Open Protocol™ Rust Interface Library

Rust Edition: 2018

Rust crate to interface with the iChen® System 4 using Open Protocol™.

Details on the protocol can be found in this document.

Crate

The ichen-openprotocol crate is available on crates.io.

Examples

Sample programs can be found in the bin directory under src.

Design Notes

Beware that all data types defined in this crate use borrowed string slices (i.e. &str) extensively. This is because the most common usage pattern is to create a data variable, set fields, immediately serialize it into JSON, then dispose of the data variable. The deserialization story is similar.

Error values also borrow heavily from the input fields as these errors are expected to be handled as soon as possible.

The result is minimal allocations and copying, but at the cost of stricter lifetime management, especially when deserializing -- the message struct cannot out-live the original JSON text string as fields are borrowed extensively from the original JSON string.

Another implication due to extensive usage of borrowed string slices is that strings literals with escape sequences will cause parsing errors because the actual string cannot be simply borrowed from the original JSON string. Luckily this is extremely rare for most fields holding names, ID's etc. For this reason, only certain user-defined text fields (such as job_card_id) that may contain escaped characters (especially the double-quote) and therefore are modeled using Cow<&str> instead.

How to Use

1. Import the ichen-openprotocol crate in Cargo.toml, and also a WebSocket client crate (such as websocket):

        [dependencies]
        ichen-openprotocol = "0.4.0"
        websocket = "0.23.*"

2. Import the namespaces:

        use ichen_openprotocol::*;
        use websocket::client::ClientBuilder;
        use websocket::OwnedMessage;

3. Connect to the iChen 4 Server via WebSocket (the default port is 5788):

        let client = ClientBuilder::new("1.2.3.4:5788").connect_insecure()?;

        // Split WebSocket into sender and receiver
        let (mut receiver, mut sender) = client.split()?;

4. Create a JOIN message with the appropriate password and filters, serialize it into JSON using Message::to_json_str(), then send the JSON string to the WebSocket:

        // Create the JOIN message
        let join = Message::new_join("mypassword", Filters::All + Filters::JobCards + Filters::Operators)?;

        // Serialize the JOIN message with to_json_str()
        let json = join.to_json_str();

        // Send it over the WebSocket
        sender.send(OwnedMessage::Text(json))?;

1. Listen to and parse messages in a loop:

        for msg in receiver.incoming_messages() {
            match msg.unwrap() {
                OwnedMessage::Text(json) => {
                    // Got a JSON message!  Parse it.
                    let message = Message::parse_from_json_str(&json)?;

                    // Process it...
                           :
                           :
                }

                // Handle other WebSocket message types, e.g. OwnedMessage::Close
                           :
                           :
            }
        }

6. Process received message:

   Remember that string fields borrow heavily from the original JSON string, so the correct usage pattern is to parse the JSON string into a Message struct (using Message::parse_from_json()), and then consume the struct immediately, releasing all the borrowed string data.

        match message {
            // Response of the `JOIN`
            // Result < 100 indicates failure
            Message::JoinResponse { result, .. } if result < 100 => {
                // Failed to join
                        :
                        :
            }
            // Response of the `JOIN`
            // Result >= 100 indicates success
            Message::JoinResponse { result, level, .. } => {
                // Success!
                        :
                        :
            }),
            // Process other messages
                        :
                        :
        }

7. Periodically send an ALIVE message to keep the connection alive:

        let alive = Message::new_alive();
        let json = alive.to_json_str();
        sender.send(OwnedMessage::Text(json))?;