RPC-Thrift（三）

　　TProtocol

　　　　TProtocol定义了消息怎么进行序列化和反序列化的。

　　　　TProtocol的类结构图如下：

　　　　

　　　　TBinaryProtocol：二进制编码格式；

　　　　TCompactProtocol：高效率，密集的二进制编码格式，使用了zigzag压缩算法，使用了类似于ProtocolBuffer的Variable-Length Quantity (VLQ) 编码方式；

　　　　TTupleProtocol：继承于TCompactProtocol，C++中不支持，Java中支持；

　　　　TJSONProtocol：JSON格式；

　　　　TProtocolFactory接口：只有getProtocol一个方法，用于通过一个TTransport对象创建一个TProtocol对象；TProtocolFactory接口的实现类都在TProtocol子类中。

　　　　TProtocol

　　　　　　TProtocol是所有消息协议的父类，定义了公用的抽象方法。

public abstract class TProtocol {
  @SuppressWarnings("unused")
  private TProtocol() {}
  protected TTransport trans_;//Transport
  protected TProtocol(TTransport trans) {
    trans_ = trans;
  }
  public TTransport getTransport() {
    return trans_;
  }
  /**
   * Writing methods.写方法
   */
  //TMessage表示一个请求，发送请求时调用的方法
  public abstract void writeMessageBegin(TMessage message) throws TException;
  public abstract void writeMessageEnd() throws TException;
  //TStruct表示一个对象，写对象时调用的方法
  public abstract void writeStructBegin(TStruct struct) throws TException;
  public abstract void writeStructEnd() throws TException;
  //TField表示一个字段，写字段时调用的方法
  public abstract void writeFieldBegin(TField field) throws TException;
  public abstract void writeFieldEnd() throws TException;
  //写字段结束标志调用的方法
  public abstract void writeFieldStop() throws TException;
  //写TMap时调用的方法
  public abstract void writeMapBegin(TMap map) throws TException;
  public abstract void writeMapEnd() throws TException;
  //写TList时调用的方法
  public abstract void writeListBegin(TList list) throws TException;
  public abstract void writeListEnd() throws TException;
  //写TSet时调用的方法
  public abstract void writeSetBegin(TSet set) throws TException;
  public abstract void writeSetEnd() throws TException;
  //String和基本数据类型的写
  public abstract void writeBool(boolean b) throws TException;
  public abstract void writeByte(byte b) throws TException;
  public abstract void writeI16(short i16) throws TException;
  public abstract void writeI32(int i32) throws TException;
  public abstract void writeI64(long i64) throws TException;
  public abstract void writeDouble(double dub) throws TException;
  public abstract void writeString(String str) throws TException;
  //将buf中的数据写出
  public abstract void writeBinary(ByteBuffer buf) throws TException;

  /**
   * Reading methods.读方法
   */
  public abstract TMessage readMessageBegin() throws TException;
  public abstract void readMessageEnd() throws TException;
  public abstract TStruct readStructBegin() throws TException;
  public abstract void readStructEnd() throws TException;
  public abstract TField readFieldBegin() throws TException;
  public abstract void readFieldEnd() throws TException;
  public abstract TMap readMapBegin() throws TException;
  public abstract void readMapEnd() throws TException;
  public abstract TList readListBegin() throws TException;
  public abstract void readListEnd() throws TException;
  public abstract TSet readSetBegin() throws TException;
  public abstract void readSetEnd() throws TException;
  public abstract boolean readBool() throws TException;
  public abstract byte readByte() throws TException;
  public abstract short readI16() throws TException;
  public abstract int readI32() throws TException;
  public abstract long readI64() throws TException;
  public abstract double readDouble() throws TException;
  public abstract String readString() throws TException;
  public abstract ByteBuffer readBinary() throws TException;

  public void reset() {}
  public Class<? extends IScheme> getScheme() {
    return StandardScheme.class;
  }
}

