Better error handling when parsing TZX files - #1158

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Hardware/Datacorder/DatacorderDevice.cs

@@ -329,30 +329,39 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         /// <param name="tapeData"></param>
         public void LoadTape(byte[] tapeData)
         {
-            // attempt TZX deserialization
+            // check TZX first
             TzxSerializer tzxSer = new TzxSerializer(this);
-            try
+            if (tzxSer.CheckType(tapeData))
             {
-                tzxSer.DeSerialize(tapeData);
-                return;
+                // this file has a tzx header - attempt serialization
+                try
+                {
+                    tzxSer.DeSerialize(tapeData);
+                    return;
+                }
+                catch (Exception ex)
+                {
+                    // exception during operation
+                    var e = ex;
+                    throw new Exception(this.GetType().ToString() +
+                    "\n\nTape image file has a valid TZX header, but threw an exception whilst data was being parsed.\n\n" + e.ToString());
+                }
             }
-            catch (Exception ex)
+            else
             {
-                // TAP format not detected
-                var e = ex;
-            }
-
-            // attempt TAP deserialization
-            TapSerializer tapSer = new TapSerializer(this);
-            try
-            {
-                tapSer.DeSerialize(tapeData);
-                return;
-            }
-            catch (Exception ex)
-            {
-                // TAP format not detected
-                var e = ex;
+                TapSerializer tapSer = new TapSerializer(this);
+                try
+                {
+                    tapSer.DeSerialize(tapeData);
+                    return;
+                }
+                catch (Exception ex)
+                {
+                    // exception during operation
+                    var e = ex;
+                    throw new Exception(this.GetType().ToString() +
+                    "\n\nAn exception was thrown whilst data from this tape image was being parsed as TAP.\n\n" + e.ToString());
+                }
             }
         }
 

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Media/MediaSerializer.cs

@@ -58,6 +58,16 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                 "DeSerialize operation is not implemented for this serializer");
         }
 
+        /// <summary>
+        /// Serializer does a quick check, returns TRUE if file is detected as this type
+        /// </summary>
+        /// <param name="data"></param>
+        public virtual bool CheckType(byte[] data)
+        {
+            throw new NotImplementedException(this.GetType().ToString() +
+                "Check type operation is not implemented for this serializer");
+        }
+
         #region Static Tools
 
         /// <summary>

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Media/Tape/TzxSerializer.cs

@@ -60,6 +60,43 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 
         #endregion
 
+        /// <summary>
+        /// Returns TRUE if tzx header is detected
+        /// </summary>
+        /// <param name="data"></param>
+        public override bool CheckType(byte[] data)
+        {
+            /*
+            // TZX Header
+            length: 10 bytes
+            Offset  Value       Type        Description
+            0x00    "ZXTape!"   ASCII[7]    TZX signature
+            0x07    0x1A        BYTE        End of text file marker
+            0x08    1           BYTE        TZX major revision number
+            0x09    20          BYTE        TZX minor revision number
+            */
+
+            // check whether this is a valid tzx format file by looking at the identifier in the header
+            // (first 7 bytes of the file)
+            string ident = Encoding.ASCII.GetString(data, 0, 7);
+            // and 'end of text' marker
+            byte eotm = data[7];
+
+            // version info
+            int majorVer = data[8];
+            int minorVer = data[9];
+
+            if (ident != "ZXTape!" || eotm != 0x1A)
+            {
+                // this is not a valid TZX format file
+                return false;
+            }
+            else
+            {
+                return true;
+            }
+        }
+
         /// <summary>
         /// DeSerialization method
         /// </summary>