1 files changed, 32 insertions, 0 deletions
diff --git a/src/io/recvfd.c b/src/io/recvfd.c
new file mode 100644
index 00000000..de376c39
--- /dev/null
+++ b/src/io/recvfd.c
@@ -0,0 +1,32 @@
+#include <sys/socket.h>
+#include <string.h>
+
+/* See https://stackoverflow.com/a/4491203
+ * Receive a file handle from socket `sock`.
+ * Sets `fd` to the result if recvmsg returns sizeof(int), otherwise to -1.
+ * Returns: the return value of recvmsg; this may be -1. */
+ssize_t recvfd(int sock, int *fd)
+{
+	ssize_t n;
+	struct iovec iov;
+	struct msghdr hdr;
+	int cmsgbuf[CMSG_SPACE(sizeof(int))];
+	struct cmsghdr *cmsg;
+	char buf = '\0';
+
+	iov.iov_base = &buf;
+	iov.iov_len = 1;
+	memset(&hdr, 0, sizeof(hdr));
+	hdr.msg_iov = &iov;
+	hdr.msg_iovlen = 1;
+	hdr.msg_control = &cmsgbuf[0];
+	hdr.msg_controllen = CMSG_SPACE(sizeof(int));
+	n = recvmsg(sock, &hdr, 0);
+	if (n <= 0) {
+		*fd = -1;
+		return n;
+	}
+	cmsg = CMSG_FIRSTHDR(&hdr);
+	*fd = *((int *)CMSG_DATA(cmsg));
+	return n;
+}