// Copyright 2019 The gVisor Authors.
//
// 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
//
//     http://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.

package proc

import (
	"bytes"
	"fmt"
	"io"
	"reflect"
	"time"

	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/context"
	"gvisor.dev/gvisor/pkg/log"
	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
	"gvisor.dev/gvisor/pkg/sentry/inet"
	"gvisor.dev/gvisor/pkg/sentry/kernel"
	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
	"gvisor.dev/gvisor/pkg/sentry/socket"
	"gvisor.dev/gvisor/pkg/sentry/socket/unix"
	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
	"gvisor.dev/gvisor/pkg/sentry/vfs"
	"gvisor.dev/gvisor/pkg/syserror"
	"gvisor.dev/gvisor/pkg/tcpip/header"
	"gvisor.dev/gvisor/pkg/usermem"
)

func (fs *filesystem) newTaskNetDir(task *kernel.Task) *kernfs.Dentry {
	k := task.Kernel()
	pidns := task.PIDNamespace()
	root := auth.NewRootCredentials(pidns.UserNamespace())

	var contents map[string]*kernfs.Dentry
	if stack := task.NetworkNamespace().Stack(); stack != nil {
		const (
			arp       = "IP address       HW type     Flags       HW address            Mask     Device\n"
			netlink   = "sk       Eth Pid    Groups   Rmem     Wmem     Dump     Locks     Drops     Inode\n"
			packet    = "sk       RefCnt Type Proto  Iface R Rmem   User   Inode\n"
			protocols = "protocol  size sockets  memory press maxhdr  slab module     cl co di ac io in de sh ss gs se re sp bi br ha uh gp em\n"
			ptype     = "Type Device      Function\n"
			upd6      = "  sl  local_address                         remote_address                        st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode\n"
		)
		psched := fmt.Sprintf("%08x %08x %08x %08x\n", uint64(time.Microsecond/time.Nanosecond), 64, 1000000, uint64(time.Second/time.Nanosecond))

		// TODO(gvisor.dev/issue/1833): Make sure file contents reflect the task
		// network namespace.
		contents = map[string]*kernfs.Dentry{
			"dev":  fs.newDentry(root, fs.NextIno(), 0444, &netDevData{stack: stack}),
			"snmp": fs.newDentry(root, fs.NextIno(), 0444, &netSnmpData{stack: stack}),

			// The following files are simple stubs until they are implemented in
			// netstack, if the file contains a header the stub is just the header
			// otherwise it is an empty file.
			"arp":       fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(arp)),
			"netlink":   fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(netlink)),
			"netstat":   fs.newDentry(root, fs.NextIno(), 0444, &netStatData{}),
			"packet":    fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(packet)),
			"protocols": fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(protocols)),

			// Linux sets psched values to: nsec per usec, psched tick in ns, 1000000,
			// high res timer ticks per sec (ClockGetres returns 1ns resolution).
			"psched": fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(psched)),
			"ptype":  fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(ptype)),
			"route":  fs.newDentry(root, fs.NextIno(), 0444, &netRouteData{stack: stack}),
			"tcp":    fs.newDentry(root, fs.NextIno(), 0444, &netTCPData{kernel: k}),
			"udp":    fs.newDentry(root, fs.NextIno(), 0444, &netUDPData{kernel: k}),
			"unix":   fs.newDentry(root, fs.NextIno(), 0444, &netUnixData{kernel: k}),
		}

		if stack.SupportsIPv6() {
			contents["if_inet6"] = fs.newDentry(root, fs.NextIno(), 0444, &ifinet6{stack: stack})
			contents["ipv6_route"] = fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(""))
			contents["tcp6"] = fs.newDentry(root, fs.NextIno(), 0444, &netTCP6Data{kernel: k})
			contents["udp6"] = fs.newDentry(root, fs.NextIno(), 0444, newStaticFile(upd6))
		}
	}

	return fs.newTaskOwnedDir(task, fs.NextIno(), 0555, contents)
}

// ifinet6 implements vfs.DynamicBytesSource for /proc/net/if_inet6.
//
// +stateify savable
type ifinet6 struct {
	kernfs.DynamicBytesFile

	stack inet.Stack
}

var _ dynamicInode = (*ifinet6)(nil)

func (n *ifinet6) contents() []string {
	var lines []string
	nics := n.stack.Interfaces()
	for id, naddrs := range n.stack.InterfaceAddrs() {
		nic, ok := nics[id]
		if !ok {
			// NIC was added after NICNames was called. We'll just ignore it.
			continue
		}

		for _, a := range naddrs {
			// IPv6 only.
			if a.Family != linux.AF_INET6 {
				continue
			}

