Dapr Binding output binding for Azure Functions

The Dapr output binding allows you to send a value to a Dapr output binding during a function execution.

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

Example

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

Execution model	Description
Isolated worker model	Your function code runs in a separate .NET worker process. Use with supported versions of .NET and .NET Framework. To learn more, see Develop .NET isolated worker process functions.
In-process model	Your function code runs in the same process as the Functions host process. Supports only Long Term Support (LTS) versions of .NET. To learn more, see Develop .NET class library functions.

In-process

The following example demonstrates using a Dapr service invocation trigger and a Dapr output binding to read and process a binding request.

[FunctionName("SendMessageToKafka")]
public static async Task Run(
    [DaprServiceInvocationTrigger] JObject payload,
    [DaprBinding(BindingName = "%KafkaBindingName%", Operation = "create")] IAsyncCollector<object> messages,
    ILogger log)
{
    log.LogInformation("C#  function processed a SendMessageToKafka request.");
    await messages.AddAsync(payload);
}

Isolated process

More samples for the Dapr output invoke binding are available in the GitHub repository.

[Function("SendMessageToKafka")]
[DaprBindingOutput(BindingName = "%KafkaBindingName%", Operation = "create")]
public static JsonElement Run(
    [DaprServiceInvocationTrigger] JsonElement payload, FunctionContext functionContext)
{
    var log = functionContext.GetLogger("SendMessageToKafka");
    log.LogInformation("C#  function processed a SendMessageToKafka request.");

    return payload;
}

The following example creates a "SendMessageToKafka" function using the DaprBindingOutput binding with the DaprServiceInvocationTrigger:

@FunctionName("SendMessageToKafka")
public String run(
        @DaprServiceInvocationTrigger(
            methodName = "SendMessageToKafka") 
        String payload,
        @DaprBindingOutput(
            bindingName = "%KafkaBindingName%", 
            operation = "create")
        OutputBinding<String> product,
        final ExecutionContext context) {
    context.getLogger().info("Java  function processed a SendMessageToKafka request.");
    product.setValue(payload);

    return payload;
}

Node.js v4

In the following example, the Dapr output binding is paired with the Dapr invoke output trigger, which is registered by the app object:

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

app.generic('SendMessageToKafka', {
    trigger: trigger.generic({
        type: 'daprServiceInvocationTrigger',
        name: "payload"
    }),
    return: daprBindingOutput,
    handler: async (request, context) => {
        context.log("Node function processed a SendMessageToKafka request from the Dapr Runtime.");
        context.log(context.triggerMetadata.payload)

        return { "data": context.triggerMetadata.payload };
    }
});

Node.js v3

The following examples show Dapr triggers in a function.json file and JavaScript code that uses those bindings.

Here's the function.json file for daprBinding:

{
  "bindings": 
    {
      "type": "daprBinding",
      "direction": "out",
      "bindingName": "%KafkaBindingName%",
      "operation": "create",
      "name": "messages"
    }
}

For more information about function.json file properties, see the Configuration section.

Here's the JavaScript code:

module.exports = async function (context) {
    context.log("Node HTTP trigger function processed a request.");
    context.bindings.messages = { "data": context.bindings.args };
};

The following examples show Dapr triggers in a function.json file and PowerShell code that uses those bindings.

Here's the function.json file for daprBinding:

{
  "bindings": 
    {
      "type": "daprBinding",
      "direction": "out",
      "bindingName": "%KafkaBindingName%",
      "operation": "create",
      "name": "messages"
    }
}

For more information about function.json file properties, see the Configuration section.

In code:

using namespace System.Net

# Input bindings are passed in via param block.
param($req, $TriggerMetadata)

Write-Host "Powershell SendMessageToKafka processed a request."

$invoke_output_binding_req_body = @{
    "data" = $req
}

# Associate values to output bindings by calling 'Push-OutputBinding'.
Push-OutputBinding -Name messages -Value $invoke_output_binding_req_body

Python v2

The following example shows a Dapr Binding output binding, which uses the v2 Python programming model. To use @dapp.dapr_binding_output in your Python function app code:

import logging
import json
import azure.functions as func

app = func.FunctionApp()

@app.function_name(name="SendMessageToKafka")
@app.dapr_service_invocation_trigger(arg_name="payload", method_name="SendMessageToKafka")
@app.dapr_binding_output(arg_name="messages", binding_name="%KafkaBindingName%", operation="create")
def main(payload: str, messages: func.Out[bytes]) -> None:
    logging.info('Python processed a SendMessageToKafka request from the Dapr Runtime.')
    messages.set(json.dumps({"data": payload}).encode('utf-8'))

Python v1

The following example shows a Dapr Binding output binding, which uses the v1 Python programming model.

