IPC Transport
DESCRIPTION
The ipc transport provides communication support between sockets within different processes on the same host. For POSIX platforms, this is implemented using UNIX domain sockets. For Windows, this is implemented using Windows named pipes. Other platforms may have different implementation strategies.
URI Formats
Traditional Names
This transport uses URIs using the scheme ipc://, followed by a path
name in the file system where the socket or named pipe should be created.
tip
On Windows, all names are prefixed by \\.\pipe\ and do not
reside in the normal file system.
On POSIX platforms, the path is taken literally, and is relative to
the current directory, unless it begins with /, in which case it is
relative to the root directory.
note
When using relative paths on POSIX systems, the address used and returned
in properties like NNG_OPT_LOCADDR and NNG_OPT_URL will also be relative.
Consequently, they will only be interpreted the same by processes that have
the same working directory.
To ensure maximum portability and safety, absolute paths are recommended
whenever possible.
note
If compatibility with legacy nanomsg applications is required,
then path names must not be longer than 122 bytes, including the final
NUL byte.
This is because legacy versions of nanomsg cannot express URLs
longer than 128 bytes, including the ipc:// prefix.
UNIX Aliases
The unix:// scheme is an alias for ipc:// and can be used inter-changeably, but only on POSIX systems.
1
Abstract Names
On Linux, this transport also can support abstract sockets.
Abstract sockets use a URI-encoded name after the abstract:// scheme, which allows arbitrary values to be conveyed
in the path, including embedded NUL bytes.
For example, the name "a\0b" would be represented as abstract://a%00b.
tip
An empty name may be used with a listener to request “auto bind” be used to select a name.
In this case the system will allocate a free name.
The name assigned may be retrieved using NNG_OPT_LOCADDR.
Abstract names do not include the leading NUL byte used in the low-level socket address.
Abstract sockets do not have any representation in the file system, and are automatically freed by the system when no longer in use.
Abstract sockets ignore socket permissions, but it is still possible to determine the credentials
of the peer with NNG_OPT_PEER_UID, and similar options.
2
Socket Address
When using an nng_sockaddr structure,
the actual structure is of type nng_sockaddr_ipc,
except for abstract sockets, which use nng_sockaddr_abstract.
Transport Options
The following transport options are supported by this transport, where supported by the underlying platform.
NNG_OPT_IPC_PERMISSIONSNNG_OPT_IPC_SECURITY_DESCRIPTORNNG_OPT_LOCADDRNNG_OPT_REMADDRNNG_OPT_PEER_GIDNNG_OPT_PEER_PIDNNG_OPT_PEER_UIDNNG_OPT_PEER_ZONEIDNNG_OPT_URL
1: The purpose of this scheme is to support a future transport making use of AF_UNIX
on Windows systems, at which time it will be necessary to discriminate between the Named Pipes and the AF_UNIX based transports.
2: This property makes it important that names be chosen randomly to prevent unauthorized access, or that checks against the peer credentials are made, or ideally, both.