Improved error handling for webservice requests.

AcoustID/AcoustID.csproj

@@ -79,10 +79,12 @@
     <Compile Include="Util\Helper.cs" />
     <Compile Include="Web\Artist.cs" />
     <Compile Include="Web\IResponseParser.cs" />
+    <Compile Include="Web\LookupResponse.cs" />
     <Compile Include="Web\LookupResult.cs" />
     <Compile Include="Web\LookupService.cs" />
     <Compile Include="Web\Recording.cs" />
     <Compile Include="Web\ReleaseGroup.cs" />
+    <Compile Include="Web\SubmitResponse.cs" />
     <Compile Include="Web\SubmitResult.cs" />
     <Compile Include="Web\SubmitService.cs" />
     <Compile Include="Web\XmlResponseParser.cs" />

AcoustID/Web/IResponseParser.cs

@@ -19,22 +19,24 @@ public interface IResponseParser
         string Format { get; }
 
         /// <summary>
-        /// Gets an error message (will be null for successful requests).
+        /// Indicates if the parser can read the given text format.
         /// </summary>
-        string Error { get; }
+        /// <param name="text">The webservice response.</param>
+        /// <returns>Returns true, if the parser can parse the given content.</returns>
+        bool CanParse(string text);
 
         /// <summary>
         /// Parse the content of a lookup response.
         /// </summary>
-        /// <param name="response">The webservice response.</param>
+        /// <param name="text">The webservice response.</param>
         /// <returns>A list of <see cref="LookupResult"/>.</returns>
-        List<LookupResult> ParseLookupResponse(string response);
+        LookupResponse ParseLookupResponse(string text);
 
         /// <summary>
         /// Parse the content of a submit response.
         /// </summary>
-        /// <param name="response">The webservice response.</param>
+        /// <param name="text">The webservice response.</param>
         /// <returns>A list of <see cref="SubmitResult"/>.</returns>
-        List<SubmitResult> ParseSubmitResponse(string response);
+        SubmitResponse ParseSubmitResponse(string text);
     }
 }

AcoustID/Web/LookupResponse.cs

@@ -0,0 +1,45 @@
+// -----------------------------------------------------------------------
+// <copyright file="LookupResponse.cs" company="">
+// Christian Woltering, https://github.com/wo80
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace AcoustID.Web
+{
+    using System.Collections.Generic;
+    using System.Net;
+
+    /// <summary>
+    /// The webservice response containing the status code and a list of lookup results.
+    /// </summary>
+    public class LookupResponse
+    {
+        public LookupResponse()
+            : this(HttpStatusCode.OK, null)
+        {
+        }
+
+        public LookupResponse(HttpStatusCode status, string error)
+        {
+            this.StatusCode = status;
+            this.ErrorMessage = error;
+
+            Results = new List<LookupResult>();
+        }
+
+        /// <summary>
+        /// Gets the status code returned by the webservice.
+        /// </summary>
+        public HttpStatusCode StatusCode { get; internal set; }
+
+        /// <summary>
+        /// Gets the error message, in case the status code is not "200 OK".
+        /// </summary>
+        public string ErrorMessage { get; internal set; }
+
+        /// <summary>
+        /// Gets a list of <see cref="LookupResult"/>s.
+        /// </summary>
+        public List<LookupResult> Results { get; private set; }
+    }
+}

AcoustID/Web/LookupService.cs

@@ -7,12 +7,10 @@
 namespace AcoustID.Web
 {
     using System;
-    using System.Collections.Generic;
     using System.IO;
     using System.IO.Compression;
     using System.Net;
     using System.Text;
-    using System.Threading;
     using System.Threading.Tasks;
 
     /// <summary>
@@ -41,21 +39,13 @@ public LookupService(IResponseParser parser)
         /// </summary>
         public bool UseCompression { get; set; }
 
