| title | description | author | ms.topic | ms.date | ms.author | ms.custom |
|---|---|---|---|---|---|---|
Azure Blob storage output binding for Azure Functions |
Learn how to provide Azure Blob storage data to an Azure Function. |
craigshoemaker |
reference |
02/13/2020 |
cshoe |
tracking-python |
The output binding allows you to modify and delete blob storage data in an Azure Function.
For information on setup and configuration details, see the overview.
The following example is a C# function that uses a blob trigger and two output blob bindings. The function is triggered by the creation of an image blob in the sample-images container. It creates small and medium size copies of the image blob.
using System.Collections.Generic;
using System.IO;
using Microsoft.Azure.WebJobs;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
public class ResizeImages
{
[FunctionName("ResizeImage")]
public static void Run([BlobTrigger("sample-images/{name}")] Stream image,
[Blob("sample-images-sm/{name}", FileAccess.Write)] Stream imageSmall,
[Blob("sample-images-md/{name}", FileAccess.Write)] Stream imageMedium)
{
IImageFormat format;
using (Image<Rgba32> input = Image.Load<Rgba32>(image, out format))
{
ResizeImage(input, imageSmall, ImageSize.Small, format);
}
image.Position = 0;
using (Image<Rgba32> input = Image.Load<Rgba32>(image, out format))
{
ResizeImage(input, imageMedium, ImageSize.Medium, format);
}
}
public static void ResizeImage(Image<Rgba32> input, Stream output, ImageSize size, IImageFormat format)
{
var dimensions = imageDimensionsTable[size];
input.Mutate(x => x.Resize(dimensions.Item1, dimensions.Item2));
input.Save(output, format);
}
public enum ImageSize { ExtraSmall, Small, Medium }
private static Dictionary<ImageSize, (int, int)> imageDimensionsTable = new Dictionary<ImageSize, (int, int)>() {
{ ImageSize.ExtraSmall, (320, 200) },
{ ImageSize.Small, (640, 400) },
{ ImageSize.Medium, (800, 600) }
};
}The following example shows blob input and output bindings in a function.json file and C# script (.csx) code that uses the bindings. The function makes a copy of a text blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.
In the function.json file, the queueTrigger metadata property is used to specify the blob name in the path properties:
{
"bindings": [
{
"queueName": "myqueue-items",
"connection": "MyStorageConnectionAppSetting",
"name": "myQueueItem",
"type": "queueTrigger",
"direction": "in"
},
{
"name": "myInputBlob",
"type": "blob",
"path": "samples-workitems/{queueTrigger}",
"connection": "MyStorageConnectionAppSetting",
"direction": "in"
},
{
"name": "myOutputBlob",
"type": "blob",
"path": "samples-workitems/{queueTrigger}-Copy",
"connection": "MyStorageConnectionAppSetting",
"direction": "out"
}
],
"disabled": false
}The configuration section explains these properties.
Here's the C# script code:
public static void Run(string myQueueItem, string myInputBlob, out string myOutputBlob, ILogger log)
{
log.LogInformation($"C# Queue trigger function processed: {myQueueItem}");
myOutputBlob = myInputBlob;
}The following example shows blob input and output bindings in a function.json file and JavaScript code that uses the bindings. The function makes a copy of a blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.
In the function.json file, the queueTrigger metadata property is used to specify the blob name in the path properties:
{
"bindings": [
{
"queueName": "myqueue-items",
"connection": "MyStorageConnectionAppSetting",
"name": "myQueueItem",
"type": "queueTrigger",
"direction": "in"
},
{
"name": "myInputBlob",
"type": "blob",
"path": "samples-workitems/{queueTrigger}",
"connection": "MyStorageConnectionAppSetting",
"direction": "in"
},
{
"name": "myOutputBlob",
"type": "blob",
"path": "samples-workitems/{queueTrigger}-Copy",
"connection": "MyStorageConnectionAppSetting",
"direction": "out"
}
],
"disabled": false
}The configuration section explains these properties.
Here's the JavaScript code:
module.exports = function(context) {
context.log('Node.js Queue trigger function processed', context.bindings.myQueueItem);
context.bindings.myOutputBlob = context.bindings.myInputBlob;
context.done();
};The following example shows blob input and output bindings in a function.json file and Python code that uses the bindings. The function makes a copy of a blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.
In the function.json file, the queueTrigger metadata property is used to specify the blob name in the path properties:
{
"bindings": [
{
"queueName": "myqueue-items",
"connection": "MyStorageConnectionAppSetting",
"name": "queuemsg",
"type": "queueTrigger",
"direction": "in"
},
{
"name": "inputblob",
"type": "blob",
"path": "samples-workitems/{queueTrigger}",
"connection": "MyStorageConnectionAppSetting",
"direction": "in"
},
{
"name": "outputblob",
"type": "blob",
"path": "samples-workitems/{queueTrigger}-Copy",
"connection": "MyStorageConnectionAppSetting",
"direction": "out"
}
],
"disabled": false,
"scriptFile": "__init__.py"
}The configuration section explains these properties.
