From 6bec248f1af7b94f7b57c4b2cefd7c2a8b80e40a Mon Sep 17 00:00:00 2001
From: Ben Kochie <superq@gmail.com>
Date: Wed, 17 Apr 2024 22:21:59 +0200
Subject: [PATCH] Revert "fix: same TCP connection appears twice (#631)" (#633)

This reverts commit 987bedc3110c2fdc82f3d486211871cecc85912f.
---
 net_ip_socket.go | 64 +++++++++++++++++++++++++++++-------------------
 1 file changed, 39 insertions(+), 25 deletions(-)

diff --git a/net_ip_socket.go b/net_ip_socket.go
index 679a91eb..b70f1fc7 100644
--- a/net_ip_socket.go
+++ b/net_ip_socket.go
@@ -14,14 +14,26 @@
 package procfs
 
 import (
+	"bufio"
 	"encoding/hex"
 	"fmt"
+	"io"
 	"net"
 	"os"
 	"strconv"
 	"strings"
 )
 
+const (
+	// readLimit is used by io.LimitReader while reading the content of the
+	// /proc/net/udp{,6} files. The number of lines inside such a file is dynamic
+	// as each line represents a single used socket.
+	// In theory, the number of available sockets is 65535 (2^16 - 1) per IP.
+	// With e.g. 150 Byte per line and the maximum number of 65535,
+	// the reader needs to handle 150 Byte * 65535 =~ 10 MB for a single IP.
+	readLimit = 4294967296 // Byte -> 4 GiB
+)
+
 // This contains generic data structures for both udp and tcp sockets.
 type (
 	// NetIPSocket represents the contents of /proc/net/{t,u}dp{,6} file without the header.
@@ -62,50 +74,49 @@ type (
 )
 
 func newNetIPSocket(file string) (NetIPSocket, error) {
-	var netIPSocket NetIPSocket
-	isUDP := strings.Contains(file, "udp")
-	content, err := os.ReadFile(file)
+	f, err := os.Open(file)
 	if err != nil {
 		return nil, err
 	}
-	lines := strings.Split(string(content), "\n")
-	if len(lines) < 1 {
-		return nil, ErrFileParse
-	}
+	defer f.Close()
 
-	for _, line := range lines[1:] {
-		fields := strings.Fields(line)
-		if len(fields) == 0 {
-			continue
-		}
+	var netIPSocket NetIPSocket
+	isUDP := strings.Contains(file, "udp")
+
+	lr := io.LimitReader(f, readLimit)
+	s := bufio.NewScanner(lr)
+	s.Scan() // skip first line with headers
+	for s.Scan() {
+		fields := strings.Fields(s.Text())
 		line, err := parseNetIPSocketLine(fields, isUDP)
 		if err != nil {
 			return nil, err
 		}
 		netIPSocket = append(netIPSocket, line)
 	}
+	if err := s.Err(); err != nil {
+		return nil, err
+	}
 	return netIPSocket, nil
 }
 
 // newNetIPSocketSummary creates a new NetIPSocket{,6} from the contents of the given file.
 func newNetIPSocketSummary(file string) (*NetIPSocketSummary, error) {
-	var netIPSocketSummary NetIPSocketSummary
-	var udpPacketDrops uint64
-	isUDP := strings.Contains(file, "udp")
-	content, err := os.ReadFile(file)
+	f, err := os.Open(file)
 	if err != nil {
 		return nil, err
 	}
-	lines := strings.Split(string(content), "\n")
-	if len(lines) < 1 {
-		return nil, ErrFileParse
-	}
+	defer f.Close()
 
-	for _, line := range lines[1:] {
-		fields := strings.Fields(line)
-		if len(fields) == 0 {
-			continue
-		}
+	var netIPSocketSummary NetIPSocketSummary
+	var udpPacketDrops uint64
+	isUDP := strings.Contains(file, "udp")
+
+	lr := io.LimitReader(f, readLimit)
+	s := bufio.NewScanner(lr)
+	s.Scan() // skip first line with headers
+	for s.Scan() {
+		fields := strings.Fields(s.Text())
 		line, err := parseNetIPSocketLine(fields, isUDP)
 		if err != nil {
 			return nil, err
@@ -118,6 +129,9 @@ func newNetIPSocketSummary(file string) (*NetIPSocketSummary, error) {
 			netIPSocketSummary.Drops = &udpPacketDrops
 		}
 	}
+	if err := s.Err(); err != nil {
+		return nil, err
+	}
 	return &netIPSocketSummary, nil
 }