YModem在Android上的实现

（一）参考文献

【安卓相关】蓝牙基于Ymodem协议发送bin文件，对硬件设备进行升级。 - 简书
当Android BLE遇上YModem - 简书

（二）收发机制

基于我们具体的需求，在原有的基础上加了一下前后的处理。

 * MY YMODEM IMPLEMTATION* *SENDER: ANDROID APP *------------------------------------------* RECEIVER: BLE DEVICE** HELLO BOOTLOADER ---------------------------------------------->** <---------------------------------------------------------------* C* SOH 00 FF filename0fileSizeInByte0MD5[90] ZERO[38] CRC CRC----->** <---------------------------------------------------------------* ACK C* STX 01 FE data[1024] CRC CRC ---------------------------------->** <---------------------------------------------------------------* ACK* STX 02 FF data[1024] CRC CRC ---------------------------------->** <---------------------------------------------------------------* ACK* ...* ...* <p>* STX 08 F7 data[1000] CPMEOF[24] CRC CRC ----------------------->** <---------------------------------------------------------------* ACK* EOT ----------------------------------------------------------->** <---------------------------------------------------------------* ACK* SOH 00 FF ZERO[128] ------------------------------------------->** <---------------------------------------------------------------* ACK* <---------------------------------------------------------------* MD5_OK

（三）核心代码模块

首先梳理一下它应该具有哪些模块：

• 协议的核心实现
  主要是负责数据传输过程中有关协议的部分，如在数据包上加入头，CRC，验证返回的正确性以及超时重发等。
• 一个协议工具类，封装包数据的提供
• 一个文件数据的读取模块：它是耗时任务，应该在子线程进行。
• 各种执行状态的监听

