Fix deterministic MVID and add PdbChecksum (#810)

* Fix deterministic MVID and add PdbChecksum (#31)

* Fix how pdb path is calculated in the tests

* Fix portable PDB stamp in CodeView header (#32)

* Introduce ISymbolWriter.Write

This mostly cleans up the code to make it easier to understand. `ISymbolWriter.GetDebugHeader` no longer actually writes the symbols, there's a new `Write` method for just that.

The assembly writer calls `Write` first and then the image writer calls `GetDebugHeader` when it's needed.

This is partially taken from https://github.com/jbevain/cecil/pull/617.

1 files changed, 25 insertions, 21 deletions

diff --git a/Mono.Cecil/AssemblyWriter.cs b/Mono.Cecil/AssemblyWriter.cs
index 6515151..25076ff 100644
--- a/Mono.Cecil/AssemblyWriter.cs
+++ b/Mono.Cecil/AssemblyWriter.cs
@@ -118,13 +118,16 @@ namespace Mono.Cecil {
 					metadata.SetSymbolWriter (symbol_writer);
 					BuildMetadata (module, metadata);
 
-					if (parameters.DeterministicMvid)
-						metadata.ComputeDeterministicMvid ();
+					if (symbol_writer != null)
+						symbol_writer.Write ();
 
 					var writer = ImageWriter.CreateWriter (module, metadata, stream);
 					stream.value.SetLength (0);
 					writer.WriteImage ();
 
+					if (parameters.DeterministicMvid)
+						ComputeDeterministicMvid (writer, module);
+
 					if (parameters.HasStrongNameKey)
 						CryptoService.StrongName (stream.value, writer, parameters);
 				}
@@ -156,6 +159,26 @@ namespace Mono.Cecil {
 
 			return symbol_writer_provider.GetSymbolWriter (module, fq_name);
 		}
+
+		static void ComputeDeterministicMvid (ImageWriter writer, ModuleDefinition module)
+		{
+			long previousPosition = writer.BaseStream.Position;
+			writer.BaseStream.Seek(0, SeekOrigin.Begin);
+
+			// The hash should be computed with the MVID set to all zeroes
+			// which it is - we explicitly write all zeroes GUID into the heap
+			// as the MVID.
+			// Same goes for strong name signature, which also already in the image but all zeroes right now.
+			Guid guid = CryptoService.ComputeGuid (CryptoService.ComputeHash (writer.BaseStream));
+
+			// The MVID GUID is always the first GUID in the GUID heap
+			writer.MoveToRVA (TextSegment.GuidHeap);
+			writer.WriteBytes (guid.ToByteArray ());
+			writer.Flush ();
+			module.Mvid = guid;
+
+			writer.BaseStream.Seek(previousPosition, SeekOrigin.Begin);
+		}
 	}
 
 	abstract class MetadataTable {
@@ -2649,25 +2672,6 @@ namespace Mono.Cecil {
 
 			method_debug_information_table.rows [rid - 1].Col2 = GetBlobIndex (signature);
 		}
-
-		public void ComputeDeterministicMvid ()
-		{
-			var guid = CryptoService.ComputeGuid (CryptoService.ComputeHash (
-				data,
-				resources,
-				string_heap,
-				user_string_heap,
-				blob_heap,
-				table_heap,
-				code));
-
-			var position = guid_heap.position;
-			guid_heap.position = 0;
-			guid_heap.WriteBytes (guid.ToByteArray ());
-			guid_heap.position = position;
-
-			module.Mvid = guid;
-		}
 	}
 
 	sealed class SignatureWriter : ByteBuffer {