How Can I Detect TCP Connection Closure in Go's `net` Package?

How to Determine TCP Connection Closure Using the Net Package

Problem:

When implementing a TCP server, it's essential to know when clients close their connections. How can you determine this using the net package?

Answer:

To detect a closed TCP connection, you can use the following method:

one := make([]byte, 1)
c.SetReadDeadline(time.Now())
if _, err := c.Read(one); err == io.EOF {
  // Connection closed
} else {
  // Connection still open
}

This approach involves:

1. Creating a single-byte buffer (one).
2. Setting a read deadline on the connection (c) to the current time to force an immediate read.
3. Reading a byte from the connection.
4. Checking the error; if it's io.EOF, the connection has closed.

Timeout Detection:

To detect a timeout, you can check if the error is a net.Error with a timeout.

if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
  // Timeout occurred
}

Update (Go 1.7 ):

In Go 1.7 , zero-byte reads return immediately and never result in an error. To account for this, it's necessary to read at least one byte.

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