3.1协议的核心实现

/*** Created by leonxtp on 2017/9/16.* Modified by leonxtp on 2017/9/16*/public class Ymodem implements FileStreamThread.DataRaderListener {private static final int STEP_HELLO = 0x00;private static final int STEP_FILE_NAME = 0x01;private static final int STEP_FILE_BODY = 0x02;private static final int STEP_EOT = 0x03;private static final int STEP_END = 0x04;private static int CURR_STEP = STEP_HELLO;private static final byte ACK = 0x06; /* ACKnowlege */private static final byte NAK = 0x15; /* Negative AcKnowlege */private static final byte CAN = 0x18; /* CANcel character */private static final byte ST_C = 'C';private static final String MD5_OK = "MD5_OK";private static final String MD5_ERR = "MD5_ERR";private Context mContext;private String filePath;private String fileNameString = "LPK001_Android";private String fileMd5String = "63e7bb6eed1de3cece411a7e3e8e763b";private YModemListener listener;private TimeOutHelper timerHelper = new TimeOutHelper();private FileStreamThread streamThread;//bytes has been sent of this transmissionprivate int bytesSent = 0;//package data of current sending, used for int case of failprivate byte[] currSending = null;private int packageErrorTimes = 0;private static final int MAX_PACKAGE_SEND_ERROR_TIMES = 5;//the timeout interval for a single packageprivate static final int PACKAGE_TIME_OUT = 6000;/*** Construct of the YModemBLE,you may don't need the fileMD5 checking,remove it** @param filePath       absolute path of the file* @param fileNameString file name for sending to the terminal* @param fileMd5String  md5 for terminal checking after transmission finished* @param listener*/public Ymodem(Context context, String filePath,String fileNameString, String fileMd5String,YModemListener listener) {this.filePath = filePath;this.fileNameString = fileNameString;this.fileMd5String = fileMd5String;this.mContext = context;this.listener = listener;}/*** Start the transmission*/public void start() {sayHello();}/*** Stop the transmission when you don't need it or shut it down in accident*/public void stop() {bytesSent = 0;currSending = null;packageErrorTimes = 0;if (streamThread != null) {streamThread.release();}timerHelper.stopTimer();}/*** Method for the outer caller when received data from the terminal*/public void onReceiveData(byte[] respData) {//Stop the package timertimerHelper.stopTimer();if (respData != null && respData.length > 0) {switch (CURR_STEP) {case STEP_HELLO:handleHello(respData);break;case STEP_FILE_NAME:handleFileName(respData);break;case STEP_FILE_BODY:handleFileBody(respData[0]);break;case STEP_EOT:handleEOT(respData);break;case STEP_END:handleEnd(respData);break;default:break;}} else {L.f("The terminal do responsed something, but received nothing??");}}/*** ==============================================================================* Methods for sending data begin* ==============================================================================*/private void sayHello() {streamThread = new FileStreamThread(mContext, filePath, this);CURR_STEP = STEP_HELLO;L.f("sayHello!!!");byte[] hello = YModemUtil.getYModelHello();if (listener != null) {listener.onDataReady(hello);}}private void sendFileName() {CURR_STEP = STEP_FILE_NAME;L.f("sendFileName");try {int fileByteSize = streamThread.getFileByteSize();byte[] hello = YModemUtil.getFileNamePackage(fileNameString, fileByteSize, fileMd5String);if (listener != null) {listener.onDataReady(hello);}} catch (IOException e) {e.printStackTrace();}}private void startSendFileData() {CURR_STEP = STEP_FILE_BODY;L.f("startSendFileData");streamThread.start();}//Callback from the data reading thread when a data package is ready@Overridepublic void onDataReady(byte[] data) {if (listener != null) {currSending = data;//Start the timer, it will be cancelled when reponse received,// or trigger the timeout and resend the current package datatimerHelper.startTimer(timeoutListener, PACKAGE_TIME_OUT);listener.onDataReady(data);}}private void sendEOT() {CURR_STEP = STEP_EOT;L.f("sendEOT");if (listener != null) {listener.onDataReady(YModemUtil.getEOT());}}private void sendEND() {CURR_STEP = STEP_END;L.f("sendEND");if (listener != null) {try {listener.onDataReady(YModemUtil.getEnd());} catch (IOException e) {e.printStackTrace();}}}/*** ==============================================================================* Method for handling the response of a package* ==============================================================================*/private void handleHello(byte[] value) {int character = value[0];if (character == ST_C) {//Receive "C" for "HELLO"packageErrorTimes = 0;sendFileName();} else {handleOthers(character);}}//The file name package was responsedprivate void handleFileName(byte[] value) {if (value.length == 2 && value[0] == ACK && value[1] == ST_C) {//Receive 'ACK C' for file namepackageErrorTimes = 0;startSendFileData();} else if (value[0] == ST_C) {//Receive 'C' for file name, this package should be resenthandlePackageFail();} else {handleOthers(value[0]);}}private void handleFileBody(int character) {if (character == ACK) {//Receive ACK for file datapackageErrorTimes = 0;bytesSent += currSending.length;try {if (listener != null) {listener.onProgress(bytesSent, streamThread.getFileByteSize());}} catch (IOException e) {e.printStackTrace();}streamThread.keepReading();} else if (character == ST_C) {//Receive C for file data, the ymodem cannot handle this circumstance, transmission failed...if (listener != null) {listener.onFailed();}} else {handleOthers(character);}}private void handleEOT(byte[] value) {if (value[0] == ACK) {packageErrorTimes = 0;sendEND();} else if (value[0] == ST_C) {//As we haven't received ACK, we should resend EOThandlePackageFail();} else {handleOthers(value[0]);}}private void handleEnd(byte[] character) {if (character[0] == ACK) {//The last ACK represents that the transmission has been finished, but we should validate the filepackageErrorTimes = 0;} else if ((new String(character)).equals(MD5_OK)) {//The file data has been checked,Well Done!stop();if (listener != null) {listener.onSuccess();}} else if ((new String(character)).equals(MD5_ERR)) {//Oops...Transmission Failed...stop();if (listener != null) {listener.onFailed();}} else {handleOthers(character[0]);}}private void handleOthers(int character) {if (character == NAK) {//We need to resend this package as the terminal failed when checking the crchandlePackageFail();} else if (character == CAN) {//Some big problem occurred, transmission failed...stop();}}//Handle a failed package data ,resend it up to MAX_PACKAGE_SEND_ERROR_TIMES times.//If still failed, then the transmission failed.private void handlePackageFail() {packageErrorTimes++;if (packageErrorTimes < MAX_PACKAGE_SEND_ERROR_TIMES) {if (listener != null) {listener.onDataReady(currSending);}} else {//Still, we stop the transmission, release the resourcesstop();if (listener != null) {listener.onFailed();}}}/* The InputStream data reading thread was done */@Overridepublic void onFinish() {sendEOT();}//The timeout listenerprivate TimeOutHelper.ITimeOut timeoutListener = new TimeOutHelper.ITimeOut() {@Overridepublic void onTimeOut() {if (currSending != null) {handlePackageFail();}}};public static class Builder {private Context context;private String filePath;private String fileNameString;private String fileMd5String;private YModemListener listener;public Builder with(Context context) {this.context = context;return this;}public Builder filePath(String filePath) {this.filePath = filePath;return this;}public Builder fileName(String fileName) {this.fileNameString = fileName;return this;}public Builder checkMd5(String fileMd5String) {this.fileMd5String = fileMd5String;return this;}public Builder callback(YModemListener listener) {this.listener = listener;return this;}public Ymodem build() {return new Ymodem(context, filePath, fileNameString, fileMd5String, listener);}}}

