Golang - Hijack Arguments

Question

When using Hijack() with a http.ResponseWriter instance

Hijack() (net.Conn, *bufio.ReadWriter, error)

What is the difference between reading from the net.Conn and the *bufio.ReadWriter?

Answer 1

net.Conn.Read and *bufio.ReadWriter.Read both read from the same connection, but the latter is buffered. The Hijack method in the standard "net/http" package directly returns the net.Conn wrapped in a bufio.ReadWriter, using the same *bufio.Reader that was already allocated for the http request.

It's possible that there is still data buffered in the bufio.Reader which you may miss when reading directly from the network connection. If you want to use the net.Conn directly, you should check if there is buffered data already with Reader.Buffered, and handle that according to the protocol being used.

In general, you should prefer to use bufio.ReadWriter, as it will be more efficient for non-optimally sized reads and writes to the network.

The net.Conn is still needed to handle the Read and Write deadlines, to close the net.Conn when you're done, and for any other network-specific activities.

Answer 2

Their difference is buffered IO.

net.Conn implements Read() and Write() thus implementing io.Reader and io.Writer. This is why bufio can wrap it up as a buffered ReadWriter and further implement functions on top using those two methods in a buffered manner.

If you only want to use Read() and Write(), you can just stick with net.Conn, otherwise you can take advantage for the buffered ReadWriter methods.

See https://golang.org/pkg/io/#Reader and https://golang.org/pkg/io/#Writer