write the stings into the data section

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

@@ -17,25 +17,97 @@
 package de.inetsoftware.jwebassembly.module;
 
 import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
 import java.util.LinkedHashMap;
 
+import javax.annotation.Nonnegative;
+
 /**
- * Handle all the constant strings
+ * Handle all the constant strings. The constant strings will be write into the data section.
  * 
  * @author Volker Berlin
  */
 class StringManager extends LinkedHashMap<String, Integer> {
 
     /**
-     * Finish the prepare. Now no new function should be added. 
+     * Finish the prepare. Now no new strings should be added.
      * 
-     * @param writer the targets for the strings
+     * @param writer
+     *            the targets for the strings
+     * @throws IOException
+     *             if any I/O error occur
      */
-    void prepareFinish( ModuleWriter writer ) {
+    void prepareFinish( ModuleWriter writer ) throws IOException {
+        // inform the writer of string count that it can allocate a table of type anyref for the constant strings
         writer.setStringCount( size() );
-        ByteArrayOutputStream data = writer.dataStream;
+
+        /* Write the strings to the data sections.
+           first there is a index table, then follows the strings
+           | .....                          |
+           ├────────────────────────────────┤
+           | start index string 1 (4 bytes) |
+           ├────────────────────────────────┤
+           | start index string 2 (4 bytes) |
+           ├────────────────────────────────┤
+           | start index string 3 (4 bytes) |
+           ├────────────────────────────────┤
+           | .....                          |
+           ├────────────────────────────────┤
+           | length string 1 (1-x bytes)    |
+           ├────────────────────────────────┤
+           | string 1        (UTF8 encoded) |
+           ├────────────────────────────────┤
+           | length string 2 (1-x bytes)    |
+           ├────────────────────────────────┤
+           | string 2        (UTF8 encoded) |
+           ├────────────────────────────────┤
+           | .....                          |
+         */
+        ByteArrayOutputStream stringOut = new ByteArrayOutputStream();
+        ByteArrayOutputStream dataStream = writer.dataStream;
+
+        int offset = dataStream.size() + size() * 4;
+
         for( String str : this.keySet() ) {
+            // write the position where the string starts in the data section
+            // little-endian byte order
+            int position = offset + stringOut.size();
+            dataStream.write( position >>> 0 );
+            dataStream.write( position >>> 8 );
+            dataStream.write( position >>> 16 );
+            dataStream.write( position >>> 24 );
+
+            byte[] bytes = str.getBytes( StandardCharsets.UTF_8 );
+            writeVaruint32( bytes.length, stringOut );
+            stringOut.write( bytes );
         }
+
+        stringOut.writeTo( dataStream );
     }
 
+    /**
+     * Write an unsigned integer.
+     * 
+     * @param value
+     *            the value
+     * @param out
+     *            target stream
+     * @throws IOException
+     *             if an I/O error occurs.
+     */
+    private static void writeVaruint32( @Nonnegative int value, OutputStream out ) throws IOException {
+        if( value < 0 ) {
+            throw new IOException( "Invalid negative value" );
+        }
+        do {
+            int b = value & 0x7F; // low 7 bits
+            value >>= 7;
+            if( value != 0 ) { /* more bytes to come */
+                b |= 0x80;
+            }
+            out.write( b );
+        } while( value != 0 );
+    }
 }