BlobTrigger in azure function ,Resize files after uploading in blob

 In previous post we saw how to create azure function for HttpTrigger. Now lets see another use of azure function.

Scenario - Suppose you are uploading file in blob either directly from azure portal or through .net code and after upload you want to create thumbnail or resize that file . For this if you will do during upload in .net code then it might take time and user will not be happy with system performance . So to tackle such kind of scenario azure has provided BlobTrigger function. which automatically trigger and resize your file after uploading in blob. if you want to know more about azure function from start please see the previous post.

So Lets see how we can achieve this.

1. Open Visual Studio -> Create New Project -> Search for Azure functions Templates and click Next

1.Enter project name “AzureFunBlobTrigger” and click Next

2.In next section you need to select Trigger Type ,so select Blob Trigger and keep storage emulator in right side , if you want to use azure storage you can browse and choose.

in Solution explorer you will see below

Local.settings.json : In this file configure storage account and runtime framework. It has key-value code. open this file and paste the below code

{

    "IsEncrypted": false,

  "Values": {

    "AzureWebJobsStorage": "your storgate connection string",

    "FUNCTIONS_WORKER_RUNTIME": "dotnet",

    "fnBlob": "your storgate connection string"

  }

}

fnBlob is the key which you are going to use for blob connection.

Function1.cs: Open the function.cs and paste the below code

using Microsoft.Azure.WebJobs;

using Microsoft.Azure.WebJobs.Host;

using SixLabors.ImageSharp;

using SixLabors.ImageSharp.Formats.Jpeg;

using SixLabors.ImageSharp.PixelFormats;

using SixLabors.ImageSharp.Processing;

using System.IO;

namespace AzureFunBlobTrigger

{

    public static class Function1

    {

        [FunctionName("Function1")]

         public static void Run(

               [BlobTrigger("mycontainer/{name}", Connection = "fnBlob")] Stream inputBlob, string name,

               [Blob("resized/{name}", FileAccess.Write, Connection = "fnBlob")] Stream outputBlob, TraceWriter log)

        {

            log.Info($"C# Blob trigger function Processed blob\n Name:{name} \n Size: {inputBlob.Length} Bytes");

         

            ResizeImage( inputBlob, outputBlob, 300,150);

         

        }

        private static void ResizeImage(Stream input, Stream output, int width,int height)

        {

            using (Image image = Image.Load(input))

            {

                image.Mutate(x => x

                        .Resize(new ResizeOptions

                        {

                            Mode = ResizeMode.BoxPad,

                            Size = new Size(width, height) // you can define size what u need

                        }).BackgroundColor(new Rgba32(0, 0, 0)));

                image.Save(output, new JpegEncoder());

            }

        }

    }

}

L Lets understand the below code block

[FunctionName("Function1")]

         public static void Run(

               [BlobTrigger("mycontainer/{name}", Connection = "fnBlob")] Stream myBlob, string name,

               [Blob("resized/{name}", FileAccess.Write, Connection = "fnBlob")] Stream outputBlob, TraceWriter log)

     [FunctionName("Function1")] - function name which you can change with any name .

   [BlobTrigger("mycontainer/{name}" -BlobTrigger is the attribute which trigger the function when any file will get upload in container "mycontainer".

    Connection = "fnBlob")] - storage connection string name which I have defined in local.setting.json

    [Blob("resized/{name}", another container where file will be save after resizing. you dont need to create ,it will be automatically created if not.

   In the above code I have created one function called ResizeImage where I am passing input blob(which has been uploaded ,output blob path and name , size.

   To resize image I am using nuget package called SixLabors.ImageSharp which you can add from package manager. I found this package more clean ,fast and easy to implement.

   Thats all about coding part.

   Lets try to upload file in container from azure portal and see what happens

L   1. Login to azure portal and go to storage account -> container -> mycontainer -> select upload and upload one file. as soon as you upload your file automatically your function will trigger in your local visual studio and resize the file and save in the output folder.

    Before that just run your project from visual studio . you will see below logs if your function run successfully in vs.

   Now let put our debugger in code just to make sure our function is triggered after uploading image in blob.

Now go to mycontainer and upload one image and you will see your local function got triggered.

   

   now you can see your function gets trigger in the code and resize uploaded image and push to resized container.

