Downloading files to Azure function app to manipulate

Question

Edited Thank you @Marco

I'm trying to write a function app that grabs an SVG from a URL and converts it to PNG. I know there are existing API's that do this like CloudConvert, but they don't work nicely with embedded fonts, which is a requirement for me.

Anyway, I wrote a very basic function app that simply downloads a file at this point. Everything works perfectly fine locally, but when I publish to Azure, I get An exception occurred during a WebClient request.

Thanks to @Marco's suggestion, I switched from WebClient to HTTPWebRequest to get more detailed error handling, and as a result, I see the following:

2018-10-11T13:53:53.558 [Info] Function started (Id=e3cbda04-140e-4ef7-ad6c-c871ffe179dd)
2018-10-11T13:53:53.590 [Info] C# HTTP trigger function processed a request. 2018-10-11T13:53:53.752 [Info] Download Fail
2018-10-11T13:53:53.752 [Info] Access to the path
'D:\Windows\system32\734e16961fc276df.svg' is denied.

Am I trying to do something that isn't possible, or is there a fix for this? Is there a way to configure permissions in an Azure function? I need to pull the file down to edit and not just work with the byte array.

Many thanks!

public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)]HttpRequestMessage req, 
        TraceWriter log, ExecutionContext context)
{
    log.Info("C# HTTP trigger function processed a request.");

    // parse query parameter
    string svgURL = req.GetQueryNameValuePairs()
        .FirstOrDefault(q => string.Compare(q.Key, "l", true) == 0)
        .Value;

    if (svgURL == null)
    {
        // Get request body
        dynamic data = await req.Content.ReadAsAsync<object>();
        svgURL = data?.svgURL;
    }
    // download file from URL
    var uniqueName = GenerateId() ;
    try 
    { 
        using (var client = new WebClient())
        {
           client.DownloadFile(svgURL, uniqueName + ".svg" );
        }
    }
    catch (Exception e)
    {
        log.Info("Download Fail");
        log.Info(e.Message);
    }
}

Please post your code, not an image of your code. Your question becomes useles, once your image does get deleted. Crawlers and screenreaders also have a hard time interpreting images. — Marco
You could also try to use an HttpWebRequest instead of a WebClient to see if you get any more detailed exception messages / Stacktraces. — Marco
@Marco got it, thanks, and updated. Didn't know that... will try HttpWebRequest now — Mike Baron
And please make sure, that svgUrl is def. not null in production. Because currently it defintily can be. — Marco
@Marco got it, thanks. yah it's definitely not. I'm using the same svgUrl testing locally and in prod to be sure. — Mike Baron

Mike Baron Mike Baron · Accepted Answer · 2018-10-11T15:17:23

The easiest way to solve this is to use temp storage. I can see why Azure wouldn't want functions cludging up the app directory anyway. Updated code below:

I replaced this:

client.DownloadFile(svgURL, uniqueName + ".svg" );

With this:

client.DownloadFile(svgURL, Path.GetTempPath() + "\\" + uniqueName + ".svg" );

Worked like a charm.

Edit: Below is the GitHub repo where I make this call. There's other stuff going on but you can see where I save to temp storage.
https://github.com/osuhomebase/SVG2PNG-AzureFunction

Downloading files to Azure function app to manipulate

1 Answers