fix ArrayIndexOutOfBoundsException when decoding a UTF-8 stream

classpath/java/io/InputStreamReader.java

@@ -13,6 +13,8 @@ package java.io;
 import avian.Utf8;
 
 public class InputStreamReader extends Reader {
+  private static final int MultibytePadding = 4;
+
   private final InputStream in;
 
   public InputStreamReader(InputStream in) {
@@ -28,19 +30,60 @@ public class InputStreamReader extends Reader {
       throw new UnsupportedEncodingException(encoding);
     }    
   }
-
   
   public int read(char[] b, int offset, int length) throws IOException {
-    byte[] buffer = new byte[length];
-    int c = in.read(buffer);
+    if (length == 0) {
+      return 0;
+    }
 
-    if (c <= 0) return c;
+    byte[] buffer = new byte[length + MultibytePadding];
+    int bufferLength = length;
+    int bufferOffset = 0;
+    while (true) {
+      int c = in.read(buffer, bufferOffset, bufferLength);
 
-    char[] buffer16 = Utf8.decode16(buffer, 0, c);
+      if (c <= 0) {
+        if (bufferOffset > 0) {
+          // if we've reached the end of the stream while trying to
+          // read a multibyte character, we still need to return any
+          // competely-decoded characters, plus \ufffd to indicate an
+          // unknown character
+          c = 1;
+          while (bufferOffset > 0) {
+            char[] buffer16 = Utf8.decode16(buffer, 0, bufferOffset);
 
-    System.arraycopy(buffer16, 0, b, offset, buffer16.length);
+            if (buffer16 != null) {
+              System.arraycopy(buffer16, 0, b, offset, buffer16.length);
+              
+              c = buffer16.length + 1;
+              break;
+            } else {
+              -- bufferOffset;
+            }
+          }
 
-    return buffer16.length;
+          b[offset + c - 1] = '\ufffd';
+        }
+
+        return c;
+      }
+
+      bufferOffset += c;
+
+      char[] buffer16 = Utf8.decode16(buffer, 0, bufferOffset);
+
+      if (buffer16 != null) {
+        bufferOffset = 0;
+
+        System.arraycopy(buffer16, 0, b, offset, buffer16.length);
+
+        return buffer16.length;
+      } else {
+        // the buffer ended in an incomplete multibyte character, so
+        // we try to read a another byte at a time until it's complete
+        bufferLength = 1;
+      }
+    }
   }
 
   public void close() throws IOException {