该代码实现了一个Ymodem类，用于通过Ymodem协议传输文件。以下是代码的简要总结：

1. 常量定义：定义了传输步骤（HELLO、FILE_NAME、FILE_BODY、EOT、END）和一些控制字符（ACK、NAK、CAN、ST_C）以及MD5校验相关的字符串。

2. 成员变量：包括上下文（Context）、文件路径、文件名、文件MD5值、传输监听器（YModemListener）、计时器助手（TimeOutHelper）、文件流线程（FileStreamThread）、已发送字节数、当前发送的数据包、错误计数等。

3. 构造函数：初始化Ymodem对象，接受文件路径、文件名、文件MD5值和监听器作为参数。

4. 传输控制方法：

   • start(): 开始传输，调用sayHello()方法。
   • stop(): 停止传输，重置相关变量，释放资源。

5. 接收数据方法：

   • onReceiveData(byte[] respData): 处理从终端接收的数据，根据当前传输步骤调用相应的处理方法。

6. 数据发送方法：

   • sayHello(): 发送HELLO包。
   • sendFileName(): 发送文件名包。
   • startSendFileData(): 开始发送文件数据包。
   • sendEOT(): 发送EOT包。
   • sendEND(): 发送END包。

7. 响应处理方法：

   • handleHello(byte[] value): 处理HELLO包的响应。
   • handleFileName(byte[] value): 处理文件名包的响应。
   • handleFileBody(int character): 处理文件数据包的响应。
   • handleEOT(byte[] value): 处理EOT包的响应。
   • handleEnd(byte[] character): 处理END包的响应。
   • handleOthers(int character): 处理其他响应（如NAK、CAN）。

