErr err;

	if (nicid >= nic_counter_) {
	err.status = fuchsia::netstack::Status::UNKNOWN_INTERFACE;
	err.message = "No such interface.";
	} else {
	err.status = fuchsia::netstack::Status::OK;
	err.message = "";
	}

	callback(std::move(err));
	}

	static uint16_t checksum(const void* _data, size_t len, uint16_t _sum) {
	uint32_t sum = _sum;
	auto data = static_cast<const uint16_t*>(_data);
	for (; len > 1; len -= 2) {
	sum += *data++;
	}
	if (len) {
	sum += (*data & UINT8_MAX);
	}
	while (sum > UINT16_MAX) {
	sum = (sum & UINT16_MAX) + (sum >> 16);
	}
	return ~sum;
	}

	static size_t make_ip_header(const uint8_t guest_mac[ETH_ALEN], uint8_t packet_type, size_t length,
	uint8_t* data) {
	// First construct the ethernet header.
	ethhdr* eth = reinterpret_cast<ethhdr*>(data);
	memcpy(eth->h_dest, guest_mac, ETH_ALEN);
	memcpy(eth->h_source, kHostMacAddress, ETH_ALEN);
	eth->h_proto = htons(kProtocolIpv4);

	// Now construct the IPv4 header.
	auto ip = reinterpret_cast<iphdr*>(data + sizeof(ethhdr));
	ip->version = 4;
	ip->ihl = sizeof(iphdr) >> 2; // Header length in 32-bit words.
	ip->tos = 0;
	ip->tot_len = htons(sizeof(iphdr) + length);
	ip->id = 0;
	ip->frag_off = 0;
	ip->ttl = UINT8_MAX;
	ip->protocol = packet_type;
	memcpy(&ip->saddr, kHostIpv4Address, sizeof(kHostIpv4Address));
	memcpy(&ip->daddr, kGuestIpv4Address, sizeof(kGuestIpv4Address));
	ip->check = 0;
	ip->check = checksum(ip, sizeof(iphdr), 0);

	return sizeof(ethhdr) + sizeof(iphdr);
	}

	fit::promise<void, zx_status_t> FakeNetstack::SendUdpPacket(
	const fuchsia::hardware::ethernet::MacAddress& mac_addr, std::vector<uint8_t> packet) {
	struct udp_hdr_t {
	uint16_t src_port;
	uint16_t dst_port;
	uint16_t length;
	uint16_t checksum;
	} __PACKED;

	size_t packet_length = sizeof(udp_hdr_t) + packet.size();
	size_t total_length = sizeof(ethhdr) + sizeof(iphdr) + packet_length;
	if (total_length > kMtu) {
	return fit::make_error_promise(ZX_ERR_BUFFER_TOO_SMALL);
	}

	std::vector<uint8_t> udp_packet(total_length);
	size_t header_len =
	make_ip_header(mac_addr.octets.data(), kPacketTypeUdp, packet_length, udp_packet.data());

	uintptr_t off = header_len;
	auto udp = reinterpret_cast<udp_hdr_t*>(udp_packet.data() + off);
	udp->src_port = htons(kTestPort);
	udp->dst_port = htons(kTestPort);
	udp->length = htons(sizeof(udp_hdr_t) + packet.size());
	// The checksum is optional for IPv4.
	udp->checksum = 0;

	off += sizeof(udp_hdr_t);
	memcpy(udp_packet.data() + off, packet.data(), packet.size());

	return SendPacket(mac_addr, std::move(udp_packet));
	}

	fit::promise<Device*> FakeNetstack::GetDevice(
	const fuchsia::hardware::ethernet::MacAddress& mac_addr) {
	std::lock_guard<std::mutex> lock(mutex_);

	// If the device is already connected the the netstack then just return a pointer to it.
	auto itr = devices_.find(mac_addr);
	if (itr != devices_.end()) {
	return fit::make_promise([device = &itr->second] { return fit::ok(device->get()); });
	}

	// Otherwise, add to the list of completers for this MAC address. The promise will complete when
	// the devices calls AddEthernetDevice.
	fit::bridge<Device*> bridge;
	auto completers_itr = completers_.find(mac_addr);
	if (completers_itr == completers_.end()) {
	std::vector<fit::completer<Device*>> vec;
	vec.push_back(std::move(bridge.completer));
	completers_.insert(std::make_pair(mac_addr, std::move(vec)));
	} else {
	completers_itr->second.push_back(std::move(bridge.completer));
	}

	return bridge.consumer.promise();
	}

	fit::promise<void, zx_status_t> FakeNetstack::SendPacket(
	const fuchsia::hardware::ethernet::MacAddress& mac_addr, std::vector<uint8_t> packet) {
	if (packet.size() > kMtu) {
	return fit::make_error_promise(ZX_ERR_INVALID_ARGS);
	}

	return GetDevice(mac_addr).then(
	[packet = std::move(packet)](
	const fit::result<Device*>& result) mutable -> fit::promise<void, zx_status_t> {
	if (!result.is_ok()) {
	return fit::make_error_promise(ZX_ERR_INTERNAL);
	}
	Device* device = result.value();
	return device->WritePacket(std::move(packet));
	});
	}

	fit::promise<std::vector<uint8_t>, zx_status_t> FakeNetstack::ReceivePacket(
	const fuchsia::hardware::ethernet::MacAddress& mac_addr) {
	return GetDevice(mac_addr).then(
	[](const fit::result<Device*>& result) -> fit::promise<std::vector<uint8_t>, zx_status_t> {
	if (!result.is_ok()) {
	return fit::make_result_promise<std::vector<uint8_t>, zx_status_t>(
	fit::error(ZX_ERR_INTERNAL));
	}
	Device* device = result.value();
	return device->ReadPacket();
	});
	}