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procnettcp.go
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procnettcp.go
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package procnettcp
import (
"bufio"
"encoding/hex"
"fmt"
"io"
"net"
"strconv"
"strings"
)
type Kind = string
const (
TCP Kind = "tcp"
TCP6 Kind = "tcp6"
// TODO: "udp", "udp6", "udplite", "udplite6"
)
type State = int
const (
TCPEstablished State = 0x1
TCPListen State = 0xA
)
type Entry struct {
Kind Kind `json:"kind"`
IP net.IP `json:"ip"`
Port uint16 `json:"port"`
State State `json:"state"`
}
func Parse(r io.Reader, kind Kind) ([]Entry, error) {
switch kind {
case TCP, TCP6:
default:
return nil, fmt.Errorf("unexpected kind %q", kind)
}
var entries []Entry
sc := bufio.NewScanner(r)
// As of kernel 5.11, ["local_address"] = 1
fieldNames := make(map[string]int)
for i := 0; sc.Scan(); i++ {
line := strings.TrimSpace(sc.Text())
if line == "" {
continue
}
fields := strings.Fields(line)
switch i {
case 0:
for j := 0; j < len(fields); j++ {
fieldNames[fields[j]] = j
}
if _, ok := fieldNames["local_address"]; !ok {
return nil, fmt.Errorf("field \"local_address\" not found")
}
if _, ok := fieldNames["st"]; !ok {
return nil, fmt.Errorf("field \"st\" not found")
}
default:
// localAddress is like "0100007F:053A"
localAddress := fields[fieldNames["local_address"]]
ip, port, err := ParseAddress(localAddress)
if err != nil {
return entries, err
}
stStr := fields[fieldNames["st"]]
st, err := strconv.ParseUint(stStr, 16, 8)
if err != nil {
return entries, err
}
ent := Entry{
Kind: kind,
IP: ip,
Port: port,
State: int(st),
}
entries = append(entries, ent)
}
}
if err := sc.Err(); err != nil {
return entries, err
}
return entries, nil
}
// ParseAddress parses a string, e.g.,
// "0100007F:0050" (127.0.0.1:80)
// "000080FE00000000FF57A6705DC771FE:0050" ([fe80::70a6:57ff:fe71:c75d]:80)
// "00000000000000000000000000000000:0050" (0.0.0.0:80)
//
// See https://serverfault.com/questions/592574/why-does-proc-net-tcp6-represents-1-as-1000
//
// ParseAddress is expected to be used for /proc/net/{tcp,tcp6} entries on
// little endian machines.
// Not sure how those entries look like on big endian machines.
func ParseAddress(s string) (net.IP, uint16, error) {
split := strings.SplitN(s, ":", 2)
if len(split) != 2 {
return nil, 0, fmt.Errorf("unparsable address %q", s)
}
switch l := len(split[0]); l {
case 8, 32:
default:
return nil, 0, fmt.Errorf("unparsable address %q, expected length of %q to be 8 or 32, got %d",
s, split[0], l)
}
ipBytes := make([]byte, len(split[0])/2) // 4 bytes (8 chars) or 16 bytes (32 chars)
for i := 0; i < len(split[0])/8; i++ {
quartet := split[0][8*i : 8*(i+1)]
quartetLE, err := hex.DecodeString(quartet) // surprisingly little endian, per 4 bytes
if err != nil {
return nil, 0, fmt.Errorf("unparsable address %q: unparsable quartet %q: %w", s, quartet, err)
}
for j := 0; j < len(quartetLE); j++ {
ipBytes[4*i+len(quartetLE)-1-j] = quartetLE[j]
}
}
ip := net.IP(ipBytes)
port64, err := strconv.ParseUint(split[1], 16, 16)
if err != nil {
return nil, 0, fmt.Errorf("unparsable address %q: unparsable port %q", s, split[1])
}
port := uint16(port64)
return ip, port, nil
}