8. 失败处理方法：

   • handlePackageFail(): 处理数据包发送失败，重试发送，超过最大重试次数则停止传输。

9. 构建器类：Builder类用于方便地创建Ymodem对象，支持链式调用设置参数。

整体来说，该代码实现了一个Ymodem文件传输协议的客户端，通过分步骤发送文件数据，并处理接收端的各种响应，确保文件能够可靠地传输和校验。

3.2协议包工具类

/*** Util for encapsulating data package of ymodem protocol* <p>* Created by leonxtp on 2017/9/16.* Modified by leonxtp on 2017/9/16*/public class YModemUtil {/*This is my concrete ymodem start signal, customise it to your needs*/private static final String HELLO = "HELLO BOOTLOADER";private static final byte SOH = 0x01; /* Start Of Header with data size :128*/private static final byte STX = 0x02; /* Start Of Header with data size : 1024*/private static final byte EOT = 0x04; /* End Of Transmission */private static final byte CPMEOF = 0x1A;/* Fill the last package if not long enough */private static CRC16 crc16 = new CRC16();/*** Get the first package data for hello with a terminal*/public static byte[] getYModelHello() {return HELLO.getBytes();}/*** Get the file name package data** @param fileNameString file name in String* @param fileByteSize   file byte size of int value* @param fileMd5String  the md5 of the file in String*/public static byte[] getFileNamePackage(String fileNameString,int fileByteSize,String fileMd5String) throws IOException {byte seperator = 0x0;String fileSize = fileByteSize + "";byte[] byteFileSize = fileSize.getBytes();byte[] fileNameBytes1 = concat(fileNameString.getBytes(),new byte[]{seperator},byteFileSize);byte[] fileNameBytes2 = Arrays.copyOf(concat(fileNameBytes1,new byte[]{seperator},fileMd5String.getBytes()), 128);byte seq = 0x00;return getDataPackage(fileNameBytes2, 128, seq);}/*** Get a encapsulated package data block** @param block      byte data array* @param dataLength the actual content length in the block without 0 filled in it.* @param sequence   the package serial number* @return a encapsulated package data block*/public static byte[] getDataPackage(byte[] block, int dataLength, byte sequence) throws IOException {byte[] header = getDataHeader(sequence, block.length == 1024 ? STX : SOH);//The last package, fill CPMEOF if the dataLength is not sufficientif (dataLength < block.length) {int startFil = dataLength;while (startFil < block.length) {block[startFil] = CPMEOF;startFil++;}}//We should use short size when writing into the data package as it only needs 2 bytesshort crc = (short) crc16.calcCRC(block);ByteArrayOutputStream baos = new ByteArrayOutputStream();DataOutputStream dos = new DataOutputStream(baos);dos.writeShort(crc);dos.close();byte[] crcBytes = baos.toByteArray();return concat(header, block, crcBytes);}/*** Get the EOT package*/public static byte[] getEOT() {return new byte[]{EOT};}/*** Get the Last package*/public static byte[] getEnd() throws IOException {byte seq = 0x00;return getDataPackage(new byte[128], 128, seq);}/*** Get InputStream from Assets, you can customize it from the other sources** @param fileAbsolutePath absolute path of the file in asstes*/public static InputStream getInputStream(Context context, String fileAbsolutePath) throws IOException {return new InputStreamSource().getStream(context, fileAbsolutePath);}private static byte[] getDataHeader(byte sequence, byte start) {//The serial number of the package increases Cyclically up to 256byte modSequence = (byte) (sequence % 0x256);byte complementSeq = (byte) ~modSequence;return concat(new byte[]{start},new byte[]{modSequence},new byte[]{complementSeq});}private static byte[] concat(byte[] a, byte[] b, byte[] c) {int aLen = a.length;int bLen = b.length;int cLen = c.length;byte[] concated = new byte[aLen + bLen + cLen];System.arraycopy(a, 0, concated, 0, aLen);System.arraycopy(b, 0, concated, aLen, bLen);System.arraycopy(c, 0, concated, aLen + bLen, cLen);return concated;}
}

这段代码实现了YModem协议的数据打包工具，主要功能包括：

1. 定义常量：

   • HELLO: 自定义的启动信号字符串。
   • SOH: 表示128字节数据包的头部标志。
   • STX: 表示1024字节数据包的头部标志。
   • EOT: 传输结束标志。
   • CPMEOF: 用于填充未满数据包的字节。

2. 计算CRC16校验：

   • 使用CRC16类来计算数据包的CRC校验值。

3. 生成数据包：

   • getYModelHello(): 获取启动信号的字节数组。
   • getFileNamePackage(): 生成包含文件名、文件大小和文件MD5值的数据包。
   • getDataPackage(): 生成带有头部、数据块和CRC校验的数据包，并填充不足部分。
   • getEOT(): 获取传输结束数据包。
   • getEnd(): 获取最后一个填充128字节的数据包。
   • getInputStream(): 从资源文件中获取输入流（可定制其他来源）。

