CODEWITHSUNDEEP
c++dynamicbufferboost-asio
orlp
orlp

Reputation: 117641

Dynamically sized boost::asio::buffer

I'm reading from a boost::asio::ip::udp::socket like this:

using boost::asio::ip::udp;

// ...

char recv_buf[128];
udp::endpoint sender_endpoint;
size_t len = socket.receive_from(boost::asio::buffer(recv_buf), sender_endpoint);

Now, this works perfectly fine, but the maximum amount of characters that I am able to recieve is now 127. However I am facing a problem because I need to accept some data input of which the length can greatly vary (and is not of well-defined length with prefixed headers, for example). A solution to this would be a dynamically expanding buffer, like a vector. Is it possible to create a dynamically expanding boost::asio::buffer to accept (theoretical) infite amounts of input and store it in a container?

Upvotes: 11

Views: 7655

Answers (4)

sehe
sehe

Reputation: 392833

Boost 1.66.0 added dynamic_buffer which can adapt a reference to std::string or std::vector<CharType>:

Upvotes: 3

Cubbi
Cubbi

Reputation: 47408

UDP datagram size does not vary all that greatly: it will never be greater than 65535, leaving room for 65,527 bytes of data after the 8-byte header.

Upvotes: 5

Sean
Sean

Reputation: 10206

If you use smaller buffers, you can easily chain them together via the *BufferSequences concepts. For example, you can pass in a MutableBufferSequence to accept data from a read(2) call or pass a ConstBufferSequence for a list of buffers that you are going to write(2) out. That said, I tend to recommend using a single buffer in each direction because it tends to simplify code (though that's not always possible).

Upvotes: 1

John Zwinck
John Zwinck

Reputation: 249103

There does not appear to be any provision for dynamic sizing. And it makes sense that there would not be. Think about what would have to happen:

  • A single UDP datagram can only be received once, and at once, therefore:
  • the buffer given to the low-level system call needs to be large enough for the largest valid message, so,
  • for it to be efficient, the buffer must be allocated up-front by the caller.

So it does not make sense for there to be a dynamically-sized buffer available. As Cubbi points out, UDP datagrams have a smallish maximum size anyway, so just make your buffer as large as the largest valid message in your system and be done with it.

Upvotes: 0

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