If we write the annotation but not the microdescriptor, rewind.

This fixes bug 9047 (and some parts of 9031, 8922, 8883 that weren't
fixed in 8822).  Bugfix on 0.2.2.6-alpha.

src/common/compat.c

@@ -900,6 +900,18 @@ tor_fd_seekend(int fd)
 #endif
 }
 
+/** Move <b>fd</b> to position <b>pos</b> in the file. Return -1 on error, 0
+ * on success. */
+int
+tor_fd_setpos(int fd, off_t pos)
+{
+#ifdef _WIN32
+  return _lseek(fd, pos, SEEK_SET) < 0 ? -1 : 0;
+#else
+  return lseek(fd, pos, SEEK_SET) < 0 ? -1 : 0;
+#endif
+}
+
 #undef DEBUG_SOCKET_COUNTING
 #ifdef DEBUG_SOCKET_COUNTING
 /** A bitarray of all fds that should be passed to tor_socket_close(). Only

src/common/compat.h

@@ -411,6 +411,7 @@ tor_lockfile_t *tor_lockfile_lock(const char *filename, int blocking,
 void tor_lockfile_unlock(tor_lockfile_t *lockfile);
 
 off_t tor_fd_getpos(int fd);
+int tor_fd_setpos(int fd, off_t pos);
 int tor_fd_seekend(int fd);
 
 #ifdef _WIN32