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The Gnutella file-sharing network and Java

Use the JTella API to easily develop applications that access Gnutella

By Ken Mccrary, JavaWorld.com, 10/06/00

I'll begin with some definitions. First, Internet file sharing is an activity performed by a community of connected users. The file-sharing system, at a minimum, allows users to share files, and to search for files within the community. Some file-sharing services offer additional capabilities, such as chatting. And some, like the notorious Napster, only allow users to share certain types of files, namely MP3s.

The Gnutella network supports sharing and searching of any file type, but does not offer any extra functionality, like chatting. Gnutella is a peer-to-peer system, with client software that also acts as a server -- software typically referred to as a servant.

Using Gnutella vs. the Internet

I will make a wild assumption that most of you are familiar with the Internet; specifically, with using an HTTP server to serve files to clients.

To publish files on a Website, you typically use FTP to transfer the documents to the Web server. Then, to make the document accessible to users, you might submit the URL to a search engine for crawling. This means downloading a document, examining it for keywords and such, and creating a searchable index in a database. Now, when a user uses an appropriate query on the Web server, he or she will receive information about the published document and its location.

When publishing files to a file-sharing service, you typically interact only with the servant program, which can access the service. The file-sharing service's servant is connected to Gnutella and is continuously responding to search queries from the network, eliminating the need for an intermediary search engine. The documents remain on the user's computer and are not transferred. Gnutella shares a document by copying the file to a shared directory and having the servant scan and index the file. Since the file-sharing system publishes and indexes documents, the user has much less work to do. Also, the user has the option to share files for a limited amount of time; simply removing the Gnutella servant from the network will end the session.

Origin of Gnutella

It has been widely reported that Gnutella was created by a group of developers at Nullsoft, a subsidiary of America Online. Not surprisingly, AOL put an end to the project. Later, the Nullsoft client's protocol was reverse-engineered and a group of developers on the Internet collaborated to further develop the system. Eventually, those developers produced a number of clients, written in various programming languages and targeted at different operating systems.

Network structure

This is where I would discuss the network's structure and describe its topology -- but there is none! Each servant on the network is connected to at least one other servant on the network; servants can also have both inbound and outbound connections to each other, forming a cyclic connection. However, there is no fixed layout or pattern to the nodes on the network.

So how do messages navigate this unordered environment? Each Gnutella message contains a unique ID, which is used to intelligently route messages through the network. For instance, as a servant forwards messages to its connected servants, it caches each message's ID in memory. When a response arrives, it uses that ID to route the response back to the original sender. Originally, message IDs were Windows's Globally Unique Identifiers (GUIDs), which was an issue for other platforms. But since the GUID is just a 16-byte value, non-Windows code can calculate its own unique data.

 

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