Here's the function.json file for daprBinding:

{
  "scriptFile": "__init__.py",
  "bindings": 
    {
      "type": "daprBinding",
      "direction": "out",
      "bindingName": "%KafkaBindingName%",
      "operation": "create",
      "name": "messages"
    }
}

For more information about function.json file properties, see the Configuration section.

Here's the Python code:

import logging
import json
import azure.functions as func

def main(args, messages: func.Out[bytes]) -> None:
    logging.info('Python processed a SendMessageToKafka request from the Dapr Runtime.')
    messages.set(json.dumps({"data": args}))

Attributes

In-process

In the in-process model, use the DaprBinding to define a Dapr binding output binding, which supports these parameters:

Parameter	Description	Can be sent via Attribute	Can be sent via RequestBody
BindingName	The name of the Dapr binding.	✔️	✔️
Operation	The configured binding operation.	✔️	✔️
Metadata	The metadata namespace.	❌	✔️
Data	Required. The data for the binding operation.	❌	✔️

Isolated process

In the isolated worker model, use the DaprBindingOutput to define a Dapr binding output binding, which supports these parameters:

Parameter	Description	Can be sent via Attribute	Can be sent via RequestBody
BindingName	The name of the Dapr binding.	✔️	✔️
Operation	The configured binding operation.	✔️	✔️
Metadata	The metadata namespace.	❌	✔️
Data	Required. The data for the binding operation.	❌	✔️

Annotations

The DaprBindingOutput annotation allows you to create a function that sends an output binding.

Element	Description	Can be sent via Attribute	Can be sent via RequestBody
bindingName	The name of the Dapr binding.	✔️	✔️
output	The configured binding operation.	✔️	✔️
metadata	The metadata namespace.	❌	✔️
data	Required. The data for the binding operation.	❌	✔️

Configuration

Node.js v4

The following table explains the binding configuration properties that you set in the code.

Property	Description	Can be sent via Attribute	Can be sent via RequestBody
bindingName	The name of the binding.	✔️	✔️
operation	The binding operation.	✔️	✔️
metadata	The metadata namespace.	❌	✔️
data	Required. The data for the binding operation.	❌	✔️

Node.js v3

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

function.json property	Description	Can be sent via Attribute	Can be sent via RequestBody
bindingName	The name of the binding.	✔️	✔️
operation	The binding operation.	✔️	✔️
metadata	The metadata namespace.	❌	✔️
data	Required. The data for the binding operation.	❌	✔️

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

function.json property	Description	Can be sent via Attribute	Can be sent via RequestBody
bindingName	The name of the binding.	✔️	✔️
operation	The binding operation.	✔️	✔️
metadata	The metadata namespace.	❌	✔️
data	Required. The data for the binding operation.	❌	✔️

Python v2

The following table explains the binding configuration properties for @dapp.dapr_binding_output that you set in your Python code.

Property	Description	Can be sent via Attribute	Can be sent via RequestBody
binding_name	The name of the binding event.	✔️	✔️
operation	The binding operation name/identifier.	✔️	✔️
metadata	The metadata namespace.	❌	✔️
data	Required. The data for the binding operation.	❌	✔️

Python v1

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

function.json property	Description	Can be sent via Attribute	Can be sent via RequestBody
bindingName	The name of the binding.	✔️	✔️
operation	The binding operation.	✔️	✔️
metadata	The metadata namespace.	❌	✔️
data	Required. The data for the binding operation.	❌	✔️

If properties are defined in both Attributes and RequestBody, priority is given to data provided in RequestBody.

See the Example section for complete examples.

Usage

To use the Dapr output binding, start by setting up a Dapr output binding component. You can learn more about which component to use and how to set it up in the official Dapr documentation.

• Dapr output binding component specs
• How to: Use output bindings to interface with external resources

Python v2

To use the daprBinding in Python v2, set up your project with the correct dependencies.

1. Create and activate a virtual environment.

2. In your requirements.text file, add the following line:

   azure-functions==1.18.0b3
   

3. In the terminal, install the Python library.

   pip install -r .\requirements.txt
   

4. Modify your local.setting.json file with the following configuration:

   "PYTHON_ISOLATE_WORKER_DEPENDENCIES":1
   

Python v1

The Python v1 model requires no additional changes, aside from setting up the output binding component.

Next steps

Learn more about Dapr service invocation.