Azure Blob storage trigger for Azure Functions

The following example shows a C# function that writes a log when a blob is added or updated in the samples-workitems container.

[FunctionName("BlobTriggerCSharp")]        
public static void Run([BlobTrigger("samples-workitems/{name}")] Stream myBlob, string name, ILogger log)
{
    log.LogInformation($"C# Blob trigger function Processed blob\n Name:{name} \n Size: {myBlob.Length} Bytes");
}

The string {name} in the blob trigger path samples-workitems/{name} creates a binding expression that you can use in function code to access the file name of the triggering blob. For more information, see Blob name patterns later in this article.

For more information about the BlobTrigger attribute, see attributes and annotations.

The following example shows a blob trigger binding in a function.json file and code that uses the binding. The function writes a log when a blob is added or updated in the samples-workitems container.

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

{
    "disabled": false,
    "bindings": [
        {
            "name": "myBlob",
            "type": "blobTrigger",
            "direction": "in",
            "path": "samples-workitems/{name}",
            "connection":"MyStorageAccountAppSetting"
        }
    ]
}

The string {name} in the blob trigger path samples-workitems/{name} creates a binding expression that you can use in function code to access the file name of the triggering blob. For more information, see Blob name patterns later in this article.

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

Here's C# script code that binds to a Stream:

public static void Run(Stream myBlob, string name, ILogger log)
{
   log.LogInformation($"C# Blob trigger function Processed blob\n Name:{name} \n Size: {myBlob.Length} Bytes");
}

Here's C# script code that binds to a CloudBlockBlob:

#r "Microsoft.WindowsAzure.Storage"

using Microsoft.WindowsAzure.Storage.Blob;

public static void Run(CloudBlockBlob myBlob, string name, ILogger log)
{
    log.LogInformation($"C# Blob trigger function Processed blob\n Name:{name}\nURI:{myBlob.StorageUri}");
}

This function writes a log when a blob is added or updated in the myblob container.

@FunctionName("blobprocessor")
public void run(
  @BlobTrigger(name = "file",
               dataType = "binary",
               path = "myblob/{name}",
               connection = "MyStorageAccountAppSetting") byte[] content,
  @BindingName("name") String filename,
  final ExecutionContext context
) {
  context.getLogger().info("Name: " + filename + " Size: " + content.length + " bytes");
}

The following example shows a blob trigger binding in a function.json file and JavaScript code that uses the binding. The function writes a log when a blob is added or updated in the samples-workitems container.

Here's the function.json file:

{
    "disabled": false,
    "bindings": [
        {
            "name": "myBlob",
            "type": "blobTrigger",
            "direction": "in",
            "path": "samples-workitems/{name}",
            "connection":"MyStorageAccountAppSetting"
        }
    ]
}

The string {name} in the blob trigger path samples-workitems/{name} creates a binding expression that you can use in function code to access the file name of the triggering blob. For more information, see Blob name patterns later in this article.

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

Here's the JavaScript code:

module.exports = function(context) {
    context.log('Node.js Blob trigger function processed', context.bindings.myBlob);
    context.done();
};

The following example demonstrates how to create a function that runs when a file is added to source blob storage container.

The function configuration file (function.json) includes a binding with the type of blobTrigger and direction set to in.

{
  "bindings": [
    {
      "name": "InputBlob",
      "type": "blobTrigger",
      "direction": "in",
      "path": "source/{name}",
      "connection": "MyStorageAccountConnectionString"
    }
  ]
}

Here's the associated code for the run.ps1 file.

param([byte[]] $InputBlob, $TriggerMetadata)

Write-Host "PowerShell Blob trigger: Name: $($TriggerMetadata.Name) Size: $($InputBlob.Length) bytes"

The following example shows a blob trigger binding in a function.json file and Python code that uses the binding. The function writes a log when a blob is added or updated in the samples-workitems container.

Here's the function.json file:

{
    "scriptFile": "__init__.py",
    "disabled": false,
    "bindings": [
        {
            "name": "myblob",
            "type": "blobTrigger",
            "direction": "in",
            "path": "samples-workitems/{name}",
            "connection":"MyStorageAccountAppSetting"
        }
    ]
}

The string {name} in the blob trigger path samples-workitems/{name} creates a binding expression that you can use in function code to access the file name of the triggering blob. For more information, see Blob name patterns later in this article.

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

Here's the Python code:

import logging
import azure.functions as func


def main(myblob: func.InputStream):
    logging.info('Python Blob trigger function processed %s', myblob.name)

In C# class libraries, use the following attributes to configure a blob trigger:

• BlobTriggerAttribute

  The attribute's constructor takes a path string that indicates the container to watch and optionally a blob name pattern. Here's an example:

  [FunctionName("ResizeImage")]
  public static void Run(
      [BlobTrigger("sample-images/{name}")] Stream image,
      [Blob("sample-images-md/{name}", FileAccess.Write)] Stream imageSmall)
  {
      ....
  }
  

  You can set the Connection property to specify the storage account to use, as shown in the following example:

  [FunctionName("ResizeImage")]
  public static void Run(
      [BlobTrigger("sample-images/{name}", Connection = "StorageConnectionAppSetting")] Stream image,
      [Blob("sample-images-md/{name}", FileAccess.Write)] Stream imageSmall)
  {
      ....
  }
  

  For a complete example, see Trigger example.