			// Fields:
			// IPv6 address displayed in 32 hexadecimal chars without colons
			// Netlink device number (interface index) in hexadecimal (use nic id)
			// Prefix length in hexadecimal
			// Scope value (use 0)
			// Interface flags
			// Device name
			lines = append(lines, fmt.Sprintf("%032x %02x %02x %02x %02x %8s\n", a.Addr, id, a.PrefixLen, 0, a.Flags, nic.Name))
		}
	}
	return lines
}

// Generate implements vfs.DynamicBytesSource.Generate.
func (n *ifinet6) Generate(ctx context.Context, buf *bytes.Buffer) error {
	for _, l := range n.contents() {
		buf.WriteString(l)
	}
	return nil
}

// netDevData implements vfs.DynamicBytesSource for /proc/net/dev.
//
// +stateify savable
type netDevData struct {
	kernfs.DynamicBytesFile

	stack inet.Stack
}

var _ dynamicInode = (*netDevData)(nil)

// Generate implements vfs.DynamicBytesSource.Generate.
func (n *netDevData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	interfaces := n.stack.Interfaces()
	buf.WriteString("Inter-|   Receive                                                |  Transmit\n")
	buf.WriteString(" face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed\n")

	for _, i := range interfaces {
		// Implements the same format as
		// net/core/net-procfs.c:dev_seq_printf_stats.
		var stats inet.StatDev
		if err := n.stack.Statistics(&stats, i.Name); err != nil {
			log.Warningf("Failed to retrieve interface statistics for %v: %v", i.Name, err)
			continue
		}
		fmt.Fprintf(
			buf,
			"%6s: %7d %7d %4d %4d %4d %5d %10d %9d %8d %7d %4d %4d %4d %5d %7d %10d\n",
			i.Name,
			// Received
			stats[0], // bytes
			stats[1], // packets
			stats[2], // errors
			stats[3], // dropped
			stats[4], // fifo
			stats[5], // frame
			stats[6], // compressed
			stats[7], // multicast
			// Transmitted
			stats[8],  // bytes
			stats[9],  // packets
			stats[10], // errors
			stats[11], // dropped
			stats[12], // fifo
			stats[13], // frame
			stats[14], // compressed
			stats[15], // multicast
		)
	}

	return nil
}

// netUnixData implements vfs.DynamicBytesSource for /proc/net/unix.
//
// +stateify savable
type netUnixData struct {
	kernfs.DynamicBytesFile

	kernel *kernel.Kernel
}

var _ dynamicInode = (*netUnixData)(nil)

// Generate implements vfs.DynamicBytesSource.Generate.
func (n *netUnixData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	buf.WriteString("Num       RefCount Protocol Flags    Type St Inode Path\n")
	for _, se := range n.kernel.ListSockets() {
		s := se.SockVFS2
		if !s.TryIncRef() {
			log.Debugf("Couldn't get reference on %v in socket table, racing with destruction?", s)
			continue
		}
		if family, _, _ := s.Impl().(socket.SocketVFS2).Type(); family != linux.AF_UNIX {
			s.DecRef(ctx)
			// Not a unix socket.
			continue
		}
		sops := s.Impl().(*unix.SocketVFS2)

		addr, err := sops.Endpoint().GetLocalAddress()
		if err != nil {
			log.Warningf("Failed to retrieve socket name from %+v: %v", s, err)
			addr.Addr = "<unknown>"
		}

		sockFlags := 0
		if ce, ok := sops.Endpoint().(transport.ConnectingEndpoint); ok {
			if ce.Listening() {
				// For unix domain sockets, linux reports a single flag
				// value if the socket is listening, of __SO_ACCEPTCON.
				sockFlags = linux.SO_ACCEPTCON
			}
		}

