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Fix packet decoding #8

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Fix packet decoding #8

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0128494
Fix ping packet decoding
0dinD Mar 3, 2023
2c88195
Clarify and comment ping formats used in fetchData
0dinD Mar 3, 2023
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40 changes: 33 additions & 7 deletions src/main/java/com/extendedclip/papi/expansion/pinger/PingerExpansion.java
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
Expand Down Expand Up @@ -248,8 +248,19 @@ public boolean fetchData() {
DataOutputStream dataOutputStream = new DataOutputStream(outputStream);
InputStream inputStream = socket.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream,
Charset.forName("UTF-16BE"));
dataOutputStream.write(new byte[]{-2, 1});
StandardCharsets.UTF_16BE);

// Send server list ping request, in 1.4-1.5 format
// See https://wiki.vg/Server_List_Ping#1.4_to_1.5
dataOutputStream.write(0xFE);
dataOutputStream.write(0x01);

// Then, read the ping response (a kick packet)
// Beta 1.8 - 1.3 servers should respond with this format: https://wiki.vg/Server_List_Ping#Beta_1.8_to_1.3
// 1.4+ servers should respond with this format: https://wiki.vg/Server_List_Ping#1.4_to_1.5
// which uses the same response format as: https://wiki.vg/Server_List_Ping#1.6

// Read packet ID field (1 byte), should be 0xFF (kick packet ID)
int packetId = inputStream.read();
if (packetId == -1) {
try {
Expand All @@ -259,14 +270,16 @@ public boolean fetchData() {
socket = null;
return false;
}
if (packetId != 255) {
if (packetId != 0xFF) {
try {
socket.close();
} catch (IOException iOException) {
}
socket = null;
return false;
}

// Read string length field (2 bytes)
int length = inputStreamReader.read();
if (length == -1) {
try {
Expand All @@ -284,6 +297,8 @@ public boolean fetchData() {
socket = null;
return false;
}

// Read string (length bytes)
char[] chars = new char[length];
if (inputStreamReader.read(chars, 0, length) != length) {
try {
Expand All @@ -294,16 +309,27 @@ public boolean fetchData() {
return false;
}
String string = new String(chars);
if (string.startsWith("&")) {
String[] data = string.split("\000");

// Read the fields of the string
if (string.startsWith("§")) {
// If the string starts with '§', the server is probably running 1.4+
// See https://wiki.vg/Server_List_Ping#1.4_to_1.5
// and https://wiki.vg/Server_List_Ping#1.6

// In this format, fields are delimited by '\0' characters
String[] data = string.split("\0");
setPingVersion(Integer.parseInt(data[0].substring(1)));
setProtocolVersion(Integer.parseInt(data[1]));
setGameVersion(data[2]);
setMotd(data[3]);
setPlayersOnline(Integer.parseInt(data[4]));
setMaxPlayers(Integer.parseInt(data[5]));
} else {
String[] data = string.split("&");
// If the string doesn't start with '§', the server is probably running Beta 1.8 - 1.3
// See https://wiki.vg/Server_List_Ping#Beta_1.8_to_1.3

// In this format, fields are delimited by '§' characters
String[] data = string.split("§");
setMotd(data[0]);
setPlayersOnline(Integer.parseInt(data[1]));
setMaxPlayers(Integer.parseInt(data[2]));
Expand Down