　　　　TBinaryProtocol

　　　　　　TBinaryProtocol是二进制编码。

public class TBinaryProtocol extends TProtocol {
  private static final TStruct ANONYMOUS_STRUCT = new TStruct();
  //版本号
  protected static final int VERSION_MASK = 0xffff0000;//掩码
  protected static final int VERSION_1 = 0x80010000;//版本号

  protected boolean strictRead_ = false;//是否严格读
  protected boolean strictWrite_ = true;//是否严格写

  protected int readLength_;
  protected boolean checkReadLength_ = false;

  //工厂类
  public static class Factory implements TProtocolFactory {
    protected boolean strictRead_ = false;
    protected boolean strictWrite_ = true;
    protected int readLength_;
    public Factory() {
      this(false, true);
    }
    public Factory(boolean strictRead, boolean strictWrite) {
      this(strictRead, strictWrite, 0);
    }
    public Factory(boolean strictRead, boolean strictWrite, int readLength) {
      strictRead_ = strictRead;
      strictWrite_ = strictWrite;
      readLength_ = readLength;
    }
    //通过TTransport实例获取一个TBinaryProtocol实例
    public TProtocol getProtocol(TTransport trans) {
      TBinaryProtocol proto = new TBinaryProtocol(trans, strictRead_, strictWrite_);
      if (readLength_ != 0) {
        proto.setReadLength(readLength_);
      }
      return proto;
    }
  }
  public TBinaryProtocol(TTransport trans) {
    this(trans, false, true);
  }
  public TBinaryProtocol(TTransport trans, boolean strictRead, boolean strictWrite) {
    super(trans);
    strictRead_ = strictRead;
    strictWrite_ = strictWrite;
  }
  /**
   * 写方法
   */
  //发送一个请求，最终转换为对基本数据类型的写
  public void writeMessageBegin(TMessage message) throws TException {
    if (strictWrite_) {//
      int version = VERSION_1 | message.type;//版本号和消息类型与运算
      writeI32(version);//调用writeI32写版本号
      writeString(message.name);//调用writeString写方法名
      writeI32(message.seqid);//调用writeI32写序列号
    } else {
      writeString(message.name);
      writeByte(message.type);
      writeI32(message.seqid);
    }
  }
  public void writeMessageEnd() {}
  public void writeStructBegin(TStruct struct) {}
  public void writeStructEnd() {}
  //写字段方法，最终转换为对基本数据类型的写
  public void writeFieldBegin(TField field) throws TException {
    writeByte(field.type);
    writeI16(field.id);
  }
  public void writeFieldEnd() {}
  public void writeFieldStop() throws TException {
    writeByte(TType.STOP);
  }
  //写Map
  public void writeMapBegin(TMap map) throws TException {
    writeByte(map.keyType);//写Key类型
    writeByte(map.valueType);//写value类型
    writeI32(map.size);//写map大小
  }
  public void writeMapEnd() {}
  //写List
  public void writeListBegin(TList list) throws TException {
    writeByte(list.elemType);//写元素类型
    writeI32(list.size);//写list大小
  }
  public void writeListEnd() {}
  //写Set
  public void writeSetBegin(TSet set) throws TException {
    writeByte(set.elemType);//写元素类型
    writeI32(set.size);//写Set大小
  }
  public void writeSetEnd() {}
  //写bool转换为写writeByte
  public void writeBool(boolean b) throws TException {
    writeByte(b ? (byte)1 : (byte)0);
  }
  private byte [] bout = new byte[1];
  public void writeByte(byte b) throws TException {
    bout[0] = b;
    trans_.write(bout, 0, 1);
  }
  private byte[] i16out = new byte[2];
  public void writeI16(short i16) throws TException {
    i16out[0] = (byte)(0xff & (i16 >> 8));
    i16out[1] = (byte)(0xff & (i16));
    trans_.write(i16out, 0, 2);
  }
  private byte[] i32out = new byte[4];
  public void writeI32(int i32) throws TException {
    i32out[0] = (byte)(0xff & (i32 >> 24));
    i32out[1] = (byte)(0xff & (i32 >> 16));
    i32out[2] = (byte)(0xff & (i32 >> 8));
    i32out[3] = (byte)(0xff & (i32));
    trans_.write(i32out, 0, 4);
  }
  private byte[] i64out = new byte[8];
  public void writeI64(long i64) throws TException {
    i64out[0] = (byte)(0xff & (i64 >> 56));
    i64out[1] = (byte)(0xff & (i64 >> 48));
    i64out[2] = (byte)(0xff & (i64 >> 40));
    i64out[3] = (byte)(0xff & (i64 >> 32));
    i64out[4] = (byte)(0xff & (i64 >> 24));
    i64out[5] = (byte)(0xff & (i64 >> 16));
    i64out[6] = (byte)(0xff & (i64 >> 8));
    i64out[7] = (byte)(0xff & (i64));
    trans_.write(i64out, 0, 8);
  }
  //写Double转换为writeI64
  public void writeDouble(double dub) throws TException {
    writeI64(Double.doubleToLongBits(dub));
  }
  //写String
  public void writeString(String str) throws TException {
    try {
      byte[] dat = str.getBytes("UTF-8");//转换为字节数组
      writeI32(dat.length);//写数组长度
      trans_.write(dat, 0, dat.length);//写数据
    } catch (UnsupportedEncodingException uex) {
      throw new TException("JVM DOES NOT SUPPORT UTF-8");
    }
  }
  //写ByteBuffer
  public void writeBinary(ByteBuffer bin) throws TException {
    int length = bin.limit() - bin.position();
    writeI32(length);
    trans_.write(bin.array(), bin.position() + bin.arrayOffset(), length);
  }

