Separate and expose ancil_recv_fd/ancil_send_fd

 The goal is to make late channel creation easy, as opposed to
textclient which always creates a new channel at start time.

 This commit also moves posixishard.h inclusions as late as possible.

1 files changed, 69 insertions, 0 deletions

diff --git a/src/libunixonacid/ancil_recv_fd.c b/src/libunixonacid/ancil_recv_fd.c
new file mode 100644
index 0000000..70f2c4f
--- /dev/null
+++ b/src/libunixonacid/ancil_recv_fd.c
@@ -0,0 +1,69 @@
+/* ISC license. */
+
+#include <skalibs/sysdeps.h>
+#include <skalibs/nonposix.h>
+
+#include <errno.h>
+#include <sys/uio.h>
+#include <sys/socket.h>
+
+#include <skalibs/allreadwrite.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/ancil.h>
+#include <skalibs/posixishard.h>
+
+union aligner_u
+{
+  struct cmsghdr cmsghdr ;
+  int i ;
+} ;
+
+int ancil_recv_fd (int sock, char expected_ch)
+{
+  static int const awesomeflags =
+#ifdef SKALIBS_HASMSGDONTWAIT
+    MSG_DONTWAIT
+#else
+    0
+#endif
+    |
+#ifdef SKALIBS_HASCMSGCLOEXEC
+    MSG_CMSG_CLOEXEC
+#else
+    0
+#endif
+    ;
+  struct cmsghdr *c ;
+  ssize_t r ;
+  char ch ;
+  struct iovec v = { .iov_base = &ch, .iov_len = 1 } ;
+  union aligner_u ancilbuf[1 + (CMSG_SPACE(sizeof(int)) - 1) / sizeof(union aligner_u)] ;
+  struct msghdr msghdr =
+  {
+    .msg_name = 0,
+    .msg_namelen = 0,
+    .msg_iov = &v,
+    .msg_iovlen = 1,
+    .msg_flags = 0,
+    .msg_control = ancilbuf,
+    .msg_controllen = CMSG_SPACE(sizeof(int))
+  } ;
+  do r = recvmsg(sock, &msghdr, awesomeflags) ;
+  while (r < 0 && errno == EINTR) ;
+  if (r < 0) return r ;
+  if (!r) return (errno = EPIPE, -1) ;
+  c = CMSG_FIRSTHDR(&msghdr) ;
+  if (ch != expected_ch
+   || !c
+   || c->cmsg_level != SOL_SOCKET
+   || c->cmsg_type != SCM_RIGHTS
+   || (size_t)(c->cmsg_len - (CMSG_DATA(c) - (unsigned char *)c)) != sizeof(int)) return (errno = EPROTO, -1) ;
+#ifndef SKALIBS_HASCMSGCLOEXEC
+  if (coe(*(int *)CMSG_DATA(c)) < 0)
+  {
+    fd_close(*(int *)CMSG_DATA(c)) ;
+    return -1 ;
+  }
+#endif
+  return *(int *)CMSG_DATA(c) ;
+}