net: add RAII socket and use it instead of bare SOCKET

Introduce a class to manage the lifetime of a socket - when the object
that contains the socket goes out of scope, the underlying socket will
be closed.

In addition, the new `Sock` class has a `Send()`, `Recv()` and `Wait()`
methods that can be overridden by unit tests to mock the socket
operations.

The `Wait()` method also hides the
`#ifdef USE_POLL poll() #else select() #endif` technique from higher
level code.

1 files changed, 100 insertions, 0 deletions

diff --git a/src/util/sock.h b/src/util/sock.h
index 0d48235043..26fe60f18f 100644
--- a/src/util/sock.h
+++ b/src/util/sock.h
@@ -7,8 +7,108 @@
 
 #include <compat.h>
 
+#include <chrono>
 #include <string>
 
+/**
+ * RAII helper class that manages a socket. Mimics `std::unique_ptr`, but instead of a pointer it
+ * contains a socket and closes it automatically when it goes out of scope.
+ */
+class Sock
+{
+public:
+    /**
+     * Default constructor, creates an empty object that does nothing when destroyed.
+     */
+    Sock();
+
+    /**
+     * Take ownership of an existent socket.
+     */
+    explicit Sock(SOCKET s);
+
+    /**
+     * Copy constructor, disabled because closing the same socket twice is undesirable.
+     */
+    Sock(const Sock&) = delete;
+
+    /**
+     * Move constructor, grab the socket from another object and close ours (if set).
+     */
+    Sock(Sock&& other);
+
+    /**
+     * Destructor, close the socket or do nothing if empty.
+     */
+    virtual ~Sock();
+
+    /**
+     * Copy assignment operator, disabled because closing the same socket twice is undesirable.
+     */
+    Sock& operator=(const Sock&) = delete;
+
+    /**
+     * Move assignment operator, grab the socket from another object and close ours (if set).
+     */
+    virtual Sock& operator=(Sock&& other);
+
+    /**
+     * Get the value of the contained socket.
+     * @return socket or INVALID_SOCKET if empty
+     */
+    virtual SOCKET Get() const;
+
+    /**
+     * Get the value of the contained socket and drop ownership. It will not be closed by the
+     * destructor after this call.
+     * @return socket or INVALID_SOCKET if empty
+     */
+    virtual SOCKET Release();
+
+    /**
+     * Close if non-empty.
+     */
+    virtual void Reset();
+
+    /**
+     * send(2) wrapper. Equivalent to `send(this->Get(), data, len, flags);`. Code that uses this
+     * wrapper can be unit-tested if this method is overridden by a mock Sock implementation.
+     */
+    virtual ssize_t Send(const void* data, size_t len, int flags) const;
+
+    /**
+     * recv(2) wrapper. Equivalent to `recv(this->Get(), buf, len, flags);`. Code that uses this
+     * wrapper can be unit-tested if this method is overridden by a mock Sock implementation.
+     */
+    virtual ssize_t Recv(void* buf, size_t len, int flags) const;
+
+    using Event = uint8_t;
+
+    /**
+     * If passed to `Wait()`, then it will wait for readiness to read from the socket.
+     */
+    static constexpr Event RECV = 0b01;
+
+    /**
+     * If passed to `Wait()`, then it will wait for readiness to send to the socket.
+     */
+    static constexpr Event SEND = 0b10;
+
+    /**
+     * Wait for readiness for input (recv) or output (send).
+     * @param[in] timeout Wait this much for at least one of the requested events to occur.
+     * @param[in] requested Wait for those events, bitwise-or of `RECV` and `SEND`.
+     * @return true on success and false otherwise
+     */
+    virtual bool Wait(std::chrono::milliseconds timeout, Event requested) const;
+
+private:
+    /**
+     * Contained socket. `INVALID_SOCKET` designates the object is empty.
+     */
+    SOCKET m_socket;
+};
+
 /** Return readable error string for a network error code */
 std::string NetworkErrorString(int err);