-        /// <summary>
-        /// Gets the last error message (check this if parse methods return empty lists).
-        /// </summary>
-        public string Error
-        {
-            get { return parser.Error; }
-        }
-
         /// <summary>
         /// Calls the webservice on a worker thread.
         /// </summary>
         /// <param name="fingerprint">The audio fingerprint.</param>
         /// <param name="duration">The total duration of the audio.</param>
-        /// <returns>A task which, on success, returns a list of lookup results.</returns>
-        public Task<List<LookupResult>> GetAsync(string fingerprint, int duration)
+        /// <returns>A task which returns a <see cref="LookupResponse"/>.</returns>
+        public Task<LookupResponse> GetAsync(string fingerprint, int duration)
         {
             return GetAsync(fingerprint, duration, null);
         }
@@ -66,19 +56,12 @@ public Task<List<LookupResult>> GetAsync(string fingerprint, int duration)
         /// <param name="fingerprint">The audio fingerprint.</param>
         /// <param name="duration">The total duration of the audio.</param>
         /// <param name="meta">Request meta information.</param>
-        /// <returns>A task which, on success, returns a list of lookup results.</returns>
-        public Task<List<LookupResult>> GetAsync(string fingerprint, int duration, string[] meta)
+        /// <returns>A task which returns a <see cref="LookupResponse"/>.</returns>
+        public Task<LookupResponse> GetAsync(string fingerprint, int duration, string[] meta)
         {
-            return Task.Factory.StartNew<List<LookupResult>>(() =>
+            return Task.Factory.StartNew<LookupResponse>(() =>
             {
-                try
-                {
-                    return Get(fingerprint, duration, meta);
-                }
-                catch (Exception)
-                {
-                    throw;
-                }
+                return Get(fingerprint, duration, meta);
             });
         }
 
@@ -87,8 +70,8 @@ public Task<List<LookupResult>> GetAsync(string fingerprint, int duration, strin
         /// </summary>
         /// <param name="fingerprint">The audio fingerprint.</param>
         /// <param name="duration">The total duration of the audio.</param>
-        /// <returns>List of lookup results.</returns>
-        public List<LookupResult> Get(string fingerprint, int duration)
+        /// <returns>A <see cref="LookupResponse"/>.</returns>
+        public LookupResponse Get(string fingerprint, int duration)
         {
             return Get(fingerprint, duration, null);
         }
@@ -99,21 +82,48 @@ public List<LookupResult> Get(string fingerprint, int duration)
         /// <param name="fingerprint">The audio fingerprint.</param>
         /// <param name="duration">The total duration of the audio.</param>
         /// <param name="meta">Request meta information.</param>
-        /// <returns>List of lookup results.</returns>
-        public List<LookupResult> Get(string fingerprint, int duration, string[] meta)
+        /// <returns>A <see cref="LookupResponse"/>.</returns>
+        public LookupResponse Get(string fingerprint, int duration, string[] meta)
         {
             try
             {
                 string request = BuildRequestString(fingerprint, duration, meta);
+
+                // If the request contains invalid parameters, the server will return "400 Bad Request" and
+                // we'll end up in the first catch block.
                 string response = RequestService(request);
 
-                // TODO: server might return an error message as json.
-                //       Should probably add a json parser anyway ...
                 return parser.ParseLookupResponse(response);
             }
-            catch (Exception)
+            catch (WebException e)
             {
-                throw;
+                // Handle bad requests gracefully.
+                return CreateErrorResponse(e.Response as HttpWebResponse);
+            }
+            catch (Exception e)
+            {
+                throw e;
+            }
+        }
+
+        private LookupResponse CreateErrorResponse(HttpWebResponse response)
+        {
+            if (response == null)
+            {
+                return new LookupResponse(HttpStatusCode.BadRequest, "Unknown error.");
+            }
+
+            using (var reader = new StreamReader(response.GetResponseStream()))
+            {
+                var text = reader.ReadToEnd();
+
+                if (parser.CanParse(text))
+                {
+                    return parser.ParseLookupResponse(text);
+                }
+
+                // TODO: parse error message (JSON).
+                return new LookupResponse(response.StatusCode, text);
             }
         }
 
