+/* Licensed under BSD-MIT - see LICENSE file for details */
+#ifndef CCAN_IO_H
+#define CCAN_IO_H
+#include <ccan/typesafe_cb/typesafe_cb.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+/**
+ * struct io_op - pointer to return from io functions.
+ *
+ * This undefined structure is just to help the compiler check that you
+ * really do return the result of an io-queueing method.
+ */
+struct io_op;
+
+/**
+ * struct io_next - pointer to what we're going to do next.
+ *
+ * Bundles up callbacks, generated by io_next().
+ */
+struct io_next;
+
+/**
+ * io_new_conn - create a new connection.
+ * @fd: the file descriptor.
+ * @start: the first function to call.
+ * @finish: the function to call when it's closed or fails.
+ * @arg: the argument to both @start and @finish.
+ *
+ * This creates a connection which owns @fd. @start will be called on the
+ * next return to io_loop(), and @finish will be called when an I/O operation
+ * fails, or you call io_close() on the connection.
+ *
+ * The @start function must call one of the io queueing functions
+ * (eg. io_read, io_write) and return the next function to call once
+ * that is done using io_next(). The alternative is to call io_close().
+ *
+ * Returns NULL on error (and sets errno).
+ */
+#define io_new_conn(fd, start, finish, arg) \
+ io_new_conn_((fd), \
+ typesafe_cb_preargs(struct io_op *, void *, \
+ (start), (arg), struct io_conn *), \
+ typesafe_cb_preargs(void, void *, (finish), (arg), \
+ struct io_conn *), \
+ (arg))
+struct io_conn *io_new_conn_(int fd,
+ struct io_op *(*start)(struct io_conn *, void *),
+ void (*finish)(struct io_conn *, void *),
+ void *arg);
+
+/**
+ * io_new_listener - create a new accepting listener.
+ * @fd: the file descriptor.
+ * @start: the first function to call on new connections.
+ * @finish: the function to call when the connection is closed or fails.
+ * @arg: the argument to both @start and @finish.
+ *
+ * When @fd becomes readable, we accept() and turn that fd into a new
+ * connection.
+ *
+ * Returns NULL on error (and sets errno).
+ */
+#define io_new_listener(fd, start, finish, arg) \
+ io_new_listener_((fd), \
+ typesafe_cb_preargs(struct io_op *, void *, \
+ (start), (arg), \
+ struct io_conn *), \
+ typesafe_cb_preargs(void, void *, (finish), \
+ (arg), struct io_conn *), \
+ (arg))
+struct io_listener *io_new_listener_(int fd,
+ struct io_op *(*start)(struct io_conn *,
+ void *arg),
+ void (*finish)(struct io_conn *,
+ void *arg),
+ void *arg);
+
+/**
+ * io_close_listener - delete a listener.
+ * @listener: the listener returned from io_new_listener.
+ *
+ * This closes the fd and frees @listener.
+ */
+void io_close_listener(struct io_listener *listener);
+
+/**
+ * io_write - queue data to be written.
+ * @data: the data buffer.
+ * @len: the length to write.
+ * @next: what to call next.
+ *
+ * This will queue the data buffer for writing. Once it's all written, the
+ * function registered with io_next() will be called: on an error, the finish
+ * function is called instead.
+ *
+ * Note that the I/O may actually be done immediately.
+ */
+struct io_op *io_write(const void *data, size_t len, struct io_next *next);
+
+/**
+ * io_read - queue buffer to be read.
+ * @data: the data buffer.
+ * @len: the length to read.
+ * @next: what to call next.
+ *
+ * This will queue the data buffer for reading. Once it's all read, the
+ * function registered with io_next() will be called: on an error, the finish
+ * function is called instead.
+ *
+ * Note that the I/O may actually be done immediately.
+ */
+struct io_op *io_read(void *data, size_t len, struct io_next *next);
+
+/**
+ * io_read_partial - queue buffer to be read (partial OK).
+ * @data: the data buffer.
