Professional Node.js: Building Javascript Based Scalable Software

Chapter 12

Building a TCP Client

WHAT’S IN THIS CHAPTER?

• Connecting to a TCP server
• Sending and receiving data from a TCP server
• Reconnecting a broken connection

Sitting a level above IP, TCP is one of the most used transport protocols on the Internet, on top of which sit application protocols like HTTP. TCP is a connection-oriented protocol, which means that one endpoint requests and establishes a dedicated connection to another endpoint. This connection is a two-way dedicated stream into which both endpoints can send and receive data to/from each other at the same time. TCP guarantees that the messages you receive are in order. It has built-in mechanisms for flow control, making it a good platform for supporting machine-to-machine and human-to-machine protocols.

As you will see, Node makes it easy to build a TCP client that establishes a connection to another endpoint, usually what is called a TCP server. This connection then forms two streams of data that allow you to interact with the remote endpoint: One is a readable stream that receives data, and the other is a writable stream that writes data.

NOTE One point you should keep in mind is that when you write to a TCP stream, you receive no acknowledgment that the other side has received the data. Even worse, because the underlying network implementation may chop and route your packets haphazardly, the other endpoint may have received only part of the message you sent (even though TCP internally tries to resend the packets ...