wangle::LengthFieldPrepender Class Reference

#include <LengthFieldPrepender.h>

Inheritance diagram for wangle::LengthFieldPrepender:

Public Member Functions
	LengthFieldPrepender (int lengthFieldLength=4, int lengthAdjustment=0, bool lengthIncludesLengthField=false, bool networkByteOrder=true)
folly::Future< folly::Unit >	write (Context *ctx, std::unique_ptr< folly::IOBuf > buf) override
Public Member Functions inherited from wangle::OutboundHandler< Win, Wout >
	~OutboundHandler () override=default
virtual folly::Future< folly::Unit >	write (Context *ctx, Win msg)=0
virtual folly::Future< folly::Unit >	writeException (Context *ctx, folly::exception_wrapper e)
virtual folly::Future< folly::Unit >	close (Context *ctx)
Public Member Functions inherited from wangle::HandlerBase< OutboundHandlerContext< Wout > >
virtual	~HandlerBase ()=default
virtual void	attachPipeline (OutboundHandlerContext< Wout > *)
virtual void	detachPipeline (OutboundHandlerContext< Wout > *)
OutboundHandlerContext< Wout > *	getContext ()

Private Attributes
int	lengthFieldLength_
int	lengthAdjustment_
bool	lengthIncludesLengthField_
bool	networkByteOrder_

Additional Inherited Members
Public Types inherited from wangle::OutboundHandler< Win, Wout >
typedef folly::Unit	rin
typedef folly::Unit	rout
typedef Win	win
typedef Wout	wout
typedef OutboundHandlerContext< Wout >	Context
Static Public Attributes inherited from wangle::OutboundHandler< Win, Wout >
static const HandlerDir	dir = HandlerDir::OUT

Detailed Description

An encoder that prepends the length of the message. The length value is prepended as a binary form.

For example, LengthFieldPrepender(2)will encode the following 12-bytes string:

+-------------—+ | "HELLO, WORLD" | +-------------—+

into the following:

+-----—+-------------—+

• 0x000C | "HELLO, WORLD" | +-----—+-------------—+

If you turned on the lengthIncludesLengthFieldLength flag in the constructor, the encoded data would look like the following (12 (original data) + 2 (prepended data) = 14 (0xE)):

+-----—+-------------—+

• 0x000E | "HELLO, WORLD" | +-----—+-------------—+

Definition at line 50 of file LengthFieldPrepender.h.

Constructor & Destructor Documentation

wangle::LengthFieldPrepender::LengthFieldPrepender ( int  lengthFieldLength = 4, int  lengthAdjustment = 0, bool  lengthIncludesLengthField = false, bool  networkByteOrder = true  )

explicit

Definition at line 25 of file LengthFieldPrepender.cpp.

    : lengthFieldLength_(lengthFieldLength)
    , lengthAdjustment_(lengthAdjustment)
    , lengthIncludesLengthField_(lengthIncludesLengthField)
    , networkByteOrder_(networkByteOrder) {
    CHECK(lengthFieldLength == 1 ||
          lengthFieldLength == 2 ||
          lengthFieldLength == 4 ||
          lengthFieldLength == 8 );
  }

Member Function Documentation

Future< Unit > wangle::LengthFieldPrepender::write ( Context *  ctx, std::unique_ptr< folly::IOBuf >  buf  )

override

Definition at line 40 of file LengthFieldPrepender.cpp.

References c, folly::IOBuf::computeChainDataLength(), folly::IOBuf::create(), wangle::OutboundHandlerContext< Out >::fireWrite(), lengthAdjustment_, lengthFieldLength_, lengthIncludesLengthField_, folly::gen::move, networkByteOrder_, uint16_t, uint32_t, uint64_t, and uint8_t.

                                            {
  int length = lengthAdjustment_ + buf->computeChainDataLength();
  if (lengthIncludesLengthField_) {
    length += lengthFieldLength_;
  }

  if (length < 0) {
    throw std::runtime_error("Length field < 0");
  }

  auto len = IOBuf::create(lengthFieldLength_);
  len->append(lengthFieldLength_);
  folly::io::RWPrivateCursor c(len.get());

  switch (lengthFieldLength_) {
    case 1: {
      if (length >= 256) {
        throw std::runtime_error("length does not fit byte");
      }
      if (networkByteOrder_) {
        c.writeBE((uint8_t)length);
      } else {
        c.writeLE((uint8_t)length);
      }
      break;
    }
    case 2: {
      if (length >= 65536) {
        throw std::runtime_error("length does not fit byte");
      }
      if (networkByteOrder_) {
        c.writeBE((uint16_t)length);
      } else {
        c.writeLE((uint16_t)length);
      }
      break;
    }
    case 4: {
      if (networkByteOrder_) {
        c.writeBE((uint32_t)length);
      } else {
        c.writeLE((uint32_t)length);
      }
      break;
    }
    case 8: {
      if (networkByteOrder_) {
        c.writeBE((uint64_t)length);
      } else {
        c.writeLE((uint64_t)length);
      }
      break;
    }
    default: {
      throw std::runtime_error("Invalid lengthFieldLength");
    }
  }

  len->prependChain(std::move(buf));
  return ctx->fireWrite(std::move(len));
}

Member Data Documentation

int wangle::LengthFieldPrepender::lengthAdjustment_

private

Definition at line 63 of file LengthFieldPrepender.h.

Referenced by write().

int wangle::LengthFieldPrepender::lengthFieldLength_

private

Definition at line 62 of file LengthFieldPrepender.h.

Referenced by write().

bool wangle::LengthFieldPrepender::lengthIncludesLengthField_

private

Definition at line 64 of file LengthFieldPrepender.h.

Referenced by write().

bool wangle::LengthFieldPrepender::networkByteOrder_

private

Definition at line 65 of file LengthFieldPrepender.h.

Referenced by write().

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The documentation for this class was generated from the following files:

• proxygen/wangle/wangle/codec/LengthFieldPrepender.h
• proxygen/wangle/wangle/codec/LengthFieldPrepender.cpp