syscall: implement Unix Socket for Windows

Add implementation of AF_UNIX. This works only on Windows 10.

https://blogs.msdn.microsoft.com/commandline/2017/12/19/af_unix-comes-to-windows/

Fixes #26072

Change-Id: I76a96a472385a17901885271622fbe55d66bb720
Reviewed-on: https://go-review.googlesource.com/125456
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

2 files changed, 56 insertions, 4 deletions

diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index 638a81882a..528ef4f26d 100644
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -634,7 +634,7 @@ type RawSockaddr struct {
 
 type RawSockaddrAny struct {
 	Addr RawSockaddr
-	Pad  [96]int8
+	Pad  [100]int8
 }
 
 type Sockaddr interface {
@@ -683,19 +683,69 @@ func (sa *SockaddrInet6) sockaddr() (unsafe.Pointer, int32, error) {
 	return unsafe.Pointer(&sa.raw), int32(unsafe.Sizeof(sa.raw)), nil
 }
 
+type RawSockaddrUnix struct {
+	Family uint16
+	Path   [UNIX_PATH_MAX]int8
+}
+
 type SockaddrUnix struct {
 	Name string
+	raw  RawSockaddrUnix
 }
 
 func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, int32, error) {
-	// TODO(brainman): implement SockaddrUnix.sockaddr()
-	return nil, 0, EWINDOWS
+	name := sa.Name
+	n := len(name)
+	if n > len(sa.raw.Path) {
+		return nil, 0, EINVAL
+	}
+	if n == len(sa.raw.Path) && name[0] != '@' {
+		return nil, 0, EINVAL
+	}
+	sa.raw.Family = AF_UNIX
+	for i := 0; i < n; i++ {
+		sa.raw.Path[i] = int8(name[i])
+	}
+	// length is family (uint16), name, NUL.
+	sl := int32(2)
+	if n > 0 {
+		sl += int32(n) + 1
+	}
+	if sa.raw.Path[0] == '@' {
+		sa.raw.Path[0] = 0
+		// Don't count trailing NUL for abstract address.
+		sl--
+	}
+
+	return unsafe.Pointer(&sa.raw), sl, nil
 }
 
 func (rsa *RawSockaddrAny) Sockaddr() (Sockaddr, error) {
 	switch rsa.Addr.Family {
 	case AF_UNIX:
-		return nil, EWINDOWS
+		pp := (*RawSockaddrUnix)(unsafe.Pointer(rsa))
+		sa := new(SockaddrUnix)
+		if pp.Path[0] == 0 {
+			// "Abstract" Unix domain socket.
+			// Rewrite leading NUL as @ for textual display.
+			// (This is the standard convention.)
+			// Not friendly to overwrite in place,
+			// but the callers below don't care.
+			pp.Path[0] = '@'
+		}
+
+		// Assume path ends at NUL.
+		// This is not technically the Linux semantics for
+		// abstract Unix domain sockets--they are supposed
+		// to be uninterpreted fixed-size binary blobs--but
+		// everyone uses this convention.
+		n := 0
+		for n < len(pp.Path) && pp.Path[n] != 0 {
+			n++
+		}
+		bytes := (*[10000]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
+		sa.Name = string(bytes)
+		return sa, nil
 
 	case AF_INET:
 		pp := (*RawSockaddrInet4)(unsafe.Pointer(rsa))
diff --git a/src/syscall/types_windows.go b/src/syscall/types_windows.go
index 6911fe509c..0b839339d2 100644
--- a/src/syscall/types_windows.go
+++ b/src/syscall/types_windows.go
@@ -1139,3 +1139,5 @@ const (
 	SYMBOLIC_LINK_FLAG_DIRECTORY     = 0x1
 	_SYMLINK_FLAG_RELATIVE           = 1
 )
+
+const UNIX_PATH_MAX = 108 // defined in afunix.h