  /**
   * Reading methods.读方法
   */
  //读一个请求，与写请求对应
  public TMessage readMessageBegin() throws TException {
    int size = readI32();//读取消息的头部（4字节），可能是版本号和消息类型的组合，也可能直接是消息方法名
    if (size < 0) {
      //如果小于0，就是二进制为第一位以1开头，说明是带有版本号的
      //校验版本号是否正确
      int version = size & VERSION_MASK;
      if (version != VERSION_1) {
        throw new TProtocolException(TProtocolException.BAD_VERSION, "Bad version in readMessageBegin");
      }
      //三个参数依次为方法名、消息类型、消息序列号
      return new TMessage(readString(), (byte)(size & 0x000000ff), readI32());
    } else {
      if (strictRead_) {
        throw new TProtocolException(TProtocolException.BAD_VERSION, "Missing version in readMessageBegin, old client?");
      }
      //readStringBody(size)为方法名，readByte()为消息类型，readI32()为消息序列号
      return new TMessage(readStringBody(size), readByte(), readI32());
    }
  }
  public void readMessageEnd() {}
  public TStruct readStructBegin() {
    return ANONYMOUS_STRUCT;
  }
  public void readStructEnd() {}
  public TField readFieldBegin() throws TException {
    byte type = readByte();
    short id = type == TType.STOP ? 0 : readI16();
    return new TField("", type, id);
  }
  public void readFieldEnd() {}
  public TMap readMapBegin() throws TException {
    return new TMap(readByte(), readByte(), readI32());
  }
  public void readMapEnd() {}
  public TList readListBegin() throws TException {
    return new TList(readByte(), readI32());
  }
  public void readListEnd() {}
  public TSet readSetBegin() throws TException {
    return new TSet(readByte(), readI32());
  }
  public void readSetEnd() {}
  public boolean readBool() throws TException {
    return (readByte() == 1);
  }
  private byte[] bin = new byte[1];
  public byte readByte() throws TException {
    if (trans_.getBytesRemainingInBuffer() >= 1) {
      byte b = trans_.getBuffer()[trans_.getBufferPosition()];
      trans_.consumeBuffer(1);
      return b;
    }
    readAll(bin, 0, 1);
    return bin[0];
  }
  private byte[] i16rd = new byte[2];
  public short readI16() throws TException {
    byte[] buf = i16rd;
    int off = 0;
    if (trans_.getBytesRemainingInBuffer() >= 2) {
      buf = trans_.getBuffer();
      off = trans_.getBufferPosition();
      trans_.consumeBuffer(2);
    } else {
      readAll(i16rd, 0, 2);
    }
    return
      (short)
      (((buf[off] & 0xff) << 8) |
       ((buf[off+1] & 0xff)));
  }
  private byte[] i32rd = new byte[4];
  public int readI32() throws TException {
    byte[] buf = i32rd;
    int off = 0;
    if (trans_.getBytesRemainingInBuffer() >= 4) {
      buf = trans_.getBuffer();
      off = trans_.getBufferPosition();
      trans_.consumeBuffer(4);
    } else {
      readAll(i32rd, 0, 4);