		// Get inode number.
		var ino uint64
		stat, statErr := s.Stat(ctx, vfs.StatOptions{Mask: linux.STATX_INO})
		if statErr != nil || stat.Mask&linux.STATX_INO == 0 {
			log.Warningf("Failed to retrieve ino for socket file: %v", statErr)
		} else {
			ino = stat.Ino
		}

		// In the socket entry below, the value for the 'Num' field requires
		// some consideration. Linux prints the address to the struct
		// unix_sock representing a socket in the kernel, but may redact the
		// value for unprivileged users depending on the kptr_restrict
		// sysctl.
		//
		// One use for this field is to allow a privileged user to
		// introspect into the kernel memory to determine information about
		// a socket not available through procfs, such as the socket's peer.
		//
		// In gvisor, returning a pointer to our internal structures would
		// be pointless, as it wouldn't match the memory layout for struct
		// unix_sock, making introspection difficult. We could populate a
		// struct unix_sock with the appropriate data, but even that
		// requires consideration for which kernel version to emulate, as
		// the definition of this struct changes over time.
		//
		// For now, we always redact this pointer.
		fmt.Fprintf(buf, "%#016p: %08X %08X %08X %04X %02X %8d",
			(*unix.SocketOperations)(nil), // Num, pointer to kernel socket struct.
			s.ReadRefs()-1,                // RefCount, don't count our own ref.
			0,                             // Protocol, always 0 for UDS.
			sockFlags,                     // Flags.
			sops.Endpoint().Type(),        // Type.
			sops.State(),                  // State.
			ino,                           // Inode.
		)

		// Path
		if len(addr.Addr) != 0 {
			if addr.Addr[0] == 0 {
				// Abstract path.
				fmt.Fprintf(buf, " @%s", string(addr.Addr[1:]))
			} else {
				fmt.Fprintf(buf, " %s", string(addr.Addr))
			}
		}
		fmt.Fprintf(buf, "\n")

		s.DecRef(ctx)
	}
	return nil
}

func networkToHost16(n uint16) uint16 {
	// n is in network byte order, so is big-endian. The most-significant byte
	// should be stored in the lower address.
	//
	// We manually inline binary.BigEndian.Uint16() because Go does not support
	// non-primitive consts, so binary.BigEndian is a (mutable) var, so calls to
	// binary.BigEndian.Uint16() require a read of binary.BigEndian and an
	// interface method call, defeating inlining.
	buf := [2]byte{byte(n >> 8 & 0xff), byte(n & 0xff)}
	return usermem.ByteOrder.Uint16(buf[:])
}

func writeInetAddr(w io.Writer, family int, i linux.SockAddr) {
	switch family {
	case linux.AF_INET:
		var a linux.SockAddrInet
		if i != nil {
			a = *i.(*linux.SockAddrInet)
		}

		// linux.SockAddrInet.Port is stored in the network byte order and is
		// printed like a number in host byte order. Note that all numbers in host
		// byte order are printed with the most-significant byte first when
		// formatted with %X. See get_tcp4_sock() and udp4_format_sock() in Linux.
		port := networkToHost16(a.Port)

		// linux.SockAddrInet.Addr is stored as a byte slice in big-endian order
		// (i.e. most-significant byte in index 0). Linux represents this as a
		// __be32 which is a typedef for an unsigned int, and is printed with
		// %X. This means that for a little-endian machine, Linux prints the
		// least-significant byte of the address first. To emulate this, we first
		// invert the byte order for the address using usermem.ByteOrder.Uint32,
		// which makes it have the equivalent encoding to a __be32 on a little
		// endian machine. Note that this operation is a no-op on a big endian
		// machine. Then similar to Linux, we format it with %X, which will print
		// the most-significant byte of the __be32 address first, which is now
		// actually the least-significant byte of the original address in
		// linux.SockAddrInet.Addr on little endian machines, due to the conversion.
		addr := usermem.ByteOrder.Uint32(a.Addr[:])

