CS 580 Client-Server Programming

Spring Semester, 2005

Doc 15 Gnutella

Contents

 

Reference    

Gnutella    

Requests and Responses    

Header    

Ping 0x00    

Pong 0x01    

Query 0x80    

QueryHit (0x81)    

Push (0x40)    

Some Routing    

File Downloads    

 

Reference

 

The Gnutella Protocol Specification v0.4, Document Revision 1.2, http://www9.limewire.com/developer/gnutella_protocol_0.4.pdf

 

Copyright ©, All rights reserved. 2005 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA. OpenContent ( http://www.opencontent.org/opl.shtml ) license defines the copyright on this document.

 

 

Gnutella

 

1. Peer-to-peer

 

2. Gnutella program is both a server and a client: servent

 

3. No central server

 

4. Protocol does not discuss how one knows about other servents

 

 

 

Basic Idea

 

 

Servent connects to 1 or more remote servents

 

Can

5. Ping the network

 

6. Send a request for a file to see who has it

 

 

To get a file from a servent

 

7. Connect to the servent directly with http request

 

 

 

 

Basic Protocol

 

Connect to another servent with

 

    GNUTELLA CONNECT/<protocol version string>\n\n

 

Where <protocol version string> is 0.4

 

If the remote servent accepts the connection it must respond with

 

    GNUTELLA OK\n\n

 

 

Both servents then can then send messages

 

 

 

Requests and Responses

 

Ping – who is on the network

 

Pong – response to a ping

 

Query – search the network for data

 

QueryHit – response to query

 

Push – Used to allow servents work behind firewall

 

Each Request/Response starts with a header

 

 

Header

 

 

 

Descriptor ID

16 byte string

Uniquely identifies Request/Response

 

Payload Descriptor

 

 

TTL

Time to live

 

Number of times message will be forwarded by servents

 

Many servents will set TTL to 5 if is it larger

 

Each servent that gets the message reduces TTL by one before forwarding the message

 

 

Hops

 

Number of times message has been forwarded

 

Each servent that gets the message increase Hop by one before forwarding

 

Payload Length

 

Length of rest of message

 

 

 

 

Ping 0x00

 

No more content other then header

 

 

 

Pong 0x01

 

Sent only in response to a ping

 

Servent can cache pongs of other servents

 

 

 

 

Port

 

Port that responding servent can accept incoming connections

 

 

IP Address

 

IP Address of responding servent

 

This field uses big-endian format

 

 

 

Query 0x80

 

 

 

 

Minimum Speed

 

Minimum speed (of connection) in kb/second of servents that should respond to this message

 

Search Criteria

 

Nul (0x00) terminated search string

 

Length of string must be included in the payload length field

 

 

 

QueryHit (0x81)

 

Sent in response to a Query

 

Descriptor ID in header should contain same value as the Query

 

 

 

Number of hits

 

Number of hits in the result set

 

Port

 

Port number on which responding servent can accept incoming connections

 

IP Address

 

IP Address of responding servent

 

This field uses big-endian format

 

Speed

 

Speed of responding host’s connection in kb/second

 

 

 

Result Set

 

 

 

 

File Index

 

A number used by host to identify the file

 

File Size

Size in bytes of the file

 

File Name

 

Double-nul (0x0000) terminated name of the file

 

Servent Identifier

 

A 16-byte string uniquely identifying the responding servent on the network.  

 

“This is typically some function of the servent’s network address”

 

 

 

Extended Query Hit

 

 

 

 

 

Trailer

 

 

 

How do we know if the trailer exists?

 

How do we know the length of the private data?

 

 

 

 

Push (0x40)

 

 

 

 

Servent Identifier

 

A 16-byte string uniquely identifying the servent on the network that should push the file

 

File Index

 

Index of the file to push

 

IP Address

 

IP Address of to which the file should be pushed

 

This field uses big-endian format

 

Port

 

Port to which the file should be pushed

 

 

Some Routing

 

Pong messages

 

Can only be send along path the carried the Ping

 

Servents should not forward a pong if they did not see the ping

 

QueryHit

 

Can only be send along path the carried the Query

 

Servents should not forward a query hit if they did not see the query

 

 

Push

 

Can only be send along path the carried the QueryHit

 

Servents should not forward a push if they did not see the query hit

 

Fowarding

 

Forward all Ping and Querys to all directly connected servents except to the one that sent it

 

Decrement TTL and increment Hops field

 

Don’t forward messages that you have seen before

 

 

File Downloads

 

In response to a QueryHit download the file by using http.

 

Request the file uses following format:

 

 

GET /get/<File Index>/<File Name>/ HTTP/1.0\r\n

Connection: Keep-Alive\r\n  

Range: bytes=0-\r\n  

User-Agent: Gnutella\r\n 3  \r\n

 

 

Remote servent responses with:

 

HTTP 200 OK\r\n  

Server: Gnutella\r\n  

Content-type: application/binary\r\n  

Content-length: fileSize\r\n  

\r\n