    }
    return
      ((buf[off] & 0xff) << 24) |
      ((buf[off+1] & 0xff) << 16) |
      ((buf[off+2] & 0xff) <<  8) |
      ((buf[off+3] & 0xff));
  }
  private byte[] i64rd = new byte[8];
  public long readI64() throws TException {
    byte[] buf = i64rd;
    int off = 0;
    if (trans_.getBytesRemainingInBuffer() >= 8) {
      buf = trans_.getBuffer();
      off = trans_.getBufferPosition();
      trans_.consumeBuffer(8);
    } else {
      readAll(i64rd, 0, 8);
    }
    return
      ((long)(buf[off]   & 0xff) << 56) |
      ((long)(buf[off+1] & 0xff) << 48) |
      ((long)(buf[off+2] & 0xff) << 40) |
      ((long)(buf[off+3] & 0xff) << 32) |
      ((long)(buf[off+4] & 0xff) << 24) |
      ((long)(buf[off+5] & 0xff) << 16) |
      ((long)(buf[off+6] & 0xff) <<  8) |
      ((long)(buf[off+7] & 0xff));
  }
  public double readDouble() throws TException {
    return Double.longBitsToDouble(readI64());
  }
  public String readString() throws TException {
    int size = readI32();
    if (trans_.getBytesRemainingInBuffer() >= size) {
      try {
        String s = new String(trans_.getBuffer(), trans_.getBufferPosition(), size, "UTF-8");
        trans_.consumeBuffer(size);
        return s;
      } catch (UnsupportedEncodingException e) {
        throw new TException("JVM DOES NOT SUPPORT UTF-8");
      }
    }
    return readStringBody(size);
  }
  public String readStringBody(int size) throws TException {
    try {
      checkReadLength(size);
      byte[] buf = new byte[size];
      trans_.readAll(buf, 0, size);
      return new String(buf, "UTF-8");
    } catch (UnsupportedEncodingException uex) {
      throw new TException("JVM DOES NOT SUPPORT UTF-8");
    }
  }
  public ByteBuffer readBinary() throws TException {
    int size = readI32();
    checkReadLength(size);
    if (trans_.getBytesRemainingInBuffer() >= size) {
      ByteBuffer bb = ByteBuffer.wrap(trans_.getBuffer(), trans_.getBufferPosition(), size);
      trans_.consumeBuffer(size);
      return bb;
    }
    byte[] buf = new byte[size];
    trans_.readAll(buf, 0, size);
    return ByteBuffer.wrap(buf);
  }
  private int readAll(byte[] buf, int off, int len) throws TException {
    checkReadLength(len);
    return trans_.readAll(buf, off, len);
  }
  public void setReadLength(int readLength) {
    readLength_ = readLength;
    checkReadLength_ = true;
  }
  protected void checkReadLength(int length) throws TException {
    if (length < 0) {
      throw new TException("Negative length: " + length);
    }
    if (checkReadLength_) {
      readLength_ -= length;
      if (readLength_ < 0) {
        throw new TException("Message length exceeded: " + length);
      }
    }
  }
}

