attempting to fix #29

pi4j-core/src/main/java/com/pi4j/wiringpi/Spi.java

@@ -120,6 +120,25 @@ private Spi()  {
      */
     public static native int wiringPiSPIDataRW(int channel, String data, int len);
 
+    /**
+     * <p>wiringPiSPIDataRW:</p>
+     * 
+     * <p>
+     * Write and Read a block of data over the SPI bus. Note the data is being read into the
+     * transmit buffer, so will overwrite it! This is also a full-duplex operation.
+     * </p>
+     * 
+     * <p>
+     * (ATTENTION: the 'data' argument can only be a maximum of 1024 characters.)
+     * </p>
+     * 
+     * @param channel SPI channel</p>
+     * @param data
+     * @param len
+     * @return return -1 on error
+     */
+    public static native int wiringPiSPIDataRW(int channel, byte[] data, int len);
+
     /**
      * <p>wiringPiSPISetup:</p>
      * 

pi4j-native/src/main/native/com_pi4j_wiringpi_Serial.c

@@ -86,7 +86,7 @@ JNIEXPORT void JNICALL Java_com_pi4j_wiringpi_Serial_serialPuts
   (JNIEnv *env, jobject obj, jint fd, jstring data)
 {
 	char datachararr[2048];
-	int len = (*env)->GetStringLength(env, data);
+	int len = (*env)->GetStringUTFLength(env, data);
 	(*env)->GetStringUTFRegion(env, data, 0, len, datachararr);
 	serialPuts(fd, datachararr);
 }

pi4j-native/src/main/native/com_pi4j_wiringpi_Spi.c

@@ -46,19 +46,48 @@ JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIGetFd
  * Method:    wiringPiSPIDataRW
  * Signature: (ILjava/lang/String;I)I
  */
-JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIDataRW
+JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIDataRW__ILjava_lang_String_2I
   (JNIEnv *env, jclass class, jint channel, jstring data, jint length)
 {
-	char datachararr[2048];
-	int len = (*env)->GetStringLength(env, data);
-	(*env)->GetStringUTFRegion(env, data, 0, len, datachararr);
-	jint result = wiringPiSPIDataRW(channel, (unsigned char *)datachararr, length);
-	jstring returnString = (*env)->NewStringUTF(env, datachararr);
+	char buffer[2048];
+	int len = (*env)->GetStringUTFLength(env, data);
+	(*env)->GetStringUTFRegion(env, data, 0, len, buffer);
+	jint result = wiringPiSPIDataRW(channel, (unsigned char *)buffer, length);
+	jstring returnString = (*env)->NewStringUTF(env, buffer);
     data = returnString;
 
 	return result;
 }
 
+/*
+ * Class:     com_pi4j_wiringpi_Spi
+ * Method:    wiringPiSPIDataRW
+ * Signature: (I[BI)I
+ */
+JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIDataRW__I_3BI
+(JNIEnv *env, jclass class, jint channel, jbyteArray data, jint length)
+{
+    int i;
+    unsigned char buffer[2048];
+
+	// copy the bytes from the data array argument into a native character buffer
+    jbyte *body = (*env)->GetByteArrayElements(env, data, 0);
+    for (i = 0; i < length; i++) {
+    	buffer[i] = body[i + offset];
+    }
+
+	jint result = wiringPiSPIDataRW(channel, (unsigned char *)buffer, length);
+
+	// copy the resulting buffer bytes back into the data array argument
+	for (i = 0; i < length; i++) {
+		body[i] = buffer[i];
+	}
+	(*env)->ReleaseByteArrayElements(env, data, bodyReturn, 0);
+
+	return result;
+}
+
+
 /*
  * Class:     com_pi4j_wiringpi_Spi
  * Method:    wiringPiSPISetup

pi4j-native/src/main/native/com_pi4j_wiringpi_Spi.h

@@ -46,9 +46,17 @@ JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIGetFd
  * Method:    wiringPiSPIDataRW
  * Signature: (ILjava/lang/String;I)I
  */
-JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIDataRW
+JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIDataRW__ILjava_lang_String_2I
   (JNIEnv *, jclass, jint, jstring, jint);
 
+/*
+ * Class:     com_pi4j_wiringpi_Spi
+ * Method:    wiringPiSPIDataRW
+ * Signature: (I[BI)I
+ */
+JNIEXPORT jint JNICALL Java_com_pi4j_wiringpi_Spi_wiringPiSPIDataRW__I_3BI
+  (JNIEnv *, jclass, jint, jbyteArray, jint);
+
 /*
  * Class:     com_pi4j_wiringpi_Spi
  * Method:    wiringPiSPISetup