io: add io_flush_sync().

This is needed for emergency handling in lightningd: we want to output
a (fatal) error packet on the socket, but we don't want to do so in the middle
of another packet.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/ccan/io/io.c b/ccan/io/io.c
index 68b95e82467194f13e87302e907cda5020fe37db..f298af70781d3fe90e606934614f5d06874e770f 100644 (file)
--- a/ccan/io/io.c
+++ b/ccan/io/io.c
@@ -483,3 +483,37 @@ struct io_plan *io_set_plan(struct io_conn *conn, enum io_direction dir,
 
        return plan;
 }
+
+bool io_flush_sync(struct io_conn *conn)
+{
+       struct io_plan *plan = &conn->plan[IO_OUT];
+       bool ok;
+
+       /* Not writing?  Nothing to do. */
+       if (plan->status != IO_POLLING)
+               return true;
+
+       /* Synchronous please. */
+       set_blocking(io_conn_fd(conn), true);
+
+again:
+       switch (plan->io(conn->fd.fd, &plan->arg)) {
+       case -1:
+               ok = false;
+               break;
+       /* Incomplete, try again. */
+       case 0:
+               goto again;
+       case 1:
+               ok = true;
+               /* In case they come back. */
+               set_always(conn, IO_OUT, plan->next, plan->next_arg);
+               break;
+       default:
+               /* IO should only return -1, 0 or 1 */
+               abort();
+       }
+
+       set_blocking(io_conn_fd(conn), false);
+       return ok;
+}

diff --git a/ccan/io/io.h b/ccan/io/io.h
index 1664df65f26e353120762f1ab89abc65ee01f1c9..fe42b53736005c4459c3b56afbbaa87ffe46f04a 100644 (file)
--- a/ccan/io/io.h
+++ b/ccan/io/io.h
@@ -673,6 +673,24 @@ void *io_loop(struct timers *timers, struct timer **expired);
  */
 int io_conn_fd(const struct io_conn *conn);
 
+/**
+ * io_flush_sync - (synchronously) complete any outstanding output.
+ * @conn: the connection.
+ *
+ * This is generally used as an emergency escape, for example when we
+ * want to write an error message on a socket before terminating, but it may
+ * be in the middle of existing I/O.  We don't want to service any other
+ * IO, either.
+ *
+ * This returns true if all pending output is complete, false on error.
+ * The next callback is not called on the conn, but will be as soon as
+ * io_loop() is called.
+ *
+ * See Also:
+ *     io_close_taken_fd
+ */
+bool io_flush_sync(struct io_conn *conn);
+
 /**
  * io_time_override - override the normal call for time.
  * @nowfn: the function to call.

diff --git a/ccan/io/test/run-30-io_flush_sync.c b/ccan/io/test/run-30-io_flush_sync.c
new file mode 100644 (file)
index 0000000..3ff8ff7
--- /dev/null
+++ b/ccan/io/test/run-30-io_flush_sync.c
@@ -0,0 +1,91 @@
+#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();
+}