　　　　　　其中TMessage表示一个请求，看一下TMessage的结构。

public final class TMessage {
  public TMessage() {
    this("", TType.STOP, 0);
  }
  public TMessage(String n, byte t, int s) {
    name = n;
    type = t;
    seqid = s;
  }
  public final String name;//方法名
  public final byte type;//消息类型
  public final int seqid;//消息序列号
  @Override
  public String toString() {
    return "<TMessage name:'" + name + "' type: " + type + " seqid:" + seqid + ">";
  }
  @Override
  public boolean equals(Object other) {
    if (other instanceof TMessage) {
      return equals((TMessage) other);
    }
    return false;
  }
  public boolean equals(TMessage other) {
    return name.equals(other.name) && type == other.type && seqid == other.seqid;
  }
}

　　　　　　消息类型定义如下：

public final class TMessageType {
  public static final byte CALL  = 1;//客户端请求
  public static final byte REPLY = 2;//服务端响应
  public static final byte EXCEPTION = 3;//服务端返回异常
  public static final byte ONEWAY = 4;//单向RPC，客户端请求不要求服务端响应
}

　　　　　　TField表示一个字段，TField结构如下：

public class TField {
  public TField() {
    this("", TType.STOP, (short)0);
  }
  public TField(String n, byte t, short i) {
    name = n;
    type = t;
    id = i;
  }
  public final String name;//字段名
  public final byte   type;//字段类型
  public final short  id;//该字段在对象中的序号，与Thrift文件中的序号一致
  public String toString() {
    return "<TField name:'" + name + "' type:" + type + " field-id:" + id + ">";
  }
  public boolean equals(TField otherField) {
    return type == otherField.type && id == otherField.id;
  }
}

　　　　　　Thrift定义的数据类型

public final class TType {
  public static final byte STOP   = 0;
  public static final byte VOID   = 1;
  public static final byte BOOL   = 2;
  public static final byte BYTE   = 3;
  public static final byte DOUBLE = 4;
  public static final byte I16    = 6;
  public static final byte I32    = 8;
  public static final byte I64    = 10;
  public static final byte STRING = 11;
  public static final byte STRUCT = 12;
  public static final byte MAP    = 13;
  public static final byte SET    = 14;
  public static final byte LIST   = 15;
  public static final byte ENUM   = 16;
}

　　TProcessor

　　　　TProcessor是服务端Thrift框架转入用户逻辑的关键。先看一下类结构图。TProcessor对TServer中一次请求的InputProtocol和OutputTProtocol进行操作，也就是从InputProtocol中读出Client的请求数据，向OutputProtcol中写入用户逻辑的返回值。

　　　　

　　　　TProcessor接口：只有一个抽象方法process()；

　　　　TBaseProcessor类：实现了TProcessor接口，给出了process()方法的具体实现；

　　　　Processor类：通过thrift文件自动生成的代码，继承了TBaseProcessor类，在Processor类内部为每一个方法生成了一个类，如sayHello类；

　　　　TProcessorFactory类：一个工厂类，返回一个TProcessor单例；

　　　　ProcessFunction类：处理函数抽象类。

　　　　HelloService类：由thrift文件自动生成的类，包含内部类Processor类、参数类、返回结果类等等。

　　　　

　　　　TProcessor

public interface TProcessor {
  public boolean process(TProtocol in, TProtocol out)
    throws TException;
}

　　　　TBaseProcessor

public abstract class TBaseProcessor<I> implements TProcessor {
  private final I iface;//业务逻辑实现的接口，接口中的方法即thrift文件中定义的方法
  private final Map<String,ProcessFunction<I, ? extends TBase>> processMap;//处理方法Map，key为方法名，Value为方法对象
  protected TBaseProcessor(I iface, Map<String, ProcessFunction<I, ? extends TBase>> processFunctionMap) {
    this.iface = iface;
    this.processMap = processFunctionMap;
  }
  @Override
  public boolean process(TProtocol in, TProtocol out) throws TException {
    TMessage msg = in.readMessageBegin();//读出客户端发的请求
    ProcessFunction fn = processMap.get(msg.name);//根据方法名从processMap中找到处理方法
    if (fn == null) {
      //如果找不到该方法，返回异常
      TProtocolUtil.skip(in, TType.STRUCT);
      in.readMessageEnd();
      TApplicationException x = new TApplicationException(TApplicationException.UNKNOWN_METHOD, "Invalid method name: '"+msg.name+"'");
      out.writeMessageBegin(new TMessage(msg.name, TMessageType.EXCEPTION, msg.seqid));
      x.write(out);
      out.writeMessageEnd();
      out.getTransport().flush();
      return true;
    }
    fn.process(msg.seqid, in, out, iface);//处理请求
    return true;
  }
}

