CODEWITHSUNDEEP
javasocketsnetwork-programming
Heidi
Heidi

Reputation: 131

How to parse a proxy socks packet in java?

Im trying to build a basic proxy 4 server, and I have to parse a packet and extract its informations that looks like this:

1 byte (version)
1 byte (command)
2 byte (port)
4 byte (ip)
X byte (userID, builds a string by looping until '\0' is found)

Here's my code so far:

InputStream reader = socket.getInputStream();

byte[] ver  = new byte[1];
byte[] cmd  = new byte[1];
byte[] port = new byte[2];
byte[] ip   = new byte[4];

reader.read(ver, 0, 1);  //should be: 4
reader.read(cmd, 1, 1);  //should be: 1
reader.read(port, 2, 2); //should be: 00, 80
reader.read(ip, 4, 4);   //should be: 217, 70, 182, 162

Here's the response I get from my code: [4, 1, 0, 80, -39, 70, -74, -94]

For some reason the IP part I get is always wrong, I really don't know why. My second issue would be: Is there an easy and clean way to get the last userID string part, without having to build a messy loop that could end up hanging for ever, if the \0 byte was not found?

Upvotes: 4

Views: 301

Answers (2)

user207421
user207421

Reputation: 311008

Throw it all away and use the methods of DataInputStream. They will give you ints, shorts, longs, and fully-read byte arrays, and take care of network byte ordering for you as well.

Upvotes: 4

Am_I_Helpful
Am_I_Helpful

Reputation: 19168

The first issue which you received is all because of byte-overflow and hence,turning to negative numbers as byte ranges from -128 to 127 in Java.

Check this question which I asked on this forum to know about the magic(issues) of byte[]...

Seriously,if this is your approach for last-field,(ip)---I am sure you're not going to get correct answer using direct reforms on byte. The possible solution seems to use other approach like storing in temporary int[], like 

int[] ip   = new int[4];
byte[] temp = new byte[4];
reader.read(temp, 4, 4);   //should be: 217, 70, 182, 162
for(int i=0;i<temp.length;i++)
{
 if(temp[i]<0)
 ip[i]=(int)(256+temp[i]);  // careful here
 else
 ip[i]=(int)temp[i];
}

And,for the second issue,I think that better solution is get length of String-part using String.length().

 int len = userID.length();  // assume user-id would be String type
 userid = new byte[len];   // notice the difference between userid and userID
 reader.read(userid,0,len);
 // I am confused as to how are you reading input from user,
 // if you clarify further,I'll update my answer...

Upvotes: 2

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