   This is the resized container.

   We are done with blob trigger azure function and this might be the real case for you where you can use azure function  ..

   Thanks and good luck.

Create and Use Azure functions in .Net Core

 Azure functions  

What : Azure function is a small pieces of code/small program which runs on cloud. Azure function is serverless i.e. no need to worry about infrastructure ,scaling etc. everything handled by provider for you. Basically it’s a Event triggered code.Keep in mind you should not write huge block of code or use as a replacement of webapi ,function should be lightweight and small piece of code.

Why to Use- We can use azure function when we have requirement to run program which might takes time.

o   File Processing

o   Scheduled Tasks

o   Reminders and Notifications

o   Sending background emails

o   Running background backup tasks

Language/script support

 All types of programming language support like C#,Java, JavaScript etc.

Types :Event triggered code

•       HTTP trigger
•       Timer Trigger
•       Blob Trigger
•       Event Grid Trigger
•       Event Hub Trigger
•       Queue Trigger
•       Service Bus Trigger and so many other triggers through which azure function can run.

Prerequisites:

•     Install azure development sdk in visual studio

Here we are going to focus Http trigger and Blob Trigger only.

Http Trigger- As per naming it a http request call , function execute when we send http request

Lets see how to create and use this ,good thing is that we don’t need to deploy azure function for testing during development in visual studio there is storage emulator which can be used for development and testing :

To create follow the steps :

Open Visual Studio -> Create New Project -> Search for Azure functions Templates and click Next

1.      .

1.Enter project name “azfunctionHttpTrigger” and click Next

2.In next section you need to select Trigger Type ,so select HttpTrigger and keep storage emulator in right side , if you want to use azure storage you can browse and choose.

3.In authorization field leave default one i.e function 

 

In solution explorer you can see project created with 3 files

•       Function1.cs
•       Host.json
•       local.settings.json

Let see uses of these files

Local.settings.json : In this file configure storage account and runtime framework. It has key-value code.

{

    "IsEncrypted": false,

    "Values": {

        "AzureWebJobsStorage": "UseDevelopmentStorage=true",

        "FUNCTIONS_WORKER_RUNTIME": "dotnet"

    }

}

AzureWebJobsStorage : can be replaced with azure storage connection string otherwise for development you can keep as it is.

Host.json : I will explain bit later.

Function1.cs: This is the class where you will put your logic what you want to get done from this app.Since we selected HttpTrigger ,automatically added template .just need to replace required code in the code block. 

Lets rename function name as ‘azhttpTriggeredFunction’

Default :

public static class Function1

    {

        [FunctionName("Function1")]

        public static async Task<IActionResult> Run( [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,

            ILogger log)

        {

            log.LogInformation("C# HTTP trigger function processed a request.");

            string name = req.Query["name"];

            string requestBody = await new StreamReader(req.Body).ReadToEndAsync();

            dynamic data = JsonConvert.DeserializeObject(requestBody);

            name = name ?? data?.name;

            string responseMessage = string.IsNullOrEmpty(name)

                ? "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response."

                : $"Hello, {name}. This HTTP triggered function executed successfully.";

            return new OkObjectResult(responseMessage);

        }

    }

 

Now lets run and see if function is working or not.press F5 and see the output.

.

If you observe the above output  ,you can see the url for http call. Copy this url and paste in browser

http://localhost:7071/api/azhttpTriggeredFunction and you can see the below output

Now Lets see details in this function :

[HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]

Http request method -get ,post. At template creation time it added by default. Can be removed one of them as required.

Route – This is the endpoint for http request.You can change the route name as "routeName"/{name}(query string). So url with new route name will be formed.

If you have noticed in the url http://localhost:7071/api/azhttpTriggeredFunction  ,

api has been appended . this is the default route prefix which is added. If you need to change this you can change in host.json.

Lets change route prefix as apiPrefix

http://localhost:7071/apiPrefix/azhttpTriggeredFunction new url with changed prefix.

Pass query string value in the url http://localhost:7071/apiPrefix/azhttpTriggeredFunction?name=%27manoj%27 and out put will be below

 

Thats it for httpTriggered function .In next section will see BlobTriggered.

 you can download all the azure samples code : https://github.com/mkumar8184/azure-sdk-services-samples