File Bindings
File bindings in Azure Functions enable your functions to interact with files stored in various file systems, such as Azure Blob Storage or local file systems. This guide details how to configure and use file bindings effectively.
Overview
File bindings can be used for both input and output operations. You can configure a function to read files from a specified location or write files to a target location. This is particularly useful for processing data files, generating reports, or moving files between different storage locations.
Input File Binding
An input file binding allows your function to read the content of a file. The file path is typically specified using a configuration property.
Example: Reading a File from Blob Storage (C#)
This example shows how to bind to a blob file as an input in a C# function.
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
public static class ProcessFile
{
[FunctionName("ReadBlobFile")]
public static void Run(
[BlobTrigger("input-container/{name}.txt", Connection = "AzureWebJobsStorage")] string fileContent,
string name,
ILogger log)
{
log.LogInformation($"C# Blob trigger function Processed blob\n Name:{name} \n Content:{fileContent}");
// Process the fileContent here
}
}
Configuration
In your function.json (for non-C# languages) or using attributes (for C#), you define the binding:
type: Set toblobfor Azure Blob Storage.path: Specifies the container and blob name. Use tokens like{name}to capture parts of the blob name.connection: The name of an app setting that contains the connection string for the storage account.direction: Set toinfor input bindings.
Output File Binding
An output file binding allows your function to write data to a file. You can specify the target path and filename.
Example: Writing to a Blob File (C#)
This example shows how to write output to a blob file.
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
public static class GenerateReport
{
[FunctionName("CreateReportFile")]
[return: Blob("output-container/{name}.txt", Connection = "AzureWebJobsStorage")]
public static string Run(
[TimerTrigger("0 0 * * * *")] TimerInfo myTimer,
ILogger log)
{
log.LogInformation("Timer trigger function executed at: " + System.DateTime.Now);
string reportContent = $"Report generated at: {System.DateTime.Now}";
return reportContent;
}
}
Configuration
Similar to input bindings, but with direction set to out.
type: Typicallyblob.path: The target container and blob name.connection: The storage connection string app setting name.direction: Set tooutfor output bindings.
Common Scenarios
- Data Processing: Reading CSV or JSON files from blob storage, processing them, and writing results to another blob.
- Log Aggregation: Functions triggered by new log files can parse and store logs in a centralized location.
- File Transformations: Converting file formats or enriching file content.
Considerations
- File Size Limits: Be aware of any size limits imposed by the underlying storage service.
- Concurrency: Design your functions to handle concurrent file operations if necessary.
- Error Handling: Implement robust error handling for file read/write operations.
- Connection Strings: Always store connection strings securely in app settings.