4. 私有辅助方法：

   • getDataHeader(): 生成数据包头部，包括起始字节、序列号及其补码。
   • concat(): 连接多个字节数组。

该工具类主要用于在YModem协议传输过程中打包和封装数据。

3.3文件数据读取类

/*** Thread for reading input Stream and encapsulating into a ymodem package* <p>* Created by leonxtp on 2017/9/16.* Modified by leonxtp on 2017/9/16*/public class FileStreamThread extends Thread {private Context mContext;private InputStream inputStream = null;private DataRaderListener listener;private String filePath;private AtomicBoolean isDataAcknowledged = new AtomicBoolean(false);private boolean isKeepRunning = false;private int fileByteSize = 0;public FileStreamThread(Context mContext, String filePath, DataRaderListener listener) {this.mContext = mContext;this.filePath = filePath;this.listener = listener;}public int getFileByteSize() throws IOException {if (fileByteSize == 0 || inputStream == null) {initStream();}return fileByteSize;}@Overridepublic void run() {try {prepareData();} catch (IOException e) {e.printStackTrace();}}private void prepareData() throws IOException {initStream();byte[] block = new byte[1024];int dataLength;byte blockSequence = 1;//The data package of a file is actually started from 1isDataAcknowledged.set(true);isKeepRunning = true;while (isKeepRunning) {if (!isDataAcknowledged.get()) {try {//We need to sleep for a while as the sending 1024 bytes data from ble would take several seconds//In my circumstances, this can be up to 3 seconds.Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}continue;}if ((dataLength = inputStream.read(block)) == -1) {L.f("The file data has all been read...");if (listener != null) {onStop();listener.onFinish();}break;}byte[] packige = YModemUtil.getDataPackage(block, dataLength, blockSequence);if (listener != null) {listener.onDataReady(packige);}blockSequence++;isDataAcknowledged.set(false);}}/*** When received response from the terminal ,we should keep the thread keep going*/public void keepReading() {isDataAcknowledged.set(true);}public void release() {onStop();listener = null;}private void onStop() {isKeepRunning = false;isDataAcknowledged.set(false);fileByteSize = 0;onReadFinished();}private void initStream() {if (inputStream == null) {try {inputStream = YModemUtil.getInputStream(mContext, filePath);fileByteSize = inputStream.available();} catch (IOException e) {e.printStackTrace();}}}private void onReadFinished() {if (inputStream != null) {try {inputStream.close();inputStream = null;} catch (IOException e) {e.printStackTrace();}}}public interface DataRaderListener {void onDataReady(byte[] data);void onFinish();}}

这段代码定义了一个名为`FileStreamThread`的类，该类继承自`Thread`，用于读取输入流并将其封装成 Ymodem 数据包。主要功能如下：

1. **构造函数**：初始化线程，接受`Context`、文件路径和`DataRaderListener`作为参数。
2. **获取文件大小**：通过`getFileByteSize`方法获取文件的字节大小。
3. **线程运行**：重写`run`方法，在`run`方法中调用`prepareData`方法读取文件数据并封装成 Ymodem 数据包。
4. **准备数据**：`prepareData`方法中：
   - 初始化输入流。
   - 读取文件数据，按块读取，并封装成 Ymodem 数据包。
   - 调用监听器`listener`的方法将封装好的数据包发送出去。
5. **继续读取**：当收到终端响应时，调用`keepReading`方法继续读取数据。
6. **释放资源**：`release`方法停止线程，释放资源。
7. **初始化流**：`initStream`方法初始化输入流并获取文件大小。
8. **读取完成**：`onReadFinished`方法关闭输入流并清理资源。
9. **监听器接口**：`DataRaderListener`接口用于处理数据包准备好和读取完成的事件。

总的来说，该类用于读取文件数据并将其按块封装成 Ymodem 数据包，通过监听器接口将数据包传递给外部处理。

3.4各种状态监听接口

/*** Listener of the transmission process*/
public interface YModemListener {/* the data package has been encapsulated */void onDataReady(byte[] data);/*just the file data progress*/void onProgress(int currentSent, int total);/* the file has been correctly sent to the terminal */void onSuccess();/* the task has failed with several remedial measures like retrying some times*/void onFailed();}

（四）具体使用步骤：
 

初始化

        ymodem = new Ymodem.Builder().with(this).filePath("assets://demo.bin").fileName("demo.bin").checkMd5("lsfjlhoiiw121241l241lgljaf").callback(new YModemListener() {@Overridepublic void onDataReady(byte[] data) {//send this data[] to your ble component here...}@Overridepublic void onProgress(int currentSent, int total) {//the progress of the file data has transmitted}@Overridepublic void onSuccess() {//we are well done with md5 checked}@Overridepublic void onFailed() {//the task has failed for several times of trying}}).build();ymodem.start();

开始传输

ymodem.start();

当接收到设备响应

ymodem.onReceiveData(data);

停止

ymodem.stop();