fixes #1041 Abstract socket address for IPC

fixes #1326 Linux IPC could use fchmod
fixes #1327 getsockname on ipc may not work

This introduces an abstract:// style transport, which on Linux
results in using the abstract socket with the given name (not
including the leading NULL byte).  A new NNG_AF_ABSTRACT is
provided.  Auto bind abstract sockets are also supported.

While here we have inlined the aios for the POSIX ipc pipe
objects, eliminating at least one set of failure paths, and
have also performed various other cleanups.

A unix:// alias is available on POSIX systems, which acts just
like ipc:// (and is fact just an alias).  This is supplied so
that in the future we can add support for AF_UNIX on Windows.

We've also absorbed the ipcperms test into the new ipc_test suite.

Finally we are now enforcing that IPC path names on Windows are
not over the maximum size, rather than just silently truncating
them.

1 files changed, 38 insertions, 4 deletions

diff --git a/docs/man/nng_ipc.7.adoc b/docs/man/nng_ipc.7.adoc
index 0d75e8d3..856a00ac 100644
--- a/docs/man/nng_ipc.7.adoc
+++ b/docs/man/nng_ipc.7.adoc
@@ -1,6 +1,6 @@
 = nng_ipc(7)
 //
-// Copyright 2019 Staysail Systems, Inc. <info@staysail.tech>
+// Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
 // Copyright 2018 Capitar IT Group BV <info@capitar.com>
 //
 // This document is supplied under the terms of the MIT License, a
@@ -38,7 +38,9 @@ Other platforms may have different implementation strategies.
 This transport is generally built-in to the core, so
 no extra steps to use it should be necessary.
 
-=== URI Format
+=== URI Formats
+
+==== Traditional Names
 
 (((URI, `ipc://`)))
 This transport uses URIs using the scheme `ipc://`, followed by a path
@@ -58,15 +60,47 @@ To ensure maximum portability and safety, absolute paths are recommended
 whenever possible.
 
 NOTE: If compatibility with legacy _nanomsg_ applications is required,
-then pathnames must not be longer than 122 bytes, including the final
+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
+
+(((URI, `unix://`)))
+The `unix://` scheme is an alias for `ipc://` and can be used inter-changeably, but only
+on POSIX systems.
+
+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.
+
+==== Abstract Names
+
+(((URI, `abstract://`)))
+On Linux, this transport also can support abstract sockets.
+Abstract sockets use a URI-encoded name after the 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`.
+
+NOTE: _NNG_ cannot represent an abstract socket with the empty name.
+
+NOTE: 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`, etc.
+
 === Socket Address
 
 When using an xref:nng_sockaddr.5.adoc[`nng_sockaddr`] structure,
-the actual structure is of type xref:nng_sockaddr_ipc.5.adoc[`nng_sockaddr_ipc`].
+the actual structure is of type xref:nng_sockaddr_ipc.5.adoc[`nng_sockaddr_ipc`],
+except for abstract sockets, which use xref:nng_sockaddr_abstract.5.adoc[`nng_sockaddr_abstract`].
 
 === Transport Options