mbed之socket封装初识
首先定义一个socket类，类的成员方法都是虚函数（即函数体，具体实现函数体需要派生类去做），这样就可以一个虚函数在不同的派生类中有不同的实现体，这也就是接口多态的体现。
socket类中的虚函数成员全部都是 lwip的socket接口的同名函数。
/** Abstract socket class
*/
class Socket {
public:
/** Destroy a socket.
*
* Closes socket if the socket is still open
*/
virtual ~Socket() {}
/** Close the socket.
*
* Closes any open connection and deallocates any memory associated
* with the socket. Called from destructor if socket is not closed.
*
* @return NSAPI_ERROR_OK on success, negative error code on failure
*/
virtual nsapi_error_t close() = 0;
/** Connects socket to a remote address.
*
* Attempt to make connection on connection-mode protocol or set or reset
* the peer address on connectionless protocol.
*
* Also connectionless protocols use the connected address to filter
* incoming packets for recv() and recvfrom() calls.
*
* To reset the peer address, zero initialized(default constructor) SocketAddress
* object have to be in the address parameter.
*
* @param address The SocketAddress of the remote peer
* @return NSAPI_ERROR_OK on success, negative error code on failure
*/
virtual nsapi_error_t connect(const SocketAddress &address) = 0;
/** Send data on a socket
*
* The socket must be connected to a remote host before send() call.
* Returns the number of bytes sent from the buffer.
* In case of connectionless socket, send data to pre-specified remote.
*
* By default, send blocks until all data is sent. If socket is set to
* non-blocking or times out, a partial amount can be written.
* NSAPI_ERROR_WOULD_BLOCK is returned if no data was written.
*
* @param data Buffer of data to send to the host
* @param size Size of the buffer in bytes
* @return Number of sent bytes on success, negative error
* code on failure.
*/
virtual nsapi_size_or_error_t send(const void *data, nsapi_size_t size) = 0;
/** Receive data from a socket.
*
* Receive data from connected socket or in case of connectionless socket
* this is equivalent of calling recvfrom(NULL, data, size).
*
* If socket is connected, only packets coming from connected peer address
* are accepted.
*
* @note recv() is allowed write to data buffer even if error occurs.
*
* By default, recv blocks until some data is received. If socket is set to
* non-blocking or times out, NSAPI_ERROR_WOULD_BLOCK can be returned to
* indicate no data.
*
* @param data Destination buffer for data received from the host
* @param size Size of the buffer in bytes
* @return Number of received bytes on success, negative error
* code on failure. If no data is available to be received
* and the peer has performed an orderly shutdown,
* recv() returns 0.
*/
virtual nsapi_size_or_error_t recv(void *data, nsapi_size_t size) = 0;
/** Send a message on a socket.
*
* The sendto() function shall send a message through a connection-mode or connectionless-mode socket.
* If the socket is connectionless-mode, the message shall be sent to the address specified.
* If the socket is connection-mode, address shall be ignored.
*
* By default, sendto blocks until data is sent. If socket is set to
* non-blocking or times out, NSAPI_ERROR_WOULD_BLOCK is returned
* immediately.
*
* @param address Remote address
* @param data Buffer of data to send to the host
* @param size Size of the buffer in bytes
* @return Number of sent bytes on success, negative error
* code on failure
*/
virtual nsapi_size_or_error_t sendto(const SocketAddress &address,
const void *data, nsapi_size_t size) = 0;
/** Receive a data from a socket
*
* Receives a data and stores the source address in address if address
* is not NULL. Returns the number of bytes written into the buffer.
*
* If socket is connected, only packets coming from connected peer address
* are accepted.
*
* @note recvfrom() is allowed write to address and data buffers even if error occurs.
*
* By default, recvfrom blocks until a datagram is received. If socket is set to
* non-blocking or times out with no data, NSAPI_ERROR_WOULD_BLOCK
* is returned.
*
* @param address Destination for the source address or NULL
* @param data Destination buffer for datagram received from the host
* @param size Size of the buffer in bytes
* @return Number of received bytes on success, negative error
* code on failure
*/
virtual nsapi_size_or_error_t recvfrom(SocketAddress *address,
void *data, nsapi_size_t size) = 0;
/** Bind a specific address to a socket.
*
* Binding a socket specifies the address and port on which to receive
* data. If the IP address is zeroed, only the port is bound.
*
* @param address Local address to bind
* @return NSAPI_ERROR_OK on success, negative error code on failure.
