Passing a file from an Azure Logic App to a Web API

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Logic App is one of my favorite tools in my cloud toolbox. It's very easy to connect things together, something without even coding! Last week, I needed to pass a file from a SharePoint folder to an API. I moved files tons of times using Azure Logic Apps, but this time something was not working. Thanks to Jeff Hollan (@jeffhollan) who put me on the good path by giving me great advice, my problem was quickly solved. In this post, I will share with you the little things that make all the difference in this case.

The Goal

When a file is created in a SharePoint folder, an Azure Logic App needs to get triggered and passes the file name and its content to a Web Api. In this case, I'm using Sharepoint, but it will work the same way for all folder connector types (ex: DropBox, OneDrive, Box, GoogleDrive, etc.)

Note:
In this post, I'm using a SharePoint Online, but the same thing could perfectly work with a SharePoint on premise or in a Virtual machine. In this situation, On-premise Data Gateway needs to be installed locally. It's very easy to do, just follow the instruction. One gotcha... You MUST use the same Microsoft account of type "work or school" to connect to the Azre.portal.com and installing the On-premise Data Gateway.

The Web API App

Let's start by building our Web API. In Visual studio create a new Web API App. If you would like to have more details about how to create one see my previous post. Now, create a new controller and add a new function UploadNewFile with the following code:

[SwaggerOperation("UploadNewFile")]
[SwaggerResponse(HttpStatusCode.OK)]
[Route("api/UploadNewFile")]
[HttpPost]
public HttpResponseMessage UploadNewFile([FromUri] string fileName)
{
    if (string.IsNullOrEmpty(fileName))
    {
        return Request.CreateResponse(HttpStatusCode.NoContent, "No File Name.");
    }

    var filebytes = Request.Content.ReadAsByteArrayAsync();

    if (filebytes.Result == null || filebytes.Result.Length <= 0)
    {
        return Request.CreateResponse(HttpStatusCode.NoContent, "No File Content.");
    }

    // Do what you need with the file.

    return Request.CreateResponse(HttpStatusCode.OK);
}

The tag [FromUri] before the parameter is just a way to specify where that information is coming from. The content of the file couldn't be passed in the querystring, so it will be passed through the body of our HTTP Request. And it will be retrieved with the code Request.Content.ReadAsByteArrayAsync(). If everything works we return a HttpResponseMessage with the HttpStatusCode.OK otherwise some message about the problem. You can now publish your Wep API App.

In order to be able to see our WebAPI App from our Logic App, one more thing needs to be done. From the Azure portal, select the freshly deployed App Service and from the options section (the left area with all properties) select CORS, then type * and save it.

The Logic App

Assuming that you already have a SharePoint up and running, let's create the new Logic App. Once the Logic App is deployed click the edit button to go in the designer. Select the Blank template. In this post, I need a SharePoint trigger when a New File is created. At this point, you will be asked to answer a few questions in order to create your SharePoint connector. Once it's done select the folder where you will be "dropping" your files.

Now that the trigger is done, we will add our first (an only) action. Click Add Step. Select available functions, then our App Service and finally the method UploadNewFile.

Thanks to swagger, Logic App will be able to generate a parameter form for us. Put the filename in the Filename parameter textbox. The Logic App should look like this.



The last thing we need to do is specify to our Logic App to pass the file content to the body of the HTTP request to the API. Today, it's not possible to do it using the interface. As you probably know, behind that gorgeous sits a simple json document, and it's by editing this one that we will be able to specify how to pass the file content.

Switch to Code view, and find the step that calls our API App. Simply add "body": "@triggerBody()" to that node. That will tell Logic App to bind the body of the trigger (the file content) and pass-it to the body of our web request. The code should look like this:

"UploadNewFile": {
    "inputs": {
        "method": "post",
        "queries": {
        "fileName": "@{triggerOutputs()['headers']['x-ms-file-name']}"
        },
        "body": "@triggerBody()",
        "uri": "https://frankdemo.azurewebsites.net/api/UploadNewFile"
    },
    "metadata": {
        "apiDefinitionUrl": "https://frankdemo.azurewebsites.net/swagger/docs/v1",
        "swaggerSource": "website"
    },
    "runAfter": {},
    "type": "Http"
}

You can now save and exit the edit mode. The solution is ready, enjoy!

References:

• stackoverflow