	CS 580 Client-Server Spring Semester, 2004 Gnutella
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Reference

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


Doc 20, Gnutella Slide # 2

Gnutella

Peer-to-peer

Gnutella program is both a server and a client: servent

No central server

Protocol does not discuss how one knows about other servents


Doc 20, Gnutella Slide # 3

Basic Idea

Servent connects to 1 or more remote servents

Can

Ping the network

Send a request for a file to see who has it

To get a file from a servent

Connect to the servent directly with http request


Doc 20, Gnutella Slide # 4

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


Doc 20, Gnutella Slide # 5

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


Doc 20, Gnutella Slide # 6

Header

	Desciptor ID	Payload Descriptor	TTL	Hops	Payload Length
Byte offset	0 - 15	16	17	18	19 - 22

Descriptor ID
16 byte string
Uniquely identifies Request/Response

Payload Descriptor

Value	Meaning
0x00	Ping
0x01	Pong
0x40	Push
0x80	Query
0x81	QueryHit

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


Doc 20, Gnutella Slide # 7

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


Doc 20, Gnutella Slide # 8

Ping 0x00

No more content other then header


Doc 20, Gnutella Slide # 9

Pong 0x01

Sent only in response to a ping

Servent can cache pongs of other servents

	Port	IP Address	Number of files shared	Number of kilobytes shared
Byte offset	0 - 1

Port
Port that responding servent can accept incoming connections

IP Address
IP Address of responding servent

This field uses big-endian format


Doc 20, Gnutella Slide # 10

Query 0x80

	Minimum Speed	Search Criteria
Byte offset	0 - 1

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


Doc 20, Gnutella Slide # 11

QueryHit (0x81)

Sent in response to a Query

Descriptor ID in header should contain same value as the Query

	Number of hits	Port	IP Address	Speed	Result Set	Servent Identifier
Byte offset	0

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


Doc 20, Gnutella Slide # 12

Result Set

	File Index	File Size	File Name
Byte offset	0 - 3

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”


Doc 20, Gnutella Slide # 13

Extended Query Hit

	Number of hits	Port	IP Address	Speed	Result Set	Trailer	Servent Identifier
Byte offset	0

Trailer

	Vender Code	Open Data Size	Open Data	Private data
Byte offset	0 - 3	4	5

How do we know if the trailer exists?

How do we know the length of the private data?


Doc 20, Gnutella Slide # 14

Push (0x40)

	Servent Identifier	File Index	IP Address	Port
Byte offset	0 - 15

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


Doc 20, Gnutella Slide # 15

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


Doc 20, Gnutella Slide # 16

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

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2004 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
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