fix: darwin netdev i/o bytes metric (#3336)

There is a bug in darwin kernel since macOS Ventura 13.2.1,
which results in interface i/o bytes values to be truncated at 4GiB.
This change uses a workaround to collect the same metrics,
taking advantage of another bug.

fixes #3333

Signed-off-by: Siavash Safi <git@hosted.run>

collector/netdev_darwin.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"log/slog"
 	"net"
+	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -71,51 +72,107 @@ func getIfaceData(index int) (*ifMsghdr2, error) {
 		return nil, err
 	}
 	err = binary.Read(bytes.NewReader(rawData), binary.LittleEndian, &data)
+	if err != nil {
+		return &data, err
+	}
+
+	/*
+		As of macOS Ventura 13.2.1, there’s a kernel bug which truncates traffic values at the 4GiB mark.
+		This is a workaround to fetch the interface traffic metrics using a sysctl call.
+		Apple wants to prevent fingerprinting by 3rdparty apps and might fix this bug in future which would break this implementation.
+	*/
+	mib := []int32{
+		unix.CTL_NET,
+		unix.AF_LINK,
+		0, // NETLINK_GENERIC: functions not specific to a type of iface
+		2, //IFMIB_IFDATA: per-interface data table
+		int32(index),
+		1, // IFDATA_GENERAL: generic stats for all kinds of ifaces
+	}
+
+	var mibData ifMibData
+	size := unsafe.Sizeof(mibData)
+
+	if _, _, errno := unix.Syscall6(
+		unix.SYS___SYSCTL,
+		uintptr(unsafe.Pointer(&mib[0])),
+		uintptr(len(mib)),
+		uintptr(unsafe.Pointer(&mibData)),
+		uintptr(unsafe.Pointer(&size)),
+		uintptr(unsafe.Pointer(nil)),
+		0,
+	); errno != 0 {
+		return &data, err
+	}
+
+	var ifdata ifData64
+	err = binary.Read(bytes.NewReader(mibData.Data[:]), binary.LittleEndian, &ifdata)
+	if err != nil {
+		return &data, err
+	}
+
+	data.Data.Ibytes = ifdata.Ibytes
+	data.Data.Obytes = ifdata.Obytes
 	return &data, err
 }
 
+// https://github.com/apple-oss-distributions/xnu/blob/main/bsd/net/if.h#L220-L232
 type ifMsghdr2 struct {
-	Msglen    uint16
+	Msglen    uint16   // to skip over non-understood messages
-	Version   uint8
+	Version   uint8    // future binary compatabilit
-	Type      uint8
+	Type      uint8    // message type
-	Addrs     int32
+	Addrs     int32    // like rtm_addrs
-	Flags     int32
+	Flags     int32    // value of if_flags
-	Index     uint16
+	Index     uint16   // index for associated ifp
-	_         [2]byte
+	_         [2]byte  // padding for alignment
-	SndLen    int32
+	SndLen    int32    // instantaneous length of send queue
-	SndMaxlen int32
+	SndMaxlen int32    // maximum length of send queue
-	SndDrops  int32
+	SndDrops  int32    // number of drops in send queue
-	Timer     int32
+	Timer     int32    // time until if_watchdog called
-	Data      ifData64
+	Data      ifData64 // statistics and other data
 }
 
-// https://github.com/apple/darwin-xnu/blob/main/bsd/net/if_var.h#L199-L231
+// https://github.com/apple-oss-distributions/xnu/blob/main/bsd/net/if_var.h#L207-L235
 type ifData64 struct {
-	Type       uint8
+	Type      uint8  // ethernet, tokenring, etc
-	Typelen    uint8
+	Typelen   uint8  // Length of frame type id
-	Physical   uint8
+	Physical  uint8  // e.g., AUI, Thinnet, 10base-T, etc
-	Addrlen    uint8
+	Addrlen   uint8  // media address length
-	Hdrlen     uint8
+	Hdrlen    uint8  // media header length
-	Recvquota  uint8
+	Recvquota uint8  // polling quota for receive intrs
-	Xmitquota  uint8
+	Xmitquota uint8  // polling quota for xmit intrs
-	Unused1    uint8
+	Unused1   uint8  // for future use
-	Mtu        uint32
+	Mtu       uint32 // maximum transmission unit
-	Metric     uint32
+	Metric    uint32 // routing metric (external only)
-	Baudrate   uint64
+	Baudrate  uint64 // linespeed
-	Ipackets   uint64
+
-	Ierrors    uint64
+	// volatile statistics
-	Opackets   uint64
+	Ipackets   uint64         // packets received on interface
-	Oerrors    uint64
+	Ierrors    uint64         // input errors on interface
-	Collisions uint64
+	Opackets   uint64         // packets sent on interface
-	Ibytes     uint64
+	Oerrors    uint64         // output errors on interface
-	Obytes     uint64
+	Collisions uint64         // collisions on csma interfaces
-	Imcasts    uint64
+	Ibytes     uint64         // total number of octets received
-	Omcasts    uint64
+	Obytes     uint64         // total number of octets sent
-	Iqdrops    uint64
+	Imcasts    uint64         // packets received via multicast
-	Noproto    uint64
+	Omcasts    uint64         // packets sent via multicast
-	Recvtiming uint32
+	Iqdrops    uint64         // dropped on input, this interface
-	Xmittiming uint32
+	Noproto    uint64         // destined for unsupported protocol
-	Lastchange unix.Timeval32
+	Recvtiming uint32         // usec spent receiving when timing
+	Xmittiming uint32         // usec spent xmitting when timing
+	Lastchange unix.Timeval32 // time of last administrative change
+}
+
+// https://github.com/apple-oss-distributions/xnu/blob/main/bsd/net/if_mib.h#L65-L74
+type ifMibData struct {
+	Name          [16]byte  // name of interface
+	PCount        uint32    // number of promiscuous listeners
+	Flags         uint32    // interface flags
+	SendLength    uint32    // instantaneous length of send queue
+	MaxSendLength uint32    // maximum length of send queue
+	SendDrops     uint32    // number of drops in send queue
+	_             [4]uint32 // for future expansion
+	Data          [128]byte // generic information and statistics
 }
 
 func getNetDevLabels() (map[string]map[string]string, error) {