SignalR Service output binding for Azure Functions

Use the SignalR output binding to send one or more messages using Azure SignalR Service. You can broadcast a message to:

• All connected clients
• Connected clients in a specified group
• Connected clients authenticated to a specific user

The output binding also allows you to manage groups, such as adding a client or user to a group, removing a client or user from a group.

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

Example

Broadcast to all clients

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.

Important

Support will end for the in-process model on November 10, 2026. We highly recommend that you migrate your apps to the isolated worker model for full support.

Isolated worker model

The following example shows a function that sends a message using the output binding to all connected clients. The newMessage is the name of the method to be invoked on each client.

[Function(nameof(BroadcastToAll))]
[SignalROutput(HubName = "chat", ConnectionStringSetting = "SignalRConnection")]
public static SignalRMessageAction BroadcastToAll([HttpTrigger(AuthorizationLevel.Anonymous, "post")] HttpRequestData req)
{
    using var bodyReader = new StreamReader(req.Body);
    return new SignalRMessageAction("newMessage")
    {
        // broadcast to all the connected clients without specifying any connection, user or group.
        Arguments = new[] { bodyReader.ReadToEnd() },
    };
}

In-process model

The following example shows a function that sends a message using the output binding to all connected clients. The target is the name of the method to be invoked on each client. The Arguments property is an array of zero or more objects to be passed to the client method.

[FunctionName("SendMessage")]
public static Task SendMessage(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post")]object message,
    [SignalR(HubName = "hubName1")]IAsyncCollector<SignalRMessage> signalROutput)
{
    return signalROutput.AddAsync(
        new SignalRMessage
        {
            Target = "newMessage",
            Arguments = new [] { message }
        });
}

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Model v4

const { app, output } = require('@azure/functions');

const signalR = output.generic({
    type: 'signalR',
    name: 'signalR',
    hubName: 'hub',
    connectionStringSetting: 'AzureSignalRConnectionString',
});

// You can use any other trigger type instead.
app.http('broadcast', {
    methods: ['GET'],
    authLevel: 'anonymous',
    extraOutputs: [signalR],
    handler: (request, context) => {
        context.extraOutputs.set(signalR, {
            "target": "newMessage",
            "arguments": [request.body]
        });
    }
});

Model v3

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Here's the JavaScript code:

module.exports = async function (context, req) {
    context.bindings.signalROutput = [{
        "target": "newMessage",
        "arguments": [ req.body ]
    }];
};

Complete PowerShell examples are pending.

Here's the Python code:

def main(req: func.HttpRequest, signalROutput: func.Out[str]) -> func.HttpResponse:
    message = req.get_json()
    signalROutput.set(json.dumps({
        'target': 'newMessage',
        'arguments': [ message ]
    }))

@FunctionName("sendMessage")
@SignalROutput(name = "$return", HubName = "hubName1")
public SignalRMessage sendMessage(
        @HttpTrigger(
            name = "req",
            methods = { HttpMethod.POST },
            authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Object> req) {

    SignalRMessage message = new SignalRMessage();
    message.target = "newMessage";
    message.arguments.add(req.getBody());
    return message;
}

Send to a user

You can send a message only to connections that have been authenticated to a user by setting the user ID in the SignalR message.

Isolated worker model

[Function(nameof(SendToUser))]
[SignalROutput(HubName = "chat", ConnectionStringSetting = "SignalRConnection")]
public static SignalRMessageAction SendToUser([HttpTrigger(AuthorizationLevel.Anonymous, "post")] HttpRequestData req)
{
    using var bodyReader = new StreamReader(req.Body);
    return new SignalRMessageAction("newMessage")
    {
        Arguments = new[] { bodyReader.ReadToEnd() },
        UserId = "userToSend",
    };
}

In-process model

[FunctionName("SendMessage")]
public static Task SendMessage(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post")]object message,
    [SignalR(HubName = "hubName1")]IAsyncCollector<SignalRMessage> signalROutput)
{
    return signalROutput.AddAsync(
        new SignalRMessage
        {
            // the message will only be sent to this user ID
            UserId = "userId1",
            Target = "newMessage",
            Arguments = new [] { message }
        });
}

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Complete PowerShell examples are pending.

