+#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>
+#include <sys/wait.h>
+#include <stdio.h>
+
+static size_t bytes_written;
+
+/* Should be called multiple times, since only writes 1 byte. */
+static int do_controlled_write(int fd, struct io_plan_arg *arg)
+{
+ ssize_t ret;
+
+ ret = write(fd, arg->u1.cp, 1);
+ if (ret < 0)
+ return -1;
+ bytes_written += ret;
+ arg->u1.cp += ret;
+ arg->u2.s -= ret;
+ return arg->u2.s == 0;
+}
+
+static int do_error(int fd, struct io_plan_arg *arg)
+{
+ errno = 1001;
+ return -1;
+}
+
+static struct io_plan *conn_wait(struct io_conn *conn, void *unused)
+{
+ return io_wait(conn, conn, io_never, NULL);
+}
+
+static struct io_plan *init_conn_writer(struct io_conn *conn, const char *str)
+{
+ struct io_plan_arg *arg = io_plan_arg(conn, IO_OUT);
+
+ arg->u1.const_vp = str;
+ arg->u2.s = strlen(str);
+
+ return io_set_plan(conn, IO_OUT, do_controlled_write, conn_wait, NULL);
+}
+
+static struct io_plan *init_conn_reader(struct io_conn *conn, void *dst)
+{
+ /* Never actually succeeds. */
+ return io_read(conn, dst, 1000, io_never, NULL);
+}
+
+static struct io_plan *init_conn_error(struct io_conn *conn, void *unused)
+{
+ io_plan_arg(conn, IO_OUT);
+ return io_set_plan(conn, IO_OUT, do_error, io_never, NULL);
+}
+
+int main(void)
+{
+ int fd = open("/dev/null", O_RDWR);
+ const tal_t *ctx = tal(NULL, char);
+ struct io_conn *conn;
+
+ /* This is how many tests you plan to run */
+ plan_tests(9);
+
+ conn = io_new_conn(ctx, fd, init_conn_writer, "hello");
+ ok1(bytes_written == 0);
+
+ ok1(io_flush_sync(conn));
+ ok1(bytes_written == strlen("hello"));
+
+ /* This won't do anything */
+ ok1(io_flush_sync(conn));
+ ok1(bytes_written == strlen("hello"));
+
+ /* It's reading, this won't do anything. */
+ conn = io_new_conn(ctx, fd, init_conn_reader, ctx);
+ ok1(io_flush_sync(conn));
+ ok1(bytes_written == strlen("hello"));
+
+ /* Now test error state. */
+ conn = io_new_conn(ctx, fd, init_conn_error, ctx);
+ ok1(!io_flush_sync(conn));
+ ok1(errno == 1001);
+
+ tal_free(ctx);
+
+ /* This exits depending on whether all tests passed */
+ return exit_status();
+}