		fmt.Fprintf(w, "%08X:%04X ", addr, port)
	case linux.AF_INET6:
		var a linux.SockAddrInet6
		if i != nil {
			a = *i.(*linux.SockAddrInet6)
		}

		port := networkToHost16(a.Port)
		addr0 := usermem.ByteOrder.Uint32(a.Addr[0:4])
		addr1 := usermem.ByteOrder.Uint32(a.Addr[4:8])
		addr2 := usermem.ByteOrder.Uint32(a.Addr[8:12])
		addr3 := usermem.ByteOrder.Uint32(a.Addr[12:16])
		fmt.Fprintf(w, "%08X%08X%08X%08X:%04X ", addr0, addr1, addr2, addr3, port)
	}
}

func commonGenerateTCP(ctx context.Context, buf *bytes.Buffer, k *kernel.Kernel, family int) error {
	// t may be nil here if our caller is not part of a task goroutine. This can
	// happen for example if we're here for "sentryctl cat". When t is nil,
	// degrade gracefully and retrieve what we can.
	t := kernel.TaskFromContext(ctx)

	for _, se := range k.ListSockets() {
		s := se.SockVFS2
		if !s.TryIncRef() {
			log.Debugf("Couldn't get reference on %v in socket table, racing with destruction?", s)
			continue
		}
		sops, ok := s.Impl().(socket.SocketVFS2)
		if !ok {
			panic(fmt.Sprintf("Found non-socket file in socket table: %+v", s))
		}
		if fa, stype, _ := sops.Type(); !(family == fa && stype == linux.SOCK_STREAM) {
			s.DecRef(ctx)
			// Not tcp4 sockets.
			continue
		}

		// Linux's documentation for the fields below can be found at
		// https://www.kernel.org/doc/Documentation/networking/proc_net_tcp.txt.
		// For Linux's implementation, see net/ipv4/tcp_ipv4.c:get_tcp4_sock().
		// Note that the header doesn't contain labels for all the fields.

		// Field: sl; entry number.
		fmt.Fprintf(buf, "%4d: ", se.ID)

		// Field: local_adddress.
		var localAddr linux.SockAddr
		if t != nil {
			if local, _, err := sops.GetSockName(t); err == nil {
				localAddr = local
			}
		}
		writeInetAddr(buf, family, localAddr)

		// Field: rem_address.
		var remoteAddr linux.SockAddr
		if t != nil {
			if remote, _, err := sops.GetPeerName(t); err == nil {
				remoteAddr = remote
			}
		}
		writeInetAddr(buf, family, remoteAddr)

		// Field: state; socket state.
		fmt.Fprintf(buf, "%02X ", sops.State())

		// Field: tx_queue, rx_queue; number of packets in the transmit and
		// receive queue. Unimplemented.
		fmt.Fprintf(buf, "%08X:%08X ", 0, 0)

		// Field: tr, tm->when; timer active state and number of jiffies
		// until timer expires. Unimplemented.
		fmt.Fprintf(buf, "%02X:%08X ", 0, 0)

		// Field: retrnsmt; number of unrecovered RTO timeouts.
		// Unimplemented.
		fmt.Fprintf(buf, "%08X ", 0)

		stat, statErr := s.Stat(ctx, vfs.StatOptions{Mask: linux.STATX_UID | linux.STATX_INO})

		// Field: uid.
		if statErr != nil || stat.Mask&linux.STATX_UID == 0 {
			log.Warningf("Failed to retrieve uid for socket file: %v", statErr)
			fmt.Fprintf(buf, "%5d ", 0)
		} else {
			creds := auth.CredentialsFromContext(ctx)
			fmt.Fprintf(buf, "%5d ", uint32(auth.KUID(stat.UID).In(creds.UserNamespace).OrOverflow()))
		}

		// Field: timeout; number of unanswered 0-window probes.
		// Unimplemented.
		fmt.Fprintf(buf, "%8d ", 0)

