1 files changed, 97 insertions, 1 deletions
diff --git a/csharp/ProtocolBuffers/UninitializedMessageException.cs b/csharp/ProtocolBuffers/UninitializedMessageException.cs
index 530f2057..01cdd2f1 100644
--- a/csharp/ProtocolBuffers/UninitializedMessageException.cs
+++ b/csharp/ProtocolBuffers/UninitializedMessageException.cs
@@ -14,15 +14,111 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Text;
+using Google.ProtocolBuffers.Collections;
+using Google.ProtocolBuffers.Descriptors;
 
 namespace Google.ProtocolBuffers {
   public class UninitializedMessageException : Exception {
 
-    public UninitializedMessageException(IMessage message) {
+    private readonly IList<string> missingFields;
+
+    public UninitializedMessageException(IMessage message)
+        : this(FindMissingFields(message)) {
+    }
+
+    private UninitializedMessageException(IList<string> missingFields)
+        : base(BuildDescription(missingFields)) {
+      this.missingFields = Lists.AsReadOnly(missingFields);
     }
 
+
+    /// <summary>
+    /// Converts this exception into an InvalidProtocolBufferException.
+    /// When a parsed message is missing required fields, this should be thrown
+    /// instead of UninitializedMessageException.
+    /// </summary>
     public InvalidProtocolBufferException AsInvalidProtocolBufferException() {
       return new InvalidProtocolBufferException(Message);
     }
+
+    /// <summary>
+    /// Constructs the description string for a given list of missing fields.
+    /// </summary>
+    private static string BuildDescription(IEnumerable<string> missingFields) {
+      StringBuilder description = new StringBuilder("Message missing required fields: ");
+      bool first = true;
+      foreach(string field in missingFields) {
+        if (first) {
+          first = false;
+        } else {
+          description.Append(", ");
+        }
+        description.Append(field);
+      }
+      return description.ToString();
+    }
+
+    /// <summary>
+    /// Returns a list of the full "paths" of missing required
+    /// fields in the specified message.
+    /// </summary>
+    private static IList<String> FindMissingFields(IMessage message) {
+      List<String> results = new List<String>();
+      FindMissingFields(message, "", results);
+      return results;
+    }
+
+    /// <summary>
+    /// Recursive helper implementing FindMissingFields.
+    /// </summary>
+    private static void FindMissingFields(IMessage message, String prefix, List<String> results) {
+      foreach (FieldDescriptor field in message.DescriptorForType.Fields) {
+        if (field.IsRequired && !message.HasField(field)) {
+          results.Add(prefix + field.Name);
+        }
+      }
+
+      foreach (KeyValuePair<FieldDescriptor, object> entry in message.AllFields) {
+        FieldDescriptor field = entry.Key;
+        object value = entry.Value;
+
+        if (field.MappedType == MappedType.Message) {
+          if (field.IsRepeated) {
+            int i = 0;
+            foreach (object element in (IEnumerable) value) {
+              FindMissingFields((IMessage) element, SubMessagePrefix(prefix, field, i++), results);
+            }
+          } else {
+            if (message.HasField(field)) {
+              FindMissingFields((IMessage) value, SubMessagePrefix(prefix, field, -1), results);
+            }
+          }
+        }
+      }
+    }
+
+    private static String SubMessagePrefix(String prefix, FieldDescriptor field, int index) {
+      StringBuilder result = new StringBuilder(prefix);
+      if (field.IsExtension) {
+        result.Append('(')
+              .Append(field.FullName)
+              .Append(')');
+      } else {
+        result.Append(field.Name);
+      }
+      if (index != -1) {
+        result.Append('[')
+              .Append(index)
+              .Append(']');
+      }
+      result.Append('.');
+      return result.ToString();
+    }
   }
 }
+
+  
+