@@ -175,6 +185,7 @@ private string RequestService(string request)
                     client.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
 
                     data = client.UploadData(URL, data);
+
                     return encoding.GetString(data);
                 }
             }

AcoustID/Web/SubmitResponse.cs

@@ -0,0 +1,12 @@
+// -----------------------------------------------------------------------
+// <copyright file="SubmitResponse.cs" company="">
+// Christian Woltering, https://github.com/wo80
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace AcoustID.Web
+{
+    public class SubmitResponse
+    {
+    }
+}

AcoustID/Web/XmlResponseParser.cs

@@ -7,8 +7,8 @@
 namespace AcoustID.Web
 {
     using System;
-    using System.Collections.Generic;
     using System.Globalization;
+    using System.Net;
     using System.Xml.Linq;
 
     /// <summary>
@@ -19,50 +19,49 @@ public class XmlResponseParser : IResponseParser
         private static NumberFormatInfo numberFormat = CultureInfo.InvariantCulture.NumberFormat;
         private static string format = "xml";
 
+        /// <inheritdoc />
         public string Format
         {
             get { return format; }
         }
+
+        /// <inheritdoc />
+        public bool CanParse(string text)
+        {
+            return !string.IsNullOrEmpty(text) && text.StartsWith("<?xml");
+        }
 
-        /// <summary>
-        /// Gets the last error message.
-        /// </summary>
-        public string Error { get; private set; }
-
-        /// <summary>
-        /// Parse the response of a lookup request.
-        /// </summary>
-        /// <param name="response">The response string.</param>
-        /// <returns>List of lookup results.</returns>
-        public List<LookupResult> ParseLookupResponse(string response)
+        /// <inheritdoc />
+        public LookupResponse ParseLookupResponse(string text)
         {
             try
             {
-                this.Error = string.Empty;
-
-                var root = XDocument.Parse(response).Element("response");
+                var root = XDocument.Parse(text).Element("response");
 
                 var status = root.Element("status");
 
-                List<LookupResult> results = new List<LookupResult>();
-
                 if (status.Value == "ok")
                 {
+                    var response = new LookupResponse();
+
                     var list = root.Element("results").Descendants("result");
 
                     foreach (var item in list)
                     {
-                        results.Add(ParseLookupResult(item));
+                        response.Results.Add(ParseLookupResult(item));
                     }
+
+                    return response;
                 }
-                else if (status.Value == "error")
+
+                if (status.Value == "error")
                 {
                     var error = root.Element("error");
 
-                    this.Error = error.Element("message").Value;
+                    return new LookupResponse(HttpStatusCode.BadRequest, error.Element("message").Value);
                 }
 
-                return results;
+                return null;
             }
             catch (Exception e)
             {
@@ -75,7 +74,7 @@ public List<LookupResult> ParseLookupResponse(string response)
         /// </summary>
         /// <param name="response">The response string.</param>
         /// <returns>List of submit results.</returns>
-        public List<SubmitResult> ParseSubmitResponse(string response)
+        public SubmitResponse ParseSubmitResponse(string response)
         {
             // TODO: implement submit response parsing
             throw new NotImplementedException();

Fingerprinter/MainForm.cs

@@ -203,20 +203,21 @@ private void Lookup(string fingerprint, int duration)
             {
                 btnOpen.Enabled = true;
 
-                var results = t.Result;
+                var response = t.Result;
 
-                if (results.Count == 0)
+                if (!string.IsNullOrEmpty(response.ErrorMessage))
                 {
-                    if (String.IsNullOrEmpty(service.Error))
-                    {
-                        MessageBox.Show("No results for given fingerprint.");
-                    }
-                    else MessageBox.Show(service.Error, "Webservice error");
+                    MessageBox.Show(response.ErrorMessage, "Webservice error");
+                    return;
+                }
 
+                if (response.Results.Count == 0)
+                {
+                    MessageBox.Show("No results for given fingerprint.");
                     return;
                 }
 
-                foreach (var result in results)
+                foreach (var result in response.Results)
                 {
                     var item = new ListViewItem(new string[]
                     {