write event section if exception handling is used.

src/de/inetsoftware/jwebassembly/binary/BinaryModuleWriter.java

@@ -64,7 +64,7 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
 
     private Map<String, Function>       functions           = new LinkedHashMap<>();
 
-    private List<AnyType>           locals              = new ArrayList<>();
+    private List<AnyType>               locals              = new ArrayList<>();
 
     private Map<String, Global>         globals             = new LinkedHashMap<>();
 
@@ -74,7 +74,9 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
 
     private Function                    function;
 
-    private FunctionTypeEntry                functionType;
+    private FunctionTypeEntry           functionType;
+
+    private int                         exceptionSignatureIndex       = -1;
 
     /**
      * Create new instance.
@@ -109,6 +111,7 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
         writeSection( SectionType.Import, imports.values() );
         writeSection( SectionType.Function, functions.values() );
         writeSection( SectionType.Global, globals.values() );
+        writeEventSection();
         writeExportSection();
         writeCodeSection();
         writeDebugNames();
@@ -138,6 +141,25 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
         }
     }
 
+    /**
+     * Write the event section if needed.
+     * 
+     * @throws IOException
+     *             if any I/O error occur
+     */
+    private void writeEventSection() throws IOException {
+        if( exceptionSignatureIndex >= 0 ) {
+            WasmOutputStream stream = new WasmOutputStream();
+            stream.writeVaruint32( 1 );
+
+            // event declaration
+            stream.writeVaruint32( 0 ); // event type: exception = 0
+            stream.writeVaruint32( exceptionSignatureIndex );
+
+            wasm.writeSection( SectionType.Export, stream );
+        }
+    }
+
     /**
      * Write the export section to the output. This section contains a mapping from the external index to the type signature index.
      * 
@@ -238,6 +260,22 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
         return typeId;
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    protected void writeException() throws IOException {
+        if( exceptionSignatureIndex <= 0 ) {
+            FunctionTypeEntry exceptionType = new FunctionTypeEntry();
+            exceptionType.params.add( ValueType.anyref );
+            exceptionSignatureIndex = functionTypes.indexOf( exceptionType );
+            if( exceptionSignatureIndex < 0 ) {
+                exceptionSignatureIndex = functionTypes.size();
+                functionTypes.add( exceptionType );
+            }
+        }
+    }
+
     /**
      * {@inheritDoc}
      */

src/de/inetsoftware/jwebassembly/module/ModuleGenerator.java

@@ -371,6 +371,15 @@ public class ModuleGenerator {
         optimizer.optimze( instructions );
         for( WasmInstruction instruction : instructions ) {
             switch( instruction.getType() ) {
+                case Block:
+                    switch( ((WasmBlockInstruction)instruction).getOperation() ) {
+                        case TRY:
+                        case CATCH:
+                            writer.writeException();
+                            break;
+                        default:
+                    }
+                    break;
                 case Call:
                     functions.functionCall( ((WasmCallInstruction)instruction).getFunctionName() );
                     break;

src/de/inetsoftware/jwebassembly/module/ModuleWriter.java

@@ -60,6 +60,14 @@ public abstract class ModuleWriter implements Closeable {
      */
     protected abstract int writeStruct( String typeName, List<NamedStorageType> fields ) throws IOException;
 
+    /**
+     * Mark to write exceptions
+     * 
+     * @throws IOException
+     *             if any I/O error occur
+     */
+    protected abstract void writeException() throws IOException;
+
     /**
      * Prepare a imported single function in the prepare phase.
      * 

src/de/inetsoftware/jwebassembly/module/WasmBlockInstruction.java

@@ -21,7 +21,6 @@ import java.io.IOException;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
-import de.inetsoftware.jwebassembly.module.WasmInstruction.Type;
 import de.inetsoftware.jwebassembly.wasm.AnyType;
 import de.inetsoftware.jwebassembly.wasm.ValueType;
 import de.inetsoftware.jwebassembly.wasm.WasmBlockOperator;
@@ -62,6 +61,14 @@ class WasmBlockInstruction extends WasmInstruction {
         return Type.Block;
     }
 
+    /**
+     * Get the operation
+     * @return the op
+     */
+    WasmBlockOperator getOperation() {
+        return op;
+    }
+
     /**
      * {@inheritDoc}
      */

src/de/inetsoftware/jwebassembly/text/TextModuleWriter.java

@@ -57,6 +57,8 @@ public class TextModuleWriter extends ModuleWriter {
 
     private HashSet<String> globals      = new HashSet<>();
 
+    private boolean         useExceptions;
+
     /**
      * Create a new instance.
      * 
@@ -117,6 +119,21 @@ public class TextModuleWriter extends ModuleWriter {
         return 0;
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    protected void writeException() throws IOException {
+        if( !useExceptions ) {
+            useExceptions = true;
+            int oldInset = inset;
+            inset = 1;
+            newline( output );
+            output.append( "(event (param anyref))" );
+            inset = oldInset;
+        }
+    }
+
     /**
      * {@inheritDoc}
      */