1# dt_fd_forward
2
3dt_fd_forward is a jdwpTransport library. It implements the [Java Debug Wire
4Protocol Transport Interface
5(jdwpTransport)](https://docs.oracle.com/javase/7/docs/technotes/guides/jpda/jdwpTransport.html).
6It allows one to handle and proxy JDWP traffic by supplying the implementation
7for Attach. This transport requires an address. The address is a single integer
8value that is the file-descriptor of an open AF\_UNIX socket.
9
10When this transport begins listening or attaching it will send the
11null-terminated string "dt_fd_forward:START-LISTEN\0" over the given socket.
12
13When this transport stops listening for connections it will send the
14null-terminated string "dt_fd_forward:END-LISTEN\0" over the socket.
15
16When this transport has successfully received fds from the proxy it sends the
17message "dt_fd_forward:ATTACHED\0" over the socket.
18
19When this transport has closed its copies of the fds it will send the proxy the
20message "dt_fd_forward:CLOSING\0" over the socket.
21
22When this transport accepts or attaches to a connection it will read from the
23socket a 1 byte message and 3 file-descriptors. The file descriptors are, in
24order, an fd that will be read from to get incoming JDWP packets (read\_fd\_),
25an fd that outgoing JDWP packets will be written to (write\_fd\_), and an
26_eventfd_ (write\_lock\_fd\_). The eventfd should not have any flags set. Prior
27to writing any data to write\_fd\_ the transport will _read_ from the
28write\_lock\_fd\_ and after finishing the write it will _write_ to it. This
29allows one to safely multiplex data on the write\_fd\_.
30
31This transport implements no optional capabilities, though this may change in
32the future.
33