Initial implementation of the Dropbox API

Dropbox.cs

public class DropboxCredentials {
	public string Email { get; set; }
	public string Token { get; set; }
	public string TokenSecret { get; set; }
	public string DisplayName { get; set; }
	public string Uid { get; set; }
	public string LastDirectory { get; set; }

	public DropboxCredentials() {
		Email = "";
		Token = "";
		TokenSecret = "";
		DisplayName = "";
		Uid = "";
		LastDirectory = "";
	}
}

public class DropboxFile {
	public bool ThumbExists { get; set; }
	public long Bytes { get; set; }
	public string Path { get; set; }
	public bool IsDir { get; set; }
	public string Icon { get; set; }
	public List<DropboxFile> Contents { get; private set; }
	public DropboxFile () {
		Path = "";
		Icon = "";
		Contents = new List<DropboxFile>();
	}
}

public class Dropbox {
	public DropboxCredentials Credentials { get; private set; }

	public string ConsumerKey = "";
	public string ConsumerSecret = "";

	readonly Random _rand = new Random();

	public Dropbox(DropboxCredentials creds){
		Credentials = creds;
	}
	public void Login (string password, Action k, Action<string> error) {
		Begin(delegate {
			try {
				if (string.IsNullOrEmpty(Credentials.Token)) {
					var resp = Request("token",
						"email", Credentials.Email,
						"password", password);
					Credentials.Token = resp["token"];
					Credentials.TokenSecret = resp["secret"];
				}
				k ();
			}
			catch (Exception ex) {
				error(ex.Message);
			}
		});
	}
	public void Metadata (string path, Action<DropboxFile> k) {
		var p = (path ?? "").Trim();
		if (p.Length == 0) {
			p = "/";
		}

		Begin(delegate {
			var resp = Request("metadata/dropbox" + p);
			k (ReadFile (resp));
		});
	}
	DropboxFile ReadFile (JsonObject obj) {
		var f = new DropboxFile() {
			ThumbExists = obj["thumb_exists"],
			Bytes = (long)obj["bytes"],
			Path = obj["path"],
			IsDir = obj["is_dir"],
			Icon = obj["icon"] ?? "",
		};
		var cs = obj.ContainsKey("contents") ? (obj["contents"] as JsonArray) : null;
		if (cs != null) {
			for (var i = 0; i < cs.Count; i++) {
				f.Contents.Add (ReadFile ((JsonObject)cs[i]));
			}
		}
		return f;
	}
	JsonObject Request (string op, params string[] args) {
		var baseUrl = "https://api.dropbox.com/0/" + Uri.EscapeUriString(op);
		var url = baseUrl;
		var qargs = new SortedDictionary<string,string>();
		for (var i = 0; (i+1) < args.Length; i += 2) {
			qargs[Uri.EscapeDataString(args[i]??"")] = Uri.EscapeDataString(args[i+1]??"");
		}
		qargs["oauth_consumer_key"] = Uri.EscapeDataString(ConsumerKey);

		if (!string.IsNullOrEmpty(Credentials.Token)) {
			qargs["oauth_nonce"] = _rand.Next().ToString();
			qargs["oauth_signature_method"] = "HMAC-SHA1";
			qargs["oauth_timestamp"] = ((long)((DateTime.UtcNow - new DateTime(1970, 1, 1)).TotalSeconds)).ToString();
			qargs["oauth_token"] = Uri.EscapeDataString(Credentials.Token);

			var addUrl = string.Join("&", from kv in qargs
				select kv.Key + "=" + kv.Value);

			var sigBase = "GET&" +
				Uri.EscapeDataString(baseUrl) + "&" +
				Uri.EscapeDataString(addUrl);

			HMACSHA1 sh = new HMACSHA1();
			sh.Key = Encoding.UTF8.GetBytes (Uri.EscapeDataString(ConsumerSecret) + "&" +
				Uri.EscapeDataString(Credentials.TokenSecret));
			var hash = sh.ComputeHash (Encoding.UTF8.GetBytes(sigBase));
			var sigHash = Convert.ToBase64String (hash);

			url += "?" + addUrl + "&oauth_signature=" + Uri.EscapeDataString(sigHash);
		}
		else {
			var addUrl = string.Join("&", from kv in qargs
				select kv.Key + "=" + kv.Value);
			url += "?" + addUrl;
		}
		var req = (HttpWebRequest)WebRequest.Create(url);
		try {
			using (var resp = req.GetResponse ()) {
				using (var s = resp.GetResponseStream()) {
					using (var r = new StreamReader (s)) {
						return (JsonObject)JsonValue.Parse (r.ReadToEnd());
					}
				}
			}
		}
		catch (WebException ex) {
			var msg = "";
			if (ex.Status == WebExceptionStatus.ProtocolError) {
				try {
					using (var s = ex.Response.GetResponseStream()) {
						using (var r = new StreamReader (s)) {
							var str = r.ReadToEnd ();
							if (str.IndexOf("\"error\":") > 0) {
								msg = JsonValue.Parse(str)["error"];
							}
						}
					}
				}
				catch (Exception) {}
			}
			if (msg.Length > 0) {
				throw new Exception (msg, ex);
			}
			else {
				throw;
			}
		}
	}
	static void Begin (Action a) {
		ThreadPool.QueueUserWorkItem(delegate {
			try {
				a ();
			}
			catch (Exception err) {
				Log.Error (err);
			}
		});
	}
}