simplesocket

simple socket helpers for C++ 2011 (or perhaps C++ 2014).

From C++ the full POSIX and OS socket functions are available. These are very powerful, offer well known semantics, but are somewhat of a pain to use.

Various libraries have attempted to offer "C++ native" socket environments, but most of these offer different semantics that are less well known. Many of them are also painful to use but in different ways.

This small set of files attempts to offer:

• A native datastructure that is understood by all socket calls, but easily manipulated and created form C++ (ComboAddress)
• Easier to use wrappers of the main BSD socket calls
• A few classes that build on the above to aid you achieve common tasks like reading a line from a socket to C++ friendly data structures

Each of these layers builds on the previous ones. If you want, you can only use only ComboAddress, or only ComboAddress and the wrappers.

Documentation (by Doxygen) is here.

Sample code

Some sample code using all three elements:

auto addresses=resolveName("ds9a.nl"); // this retrieves IPv4 and IPv6

for(auto& a : addresses) {
  a.setPort(80);
  cout << "Connecting to: " << a.toStringWithPort() << endl;

  RAIISocket rs(a.sin.sin_family, SOCK_STREAM);
  SocketCommunicator sc(rs);
  sc.connect(a);
  sc.writen("GET / HTTP/1.1\r\nHost: ds9a.nl\r\nConnection: Close\r\n\r\n");

  std::string line;
  while(sc.getLine(line)) {
    cout<<"Got: "<<line;
  }
}

This shows the use of resolveName() which when called like this retrieves IPv4 and IPv6 addresses.

In the for loop, we set the destination port to 80. The RAIISocket class creates a socket that is closed when rs goes out of scope. RAIISocket has no state, it is an int.

The SocketCommunicator class provides an interface that provides for sending of whole messages (even in the face of partial writes) and retrieving whole lines (even if they appear in multiple reads). SocketCommunicator als supports timeouts.

History

ComboAddress was first described in a 2006 blogpost and has since become a part of PowerDNS.

The simple wrappers have also long been used in various projects. The top-most classes are new.

Mission statements

To repeat, the goal of this library is in no way to sugarcoat the BSD socket API. The underlying semantics are exposed to you 100%, including the 'tristate' return codes for operations. A 0 means EOF, a negative value is an error. A positive value continues to mean what it meant.

We do translate the error conditions to exceptions. But an EOF is not an error.

The underlying socket API is not straightforward, but it is well documented. In this library, it is exactly what you get. Except with less typing.

ComboAddress

ComboAddress is and will remain a minimal wrapper around the IPv4 and IPv6 sockaddrs. It will not address other address families.

ComboAddress will contain a few hashing primitives that facilitate storing in hashed data structures.

Sample code, showing how to use ComboAddress with the native socket API:

ComboAddress aroot("198.41.0.4", 53);
sendto(s, "hello", 5, 0, (struct sockaddr*)&aroot, aroot.getSocklen());
...
ComboAddress client("::");
socklen_t slen = client.getSocklen();

csock = accept(s, (struct sockaddr*)&client, &slen);

Simple wrappers

These use the file descriptor of the socket as an object. In other words, there is absolutely no state in our code, everything lives in the kernel. The wrappers do not change semantics but only provide efficient variants that can talk to C++ objects like ComboAddress and std::string (-wrappers).

Sample code:

s = SSocket(AF_INET, SOCK_DGRAM);
ComboAddress aroot("198.41.0.4", 53);
SConnect(s, aroot);
SSend(s, "hello");

Regular return codes get returned, negative return codes get turned into exceptions. EOF is not an error.

Simple classes

Operate on bare sockets. Do provide a minimal set of non-POSIX semantics, like 'getline' on a TCP/IP socket, or 'writen' which deals with partial writes.

Optionally knows about timeouts. If a class has state, this is noted very clearly. This is done to make sure that sockets passed to instances can continue to interoperate with all other socket calls.

Status

Very early. API is likely to evolve. It is also not sure if this code will depend on Boost and/or C++ 2014. C++ 2011 is a given.

How to report errors is also still an open question. This will likely end up as a safe default which can globally be overwritten.