		// Field: inode.
		if statErr != nil || stat.Mask&linux.STATX_INO == 0 {
			log.Warningf("Failed to retrieve inode for socket file: %v", statErr)
			fmt.Fprintf(buf, "%8d ", 0)
		} else {
			fmt.Fprintf(buf, "%8d ", stat.Ino)
		}

		// Field: refcount. Don't count the ref we obtain while deferencing
		// the weakref to this socket.
		fmt.Fprintf(buf, "%d ", s.ReadRefs()-1)

		// Field: Socket struct address. Redacted due to the same reason as
		// the 'Num' field in /proc/net/unix, see netUnix.ReadSeqFileData.
		fmt.Fprintf(buf, "%#016p ", (*socket.Socket)(nil))

		// Field: retransmit timeout. Unimplemented.
		fmt.Fprintf(buf, "%d ", 0)

		// Field: predicted tick of soft clock (delayed ACK control data).
		// Unimplemented.
		fmt.Fprintf(buf, "%d ", 0)

		// Field: (ack.quick<<1)|ack.pingpong, Unimplemented.
		fmt.Fprintf(buf, "%d ", 0)

		// Field: sending congestion window, Unimplemented.
		fmt.Fprintf(buf, "%d ", 0)

		// Field: Slow start size threshold, -1 if threshold >= 0xFFFF.
		// Unimplemented, report as large threshold.
		fmt.Fprintf(buf, "%d", -1)

		fmt.Fprintf(buf, "\n")

		s.DecRef(ctx)
	}

	return nil
}

// netTCPData implements vfs.DynamicBytesSource for /proc/net/tcp.
//
// +stateify savable
type netTCPData struct {
	kernfs.DynamicBytesFile

	kernel *kernel.Kernel
}

var _ dynamicInode = (*netTCPData)(nil)

func (d *netTCPData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	buf.WriteString("  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode                                                     \n")
	return commonGenerateTCP(ctx, buf, d.kernel, linux.AF_INET)
}

// netTCP6Data implements vfs.DynamicBytesSource for /proc/net/tcp6.
//
// +stateify savable
type netTCP6Data struct {
	kernfs.DynamicBytesFile

	kernel *kernel.Kernel
}

var _ dynamicInode = (*netTCP6Data)(nil)

func (d *netTCP6Data) Generate(ctx context.Context, buf *bytes.Buffer) error {
	buf.WriteString("  sl  local_address                         remote_address                        st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode\n")
	return commonGenerateTCP(ctx, buf, d.kernel, linux.AF_INET6)
}

// netUDPData implements vfs.DynamicBytesSource for /proc/net/udp.
//
// +stateify savable
type netUDPData struct {
	kernfs.DynamicBytesFile

	kernel *kernel.Kernel
}

var _ dynamicInode = (*netUDPData)(nil)

// Generate implements vfs.DynamicBytesSource.Generate.
func (d *netUDPData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	// t may be nil here if our caller is not part of a task goroutine. This can
	// happen for example if we're here for "sentryctl cat". When t is nil,
	// degrade gracefully and retrieve what we can.
	t := kernel.TaskFromContext(ctx)

	buf.WriteString("  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode ref pointer drops             \n")

	for _, se := range d.kernel.ListSockets() {
		s := se.SockVFS2
		if !s.TryIncRef() {
			log.Debugf("Couldn't get reference on %v in socket table, racing with destruction?", s)
			continue
		}
		sops, ok := s.Impl().(socket.SocketVFS2)
		if !ok {
			panic(fmt.Sprintf("Found non-socket file in socket table: %+v", s))
		}
		if family, stype, _ := sops.Type(); family != linux.AF_INET || stype != linux.SOCK_DGRAM {
			s.DecRef(ctx)
			// Not udp4 socket.
			continue
		}

		// For Linux's implementation, see net/ipv4/udp.c:udp4_format_sock().

