Setting the content-type of a blob in Azure functions app blobtrigger

Question

I am trying to resize the images uploaded to my container in order to create thumbnails and various other versions of my images for my site.

The images I upload have to correct content-type "image/jpeg" but when I create a new version of them using the code below it turns out as "application/octet-stream".

What am I missing here?

using ImageResizer;
using ImageResizer.ExtensionMethods;
 
public static void Run(Stream myBlob, string blobname, string blobextension, Stream outputBlob, TraceWriter log)
{
    log.Info($"C# Blob trigger function Processed blob\n Name:{blobname} \n Size: {myBlob.Length} Bytes");
    
    var instructions = new Instructions
    {
        Width = 570,
        Mode = FitMode.Crop,
        Scale = ScaleMode.Both,
    };
    ImageBuilder.Current.Build(new ImageJob(myBlob, outputBlob, instructions));
}

Edit: The solution.

#r "Microsoft.WindowsAzure.Storage"
using ImageResizer;
using ImageResizer.ExtensionMethods;
using Microsoft.WindowsAzure.Storage.Blob;

public static void Run(Stream myBlob, string blobname, string blobextension, CloudBlockBlob outputBlob, TraceWriter log)
{
    log.Info($"C# Blob trigger function Processed blob\n Name:{blobname} \n Size: {myBlob.Length} Bytes");
    
    var instructions = new Instructions
    {
        Width = 570,
        Mode = FitMode.Crop,
        Scale = ScaleMode.Both
    };

    Stream stream = new MemoryStream();
    ImageBuilder.Current.Build(new ImageJob(myBlob, stream, instructions));
    stream.Seek(0, SeekOrigin.Begin);
 
    outputBlob.Properties.ContentType = "image/jpeg";
    outputBlob.UploadFromStream(stream);
}

Answer 1

When you use the stream output, functions will default your content-type to application/octet-stream.

Use one of the ICloudBlob types, which should allow you to specify the content type of your blob.

Here's a cheatsheet of types you can bind to as parameters: https://jhaleyfiles2016.blob.core.windows.net/public/Azure%20WebJobs%20SDK%20Cheat%20Sheet%202014.pdf

Answer 2

Here's a complete working example of an image-resizing Azure Function:

run.csx

#r "Microsoft.WindowsAzure.Storage"

using Microsoft.WindowsAzure.Storage.Blob;
using ImageResizer;
using ImageResizer.ExtensionMethods;

public static void Run(Stream imageStream, string blobName, CloudBlockBlob outputBlob, TraceWriter log)
{
    log.Info($"Function triggered by blob\n Name:{blobName} \n Size: {imageStream.Length} Bytes");

    var instructions = new Instructions
    {
        Width = 400,
        Height = 350,
        Mode = FitMode.Max,
        OutputFormat = OutputFormat.Jpeg,
        JpegQuality = 85
    };

    using (var outputStream = new MemoryStream())
    {
        ImageBuilder.Current.Build(new ImageJob(imageStream, outputStream, instructions));
        outputStream.Position = 0;
        outputBlob.Properties.ContentType = "image/jpeg";
        outputBlob.UploadFromStream(outputStream);
    }
}

function.json

{
  "bindings": [
    {
      "name": "imageStream",
      "type": "blobTrigger",
      "direction": "in",
      "path": "watched-container/{blobName}.jpg",
      "connection": "AzureWebJobsDashboard"
    },
    {
      "type": "blob",
      "name": "outputBlob",
      "path": "output-container/{blobName}.jpg",
      "connection": "AzureWebJobsDashboard",
      "direction": "inout"
    }
  ],
  "disabled": false
}

project.json

{
"frameworks": {
  "net46":{
    "dependencies": {
      "ImageResizer": "4.0.5"
    }
  }
 }
}