*/
virtual nsapi_error_t bind(const SocketAddress &address) = 0;
/** Set blocking or non-blocking mode of the socket.
*
* Initially all sockets are in blocking mode. In non-blocking mode
* blocking operations such as send/recv/accept return
* NSAPI_ERROR_WOULD_BLOCK if they can not continue.
*
* set_blocking(false) is equivalent to set_timeout(0)
* set_blocking(true) is equivalent to set_timeout(-1)
*
* @param blocking true for blocking mode, false for non-blocking mode.
*/
virtual void set_blocking(bool blocking) = 0;
/** Set timeout on blocking socket operations.
*
* Initially all sockets have unbounded timeouts. NSAPI_ERROR_WOULD_BLOCK
* is returned if a blocking operation takes longer than the specified
* timeout. A timeout of 0 removes the timeout from the socket. A negative
* value give the socket an unbounded timeout.
*
* set_timeout(0) is equivalent to set_blocking(false)
* set_timeout(-1) is equivalent to set_blocking(true)
*
* @param timeout Timeout in milliseconds
*/
virtual void set_timeout(int timeout) = 0;
/** Register a callback on state change of the socket.
*
* The specified callback will be called on state changes such as when
* the socket can recv/send/accept successfully and on when an error
* occurs. The callback may also be called spuriously without reason.
*
* The callback may be called in an interrupt context and should not
* perform expensive operations such as recv/send calls.
*
* Note! This is not intended as a replacement for a poll or attach-like
* asynchronous api, but rather as a building block for constructing
* such functionality. The exact timing of when the registered function
* is called is not guaranteed and susceptible to change.
*
* @param func Function to call on state change.
*/
virtual void sigio(mbed::Callback func) = 0;
/** Set socket options.
*
* setsockopt() allows an application to pass stack-specific options
* to the underlying stack using stack-specific level and option names,
* or to request generic options using levels from nsapi_socket_level_t.
*
* For unsupported options, NSAPI_ERROR_UNSUPPORTED is returned
* and the socket is unmodified.
*
* @param level Stack-specific protocol level or nsapi_socket_level_t.
* @param optname Level-specific option name.
* @param optval Option value.
* @param optlen Length of the option value.
* @return NSAPI_ERROR_OK on success, negative error code on failure.
*/
virtual nsapi_error_t setsockopt(int level, int optname, const void *optval, unsigned optlen) = 0;
/** Get socket options.
*
* getsockopt() allows an application to retrieve stack-specific options
* from the underlying stack using stack-specific level and option names,
* or to request generic options using levels from nsapi_socket_level_t.
*
* For unsupported options, NSAPI_ERROR_UNSUPPORTED is returned
* and the socket is unmodified.
*
* @param level Stack-specific protocol level or nsapi_socket_level_t.
* @param optname Level-specific option name.
* @param optval Destination for option value.
* @param optlen Length of the option value.
* @return NSAPI_ERROR_OK on success, negative error code on failure.
*/
virtual nsapi_error_t getsockopt(int level, int optname, void *optval, unsigned *optlen) = 0;
/** Accepts a connection on a socket.
*
* The server socket must be bound and set to listen for connections.
* On a new connection, returns connected network socket which user is expected to call close()
* and that deallocates the resources. Referencing a returned pointer after a close()
* call is not allowed and leads to undefined behavior.
*
* By default, accept blocks until incoming connection occurs. If socket is set to
* non-blocking or times out, error is set to NSAPI_ERROR_WOULD_BLOCK.
*
* @param error pointer to storage of the error value or NULL
* @return pointer to a socket
*/
virtual Socket *accept(nsapi_error_t *error = NULL) = 0;
/** Listen for incoming connections.
*
* Marks the socket as a passive socket that can be used to accept
* incoming connections.
*
* @param backlog Number of pending connections that can be queued
* simultaneously, defaults to 1
* @return NSAPI_ERROR_OK on success, negative error code on failure
*/
virtual nsapi_error_t listen(int backlog = 1) = 0;
/** Get the remote-end peer associated with this socket.
*
* Copy the remote peer address to a SocketAddress structure pointed by
* address parameter. Socket must be connected to have a peer address
* associated.
*
* @param address Pointer to SocketAddress structure.
* @return NSAPI_ERROR_OK on success, negative error code on failure.
*/
virtual nsapi_error_t getpeername(SocketAddress *address) = 0;
};
Socket派生出一个类TLSSocketWrapper，但是socket接口还是虚函数。
class TLSSocketWrapper : public Socket {
｝