		// Field: sl; entry number.
		fmt.Fprintf(buf, "%5d: ", se.ID)

		// Field: local_adddress.
		var localAddr linux.SockAddrInet
		if t != nil {
			if local, _, err := sops.GetSockName(t); err == nil {
				localAddr = *local.(*linux.SockAddrInet)
			}
		}
		writeInetAddr(buf, linux.AF_INET, &localAddr)

		// Field: rem_address.
		var remoteAddr linux.SockAddrInet
		if t != nil {
			if remote, _, err := sops.GetPeerName(t); err == nil {
				remoteAddr = *remote.(*linux.SockAddrInet)
			}
		}
		writeInetAddr(buf, linux.AF_INET, &remoteAddr)

		// Field: state; socket state.
		fmt.Fprintf(buf, "%02X ", sops.State())

		// Field: tx_queue, rx_queue; number of packets in the transmit and
		// receive queue. Unimplemented.
		fmt.Fprintf(buf, "%08X:%08X ", 0, 0)

		// Field: tr, tm->when. Always 0 for UDP.
		fmt.Fprintf(buf, "%02X:%08X ", 0, 0)

		// Field: retrnsmt. Always 0 for UDP.
		fmt.Fprintf(buf, "%08X ", 0)

		stat, statErr := s.Stat(ctx, vfs.StatOptions{Mask: linux.STATX_UID | linux.STATX_INO})

		// Field: uid.
		if statErr != nil || stat.Mask&linux.STATX_UID == 0 {
			log.Warningf("Failed to retrieve uid for socket file: %v", statErr)
			fmt.Fprintf(buf, "%5d ", 0)
		} else {
			creds := auth.CredentialsFromContext(ctx)
			fmt.Fprintf(buf, "%5d ", uint32(auth.KUID(stat.UID).In(creds.UserNamespace).OrOverflow()))
		}

		// Field: timeout. Always 0 for UDP.
		fmt.Fprintf(buf, "%8d ", 0)

		// Field: inode.
		if statErr != nil || stat.Mask&linux.STATX_INO == 0 {
			log.Warningf("Failed to retrieve inode for socket file: %v", statErr)
			fmt.Fprintf(buf, "%8d ", 0)
		} else {
			fmt.Fprintf(buf, "%8d ", stat.Ino)
		}

		// Field: ref; reference count on the socket inode. Don't count the ref
		// we obtain while deferencing the weakref to this socket.
		fmt.Fprintf(buf, "%d ", s.ReadRefs()-1)

		// Field: Socket struct address. Redacted due to the same reason as
		// the 'Num' field in /proc/net/unix, see netUnix.ReadSeqFileData.
		fmt.Fprintf(buf, "%#016p ", (*socket.Socket)(nil))

		// Field: drops; number of dropped packets. Unimplemented.
		fmt.Fprintf(buf, "%d", 0)

		fmt.Fprintf(buf, "\n")

		s.DecRef(ctx)
	}
	return nil
}

// netSnmpData implements vfs.DynamicBytesSource for /proc/net/snmp.
//
// +stateify savable
type netSnmpData struct {
	kernfs.DynamicBytesFile

	stack inet.Stack
}

var _ dynamicInode = (*netSnmpData)(nil)

type snmpLine struct {
	prefix string
	header string
}

var snmp = []snmpLine{
	{
		prefix: "Ip",
		header: "Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests OutDiscards OutNoRoutes ReasmTimeout ReasmReqds ReasmOKs ReasmFails FragOKs FragFails FragCreates",
	},
	{
		prefix: "Icmp",
		header: "InMsgs InErrors InCsumErrors InDestUnreachs InTimeExcds InParmProbs InSrcQuenchs InRedirects InEchos InEchoReps InTimestamps InTimestampReps InAddrMasks InAddrMaskReps OutMsgs OutErrors OutDestUnreachs OutTimeExcds OutParmProbs OutSrcQuenchs OutRedirects OutEchos OutEchoReps OutTimestamps OutTimestampReps OutAddrMasks OutAddrMaskReps",
	},
	{
		prefix: "IcmpMsg",
	},
	{
		prefix: "Tcp",
		header: "RtoAlgorithm RtoMin RtoMax MaxConn ActiveOpens PassiveOpens AttemptFails EstabResets CurrEstab InSegs OutSegs RetransSegs InErrs OutRsts InCsumErrors",
	},
	{
		prefix: "Udp",
		header: "InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti",
	},
	{
		prefix: "UdpLite",
		header: "InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti",
	},
}

func toSlice(a interface{}) []uint64 {
	v := reflect.Indirect(reflect.ValueOf(a))
	return v.Slice(0, v.Len()).Interface().([]uint64)
}

func sprintSlice(s []uint64) string {
	if len(s) == 0 {
		return ""
	}
	r := fmt.Sprint(s)
	return r[1 : len(r)-1] // Remove "[]" introduced by fmt of slice.
}

