Avoid decompressing/compressing unresolved embedded source information

Mono.Cecil.Cil/Symbols.cs

@@ -619,17 +619,36 @@ public StateMachineScopeDebugInformation ()
 
 	public sealed class EmbeddedSourceDebugInformation : CustomDebugInformation {
 
+		internal uint index;
+		internal MetadataReader debug_reader;
+		internal bool resolved;
 		internal byte [] content;
 		internal bool compress;
 
 		public byte [] Content {
-			get { return content; }
-			set { content = value; }
+			get {
+				if (!resolved)
+					Resolve ();
+
+				return content;
+			}
+			set {
+				content = value;
+				resolved = true;
+			}
 		}
 
 		public bool Compress {
-			get { return compress; }
-			set { compress = value; }
+			get {
+				if (!resolved)
+					Resolve ();
+
+				return compress;
+			}
+			set {
+				compress = value;
+				resolved = true;
+			}
 		}
 
 		public override CustomDebugInformationKind Kind {
@@ -638,12 +657,42 @@ public override CustomDebugInformationKind Kind {
 
 		public static Guid KindIdentifier = new Guid ("{0E8A571B-6926-466E-B4AD-8AB04611F5FE}");
 
+		internal EmbeddedSourceDebugInformation (uint index, MetadataReader debug_reader)
+			: base (KindIdentifier)
+		{
+			this.index = index;
+			this.debug_reader = debug_reader;
+		}
+
 		public EmbeddedSourceDebugInformation (byte [] content, bool compress)
 			: base (KindIdentifier)
 		{
+			this.resolved = true;
 			this.content = content;
 			this.compress = compress;
 		}
+
+		internal byte [] ReadRawEmbeddedSourceDebugInformation ()
+		{
+			if (debug_reader == null)
+				throw new InvalidOperationException ();
+
+			return debug_reader.ReadRawEmbeddedSourceDebugInformation (index);
+		}
+
+		void Resolve ()
+		{
+			if (resolved)
+				return;
+
+			if (debug_reader == null)
+				throw new InvalidOperationException ();
+
+			var row = debug_reader.ReadEmbeddedSourceDebugInformation (index);
+			content = row.Col1;
+			compress = row.Col2;
+			resolved = true;
+		}
 	}
 
 	public sealed class SourceLinkDebugInformation : CustomDebugInformation {

Mono.Cecil/AssemblyReader.cs

@@ -3223,28 +3223,7 @@ public Collection<CustomDebugInformation> GetCustomDebugInformation (ICustomDebu
 
 					infos.Add (async_body);
 				} else if (rows [i].Col1 == EmbeddedSourceDebugInformation.KindIdentifier) {
-					var signature = ReadSignature (rows [i].Col2);
-					var format = signature.ReadInt32 ();
-					var length = signature.sig_length - 4;
-
-					var info = null as CustomDebugInformation;
-
-					if (format == 0) {
-						info = new EmbeddedSourceDebugInformation (signature.ReadBytes ((int) length), compress: false);
-					} else if (format > 0) {
-						var compressed_stream = new MemoryStream (signature.ReadBytes ((int) length));
-						var decompressed_document = new byte [format]; // if positive, format is the decompressed length of the document
-						var decompressed_stream = new MemoryStream (decompressed_document);
-
-						using (var deflate_stream = new DeflateStream (compressed_stream, CompressionMode.Decompress, leaveOpen: true))
-							deflate_stream.CopyTo (decompressed_stream);
-
-						info = new EmbeddedSourceDebugInformation (decompressed_document, compress: true);
-					} else if (format < 0) {
-						info = new BinaryCustomDebugInformation (rows [i].Col1, ReadBlob (rows [i].Col2));
-					}
-
-					infos.Add (info);
+					infos.Add (new EmbeddedSourceDebugInformation (rows [i].Col2, this));
 				} else if (rows [i].Col1 == SourceLinkDebugInformation.KindIdentifier) {
 					infos.Add (new SourceLinkDebugInformation (Encoding.UTF8.GetString (ReadBlob (rows [i].Col2))));
 				} else {
@@ -3256,6 +3235,33 @@ public Collection<CustomDebugInformation> GetCustomDebugInformation (ICustomDebu
 
 			return infos;
 		}
+
+		public byte [] ReadRawEmbeddedSourceDebugInformation (uint index)
+		{
+			var signature = ReadSignature (index);
+			return signature.ReadBytes ((int) signature.sig_length);
+		}
+
+		public Row<byte [], bool> ReadEmbeddedSourceDebugInformation (uint index)
+		{
+			var signature = ReadSignature (index);
+			var format = signature.ReadInt32 ();
+			var length = signature.sig_length - 4;
+
+			if (format == 0) {
+				return new Row<byte [], bool> (signature.ReadBytes ((int) length), false);
+			} else if (format > 0) {
+				var compressed_stream = new MemoryStream (signature.ReadBytes ((int) length));
+				var decompressed_document = new byte [format]; // if positive, format is the decompressed length of the document
+				var decompressed_stream = new MemoryStream (decompressed_document);
+
+				using (var deflate_stream = new DeflateStream (compressed_stream, CompressionMode.Decompress, leaveOpen: true))
+					deflate_stream.CopyTo (decompressed_stream);
+
+				return new Row<byte [], bool> (decompressed_document, true);
+			} else
+				throw new NotSupportedException ();
+		}
 	}
 
 	sealed class SignatureReader : ByteBuffer {

Mono.Cecil/AssemblyWriter.cs

@@ -2422,6 +2422,13 @@ void AddAsyncMethodBodyDebugInformation (ICustomDebugInformationProvider provide
 		void AddEmbeddedSourceDebugInformation (ICustomDebugInformationProvider provider, EmbeddedSourceDebugInformation embedded_source)
 		{
 			var signature = CreateSignatureWriter ();
+
+			if (!embedded_source.resolved) {
+				signature.WriteBytes (embedded_source.ReadRawEmbeddedSourceDebugInformation ());
+				AddCustomDebugInformation (provider, embedded_source, signature);
+				return;
+			}
+
 			var content = embedded_source.content ?? Empty<byte>.Array;
 			if (embedded_source.compress) {
 				signature.WriteInt32 (content.Length);

Test/Mono.Cecil.Tests/PortablePdbTests.cs

@@ -490,10 +490,13 @@ public void SourceLink ()
 		[Test]
 		public void EmbeddedSource ()
 		{
+			TestModule ("embedcs.exe", module => {
+			}, symbolReaderProvider: typeof (PortablePdbReaderProvider), symbolWriterProvider: typeof (PortablePdbWriterProvider));
+
 			TestModule ("embedcs.exe", module => {
 				var program = GetDocument (module.GetType ("Program"));
 				var program_src = GetSourceDebugInfo (program);
-				Assert.IsTrue (program_src.compress);
+				Assert.IsTrue (program_src.Compress);
 				var program_src_content = Encoding.UTF8.GetString (program_src.Content);
 				Assert.AreEqual (Normalize (@"using System;
 
@@ -533,7 +536,7 @@ static void Main()
 
 				var a = GetDocument (module.GetType ("A"));
 				var a_src = GetSourceDebugInfo (a);
-				Assert.IsFalse (a_src.compress);
+				Assert.IsFalse (a_src.Compress);
 				var a_src_content = Encoding.UTF8.GetString (a_src.Content);
 				Assert.AreEqual (Normalize (@"class A
 {