Here's the Python code:
import logging
import azure.functions as func
def main(queuemsg: func.QueueMessage, inputblob: func.InputStream,
outputblob: func.Out[func.InputStream]):
logging.info('Python Queue trigger function processed %s', inputblob.name)
outputblob.set(inputblob)This section contains the following examples:
The following example shows a Java function that uses the HttpTrigger annotation to receive a parameter containing the name of a file in a blob storage container. The BlobInput annotation then reads the file and passes its contents to the function as a byte[]. The BlobOutput annotation binds to OutputBinding outputItem, which is then used by the function to write the contents of the input blob to the configured storage container.
@FunctionName("copyBlobHttp")
@StorageAccount("Storage_Account_Connection_String")
public HttpResponseMessage copyBlobHttp(
@HttpTrigger(name = "req",
methods = {HttpMethod.GET},
authLevel = AuthorizationLevel.ANONYMOUS)
HttpRequestMessage<Optional<String>> request,
@BlobInput(
name = "file",
dataType = "binary",
path = "samples-workitems/{Query.file}")
byte[] content,
@BlobOutput(
name = "target",
path = "myblob/{Query.file}-CopyViaHttp")
OutputBinding<String> outputItem,
final ExecutionContext context) {
// Save blob to outputItem
outputItem.setValue(new String(content, StandardCharsets.UTF_8));
// build HTTP response with size of requested blob
return request.createResponseBuilder(HttpStatus.OK)
.body("The size of \"" + request.getQueryParameters().get("file") + "\" is: " + content.length + " bytes")
.build();
}The following example shows a Java function that uses the QueueTrigger annotation to receive a message containing the name of a file in a blob storage container. The BlobInput annotation then reads the file and passes its contents to the function as a byte[]. The BlobOutput annotation binds to the function return value, which is then used by the runtime to write the contents of the input blob to the configured storage container.
@FunctionName("copyBlobQueueTrigger")
@StorageAccount("Storage_Account_Connection_String")
@BlobOutput(
name = "target",
path = "myblob/{queueTrigger}-Copy")
public String copyBlobQueue(
@QueueTrigger(
name = "filename",
dataType = "string",
queueName = "myqueue-items")
String filename,
@BlobInput(
name = "file",
path = "samples-workitems/{queueTrigger}")
String content,
final ExecutionContext context) {
context.getLogger().info("The content of \"" + filename + "\" is: " + content);
return content;
}In the Java functions runtime library, use the @BlobOutput annotation on function parameters whose value would be written to an object in blob storage. The parameter type should be OutputBinding<T>, where T is any native Java type or a POJO.
In C# class libraries, use the BlobAttribute.
The attribute's constructor takes the path to the blob and a FileAccess parameter indicating read or write, as shown in the following 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}")] Stream image,
[Blob("sample-images-md/{name}", FileAccess.Write, Connection = "StorageConnectionAppSetting")] Stream imageSmall)
{
...
}Attributes are not supported by C# Script.
Attributes are not supported by JavaScript.
Attributes are not supported by Python.
The @BlobOutput attribute gives you access to the blob that triggered the function. If you use a byte array with the attribute, set dataType to binary. Refer to the output example for details.
For a complete example, see Output example.
You can use the StorageAccount attribute to specify the storage account at class, method, or parameter level. For more information, see Trigger - attributes.
The following table explains the binding configuration properties that you set in the function.json file and the Blob attribute.
| function.json property | Attribute property | Description |
|---|---|---|
| type | n/a | Must be set to blob. |
| direction | n/a | Must be set to out for an output binding. Exceptions are noted in the usage section. |
| name | n/a | The name of the variable that represents the blob in function code. Set to $return to reference the function return value. |
| path | BlobPath | The path to the blob container. |
| connection | Connection | The name of an app setting that contains the Storage connection string to use for this binding. If the app setting name begins with "AzureWebJobs", you can specify only the remainder of the name here. For example, if you set connection to "MyStorage", the Functions runtime looks for an app setting that is named "AzureWebJobsMyStorage." If you leave connection empty, the Functions runtime uses the default Storage connection string in the app setting that is named AzureWebJobsStorage.The connection string must be for a general-purpose storage account, not a blob-only storage account. |
| n/a | Access | Indicates whether you will be reading or writing. |
[!INCLUDE app settings to local.settings.json]
[!INCLUDE functions-bindings-blob-storage-output-usage.md]
[!INCLUDE functions-bindings-blob-storage-output-usage.md]
In JavaScript, access the blob data using context.bindings.<name from function.json>.
You can declare function parameters as the following types to write out to blob storage:
- Strings as
func.Out(str) - Streams as
func.Out(func.InputStream)
Refer to the output example for details.
The @BlobOutput attribute gives you access to the blob that triggered the function. If you use a byte array with the attribute, set dataType to binary. Refer to the output example for details.
| Binding | Reference |
|---|---|
| Blob | Blob Error Codes |
| Blob, Table, Queue | Storage Error Codes |
| Blob, Table, Queue | Troubleshooting |