diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/tsocket/tsocket_guide.txt | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/lib/tsocket/tsocket_guide.txt b/lib/tsocket/tsocket_guide.txt index 929875d31a..5e40acfeba 100644 --- a/lib/tsocket/tsocket_guide.txt +++ b/lib/tsocket/tsocket_guide.txt @@ -280,3 +280,145 @@ on failure. Note: if the socket is readable and writeable, only the writeable handler is called, this avoids deadlocks at the application level. +Async helper functions +====================== + +To make the life easier for the callers, there're 'tevent_req' based +helper functions for non-blocking io-operations. For each of this functions +to work the caller must attach the tevent_context to the tsocket_context +with tsocket_set_event_context(). Please remember that attching a new +tevent_context will reset the event state of the socket and should only +be done, when there's no async request is pending on the socket! + +The detailed calling conventions for 'tevent_req' based programming +will be explained in the 'tevent' documentation. + +To receive the next availabe datagram from socket there's a wrapper +for tsocket_recvfrom(). The caller virtually sends its desire to receive +the next available datagram by calling the tsocket_recvfrom_send() function +and attaches a callback function to the returned tevent_req via tevent_req_set_callback(). +The callback function is called when a datagram is available or an error has happened. +The callback function needs to get the result by calling +tsocket_recvfrom_recv(). The return value of tsocket_recvfrom_recv() +matches the return value from tsocket_recvfrom(). A possible errno is delivered +via the perrno parameter instead of the global errno variable. The datagram +buffer and optional the source tsocket_address of the datagram are returned as talloc +childs of the mem_ctx passed to tsocket_recvfrom_recv(). +It's important that the caller garanties that there's only one async +read request on the socket at a time. + + struct tevent_req *tsocket_recvfrom_send(struct tsocket_context *sock, + TALLOC_CTX *mem_ctx); + ssize_t tsocket_recvfrom_recv(struct tevent_req *req, + int *perrno, + TALLOC_CTX *mem_ctx, + uint8_t **buf, + struct tsocket_address **src); + +To send a datagram there's a wrapper for tsocket_sendto(). +The caller calls tsocket_sendto_send() instead of tsocket_sendto() +which returns a tevent_req allocated on the given TALLOC_CTX. +The caller attaches a callback function to the returned tevent_req via +tevent_req_set_callback(). The callback function is called when a datagram was +deliviered into the socket or an error has happened. +The callback function needs to get the result by calling +tsocket_sendto_recv(). The return value of tsocket_sendto_recv() +matches the return value from tsocket_sendto(). A possible errno is delivered +via the perrno parameter instead of the global errno variable. +Normal callers should not use this function directly, they should use +tsocket_sendto_queue_send/recv() instead. + + struct tevent_req *tsocket_sendto_send(struct tsocket_context *sock, + TALLOC_CTX *mem_ctx, + const uint8_t *buf, + size_t len, + const struct tsocket_address *dst); + ssize_t tsocket_sendto_recv(struct tevent_req *req, int *perrno); + +As only one async tsocket_sendto() call should happen at a time, +there's a 'tevent_queue' is used to serialize the sendto requests. + + struct tevent_req *tsocket_sendto_queue_send(TALLOC_CTX *mem_ctx, + struct tsocket_context *sock, + struct tevent_queue *queue, + const uint8_t *buf, + size_t len, + struct tsocket_address *dst); + ssize_t tsocket_sendto_queue_recv(struct tevent_req *req, int *perrno); + +Ther's an async helper for tsocket_connect(), which should be used +to connect TSOCKET_TYPE_STREAM based sockets. +The caller virtually sends its desire to connect to the destination +tsocket_address by calling tsocket_connect_send() and gets back a tevent_req. +The caller sets a callback function via tevent_req_set_callback(). +The callback function is called if the tsocket is connected or an error has happened. +The callback function needs to get the result by calling +tsocket_connect_recv(). The return value of tsocket_connect_recv() +matches the return value from tsocket_connect()/tsocket_get_status(). +A possible errno is delivered via the perrno parameter instead of the global +errno variable. + + struct tevent_req *tsocket_connect_send(struct tsocket_context *sock, + TALLOC_CTX *mem_ctx, + const struct tsocket_address *dst); + int tsocket_connect_recv(struct tevent_req *req, int *perrno); + +To send an 'iovec' there's a wrapper for tsocket_writev(). +The caller calls tsocket_writev_send() instead of tsocket_writev() +which returns a tevent_req allocated on the given TALLOC_CTX. +The caller attaches a callback function to the returned tevent_req via +tevent_req_set_callback(). The callback function is called when the whole iovec +was deliviered into the socket or an error has happened. +The callback function needs to get the result by calling +tsocket_writev_recv(). The return value of tsocket_writev_recv() +matches the return value from tsocket_writev(). A possible errno is delivered +via the perrno parameter instead of the global errno variable. +Normal callers should not use this function directly, they should use +tsocket_writev_queue_send/recv() instead. + + struct tevent_req *tsocket_writev_send(struct tsocket_context *sock, + TALLOC_CTX *mem_ctx, + const struct iovec *vector, + size_t count); + int tsocket_writev_recv(struct tevent_req *req, int *perrno); + +As only one async tsocket_writev() call should happen at a time, +there's a 'tevent_queue' is used to serialize the writev requests. + + struct tevent_req *tsocket_writev_queue_send(TALLOC_CTX *mem_ctx, + struct tsocket_context *sock, + struct tevent_queue *queue, + const struct iovec *vector, + size_t count); + int tsocket_writev_queue_recv(struct tevent_req *req, int *perrno); + +For TSOCKET_TYPE_STREAM sockets, it's typically desired to split the stream +into PDUs. That's why the helper function for tsocket_readv() is a bit +different compared to the other helper functions. The general rule +is still to get a tevent_req, set a callback which gets called when the +operation is done. The callback function needs to get the result by +calling tsocket_readv_recv(). The 'next_iovec' callback function +makes the difference to the other helper function. +The tsocket_writev_send/recv() logic asks the caller via the +next_iovec_fn for an iovec array, which will be filled completely +with bytes from the socket, then the next_iovec_fn is called for +the next iovec array to fill, untill the next_iovec_fn returns an empty +iovec array. That next_iovec_fn should allocate the array as child of the +passed mem_ctx, while the buffers the array referr to belong to the caller. +The tsocket_writev_send/recv() engine will modify and free the given array! +The basic idea is that the caller allocates and maintains the real buffers. +The next_iovec_fn should report error by returning -1 and setting errno to +the specific error code. The engine will pass the error to the caller +via tsocket_readv_recv(). + +typedef int (*tsocket_readv_next_iovec_t)(struct tsocket_context *sock, + void *private_data, + TALLOC_CTX *mem_ctx, + struct iovec **vector, + size_t *count); +struct tevent_req *tsocket_readv_send(struct tsocket_context *sock, + TALLOC_CTX *mem_ctx, + tsocket_readv_next_iovec_t next_iovec_fn, + void *private_data); +int tsocket_readv_recv(struct tevent_req *req, int *perrno); + |