+ * @len: the maximum length to read, set to the length actually read.
+ * @next: what to call next.
+ *
+ * This will queue the data buffer for reading. Once any data is
+ * read, @len is updated and the function registered with io_next()
+ * will be called: on an error, the finish function is called instead.
+ *
+ * Note that the I/O may actually be done immediately.
+ */
+struct io_op *io_read_partial(void *data, size_t *len, struct io_next *next);
+
+/**
+ * io_write_partial - queue data to be written (partial OK).
+ * @data: the data buffer.
+ * @len: the maximum length to write, set to the length actually written.
+ * @next: what to call next.
+ *
+ * This will queue the data buffer for writing. Once any data is
+ * written, @len is updated and the function registered with io_next()
+ * will be called: on an error, the finish function is called instead.
+ *
+ * Note that the I/O may actually be done immediately.
+ */
+struct io_op *io_write_partial(const void *data, size_t *len,
+ struct io_next *next);
+
+/**
+ * io_idle - explicitly note that this connection will do nothing.
+ * @conn: the current connection.
+ *
+ * This indicates the connection is idle: some other function will
+ * later call io_read/io_write etc. (or io_close) on it, in which case
+ * it will do that.
+ */
+struct io_op *io_idle(struct io_conn *conn);
+
+/**
+ * io_wake - wake up and idle connection.
+ * @conn: an idle connection.
+ * @next: the next function to call once queued IO is complete.
+ * @arg: the argument to @next.
+ *
+ * This makes @conn run its @next function the next time around the
+ * io_loop().
+ */
+#define io_wake(conn, next, arg) \
+ io_wake_((conn), \
+ typesafe_cb_preargs(struct io_op *, void *, \
+ (next), (arg), struct io_conn *), \
+ (arg))
+void io_wake_(struct io_conn *conn,
+ struct io_op *(*next)(struct io_conn *, void *), void *arg);
+
+/**
+ * io_break - return from io_loop()
+ * @arg: non-NULL value to return from io_loop().
+ * @next: what to call next (can be NULL if we expect no return).
+ *
+ * This breaks out of the io_loop. As soon as the current @next
+ * function returns, any io_closed()'d connections will have their
+ * finish callbacks called, then io_loop() with return with @arg.
+ *
+ * If io_loop() is called again, then @next will be called.
+ */
+struct io_op *io_break(void *arg, struct io_next *next);
+
+/**
+ * io_next - indicate what callback to call next.
+ * @conn: this connection.
+ * @next: the next function to call once queued IO is complete.
+ * @arg: the argument to @next.
+ *
+ * Every @next (or @start) function should "return io_next(...);" once
+ * they have indicated what io to perform (eg. io_write, io_idle).
+ * The exception is io_close(), which can be used instead of io_next().
+ *
+ * Note that as an optimization, the next function may be called
+ * immediately, which is why this should be the last statement in your
+ * function.
+ */
+#define io_next(conn, next, arg) \
+ io_next_((conn), \
+ typesafe_cb_preargs(struct io_op *, void *, \
+ (next), (arg), struct io_conn *), \
+ (arg))
+struct io_next *io_next_(struct io_conn *conn,
+ struct io_op *(*next)(struct io_conn *, void *arg),
+ void *arg);
+
+/* FIXME: io_recvfrom/io_sendto */
+
+/**
+ * io_close - terminate a connection.
+ * @conn: any connection.
+ *
+ * The schedules a connection to be closed. It can be done on any
+ * connection, whether it has I/O queued or not (though that I/O may
+ * be performed first).
+ *
+ * It's common to 'return io_close(...)' from a @next function, but
+ * io_close can also be used as an argument to io_next().
+ */
+struct io_op *io_close(struct io_conn *, void *unused);
+
+/**
+ * io_loop - process fds until all closed on io_break.
+ *
+ * This is the core loop; it exits with the io_break() arg, or NULL if
+ * all connections and listeners are closed.
+ */
+void *io_loop(void);
+#endif /* CCAN_IO_H */