• StorageAccountAttribute

  Provides another way to specify the storage account to use. The constructor takes the name of an app setting that contains a storage connection string. The attribute can be applied at the parameter, method, or class level. The following example shows class level and method level:

  [StorageAccount("ClassLevelStorageAppSetting")]
  public static class AzureFunctions
  {
      [FunctionName("BlobTrigger")]
      [StorageAccount("FunctionLevelStorageAppSetting")]
      public static void Run( //...
  {
      ....
  }
  

The storage account to use is determined in the following order:

• The BlobTrigger attribute's Connection property.
• The StorageAccount attribute applied to the same parameter as the BlobTrigger attribute.
• The StorageAccount attribute applied to the function.
• The StorageAccount attribute applied to the class.
• The default storage account for the function app ("AzureWebJobsStorage" app setting).

Attributes are not supported by C# Script.

The @BlobTrigger attribute is used to give you access to the blob that triggered the function. Refer to the trigger example for details.

Attributes are not supported by JavaScript.

Attributes are not supported by PowerShell.

Attributes are not supported by Python.

Default

You can use the following parameter types for the triggering blob:

• Stream
• TextReader
• string
• Byte[]
• ICloudBlob¹
• CloudBlockBlob¹
• CloudPageBlob¹
• CloudAppendBlob¹

¹ Requires "inout" binding direction in function.json or FileAccess.ReadWrite in a C# class library.

If you try to bind to one of the Storage SDK types and get an error message, make sure that you have a reference to the correct Storage SDK version.

Binding to string, or Byte[] is only recommended if the blob size is small, as the entire blob contents are loaded into memory. Generally, it is preferable to use a Stream or CloudBlockBlob type. For more information, see Concurrency and memory usage later in this article.

Additional types

Apps using the 5.0.0 or higher version of the Storage extension may also use types from the Azure SDK for .NET. This version drops support for the legacy ICloudBlob, CloudBlockBlob, CloudPageBlob, and CloudAppendBlob types in favor of the following types:

• BlobClient¹
• BlockBlobClient¹
• PageBlobClient¹
• AppendBlobClient¹
• BlobBaseClient¹

¹ Requires "inout" binding direction in function.json or FileAccess.ReadWrite in a C# class library.

For examples using these types, see the GitHub repository for the extension.

Default

You can use the following parameter types for the triggering blob:

• Stream
• TextReader
• string
• Byte[]
• ICloudBlob¹
• CloudBlockBlob¹
• CloudPageBlob¹
• CloudAppendBlob¹

¹ Requires "inout" binding direction in function.json or FileAccess.ReadWrite in a C# class library.

If you try to bind to one of the Storage SDK types and get an error message, make sure that you have a reference to the correct Storage SDK version.

Binding to string, or Byte[] is only recommended if the blob size is small, as the entire blob contents are loaded into memory. Generally, it is preferable to use a Stream or CloudBlockBlob type. For more information, see Concurrency and memory usage later in this article.

Additional types

Apps using the 5.0.0 or higher version of the Storage extension may also use types from the Azure SDK for .NET. This version drops support for the legacy ICloudBlob, CloudBlockBlob, CloudPageBlob, and CloudAppendBlob types in favor of the following types:

• BlobClient¹
• BlockBlobClient¹
• PageBlobClient¹
• AppendBlobClient¹
• BlobBaseClient¹

¹ Requires "inout" binding direction in function.json or FileAccess.ReadWrite in a C# class library.

For examples using these types, see the GitHub repository for the extension.

The @BlobTrigger attribute is used to give you access to the blob that triggered the function. Refer to the trigger example for details.

Access blob data using context.bindings.<NAME> where <NAME> matches the value defined in function.json.

Access the blob data via a parameter that matches the name designated by binding's name parameter in the function.json file.

Access blob data via the parameter typed as InputStream. Refer to the trigger example for details.

The blob trigger provides several metadata properties. These properties can be used as part of binding expressions in other bindings or as parameters in your code. These values have the same semantics as the Cloud​Blob type.

For example, the following C# script and JavaScript examples log the path to the triggering blob, including the container:

public static void Run(string myBlob, string blobTrigger, ILogger log)
{
    log.LogInformation($"Full blob path: {blobTrigger}");
} 

The blob trigger provides several metadata properties. These properties can be used as part of binding expressions in other bindings or as parameters in your code. These values have the same semantics as the Cloud​Blob type.

For example, the following C# script and JavaScript examples log the path to the triggering blob, including the container:

public static void Run(string myBlob, string blobTrigger, ILogger log)
{
    log.LogInformation($"Full blob path: {blobTrigger}");
} 

Metadata is not available in Java.

module.exports = function (context, myBlob) {
    context.log("Full blob path:", context.bindingData.blobTrigger);
    context.done();
};

Metadata is available through the $TriggerMetadata parameter.

Metadata is not available in Python.