SignalR Service trigger binding for Azure Functions

Use the SignalR trigger binding to respond to messages sent from Azure SignalR Service. When function is triggered, messages passed to the function is parsed as a json object.

In SignalR Service serverless mode, SignalR Service uses the Upstream feature to send messages from client to Function App. And Function App uses SignalR Service trigger binding to handle these messages. The general architecture is shown below:

SignalR Trigger Architecture

For information on setup and configuration details, see the overview.

Example

A C# function can be created by using one of the following C# modes:

  • Isolated worker model: Compiled C# function that runs in a worker process that's isolated from the runtime. Isolated worker process is required to support C# functions running on LTS and non-LTS versions .NET and the .NET Framework.
  • In-process model: Compiled C# function that runs in the same process as the Functions runtime.
  • C# script: Used primarily when you create C# functions in the Azure portal.

The following sample shows a C# function that receives a message event from clients and logs the message content.

[Function(nameof(OnClientMessage))]
public static void OnClientMessage(
    [SignalRTrigger("Hub", "messages", "sendMessage", "content", ConnectionStringSetting = "SignalRConnection")]
        SignalRInvocationContext invocationContext, string content, FunctionContext functionContext)
{
    var logger = functionContext.GetLogger(nameof(OnClientMessage));
    logger.LogInformation("Connection {connectionId} sent a message. Message content: {content}", invocationContext.ConnectionId, content);
}

SignalR trigger isn't currently supported for Java.

Here's binding data in the function.json file:

{
    "type": "signalRTrigger",
    "name": "invocation",
    "hubName": "SignalRTest",
    "category": "messages",
    "event": "SendMessage",
    "parameterNames": [
        "message"
    ],
    "direction": "in"
}

Here's the JavaScript code:

module.exports = async function (context, invocation) {
    context.log(`Receive ${context.bindingData.message} from ${invocation.ConnectionId}.`)
};

Complete PowerShell examples are pending.

Here's the Python code:

import logging
import json
import azure.functions as func

def main(invocation) -> None:
    invocation_json = json.loads(invocation)
    logging.info("Receive {0} from {1}".format(invocation_json['Arguments'][0], invocation_json['ConnectionId']))

Attributes

Both in-process and isolated worker process C# libraries use the SignalRTrigger attribute to define the function. C# script instead uses a function.json configuration file.

The following table explains the properties of the SignalRTrigger attribute.

Attribute property Description
HubName This value must be set to the name of the SignalR hub for the function to be triggered.
Category This value must be set as the category of messages for the function to be triggered. The category can be one of the following values:
  • connections: Including connected and disconnected events
  • messages: Including all other events except those in connections category
Event This value must be set as the event of messages for the function to be triggered. For messages category, event is the target in invocation message that clients send. For connections category, only connected and disconnected is used.
ParameterNames (Optional) A list of names that binds to the parameters.
ConnectionStringSetting The name of the app setting that contains the SignalR Service connection string, which defaults to AzureSignalRConnectionString.

Annotations

There isn't currently a supported Java annotation for a SignalR trigger.

Configuration

The following table explains the binding configuration properties that you set in the function.json file.

function.json property Description
type Must be set to SignalRTrigger.
direction Must be set to in.
name Variable name used in function code for trigger invocation context object.
hubName This value must be set to the name of the SignalR hub for the function to be triggered.
category This value must be set as the category of messages for the function to be triggered. The category can be one of the following values:
  • connections: Including connected and disconnected events
  • messages: Including all other events except those in connections category
event This value must be set as the event of messages for the function to be triggered. For messages category, event is the target in invocation message that clients send. For connections category, only connected and disconnected is used.
parameterNames (Optional) A list of names that binds to the parameters.
connectionStringSetting The name of the app setting that contains the SignalR Service connection string, which defaults to AzureSignalRConnectionString.

See the Example section for complete examples.

Usage

Payloads

The trigger input type is declared as either InvocationContext or a custom type. If you choose InvocationContext you get full access to the request content. For a custom type, the runtime tries to parse the JSON request body to set the object properties.

InvocationContext

InvocationContext contains all the content in the message sent from a SignalR service, which includes the following properties:

Property Description
Arguments Available for messages category. Contains arguments in invocation message
Error Available for disconnected event. It can be Empty if the connection closed with no error, or it contains the error messages.
Hub The hub name which the message belongs to.
Category The category of the message.
Event The event of the message.
ConnectionId The connection ID of the client which sends the message.
UserId The user identity of the client which sends the message.
Headers The headers of the request.
Query The query of the request when clients connect to the service.
Claims The claims of the client.

Using ParameterNames

The property ParameterNames in SignalRTrigger lets you bind arguments of invocation messages to the parameters of functions. You can use the name you defined as part of binding expressions in other binding or as parameters in your code. That gives you a more convenient way to access arguments of InvocationContext.

Say you have a JavaScript SignalR client trying to invoke method broadcast in Azure Function with two arguments message1, message2.

await connection.invoke("broadcast", message1, message2);

After you set parameterNames, the names you defined correspond to the arguments sent on the client side.

[SignalRTrigger(parameterNames: new string[] {"arg1, arg2"})]

Then, the arg1 will contain the content of message1, and arg2 will contain the content of message2.

ParameterNames considerations

For the parameter binding, the order matters. If you're using ParameterNames, the order in ParameterNames matches the order of the arguments you invoke in the client. If you're using attribute [SignalRParameter] in C#, the order of arguments in Azure Function methods matches the order of arguments in clients.

ParameterNames and attribute [SignalRParameter] cannot be used at the same time, or you will get an exception.

SignalR Service integration

SignalR Service needs a URL to access Function App when you're using SignalR Service trigger binding. The URL should be configured in Upstream Settings on the SignalR Service side.

Upstream Portal

When using SignalR Service trigger, the URL can be simple and formatted as shown below:

<Function_App_URL>/runtime/webhooks/signalr?code=<API_KEY>

The Function_App_URL can be found on Function App's Overview page and The API_KEY is generated by Azure Function. You can get the API_KEY from signalr_extension in the App keys blade of Function App. API key

If you want to use more than one Function App together with one SignalR Service, upstream can also support complex routing rules. Find more details at Upstream settings.

Step-by-step sample

You can follow the sample in GitHub to deploy a chat room on Function App with SignalR Service trigger binding and upstream feature: Bidirectional chat room sample

Next steps