Thrift transport

transport.cpp

/**
 * Generic interface for a method of transporting data. A TTransport may be
 * capable of either reading or writing, but not necessarily both.
 *
 */
class TTransport {

      /**
   * Attempt to read up to the specified number of bytes into the string.
   *
   * @param buf  Reference to the location to write the data
   * @param len  How many bytes to read
   * @return How many bytes were actually read
   * @throws TTransportException If an error occurs
   */
  uint32_t read(uint8_t* buf, uint32_t len) {
    T_VIRTUAL_CALL();
    return read_virt(buf, len);
  }
  virtual uint32_t read_virt(uint8_t* /* buf */, uint32_t /* len */) {
    throw TTransportException(TTransportException::NOT_OPEN, "Base TTransport cannot read.");
  }
  // ...
}

/**
 * Helper class that provides default implementations of TTransport methods.
 *
 * This class provides default implementations of read(), readAll(), write(),
 * borrow() and consume().
 *
 * In the TTransport base class, each of these methods simply invokes its
 * virtual counterpart.  This class overrides them to always perform the
 * default behavior, without a virtual function call.
 *
 * The primary purpose of this class is to serve as a base class for
 * TVirtualTransport, and prevent infinite recursion if one of its subclasses
 * does not override the TTransport implementation of these methods.  (Since
 * TVirtualTransport::read_virt() calls read(), and TTransport::read() calls
 * read_virt().)
 */
class TTransportDefaults : public TTransport {
public:
  /*
   * TTransport *_virt() methods provide reasonable default implementations.
   * Invoke them non-virtually.
   */
  uint32_t read(uint8_t* buf, uint32_t len) { return this->TTransport::read_virt(buf, len); }
  uint32_t readAll(uint8_t* buf, uint32_t len) { return this->TTransport::readAll_virt(buf, len); }
  void write(const uint8_t* buf, uint32_t len) { this->TTransport::write_virt(buf, len); }
  const uint8_t* borrow(uint8_t* buf, uint32_t* len) {
    return this->TTransport::borrow_virt(buf, len);
  }
  void consume(uint32_t len) { this->TTransport::consume_virt(len); }

protected:
  TTransportDefaults() {}
};

/**
 * Helper class to provide polymorphism for subclasses of TTransport.
 *
 * This class implements *_virt() methods of TTransport, to call the
 * non-virtual versions of these functions in the proper subclass.
 *
 * To define your own transport class using TVirtualTransport:
 * 1) Derive your subclass from TVirtualTransport<your class>
 *    e.g:  class MyTransport : public TVirtualTransport<MyTransport> {
 * 2) Provide your own implementations of read(), readAll(), etc.
 *    These methods should be non-virtual.
 *
 * Transport implementations that need to use virtual inheritance when
 * inheriting from TTransport cannot use TVirtualTransport.
 *
 * @author Chad Walters <chad@powerset.com>
 */
template <class Transport_, class Super_ = TTransportDefaults>
class TVirtualTransport : public Super_ {
public:
  /*
   * Implementations of the *_virt() functions, to call the subclass's
   * non-virtual implementation function.
   */
  virtual uint32_t read_virt(uint8_t* buf, uint32_t len) {
    return static_cast<Transport_*>(this)->read(buf, len);
  }
}


/**
 * Base class for all transports that use read/write buffers for performance.
 *
 * TBufferBase is designed to implement the fast-path "memcpy" style
 * operations that work in the common case.  It does so with small and
 * (eventually) nonvirtual, inlinable methods.  TBufferBase is an abstract
 * class.  Subclasses are expected to define the "slow path" operations
 * that have to be done when the buffers are full or empty.
 *
 */
class TBufferBase : public TVirtualTransport<TBufferBase> {

public:
  /**
   * Fast-path read.
   *
   * When we have enough data buffered to fulfill the read, we can satisfy it
   * with a single memcpy, then adjust our internal pointers.  If the buffer
   * is empty, we call out to our slow path, implemented by a subclass.
   * This method is meant to eventually be nonvirtual and inlinable.
   */
  uint32_t read(uint8_t* buf, uint32_t len) {
    uint8_t* new_rBase = rBase_ + len;
    if (TDB_LIKELY(new_rBase <= rBound_)) {
      std::memcpy(buf, rBase_, len);
      rBase_ = new_rBase;
      return len;
    }
    return readSlow(buf, len);
  }
}


/**
 * Buffered transport. For reads it will read more data than is requested
 * and will serve future data out of a local buffer. For writes, data is
 * stored to an in memory buffer before being written out.
 *
 */
class TBufferedTransport : public TVirtualTransport<TBufferedTransport, TBufferBase> {
}