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.

3 files changed, 131 insertions, 16 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
 
diff --git a/docs/man/nng_sockaddr.5.adoc b/docs/man/nng_sockaddr.5.adoc
index cf347f66..cd10cab4 100644
--- a/docs/man/nng_sockaddr.5.adoc
+++ b/docs/man/nng_sockaddr.5.adoc
@@ -20,21 +20,23 @@ nng_sockaddr - socket address
 #include <nng/nng.h>
 
 typedef union nng_sockaddr {
-    uint16_t            s_family;
-    nng_sockaddr_ipc    s_ipc;
-    nng_sockaddr_inproc s_inproc;
-    nng_sockaddr_in     s_in;
-    nng_sockaddr_in6    s_in6;
-    nng_sockaddr_zt     s_zt;
+    uint16_t              s_family;
+    nng_sockaddr_ipc      s_ipc;
+    nng_sockaddr_inproc   s_inproc;
+    nng_sockaddr_in       s_in;
+    nng_sockaddr_in6      s_in6;
+    nng_sockaddr_zt       s_zt;
+    nng_sockaddr_abstract s_abstract;
 } nng_sockaddr;
 
 enum sockaddr_family {
-    NNG_AF_UNSPEC = 0,
-    NNG_AF_INPROC = 1,
-    NNG_AF_IPC    = 2,
-    NNG_AF_INET   = 3,
-    NNG_AF_INET6  = 4,
-    NNG_AF_ZT     = 5,
+    NNG_AF_UNSPEC   = 0,
+    NNG_AF_INPROC   = 1,
+    NNG_AF_IPC      = 2,
+    NNG_AF_INET     = 3,
+    NNG_AF_INET6    = 4,
+    NNG_AF_ZT       = 5,
+    NNG_AF_ABSTRACT = 6
 };
 ----
 
@@ -70,12 +72,14 @@ The values of `s_family` are as follows:
 `NNG_AF_INET`:: Address for TCP/IP (v4) communication.  The `s_in` member is valid.
 `NNG_AF_INET6`:: Address for TCP/IP (v6) communication.  The `s_in6` member is valid.
 `NNG_AF_ZT`:: Address for ZeroTier transport (xref:nng_zerotier.7.adoc[nng_zerotier(7)]).  The `s_zt` member is valid.
+`NNG_AF_ABSTRACT`:: Address for an abstract UNIX domain socket.  The `s_abstract` member is valid.
 
 Please see the manual pages for each individual type for more information.
 
 == SEE ALSO
 
 [.text-left]
+xref:nng_sockaddr_abstract.5.adoc[nng_sockaddr_abstract(5)],
 xref:nng_sockaddr_in.5.adoc[nng_sockaddr_in(5)],
 xref:nng_sockaddr_in6.5.adoc[nng_sockaddr_in6(5)],
 xref:nng_sockaddr_inproc.5.adoc[nng_sockaddr_inproc(5)],
diff --git a/docs/man/nng_sockaddr_abstract.5.adoc b/docs/man/nng_sockaddr_abstract.5.adoc
new file mode 100644
index 00000000..ccdbb6c5
--- /dev/null
+++ b/docs/man/nng_sockaddr_abstract.5.adoc
@@ -0,0 +1,77 @@
+= nng_sockaddr_abstract(5)
+//
+// Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
+//
+// This document is supplied under the terms of the MIT License, a
+// copy of which should be located in the distribution where this
+// file was obtained (LICENSE.txt).  A copy of the license may also be
+// found online at https://opensource.org/licenses/MIT.
+//
+
+== NAME
+
+nng_sockaddr_abstract - abstract IPC socket address
+
+== SYNOPSIS
+
+[source,c]
+----
+#include <nng/nng.h>
+
+enum sockaddr_family {
+    NNG_AF_ABSTRACT = 6,
+};
+
+typedef struct {
+    uint16_t sa_family;
+    uint16_t sa_len;
+    char     sa_name[107];
+} nng_sockaddr_abstract;
+----
+
+== DESCRIPTION
+
+(((socket, address, abstract))) An `nng_sockaddr_abstract` is the flavor of xref:nng_sockaddr.5.adoc[`nng_sockaddr`]
+used to represent addresses associated with IPC communication using "`abstract`" sockets.
+
+Abstract sockets are only supported on Linux at present.
+These sockets have a name that is simply an array of bytes, with no special meaning.
+Abstract sockets also have no presence in the file system, do not honor any permissions, and are automatically
+cleaned up by the operating system when no longer in use.
+
+NOTE: Support for abstract sockets is a new feature in _NNG_, and it is only available on Linux.
+As such their use is not recommended for portable applications.
+
+The following structure members are present:
+
+`sa_family`::
+This field will always have the value ((`NNG_AF_ABSTRACT`)).
+
+`sa_len`::
+This field provides the name of the length stored in `sa_name`.
+
+`sa_name`::
+This field holds the name of the abstract socket.
+The bytes of name can have any value, including zero.
+
+NOTE: The name does _not_ include the leading `NUL` byte used on Linux to discriminate between
+abstract and path name sockets.
+
+=== Auto Bind
+
+An empty value (`sa_len` equal to zero) can be used on listening sockets to request the
+system allocate a name.
+On Linux systems, this will result in a name with either 5 or 8 hexadecimal ASCII characters.
+The name chosen can be obtained by retrieving the `NNG_OPT_LOCADDR` option on the listening entity.
+
+NOTE: Because a zero length name is used to indicate auto bind be used, it is impossible to specify
+an actual empty name.  This name are not supported by _NNG_, although the underlying system can support it.
+The use of that name is inadvisable anyway.
+
+
+== SEE ALSO
+
+[.text-left]
+xref:nng_sockaddr.5.adoc[nng_sockaddr(5)],
+xref:nng_ipc.7.adoc[nng_ipc(7)]
+xref:nng.7.adoc[nng(7)]