// Generate implements vfs.DynamicBytesSource.Generate.
func (d *netSnmpData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	types := []interface{}{
		&inet.StatSNMPIP{},
		&inet.StatSNMPICMP{},
		nil, // TODO(gvisor.dev/issue/628): Support IcmpMsg stats.
		&inet.StatSNMPTCP{},
		&inet.StatSNMPUDP{},
		&inet.StatSNMPUDPLite{},
	}
	for i, stat := range types {
		line := snmp[i]
		if stat == nil {
			fmt.Fprintf(buf, "%s:\n", line.prefix)
			fmt.Fprintf(buf, "%s:\n", line.prefix)
			continue
		}
		if err := d.stack.Statistics(stat, line.prefix); err != nil {
			if err == syserror.EOPNOTSUPP {
				log.Infof("Failed to retrieve %s of /proc/net/snmp: %v", line.prefix, err)
			} else {
				log.Warningf("Failed to retrieve %s of /proc/net/snmp: %v", line.prefix, err)
			}
		}

		fmt.Fprintf(buf, "%s: %s\n", line.prefix, line.header)

		if line.prefix == "Tcp" {
			tcp := stat.(*inet.StatSNMPTCP)
			// "Tcp" needs special processing because MaxConn is signed. RFC 2012.
			fmt.Fprintf(buf, "%s: %s %d %s\n", line.prefix, sprintSlice(tcp[:3]), int64(tcp[3]), sprintSlice(tcp[4:]))
		} else {
			fmt.Fprintf(buf, "%s: %s\n", line.prefix, sprintSlice(toSlice(stat)))
		}
	}
	return nil
}

// netRouteData implements vfs.DynamicBytesSource for /proc/net/route.
//
// +stateify savable
type netRouteData struct {
	kernfs.DynamicBytesFile

	stack inet.Stack
}

var _ dynamicInode = (*netRouteData)(nil)

// Generate implements vfs.DynamicBytesSource.Generate.
// See Linux's net/ipv4/fib_trie.c:fib_route_seq_show.
func (d *netRouteData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	fmt.Fprintf(buf, "%-127s\n", "Iface\tDestination\tGateway\tFlags\tRefCnt\tUse\tMetric\tMask\tMTU\tWindow\tIRTT")

	interfaces := d.stack.Interfaces()
	for _, rt := range d.stack.RouteTable() {
		// /proc/net/route only includes ipv4 routes.
		if rt.Family != linux.AF_INET {
			continue
		}

		// /proc/net/route does not include broadcast or multicast routes.
		if rt.Type == linux.RTN_BROADCAST || rt.Type == linux.RTN_MULTICAST {
			continue
		}

		iface, ok := interfaces[rt.OutputInterface]
		if !ok || iface.Name == "lo" {
			continue
		}

		var (
			gw     uint32
			prefix uint32
			flags  = linux.RTF_UP
		)
		if len(rt.GatewayAddr) == header.IPv4AddressSize {
			flags |= linux.RTF_GATEWAY
			gw = usermem.ByteOrder.Uint32(rt.GatewayAddr)
		}
		if len(rt.DstAddr) == header.IPv4AddressSize {
			prefix = usermem.ByteOrder.Uint32(rt.DstAddr)
		}
		l := fmt.Sprintf(
			"%s\t%08X\t%08X\t%04X\t%d\t%d\t%d\t%08X\t%d\t%d\t%d",
			iface.Name,
			prefix,
			gw,
			flags,
			0, // RefCnt.
			0, // Use.
			0, // Metric.
			(uint32(1)<<rt.DstLen)-1,
			0, // MTU.
			0, // Window.
			0, // RTT.
		)
		fmt.Fprintf(buf, "%-127s\n", l)
	}
	return nil
}

