Add abstract namespace support for ipc sockets on LInux
Description
The abstract socket namespace on Linux allows one to create Unix domain sockets which are not bound to the filesystem.
Abstract Unix sockets have the following benefits:
Reduces filesystem clutter
Obviates target directory existence and permissions checks
No file to remove on close
Access to abstract sockets are not restricted by filesystem permissions checks (it is questionable whether this really is a benefit)
This feature has been discussed previously in the following issues:
LIBZMQ-134
LIBZMQ-48
LIBZMQ-260
The suggested feature would allow specifying the abstract namespace by prefixing the ipc path with a strudel or "at symbol" (@) like ipc://@abstract-socket. Internally, the strudel is replaced with the NULL character ('\0'), indicating a socket in the abstract namespace. The use of the strudel as the first character prevents premature termination of the string on systems where strings are NULL terminated. It is used elsewhere, including the Linux version of netstat.
On non-Linux systems, the strudel is not replaced and an error will likely occur if a slash is included in the path because of the missing directory. Alternately, the use of the strudel as the first character of the path could produce an error on non-Linux systems.
If one needs to create a socket in the local directory with a name starting with the strudel, it can be done by prefixing the path with "./" such as ipc://./@my-socket.
The abstract socket namespace on Linux allows one to create Unix domain sockets which are not bound to the filesystem.
Abstract Unix sockets have the following benefits:
Reduces filesystem clutter
Obviates target directory existence and permissions checks
No file to remove on close
Access to abstract sockets are not restricted by filesystem permissions checks (it is questionable whether this really is a benefit)
This feature has been discussed previously in the following issues:
LIBZMQ-134
LIBZMQ-48
LIBZMQ-260
The suggested feature would allow specifying the abstract namespace by prefixing the ipc path with a strudel or "at symbol" (@) like
ipc://@abstract-socket. Internally, the strudel is replaced with the NULL character ('\0'), indicating a socket in the abstract namespace. The use of the strudel as the first character prevents premature termination of the string on systems where strings are NULL terminated. It is used elsewhere, including the Linux version of netstat.On non-Linux systems, the strudel is not replaced and an error will likely occur if a slash is included in the path because of the missing directory. Alternately, the use of the strudel as the first character of the path could produce an error on non-Linux systems.
If one needs to create a socket in the local directory with a name starting with the strudel, it can be done by prefixing the path with "./" such as
ipc://./@my-socket.Feature implemented in changeset.
Test implemented in changeset.