　　　　ProcessFunction

　　　　　　Thrift将方法抽象为ProcessFunction类，每一个方法都会生成一个ProcessFunction类的子类。

public abstract class ProcessFunction<I, T extends TBase> {
  private final String methodName;//方法名
  public ProcessFunction(String methodName) {
    this.methodName = methodName;
  }
  //处理请求
  public final void process(int seqid, TProtocol iprot, TProtocol oprot, I iface) throws TException {
    T args = getEmptyArgsInstance();//获取一个参数实例（TBase子类的参数实例），由子类实现
    try {
      args.read(iprot);//从iprot中读取参数，具体实现由thrift文件自动生成（见sayHello_args类）
    } catch (TProtocolException e) {
      //读取参数异常，返回异常
      iprot.readMessageEnd();
      TApplicationException x = new TApplicationException(TApplicationException.PROTOCOL_ERROR, e.getMessage());
      oprot.writeMessageBegin(new TMessage(getMethodName(), TMessageType.EXCEPTION, seqid));
      x.write(oprot);
      oprot.writeMessageEnd();
      oprot.getTransport().flush();
      return;
    }
    iprot.readMessageEnd();
    TBase result = getResult(iface, args);//获取处理结果，此时调用业务逻辑，具体实现由thrift文件自动生成（见sayHello类）
    oprot.writeMessageBegin(new TMessage(getMethodName(), TMessageType.REPLY, seqid));
    result.write(oprot);//将result写到oprot，具体实现由thrift文件自动生成（见sayHello_result类）
    oprot.writeMessageEnd();
    oprot.getTransport().flush();
  }
  //获取处理结果，调用业务逻辑，由子类实现
  protected abstract TBase getResult(I iface, T args) throws TException;
  //获取一个参数实例，由子类实现
  protected abstract T getEmptyArgsInstance();
  public String getMethodName() {
    return methodName;
  }
}

　　　　Processor

  public static class Processor<I extends Iface> extends org.apache.thrift.TBaseProcessor<I> implements org.apache.thrift.TProcessor {
    private static final Logger LOGGER = LoggerFactory.getLogger(Processor.class.getName());
    public Processor(I iface) {
      super(iface, getProcessMap(new HashMap<String, org.apache.thrift.ProcessFunction<I, ? extends org.apache.thrift.TBase>>()));
    }
    protected Processor(I iface, Map<String,  org.apache.thrift.ProcessFunction<I, ? extends  org.apache.thrift.TBase>> processMap) {
      super(iface, getProcessMap(processMap));
    }
    //初始化processMap,在Processor初始化时会调用该方法
    private static <I extends Iface> Map<String,  org.apache.thrift.ProcessFunction<I, ? extends  org.apache.thrift.TBase>> getProcessMap(Map<String,  org.apache.thrift.ProcessFunction<I, ? extends  org.apache.thrift.TBase>> processMap) {
      processMap.put("sayHello", new sayHello());
      return processMap;
    }
    //每个方法生成一个类
    private static class sayHello<I extends Iface> extends org.apache.thrift.ProcessFunction<I, sayHello_args> {
      public sayHello() {
        super("sayHello");
      }
      //获取空参数实例
      protected sayHello_args getEmptyArgsInstance() {
        return new sayHello_args();
      }
      //获取返回结果
      protected sayHello_result getResult(I iface, sayHello_args args) throws org.apache.thrift.TException {
        sayHello_result result = new sayHello_result();
        result.success = iface.sayHello(args.paramJson);//调用业务逻辑接口的sayHello方法，
        return result;
      }
    }
  }

　　

　　最后总结一下TProcessor的处理流程：

　　　　1）TServer接收到请求后，调用TProcessor的process(TProtocol in, TProtocol out)方法进行处理；

　　　　2）TProcessor通过in.readMessageBegin()获取客户端请求，并根据请求方法名找到对应的ProcessFunction实例；

　　　　3）调用ProcessFunction的process方法；

　　　　　　首先从inTProtocol中读取参数，

　　　　　　然后通过调用getResult(iface, args)方法调用业务逻辑，获取到返回结果，

　　　　　　最后将返回结果写入到outTProtocol。

　　　　

　　　

参考资料

　　Apache Thrift设计概要

　　Thrift源码分析（二）-- 协议和编解码

　　Thrift RPC详解