feat: add ability to listen on unix socket/named pipe

Add a -socket option that configures the server to listen on a Unix-domain socket or Windows named pipe instead of a TCP port.  This allows webhook to be used behind a reverse proxy on multi-tenant shared hosting without the need to choose (and the permission to bind to) a free port number.

On Windows, -socket is expected to be a named pipe such as \\.\pipe\webhook, and the code uses https://github.com/microsoft/go-winio to bind the listening socket.  On other platforms, -socket is the path to a Unix domain socket such as /tmp/webhook.sock, or an abstract socket name starting with @, bound using the regular net.Listen function with the "network" parameter set to "unix".

Note: this pushes our minimum Go version up to 1.21 as that is what go-winio requires, but that is already the minimum version against which we are testing in the CI matrix.

vendor/github.com/Microsoft/go-winio/fileinfo.go

@@ -0,0 +1,106 @@
+//go:build windows
+// +build windows
+
+package winio
+
+import (
+	"os"
+	"runtime"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+// FileBasicInfo contains file access time and file attributes information.
+type FileBasicInfo struct {
+	CreationTime, LastAccessTime, LastWriteTime, ChangeTime windows.Filetime
+	FileAttributes                                          uint32
+	_                                                       uint32 // padding
+}
+
+// alignedFileBasicInfo is a FileBasicInfo, but aligned to uint64 by containing
+// uint64 rather than windows.Filetime. Filetime contains two uint32s. uint64
+// alignment is necessary to pass this as FILE_BASIC_INFO.
+type alignedFileBasicInfo struct {
+	CreationTime, LastAccessTime, LastWriteTime, ChangeTime uint64
+	FileAttributes                                          uint32
+	_                                                       uint32 // padding
+}
+
+// GetFileBasicInfo retrieves times and attributes for a file.
+func GetFileBasicInfo(f *os.File) (*FileBasicInfo, error) {
+	bi := &alignedFileBasicInfo{}
+	if err := windows.GetFileInformationByHandleEx(
+		windows.Handle(f.Fd()),
+		windows.FileBasicInfo,
+		(*byte)(unsafe.Pointer(bi)),
+		uint32(unsafe.Sizeof(*bi)),
+	); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	// Reinterpret the alignedFileBasicInfo as a FileBasicInfo so it matches the
+	// public API of this module. The data may be unnecessarily aligned.
+	return (*FileBasicInfo)(unsafe.Pointer(bi)), nil
+}
+
+// SetFileBasicInfo sets times and attributes for a file.
+func SetFileBasicInfo(f *os.File, bi *FileBasicInfo) error {
+	// Create an alignedFileBasicInfo based on a FileBasicInfo. The copy is
+	// suitable to pass to GetFileInformationByHandleEx.
+	biAligned := *(*alignedFileBasicInfo)(unsafe.Pointer(bi))
+	if err := windows.SetFileInformationByHandle(
+		windows.Handle(f.Fd()),
+		windows.FileBasicInfo,
+		(*byte)(unsafe.Pointer(&biAligned)),
+		uint32(unsafe.Sizeof(biAligned)),
+	); err != nil {
+		return &os.PathError{Op: "SetFileInformationByHandle", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	return nil
+}
+
+// FileStandardInfo contains extended information for the file.
+// FILE_STANDARD_INFO in WinBase.h
+// https://docs.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-file_standard_info
+type FileStandardInfo struct {
+	AllocationSize, EndOfFile int64
+	NumberOfLinks             uint32
+	DeletePending, Directory  bool
+}
+
+// GetFileStandardInfo retrieves ended information for the file.
+func GetFileStandardInfo(f *os.File) (*FileStandardInfo, error) {
+	si := &FileStandardInfo{}
+	if err := windows.GetFileInformationByHandleEx(windows.Handle(f.Fd()),
+		windows.FileStandardInfo,
+		(*byte)(unsafe.Pointer(si)),
+		uint32(unsafe.Sizeof(*si))); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	return si, nil
+}
+
+// FileIDInfo contains the volume serial number and file ID for a file. This pair should be
+// unique on a system.
+type FileIDInfo struct {
+	VolumeSerialNumber uint64
+	FileID             [16]byte
+}
+
+// GetFileID retrieves the unique (volume, file ID) pair for a file.
+func GetFileID(f *os.File) (*FileIDInfo, error) {
+	fileID := &FileIDInfo{}
+	if err := windows.GetFileInformationByHandleEx(
+		windows.Handle(f.Fd()),
+		windows.FileIdInfo,
+		(*byte)(unsafe.Pointer(fileID)),
+		uint32(unsafe.Sizeof(*fileID)),
+	); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	return fileID, nil
+}