Blob Input Bindings

Blob input bindings allow your Azure Function to read data from Azure Blob Storage as input. This can be used to access configuration files, data payloads, or any other data stored in blobs.

How it Works

When you define a blob input binding in your function's configuration (e.g., function.json or using attributes in C#), Azure Functions runtime handles the retrieval of the blob content. The content is then provided to your function as a parameter.

Configuration

function.json Example

{
  "bindings": [
    {
      "name": "myBlob",
      "type": "blob",
      "direction": "in",
      "path": "samples-data/my-file.json",
      "connection": "AzureWebJobsStorage"
    }
  ],
  "disabled": false
}
                

Attribute-based (C#) Example

using Microsoft.Azure.WebJobs;

public static class BlobTriggerFunction
{
    public static void Run(
        [BlobTrigger("samples-data/my-file.json", Connection = "AzureWebJobsStorage")] Stream myBlob,
        string name)
    {
        // Function logic here
    }
}
                

Key Properties:

• name: The name of the parameter in your function code that will receive the blob content.
• type: Must be "blob".
• direction: Must be "in" for input bindings.
• path: The path to the blob within your storage account. This can include wildcards.
• connection: The name of the app setting that contains your Azure Blob Storage connection string.

Supported Data Types

The blob content can be bound to various data types in your function, depending on your needs:

• byte[]: The entire blob content as a byte array.
• string: The entire blob content as a string.
• Stream: A readable stream of the blob content.
• CloudBlockBlob (or equivalent SDK type): Provides access to the Blob Storage SDK object for more advanced operations.
• Custom POCOs (Plain Old CLR Objects) or JSON objects: If the blob content is JSON, it can be automatically deserialized.

Working with Different Paths

The path property is powerful and supports wildcards for flexible blob selection:

• samples-data/{name}: Binds to a blob named my-file.json in the samples-data container. The value my-file.json is passed to a parameter named name.
• samples-data/{*filePath}: Binds to any blob within the samples-data container. The entire blob path (e.g., my-folder/my-file.txt) is passed to a parameter named filePath.

Example: Reading JSON Data

This example demonstrates reading a JSON file and deserializing it into a C# object.

config.json (in Blob Storage)

{
  "setting1": "value1",
  "setting2": 123
}
                

C# Function

using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using System.IO;

public class Settings
{
    public string setting1 { get; set; }
    public int setting2 { get; set; }
}

public static class ReadSettingsFunction
{
    public static void Run(
        [Blob("config/config.json", Connection = "AzureWebJobsStorage")] Settings appSettings,
        ILogger log)
    {
        if (appSettings != null)
        {
            log.LogInformation($"Setting1: {appSettings.setting1}");
            log.LogInformation($"Setting2: {appSettings.setting2}");
        }
        else
        {
            log.LogError("Failed to load app settings.");
        }
    }
}
                

Error Handling

If the specified blob does not exist, the function might not be triggered or may result in an error, depending on the binding configuration and language runtime. It's good practice to check if the input parameter is null or handle potential exceptions.