Deserialize blob and output to different container with a name from the blob's contents

Question

I have a json in an azure blob that I need to deserialize and get a string from. The string is the name of a blob. I need to then copy the blob that is the input to this function with the name I just extracted to a storage container.

public static void Run([BlobTrigger("output/{name}", Connection = "AzureWebJobsStorage")]Stream myBlob, string name, TraceWriter log)
using (var sr = new StreamReader(myBlob))
using (var jsonTextReader = new JsonTextReader(sr))
{
    var transcript = (someobject)serializer.Deserialize(jsonTextReader, typeof(Transcript));
    string blobname = (someobject.Results[0].FileName).Substring(0, name.LastIndexOf('.'));

Above is the definiton of my current function and the method I am using to extract the filename from the json. Is this possible to do with blob input and output bindings? If so, is there a way to dynamically allocate the name of the output blob?

Mikhail Shilkov · Accepted Answer · 2018-03-23 22:38:02Z

1

You can use imperative binding to write output blob, something in lines with:

public static void Run(
    [BlobTrigger("input/{name}", Connection = "AzureWebJobsStorage")] string myBlob, 
    string name, 
    Binder binder)
{
  var someobject= serializer.Deserialize<Transcript>(myBlob);
  string blobname = (someobject.Results[0].FileName).Substring(0, name.LastIndexOf('.'));

  using (var writer = binder.Bind<TextWriter>(
              new BlobAttribute($"output/{blobname}")))
  {
      writer.Write(myBlob);
  }
}

I changed your function a bit to make my example easier to read.

edited Mar 23, 2018 at 22:38

answered Mar 23, 2018 at 21:03

Mikhail Shilkov

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6 Comments

Darth Veder Over a year ago

the problem I am having is that the Blob is being uploaded empty to the destination blob

Mikhail Shilkov Over a year ago

@DarthVeder Are you still using Streams? If so, you might copy streams incorrectly.

Darth Veder Over a year ago

Yup I'm using streams.

Mikhail Shilkov Over a year ago

@DarthVeder Don't forget to reset input stream to position 0 before copying to output. Or refactor to strings :)

Darth Veder Over a year ago

I kept getting this error when I tried to reset the stream to 0: Object reference not set to an instance of an object

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McGuireV10 · Accepted Answer · 2018-03-23 21:01:57Z

If you configure a CloudBlockBlob output binding, the Container and Name properties will be read-only, defined by the [Blob] binding attribute. However, there is something called "imperative binding" that lets you defer the binding until runtime, and the example even demonstrates writing to an arbitrary blob container and filename:

using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Host.Bindings.Runtime;

public static async Task Run(string input, Binder binder)
{
    using (var writer = await binder.BindAsync<TextWriter>(new BlobAttribute("samples-output/path")))
    {
        writer.Write("Hello World!!");
    }
}

For pre-compiled applications I personally find the "old fashioned way" easier to read, but I suppose it's a matter of preference.

CloudStorageAccount storage = CloudStorageAccount.Parse(conn_str);
CloudBlobClient blobClient = storage.CreateCloudBlobClient();
CloudBlobContainer blobContainer = blobClient.GetContainerReference(container);
CloudBlockBlob blob =blobContainer.GetBlockBlobReference(filename);
// etc.

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