Here's the Python code:

def main(req: func.HttpRequest, signalROutput: func.Out[str]) -> func.HttpResponse:
    message = req.get_json()
    signalROutput.set(json.dumps({
        #message will only be sent to this user ID
        'userId': 'userId1',
        'target': 'newMessage',
        'arguments': [ message ]
    }))

@FunctionName("sendMessage")
@SignalROutput(name = "$return", HubName = "hubName1")
public SignalRMessage sendMessage(
        @HttpTrigger(
            name = "req",
            methods = { HttpMethod.POST },
            authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Object> req) {

    SignalRMessage message = new SignalRMessage();
    message.userId = "userId1";
    message.target = "newMessage";
    message.arguments.add(req.getBody());
    return message;
}

Model v4

const { app, output } = require('@azure/functions');

const signalR = output.generic({
    type: 'signalR',
    name: 'signalR',
    hubName: 'hub',
    connectionStringSetting: 'AzureSignalRConnectionString',
});

app.http('sendToUser', {
    methods: ['GET'],
    authLevel: 'anonymous',
    extraOutputs: [signalR],
    handler: (request, context) => {
        context.extraOutputs.set(signalR, {
            "target": "newMessage",
            "arguments": [request.body],
            "userId": "userId1",
        });
    }
});

Model v3

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Here's the JavaScript code:

module.exports = async function (context, req) {
    context.bindings.signalROutput = [{
        "target": "newMessage",
        "arguments": [ req.body ],
        "userId": "userId1",
    }];
};

Send to a group

You can send a message only to connections that have been added to a group by setting the group name in the SignalR message.

Isolated worker model

[Function(nameof(SendToGroup))]
[SignalROutput(HubName = "chat", ConnectionStringSetting = "SignalRConnection")]
public static SignalRMessageAction SendToGroup([HttpTrigger(AuthorizationLevel.Anonymous, "post")] HttpRequestData req)
{
    using var bodyReader = new StreamReader(req.Body);
    return new SignalRMessageAction("newMessage")
    {
        Arguments = new[] { bodyReader.ReadToEnd() },
        GroupName = "groupToSend"
    };
}

In-process model

[FunctionName("SendMessage")]
public static Task SendMessage(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post")]object message,
    [SignalR(HubName = "hubName1")]IAsyncCollector<SignalRMessage> signalROutput)
{
    return signalROutput.AddAsync(
        new SignalRMessage
        {
            // the message will be sent to the group with this name
            GroupName = "myGroup",
            Target = "newMessage",
            Arguments = new [] { message }
        });
}

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Model v4

const { app, output } = require('@azure/functions');

const signalR = output.generic({
    type: 'signalR',
    name: 'signalR',
    hubName: 'hub',
    connectionStringSetting: 'AzureSignalRConnectionString',
});

app.http('sendToGroup', {
    methods: ['GET'],
    authLevel: 'anonymous',
    extraOutputs: [signalR],
    handler: (request, context) => {
        context.extraOutputs.set(signalR, {
            "target": "newMessage",
            "arguments": [request.body],
            "groupName": "myGroup",
        });
    }
});

Model v3

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Here's the JavaScript code:

module.exports = async function (context, req) {
    context.bindings.signalROutput = [{
        "target": "newMessage",
        "arguments": [ req.body ],
        "groupName": "myGroup",
    }];
};

Complete PowerShell examples are pending.

Here's the Python code:

def main(req: func.HttpRequest, signalROutput: func.Out[str]) -> func.HttpResponse:
    message = req.get_json()
    signalROutput.set(json.dumps({
        #message will only be sent to this group
        'groupName': 'myGroup',
        'target': 'newMessage',
        'arguments': [ message ]
    }))

@FunctionName("sendMessage")
@SignalROutput(name = "$return", HubName = "hubName1")
public SignalRMessage sendMessage(
        @HttpTrigger(
            name = "req",
            methods = { HttpMethod.POST },
            authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Object> req) {

    SignalRMessage message = new SignalRMessage();
    message.groupName = "myGroup";
    message.target = "newMessage";
    message.arguments.add(req.getBody());
    return message;
}

Group management

SignalR Service allows users or connections to be added to groups. Messages can then be sent to a group. You can use the SignalR output binding to manage groups.

Isolated worker model

Specify SignalRGroupActionType to add or remove a member. The following example removes a user from a group.

[Function(nameof(RemoveFromGroup))]
[SignalROutput(HubName = "chat", ConnectionStringSetting = "SignalRConnection")]
public static SignalRGroupAction RemoveFromGroup([HttpTrigger(AuthorizationLevel.Anonymous, "post")] HttpRequestData req)
{
    return new SignalRGroupAction(SignalRGroupActionType.Remove)
    {
        GroupName = "group1",
        UserId = "user1"
    };
}

In-process model

Specify GroupAction to add or remove a member. The following example adds a user to a group.

[FunctionName("addToGroup")]
public static Task AddToGroup(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post")]HttpRequest req,
    ClaimsPrincipal claimsPrincipal,
    [SignalR(HubName = "hubName1")]
        IAsyncCollector<SignalRGroupAction> signalRGroupActions)
{
    var userIdClaim = claimsPrincipal.FindFirst(ClaimTypes.NameIdentifier);
    return signalRGroupActions.AddAsync(
        new SignalRGroupAction
        {
            UserId = userIdClaim.Value,
            GroupName = "myGroup",
            Action = GroupAction.Add
        });
}

Note

In order to get the ClaimsPrincipal correctly bound, you must have configured the authentication settings in Azure Functions.

