121_framer.md

Framer

Let's start by implementing the Framer trait. This trait is responsible for determining if the inbound network buffer contains sufficient number of bytes to create a complete message. In our example we will use a delimiter based strategy, where each message sent will be delimited by a \n character

You only need to implement one method here, called get_frame_length, which will be called every time you call Clt's or Svcs recv method. The get_frame_length method will be passed a reference to a bytes::BytesMut buffer which will contain accumulated incoming network data. Application developer's job is to simply return an Option with position on which the frame ends or None when frame is incomplete.

Below example looks for the \n new line character and returns its positions.

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Note: Your Framer, Messenger, Protocol handling structure must also implement Debug & Clone which are typically done via derive macro.

• Clone is necessary because each new connection that the Svc accepts will get a new and independent "copy" of the Protocol instance. This is necessary because some methods in the Protocol trait require a self reference that enables feature of the protocol to track the state of each individual connection separately from one another.
• Debug is required to provide a meaningful messages during logging or exception handling under certain conditions.

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# use links_nonblocking::prelude::*;
#
#[derive(Debug, Clone)] // Note that Debug & Clone are required for Protocol `struct`
struct MessageProtocol;

impl Framer for MessageProtocol {
    fn get_frame_length(bytes: &bytes::BytesMut) -> Option<usize> {
        for (idx, byte) in bytes.iter().enumerate() {
            if *byte == b'\n' {
                return Some(idx + 1);
            }
        }
        None
    }
}