protected async Task<JsonValue> Fetch(
Uri endPoint,
RequestType requestType,
bool needsToken,
CancellationToken cancel,
IProgress<ProgressChangedEventArgs> progress = null,
IDictionary<string, string> postData = null,
KeyValuePair<string,string>? overrideAuth = null)
{
if (endPoint == null)
throw new ArgumentNullException("endPoint");
var wc = new WebClient();
if (needsToken && !Credentials.HasValue)
throw new InvalidOperationException("Cannot access this part of the Quizlet service without logging in.");
wc.Headers["User-Agent"] = "FlashcardsWP8/0.1 (" + Environment.OSVersion + "; .NET " + Environment.Version + ")";
// Overriding is used for basic authentication for OAuth process.
bool useClientID = false;
if (overrideAuth != null)
wc.Headers["Authorization"] = "Basic " + Convert.ToBase64String(Encoding.UTF8.GetBytes(overrideAuth.Value.Key + ":" + overrideAuth.Value.Value));
else if (Credentials != null)
wc.Headers["Authorization"] = "Bearer " + Credentials.Value.ApiToken;
else
useClientID = true;
try {
string result;
if (requestType == RequestType.Get) {
var uri = new Uri(ServiceUri, endPoint);
uri = new Uri(uri + (uri.Query == "" ? "?" : "&") + "client_id=" + clientID);
result = await wc.DownloadStringAsTask(uri, cancel, progress);
} else {
var sb = new StringBuilder();
wc.Headers["Content-Type"] = "application/x-www-form-urlencoded; charset=UTF-8";
wc.Encoding = Encoding.UTF8;
if (postData != null) {
if (useClientID)
postData["client_id"] = clientID;
foreach (var kvp in postData) {
if (sb.Length > 0)
sb.Append('&');
sb.Append(kvp.Key).Append('=').Append(Uri.EscapeDataString(kvp.Value));
}
}
result = await wc.UploadStringAsTask(new Uri(ServiceUri, endPoint), requestType.ToString().ToUpperInvariant(), sb.ToString(), cancel, progress);
}
JsonValue json = null;
// In case of HTTP status 204 (no content). This is produced, for example, as the result of
// a DELETE call to an endpoint.
if (!string.IsNullOrWhiteSpace(result))
json = JsonValue.Parse(new StringReader(result));
return json;
} catch (WebException e) {
// The Quizlet API returns a JSON document explaining the error if there is one,
// so try to use that if possible.
try {
if (e.Response != null) {
var response = (e.Response as HttpWebResponse).GetResponseStream();
using (var reader = new StreamReader(response)) {
var dict = JsonDictionary.FromValue(JsonValue.Parse(reader));
var ctx = new JsonContext();
var errorCode = ctx.FromJson<string>(dict["error"]);
var errorText = ctx.FromJson<string>(dict["error_description"]);
if (errorCode != null && errorText != null) {
switch (errorCode) {
case "invalid_access": throw new AccessDeniedException(errorText);
case "item_not_found": throw new ItemNotFoundException(errorText);
case "item_deleted": throw new ItemDeletedException(errorText);
default: throw new QuizletException(errorText);
}
}
}
}
throw new QuizletException(string.Format("Unable to contact the Quizlet server ({0}).", e.Message), e);
} catch (FormatException) {
// Not JSON or invalid - just wrap the original exception
throw new QuizletException(e.Message, e);
} catch (KeyNotFoundException) {
throw new QuizletException(e.Message, e);
}
}
}