util: add fd passing to the iobufs

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

src/util-io.h

@@ -33,6 +33,7 @@
 #include <unistd.h>
 #include <sys/socket.h>
 
+#include "util-macros.h"
 #include "util-mem.h"
 
 /**
@@ -194,6 +195,7 @@ struct iobuf {
 	size_t sz;
 	size_t len;
 	char *data;
+	int fds[32];
 };
 
 /**
@@ -214,6 +216,11 @@ iobuf_new(size_t size)
 		.data = data,
 	};
 
+	int *fd;
+	ARRAY_FOR_EACH(buf->fds, fd) {
+		*fd = -1;
+	}
+
 	return buf;
 }
 
@@ -254,6 +261,19 @@ iobuf_data(struct iobuf *buf)
 	return buf->data;
 }
 
+/**
+ * Return the next available file descriptor in this buffer or -1.
+ * The fd is removed from this buffer and belongs to the caller.
+ */
+static inline int
+iobuf_take_fd(struct iobuf *buf)
+{
+	int fd = buf->fds[0];
+	if (fd != -1)
+		memmove(buf->fds, buf->fds + 1, ARRAY_LENGTH(buf->fds) - 1);
+	return fd;
+}
+
 /**
  * Remove the data bytes from the buffer. The caller must free() the data.
  * The buffer state is the same as iobuf_new() after this call.
@@ -315,6 +335,48 @@ iobuf_append_from_fd(struct iobuf *buf, int fd)
 	return nread == 0 ? rc : (int)nread;
 }
 
+/**
+ * Append all available data from the file descriptor to the pointer. The
+ * file descriptor shold be in O_NONBLOCK or this call will block. If the
+ * data exceeds the current buffer size it is resized automatically.
+ *
+ * Any file descriptors passed through the fd are placed
+ *
+ * @return The number of bytes read or a negative errno on failure. Zero
+ * indicates EOF.
+ */
+static inline int
+iobuf_recv_from_fd(struct iobuf *buf, int fd)
+{
+	char data[1024];
+	size_t nread = 0;
+	ssize_t rc;
+	do {
+		_cleanup_free_ int *fds = NULL;
+		rc = xread_with_fds(fd, data, sizeof(data), &fds);
+		if (rc == 0 || rc == -EAGAIN) {
+			break;
+		} else if (rc < 0) {
+			return rc;
+		}
+		iobuf_append(buf, data, rc);
+
+		if (fds) {
+			int *fd = fds;
+			for (size_t idx = 0; *fd != -1 && idx < ARRAY_LENGTH(buf->fds) - 1; idx++) {
+				if (buf->fds[idx] == -1) {
+					buf->fds[idx] = *fd;
+					fd++;
+				}
+			}
+		}
+
+		nread += rc;
+	} while (rc == sizeof(data));
+
+	return nread == 0 ? rc : (int)nread;
+}
+
 /**
  * Release the memory associated with this iobuf. Use iobuf_take_data()
  * prevent the data from being free()d.
@@ -327,6 +389,10 @@ iobuf_free(struct iobuf *buf)
 		buf->sz = 0;
 		buf->len = 0;
 		buf->data = NULL;
+
+		int fd;
+		while ((fd = iobuf_take_fd(buf)) != -1)
+			xclose(fd);
 		free(buf);
 	}
 	return NULL;

test/iotest.c

@@ -166,6 +166,34 @@ MUNIT_TEST(test_iobuf_append_fd)
 	return MUNIT_OK;
 }
 
+MUNIT_TEST(test_iobuf_recv_fd)
+{
+	int fds[2];
+	int rc = socketpair(AF_UNIX, SOCK_STREAM|SOCK_NONBLOCK|SOCK_CLOEXEC, 0, fds);
+	munit_assert_int(rc, ==, 0);
+
+	_cleanup_close_ int left = fds[0];
+	_cleanup_close_ int right = fds[1];
+	_cleanup_fclose_ FILE *fp = tmpfile();
+
+	/* actual message data to be sent */
+	char data[] = "some data\n";
+
+	/* Send the fd from left to right */
+	int sendfds[2] = { fileno(fp), -1 };
+	int sendrc = xsend_with_fd(left, data, sizeof(data), sendfds);
+	munit_assert_int(sendrc, ==, sizeof(data));
+
+	_cleanup_iobuf_ struct iobuf *buf = iobuf_new(64);
+	rc = iobuf_recv_from_fd(buf, right);
+	munit_assert_int(rc, ==, sizeof(data));
+
+	_cleanup_close_ int fd = iobuf_take_fd(buf);
+	munit_assert_int(fd, !=, -1);
+
+	return MUNIT_OK;
+}
+
 MUNIT_TEST(test_pass_fd)
 {
 	int fds[2];