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Model v4

const { app, output } = require('@azure/functions');

const signalR = output.generic({
    type: 'signalR',
    name: 'signalR',
    hubName: 'hub',
    connectionStringSetting: 'AzureSignalRConnectionString',
});

// The following function adds a user to a group
app.http('addUserToGroup', {
    methods: ['POST'],
    authLevel: 'anonymous',
    extraOutputs: [signalR],
    handler: (request, context) => {
        context.extraOutputs.set(signalR, {
            "userId": req.query.userId,
            "groupName": "myGroup",
            "action": "add"
        });
    }
});

// The following function removes a user from a group
app.http('removeUserFromGroup', {
    methods: ['POST'],
    authLevel: 'anonymous',
    extraOutputs: [signalR],
    handler: (request, context) => {
        context.extraOutputs.set(signalR, {
            "userId": req.query.userId,
            "groupName": "myGroup",
            "action": "remove"
        });
    }
});

Model v3

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

Example function.json:

{
  "type": "signalR",
  "name": "signalROutput",
  "hubName": "hubName1",
  "connectionStringSetting": "<name of setting containing SignalR Service connection string>",
  "direction": "out"
}

Here's the JavaScript code:

The following example adds a user to a group.

module.exports = async function (context, req) {
  context.bindings.signalROutput = [{
    "userId": req.query.userId,
    "groupName": "myGroup",
    "action": "add"
  }];
};

The following example removes a user from a group.

module.exports = async function (context, req) {
  context.bindings.signalROutput = [{
    "userId": req.query.userId,
    "groupName": "myGroup",
    "action": "remove"
  }];
};

Complete PowerShell examples are pending.

The following example adds a user to a group.

def main(req: func.HttpRequest, signalROutput: func.Out[str]) -> func.HttpResponse:
    signalROutput.set(json.dumps({
        'userId': 'userId1',
        'groupName': 'myGroup',
        'action': 'add'
    }))

The following example removes a user from a group.

def main(req: func.HttpRequest, signalROutput: func.Out[str]) -> func.HttpResponse:
    signalROutput.set(json.dumps({
        'userId': 'userId1',
        'groupName': 'myGroup',
        'action': 'remove'
    }))

The following example adds a user to a group.

@FunctionName("addToGroup")
@SignalROutput(name = "$return", HubName = "hubName1")
public SignalRGroupAction addToGroup(
        @HttpTrigger(
            name = "req",
            methods = { HttpMethod.POST },
            authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Object> req,
        @BindingName("userId") String userId) {

    SignalRGroupAction groupAction = new SignalRGroupAction();
    groupAction.action = "add";
    groupAction.userId = userId;
    groupAction.groupName = "myGroup";
    return action;
}

The following example removes a user from a group.

@FunctionName("removeFromGroup")
@SignalROutput(name = "$return", HubName = "hubName1")
public SignalRGroupAction removeFromGroup(
        @HttpTrigger(
            name = "req",
            methods = { HttpMethod.POST },
            authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Object> req,
        @BindingName("userId") String userId) {

    SignalRGroupAction groupAction = new SignalRGroupAction();
    groupAction.action = "remove";
    groupAction.userId = userId;
    groupAction.groupName = "myGroup";
    return action;
}

Attributes

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

Isolated worker model

The following table explains the properties of the SignalROutput attribute.

Attribute property	Description
HubName	This value must be set to the name of the SignalR hub for which the connection information is generated.
ConnectionStringSetting	The name of the app setting or settings collection that contains the SignalR Service connection string, which defaults to AzureSignalRConnectionString.

In-process model

The following table explains the properties of the SignalR output attribute.

Attribute property	Description
HubName	This value must be set to the name of the SignalR hub for which the connection information is generated.
ConnectionStringSetting	The name of the app setting or settings collection that contains the SignalR Service connection string, which defaults to AzureSignalRConnectionString.

Annotations

The following table explains the supported settings for the SignalROutput annotation.

Setting	Description
name	Variable name used in function code for connection info object.
hubName	This value must be set to the name of the SignalR hub for which the connection information is generated.
connectionStringSetting	The name of the app setting or settings collection that contains the SignalR Service connection string, which defaults to AzureSignalRConnectionString.

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 signalR.
direction	Must be set to out.
name	Variable name used in function code for connection info object.
hubName	This value must be set to the name of the SignalR hub for which the connection information is generated.
connectionStringSetting	The name of the app setting or settings collection that contains the SignalR Service connection string, which defaults to AzureSignalRConnectionString.

When you're developing locally, add your application settings in the local.settings.json file in the Values collection.

Usage

For optimal security, your function app should use managed idenities when connecting to the Azure SignalR service instead of using a connection string, which contains a shared secret key. For more information, see Authorize requests to Azure SignalR Service resources with Microsoft Entra managed identities.

Next steps

• Handle messages from SignalR Service (Trigger binding)
• Return the service endpoint URL and access token (Input binding)