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netstat.go
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netstat.go
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// Copyright 2018 Authors of Cilium
//
// 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 proxy
import (
"bytes"
"os"
"regexp"
"strconv"
"github.com/cilium/cilium/pkg/logging/logfields"
)
var (
// procNetTCPFiles is the constant list of /proc/net files to read to get
// the same information about open TCP connections as output by netstat.
procNetTCPFiles = []string{
"/proc/net/tcp",
"/proc/net/tcp6",
}
// procNetUDPFiles is the constant list of /proc/net files to read to get
// the same information about open UDP connections as output by netstat.
procNetUDPFiles = []string{
"/proc/net/udp",
"/proc/net/udp6",
}
// procNetFileRegexp matches the first two columns of /proc/net/{tcp,udp}*
// files and submatches on the local port number.
procNetFileRegexp = regexp.MustCompile("^ *[[:digit:]]*: *[[:xdigit:]]*:([[:xdigit:]]*) ")
)
// readOpenLocalPorts returns the set of L4 ports currently open locally.
// procNetFiles should be procNetTCPFiles or procNetUDPFiles (or both).
func readOpenLocalPorts(procNetFiles []string) map[uint16]struct{} {
openLocalPorts := make(map[uint16]struct{}, 128)
for _, file := range procNetFiles {
b, err := os.ReadFile(file)
if err != nil {
log.WithError(err).WithField(logfields.Path, file).Errorf("cannot read proc file")
continue
}
lines := bytes.Split(b, []byte("\n"))
// Extract the local port number from the "local_address" column.
// The header line won't match and will be ignored.
for _, line := range lines {
groups := procNetFileRegexp.FindSubmatch(line)
if len(groups) != 2 { // no match
continue
}
// The port number is in hexadecimal.
localPort, err := strconv.ParseUint(string(groups[1]), 16, 16)
if err != nil {
log.WithError(err).WithField(logfields.Path, file).Errorf("cannot read proc file")
continue
}
openLocalPorts[uint16(localPort)] = struct{}{}
}
}
return openLocalPorts
}