christian
/
punchd
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

clarify 'Receiving sockets' section

This commit is contained in:
Christian Ulrich 2020-10-21 00:50:34 +02:00
parent 038b6b3f2e
commit a66f1e2e51
No known key found for this signature in database
GPG Key ID: 8241BE099775A097
1 changed files with 12 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
README.md
View File

@ -116,20 +116,23 @@ AA <- PA: ok|645
``` ```
## Receiving sockets using recvmsg ## Receiving sockets using sendmsg/recvmsg
When ``punchd`` successfully has punched a hole, i.e. has a socket that is When ``punchd`` successfully has punched a hole, i.e. has a socket that is
connected to the other peer, it will report back status "ok" to the application. connected to the other peer, it will report back status "ok" to the application.
The file descriptor representing that socket will be included in the status But how can the application now use the socket? The answer is: ``punchd`` has to
message in a control message, a.k.a ancillary message. pass the corresponding file descriptor to the application's process. On Unix
systems that is possible using the system calls ``sendmsg`` (on ``punchd``'s
side) and ``recvmsg`` (on the application's side). This allows ``punchd``
passing a control message, a.k.a. ancillary message, of type ``SCM_RIGHTS``
along with the actual contents of the status message. This control message will
contain the file descriptor.
The application has to use the ``recvmsg`` system call to receive that control The mechanism of passing file descriptors to other processes is described in the
message (it has the type ``SCM_RIGHTS``) and access the file descriptor. This man pages [unix(7)](https://linux.die.net/man/7/unix),
mechanism is described in the man pages
[unix(7)](https://linux.die.net/man/7/unix),
[cmsg(3)](https://linux.die.net/man/3/cmsg) and [cmsg(3)](https://linux.die.net/man/3/cmsg) and
[recv(2)](https://linux.die.net/man/2/recv). The example applications can be used [recv(2)](https://linux.die.net/man/2/recv). The example applications can be used
as a reference too. After receiving the file descriptor it can immediately be as a reference too. After receiving the file descriptor the application can
used to send data to the other peer. immediately use it to send data to the other peer.
# FAQ # FAQ