+#include <ccan/io/io.h>
+/* Include the C files directly. */
+#include <ccan/io/poll.c>
+#include <ccan/io/io.c>
+#include <ccan/tap/tap.h>
+
+static struct io_conn *out_conn;
+
+/* Write one byte at a time. */
+static int do_slow_write(int fd, struct io_plan_arg *arg)
+{
+ ssize_t ret = write(fd, arg->u1.cp, 1);
+ if (ret < 0)
+ return -1;
+
+ arg->u1.cp += ret;
+ arg->u2.s -= ret;
+ return arg->u2.s == 0;
+}
+
+static struct io_plan *io_slow_write(struct io_conn *conn,
+ const void *data, size_t len,
+ struct io_plan *(*next)(struct io_conn *,
+ void *),
+ void *next_arg)
+{
+ struct io_plan_arg *arg = io_plan_arg(conn, IO_OUT);
+
+ arg->u1.const_vp = data;
+ arg->u2.s = len;
+
+ return io_set_plan(conn, IO_OUT, do_slow_write, next, next_arg);
+}
+
+static struct io_plan *out_conn_done(struct io_conn *conn, void *unused)
+{
+ ok1(!io_plan_out_started(conn));
+ return io_close(conn);
+}
+
+static struct io_plan *init_out_conn(struct io_conn *conn, void *unused)
+{
+ ok1(!io_plan_out_started(conn));
+ return io_slow_write(conn, "12", 2, out_conn_done, NULL);
+}
+
+static int do_nothing(int fd, struct io_plan_arg *arg)
+{
+ return 1;
+}
+
+static struct io_plan *dummy_read(struct io_conn *conn,
+ struct io_plan *(*next)
+ (struct io_conn *, void *),
+ void *next_arg)
+{
+ io_plan_arg(conn, IO_IN);
+ return io_set_plan(conn, IO_IN, do_nothing, next, next_arg);
+}
+
+static struct io_plan *in_post_read(struct io_conn *conn, void *buf)
+{
+ /* It might not have started yet: try again. */
+ if (!io_plan_out_started(out_conn))
+ return dummy_read(conn, in_post_read, NULL);
+ ok1(io_plan_out_started(out_conn));
+
+ /* Final read, then close */
+ return io_read(conn, (char *)buf+1, 1, io_close_cb, NULL);
+}
+
+static struct io_plan *init_in_conn(struct io_conn *conn, char *buf)
+{
+ return io_read(conn, buf, 1, in_post_read, buf);
+}
+
+int main(void)
+{
+ int fds[2];
+ const tal_t *ctx = tal(NULL, char);
+ char *buf = tal_arr(ctx, char, 3);
+
+ /* This is how many tests you plan to run */
+ plan_tests(4);
+
+ if (pipe(fds) != 0)
+ abort();
+
+ buf[2] = '\0';
+
+ io_new_conn(ctx, fds[0], init_in_conn, buf);
+ out_conn = io_new_conn(ctx, fds[1], init_out_conn, NULL);
+
+ io_loop(NULL, NULL);
+ ok1(strcmp(buf, "12") == 0);
+ tal_free(ctx);
+
+ /* This exits depending on whether all tests passed */
+ return exit_status();
+}