Add binary encoding of WASM type section

5 files changed, 108 insertions, 26 deletions

diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/BinaryWriter.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/BinaryWriter.java
index d5600a5c..ade47714 100644
--- a/src/main/java/org/shedlang/compiler/backends/wasm/structure/BinaryWriter.java
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/BinaryWriter.java
@@ -15,12 +15,6 @@ public class BinaryWriter {
         buffer.put(bytes, 0, bytes.length);
     }
 
-    public ReservedBytes reserve(int length) {
-        var position = buffer.position();
-        advance(length);
-        return new ReservedBytes(position);
-    }
-
     private void ensureSpareCapacity(int length) {
         ensureCapacity(buffer.position() + length);
     }
@@ -38,20 +32,17 @@ public class BinaryWriter {
         }
     }
 
-    private void advance(int length) {
-        ensureSpareCapacity(length);
-        buffer.position(buffer.position() + length);
-    }
-
     public byte[] toBytes() {
         var result = new byte[buffer.position()];
         buffer.get(0, result);
         return result;
     }
 
-    public static class ReservedBytes {
-        public ReservedBytes(int position) {
+    public int position() {
+        return buffer.position();
+    }
 
-        }
+    public void seek(int newPosition) {
+        buffer.position(newPosition);
     }
 }
diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/WasmBinaryFormat.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/WasmBinaryFormat.java
index ab43d70d..c87a86e5 100644
--- a/src/main/java/org/shedlang/compiler/backends/wasm/structure/WasmBinaryFormat.java
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/WasmBinaryFormat.java
@@ -1,10 +1,15 @@
 package org.shedlang.compiler.backends.wasm.structure;
 
+import org.pcollections.PVector;
 import org.shedlang.compiler.backends.wasm.structure.ast.WasmModule;
+import org.shedlang.compiler.backends.wasm.structure.ast.types.WasmFuncType;
+import org.shedlang.compiler.backends.wasm.structure.ast.types.WasmValueType;
+import org.shedlang.compiler.util.Action;
 
-import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.util.HexFormat;
+import java.util.List;
 
 public class WasmBinaryFormat {
     private static final byte[] WASM_MAGIC = HexFormat.of().parseHex("0061736D");
@@ -33,8 +38,75 @@ public class WasmBinaryFormat {
         }
     }
 
-    public static void serializeModule(WasmModule module, FileOutputStream outputStream) throws IOException {
-        outputStream.write(WASM_MAGIC);
-        outputStream.write(WASM_VERSION);
+    public static void serializeModule(WasmModule module, OutputStream outputStream) throws IOException {
+        var writer = new BinaryWriter();
+        writer.writeBytes(WASM_MAGIC);
+        writer.writeBytes(WASM_VERSION);
+        writeTypeSection(module.types(), writer);
+
+        outputStream.write(writer.toBytes());
+    }
+
+    private static void writeTypeSection(
+        PVector<WasmFuncType> types,
+        BinaryWriter writer
+    ) throws IOException {
+        if (types.size() > 0) {
+            writeSection(SectionType.TYPE, writer, () -> {
+                Leb128Encoding.encodeUnsignedInt32(types.size(), writer);
+                for (var type : types) {
+                    writeFuncType(type, writer);
+                }
+            });
+        }
+    }
+
+    private static void writeFuncType(WasmFuncType type, BinaryWriter writer) {
+        writer.writeByte((byte) 0x60);
+        writeValueTypeVector(type.params(), writer);
+        writeValueTypeVector(type.results(), writer);
+    }
+
+    private static void writeValueTypeVector(List<WasmValueType> types, BinaryWriter writer) {
+        Leb128Encoding.encodeUnsignedInt32(types.size(), writer);
+        for (var type : types) {
+            writeValueType(type, writer);
+        }
+    }
+
+    private static void writeValueType(WasmValueType type, BinaryWriter writer) {
+        var encoding = switch (type) {
+            case I32 -> 0x7f;
+            case I64 -> 0x7e;
+            case F32 -> 0x7d;
+            case F64 -> 0x7c;
+        };
+        writer.writeByte((byte) encoding);
+    }
+
+    private static void writeSection(
+        SectionType sectionType,
+        BinaryWriter writer,
+        Action writeContent
+    ) throws IOException {
+        // https://webassembly.github.io/spec/core/binary/modules.html#sections
+        //
+        // Each section consists of:
+        // * a one-byte section ID
+        // * the u32 size of the contents, in bytes
+        // * the actual contents
+        writer.writeByte(sectionType.id);
+
+        var sizePosition = writer.position();
+        Leb128Encoding.encodePaddedUnsignedInt32(0, writer);
+
+        var contentStartPosition = writer.position();
+        writeContent.call();
+        var contentEndPosition = writer.position();
+
+        var size = contentEndPosition - contentStartPosition;
+        writer.seek(sizePosition);
+        Leb128Encoding.encodePaddedUnsignedInt32(size, writer);
+        writer.seek(contentEndPosition);
     }
 }
diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/WasmModule.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/WasmModule.java
index a5827d58..ed0d88f2 100644
--- a/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/WasmModule.java
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/WasmModule.java
@@ -1,13 +1,15 @@
 package org.shedlang.compiler.backends.wasm.structure.ast;
 
-public record WasmModule() {
-    public static Builder builder() {
-        return new Builder();
-    }
+import org.pcollections.PVector;
+import org.shedlang.compiler.backends.wasm.structure.ast.types.WasmFuncType;
+import org.shedlang.compiler.util.P;
+
+public record WasmModule(
+    PVector<WasmFuncType> types
+) {
+    public static final WasmModule EMPTY = new WasmModule(P.vector());
 
-    public record Builder() {
-        public WasmModule build() {
-            return new WasmModule();
-        }
+    public WasmModule addType(WasmFuncType type) {
+        return new WasmModule(types.plus(type));
     }
 }
diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/types/WasmFuncType.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/types/WasmFuncType.java
new file mode 100644
index 00000000..abb58fe3
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/types/WasmFuncType.java
@@ -0,0 +1,9 @@
+package org.shedlang.compiler.backends.wasm.structure.ast.types;
+
+import java.util.List;
+
+public record WasmFuncType(
+    List<WasmValueType> params,
+    List<WasmValueType> results
+) {
+}
diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/types/WasmValueType.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/types/WasmValueType.java
new file mode 100644
index 00000000..d46bc8e8
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/types/WasmValueType.java
@@ -0,0 +1,8 @@
+package org.shedlang.compiler.backends.wasm.structure.ast.types;
+
+public enum WasmValueType {
+    I32,
+    I64,
+    F32,
+    F64
+}