Reading local files from a .Net Azure Function

When working with Azure Functions, you might find yourself in the need of reading the content of some local files located in the same directory as the function your are working on.

I found two ways of achieving this without having to hard-code the full path of the file you are trying to read; the two options are:

1. Using the Context of the Function.
2. Using an Environment Variable

For the purposes of this post, I created two functions ReadFileByContext and ReadFileByVariable respectively.

Also, uploaded two documents through Advanced tools (Kudu) to a folder called Files.

Using Function Context

Initially, when you create a function from Visual Studio or from Azure portal, you get a very basic structure of a function thats receives two parameters. Something like this:

public static HttpResponseMessage Run(HttpRequestMessage req, TraceWriter log)

The trick is to add a third parameter of type ExecutionContext to the function. With the context parameter you can get the FunctionAppDirectory property path and the value of this property should be D:\home\site\wwwroot.

With this value you only need to put together the rest of the paths and read the content of the file.

public static HttpResponseMessage Run(HttpRequestMessage req, TraceWriter log, ExecutionContext ctx)
{
    var filePath = Path.Combine(ctx.FunctionAppDirectory, "Files", "DummyFileByContext.txt");
 
    var fileContent = System.IO.File.ReadAllText(filePath);
    return  req.CreateResponse(HttpStatusCode.OK, $"File Content: {fileContent}");
}

Here is a screenshot of the response when calling the Azure function.

Using Environment Variable

For this approach you only need to get the value of the HOME Environment Variable and the value could be similar to D:\home, the following line of code shows how to get this value.

Environment.GetEnvironmentVariable("HOME", EnvironmentVariableTarget.Process);

Once you have the value of the variable, just concatenate the rest of the path of the file’s location and you should be good to go.

public static HttpResponseMessage Run(HttpRequestMessage req, TraceWriter log)
{
    var home = Environment.GetEnvironmentVariable("HOME", EnvironmentVariableTarget.Process);
    var filePath =  Path.Combine(home, @"site\wwwroot\Files", "DummyFile_ReadByVariable.txt");
    
    var fileContent = System.IO.File.ReadAllText(filePath);
    return  req.CreateResponse(HttpStatusCode.OK, $"File Content: {fileContent}");
}

Here is a screenshot of the response when calling the Azure function.

That’s it! By following any of the mentioned options, you will forget about hard-coded paths and the best of everything is that it also works on local environments when working with Visual Studio in your development machine.

Hope you like it and find it useful.

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