Download PDF File from API Using C#

Question

I am creating a console application that

1. Connects to a vendor API to pull voucher numbers for submitted expenses between two dates and
2. Downloads a PDF copy of receipts submitted with the expense

The first part, I have working fine. I am able to connect to the Vendor API and parse out the returned XML to create an array of voucher numbers (needed to get the PDF images) using the following code:

static async Task RunAsyncCR()
        {
            using (var client = new HttpClient())
            {
                var values = new Dictionary<string, string>
                {
                    {"un","SomeUser"},
                    {"pw","SomePassword"},
                    {"method","getVoucherInvoices"},
                    {"fromDate","05/30/2016"},
                    {"toDate", "06/13/2016"}
                };

                var content = new FormUrlEncodedContent(values);

                Console.WriteLine("Connecting...");

                var response = await client.PostAsync("https://www.chromeriver.com/receipts/doit", content);

                Console.WriteLine("Connected...");

                var responseString = await response.Content.ReadAsStringAsync();

                char[] DelimiterChars = {'<'};

                String[] xmlReturn = responseString.Split(DelimiterChars);

                string[] VoucherNumber = new string[500];

                int i = 0;

                foreach (string s in xmlReturn)
                {
                    if (s.Contains("voucherInvoice>") && s != "/voucherInvoice>\n    ")
                    {
                        VoucherNumber[i] = s.Substring(15, 16);

                        i++;
                    }
                }

                Array.Resize(ref VoucherNumber, i);

Yes, there is likely a better way of doing this, but it works and returns the values I am expecting.

Now, what I am having trouble with, is when I connect back to the API to retrieve the file, I cannot seem to be able to download the file to a specified file path.

I can connect back to the API using

            i = 0;

            foreach (string x in VoucherNumber)
            {
                Console.WriteLine("Get receipt: " + x);

                var NewValues = new Dictionary<string, string>
                {
                    {"un","SomeUser"},
                    {"pw","SomePassword"},
                    {"method","getReceiptsWithCoverPage"},
                    {"voucherInvoiceForPdf", VoucherNumber[i]}
                };

                var NewContent = new FormUrlEncodedContent(NewValues);

                var NewResponse = await client.PostAsync("https://www.chromeriver.com/receipts/doit", NewContent);

                string NewResponseString = await NewResponse.Content.ReadAsStringAsync();

But I cannot seem to write the response to a valid file (PDF)

Here is a screen shot of my Autos window as I step through the code, where I would need to download the file:

My question is, from this point, how do I go about saving the file to my system?

I have tried to take the encoded response I get from doing Console.WriteLine(NewResponseString); and write it to a file using the System.IO.File.WriteAllLines() method, using a specified filepath/name, but this results in a blank file. I have also spent some time researching the depths of Google/Stackoverflow, but do not understand how to implement the results I find.

Any and all help would be greatly appreciated.

Answer 1

So I think you need help with Streams. The returned HttpContent is actually a System.Net.Http.StreamContent instance which shows that you are getting content back. Its just a matter of getting the Stream (content) from that instance and saving that to a file.

var NewResponse = await client.PostAsync("https://www.chromeriver.com/receipts/doit", NewContent);

System.Net.Http.HttpContent content = NewResponse.Content; // actually a System.Net.Http.StreamContent instance but you do not need to cast as the actual type does not matter in this case

using(var file = System.IO.File.Create("somePathHere.pdf")){ // create a new file to write to
    var contentStream = await content.ReadAsStreamAsync(); // get the actual content stream
    await contentStream.CopyToAsync(file); // copy that stream to the file stream
}

---

I respectfully recommend that you do a little reading on how Streams work. This is a common construct in many languages that you will probably have to deal with again in the near future.