// netStatData implements vfs.DynamicBytesSource for /proc/net/netstat.
//
// +stateify savable
type netStatData struct {
	kernfs.DynamicBytesFile

	stack inet.Stack
}

var _ dynamicInode = (*netStatData)(nil)

// Generate implements vfs.DynamicBytesSource.Generate.
// See Linux's net/ipv4/fib_trie.c:fib_route_seq_show.
func (d *netStatData) Generate(ctx context.Context, buf *bytes.Buffer) error {
	buf.WriteString("TcpExt: SyncookiesSent SyncookiesRecv SyncookiesFailed " +
		"EmbryonicRsts PruneCalled RcvPruned OfoPruned OutOfWindowIcmps " +
		"LockDroppedIcmps ArpFilter TW TWRecycled TWKilled PAWSPassive " +
		"PAWSActive PAWSEstab DelayedACKs DelayedACKLocked DelayedACKLost " +
		"ListenOverflows ListenDrops TCPPrequeued TCPDirectCopyFromBacklog " +
		"TCPDirectCopyFromPrequeue TCPPrequeueDropped TCPHPHits TCPHPHitsToUser " +
		"TCPPureAcks TCPHPAcks TCPRenoRecovery TCPSackRecovery TCPSACKReneging " +
		"TCPFACKReorder TCPSACKReorder TCPRenoReorder TCPTSReorder TCPFullUndo " +
		"TCPPartialUndo TCPDSACKUndo TCPLossUndo TCPLostRetransmit " +
		"TCPRenoFailures TCPSackFailures TCPLossFailures TCPFastRetrans " +
		"TCPForwardRetrans TCPSlowStartRetrans TCPTimeouts TCPLossProbes " +
		"TCPLossProbeRecovery TCPRenoRecoveryFail TCPSackRecoveryFail " +
		"TCPSchedulerFailed TCPRcvCollapsed TCPDSACKOldSent TCPDSACKOfoSent " +
		"TCPDSACKRecv TCPDSACKOfoRecv TCPAbortOnData TCPAbortOnClose " +
		"TCPAbortOnMemory TCPAbortOnTimeout TCPAbortOnLinger TCPAbortFailed " +
		"TCPMemoryPressures TCPSACKDiscard TCPDSACKIgnoredOld " +
		"TCPDSACKIgnoredNoUndo TCPSpuriousRTOs TCPMD5NotFound TCPMD5Unexpected " +
		"TCPMD5Failure TCPSackShifted TCPSackMerged TCPSackShiftFallback " +
		"TCPBacklogDrop TCPMinTTLDrop TCPDeferAcceptDrop IPReversePathFilter " +
		"TCPTimeWaitOverflow TCPReqQFullDoCookies TCPReqQFullDrop TCPRetransFail " +
		"TCPRcvCoalesce TCPOFOQueue TCPOFODrop TCPOFOMerge TCPChallengeACK " +
		"TCPSYNChallenge TCPFastOpenActive TCPFastOpenActiveFail " +
		"TCPFastOpenPassive TCPFastOpenPassiveFail TCPFastOpenListenOverflow " +
		"TCPFastOpenCookieReqd TCPSpuriousRtxHostQueues BusyPollRxPackets " +
		"TCPAutoCorking TCPFromZeroWindowAdv TCPToZeroWindowAdv " +
		"TCPWantZeroWindowAdv TCPSynRetrans TCPOrigDataSent TCPHystartTrainDetect " +
		"TCPHystartTrainCwnd TCPHystartDelayDetect TCPHystartDelayCwnd " +
		"TCPACKSkippedSynRecv TCPACKSkippedPAWS TCPACKSkippedSeq " +
		"TCPACKSkippedFinWait2 TCPACKSkippedTimeWait TCPACKSkippedChallenge " +
		"TCPWinProbe TCPKeepAlive TCPMTUPFail TCPMTUPSuccess\n")
	return nil
}