2 files changed, 152 insertions, 0 deletions
diff --git a/internal/linux/interface.go b/internal/linux/interface.go
new file mode 100644
index 00000000..cf984a32
--- /dev/null
+++ b/internal/linux/interface.go
@@ -0,0 +1,69 @@
+package linux
+
+import (
+	"io/fs"
+	"os/user"
+	"path"
+	"strconv"
+
+	"git.ophivana.moe/security/fortify/internal/fmsg"
+)
+
+// System provides safe access to operating system resources.
+type System interface {
+	// Geteuid provides [os.Geteuid].
+	Geteuid() int
+	// LookupEnv provides [os.LookupEnv].
+	LookupEnv(key string) (string, bool)
+	// TempDir provides [os.TempDir].
+	TempDir() string
+	// LookPath provides [exec.LookPath].
+	LookPath(file string) (string, error)
+	// Executable provides [os.Executable].
+	Executable() (string, error)
+	// Lookup provides [user.Lookup].
+	Lookup(username string) (*user.User, error)
+	// ReadDir provides [os.ReadDir].
+	ReadDir(name string) ([]fs.DirEntry, error)
+	// Stat provides [os.Stat].
+	Stat(name string) (fs.FileInfo, error)
+	// Open provides [os.Open]
+	Open(name string) (fs.File, error)
+	// Exit provides [os.Exit].
+	Exit(code int)
+
+	// FshimPath returns an absolute path to the fshim binary.
+	FshimPath() string
+	// Paths returns a populated [Paths] struct.
+	Paths() Paths
+	// SdBooted implements https://www.freedesktop.org/software/systemd/man/sd_booted.html
+	SdBooted() bool
+}
+
+// Paths contains environment dependent paths used by fortify.
+type Paths struct {
+	// path to shared directory e.g. /tmp/fortify.%d
+	SharePath string `json:"share_path"`
+	// XDG_RUNTIME_DIR value e.g. /run/user/%d
+	RuntimePath string `json:"runtime_path"`
+	// application runtime directory e.g. /run/user/%d/fortify
+	RunDirPath string `json:"run_dir_path"`
+}
+
+// CopyPaths is a generic implementation of [System.Paths].
+func CopyPaths(os System, v *Paths) {
+	v.SharePath = path.Join(os.TempDir(), "fortify."+strconv.Itoa(os.Geteuid()))
+
+	fmsg.VPrintf("process share directory at %q", v.SharePath)
+
+	if r, ok := os.LookupEnv(xdgRuntimeDir); !ok || r == "" || !path.IsAbs(r) {
+		// fall back to path in share since fortify has no hard XDG dependency
+		v.RunDirPath = path.Join(v.SharePath, "run")
+		v.RuntimePath = path.Join(v.RunDirPath, "compat")
+	} else {
+		v.RuntimePath = r
+		v.RunDirPath = path.Join(v.RuntimePath, "fortify")
+	}
+
+	fmsg.VPrintf("runtime directory at %q", v.RunDirPath)
+}
diff --git a/internal/linux/std.go b/internal/linux/std.go
new file mode 100644
index 00000000..704ba162
--- /dev/null
+++ b/internal/linux/std.go
@@ -0,0 +1,83 @@
+package linux
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"os/exec"
+	"os/user"
+	"sync"
+
+	"git.ophivana.moe/security/fortify/internal"
+	"git.ophivana.moe/security/fortify/internal/fmsg"
+)
+
+// Std implements System using the standard library.
+type Std struct {
+	paths     Paths
+	pathsOnce sync.Once
+
+	sdBooted     bool
+	sdBootedOnce sync.Once
+
+	fshim     string
+	fshimOnce sync.Once
+}
+
+func (s *Std) Geteuid() int                               { return os.Geteuid() }
+func (s *Std) LookupEnv(key string) (string, bool)        { return os.LookupEnv(key) }
+func (s *Std) TempDir() string                            { return os.TempDir() }
+func (s *Std) LookPath(file string) (string, error)       { return exec.LookPath(file) }
+func (s *Std) Executable() (string, error)                { return os.Executable() }
+func (s *Std) Lookup(username string) (*user.User, error) { return user.Lookup(username) }
+func (s *Std) ReadDir(name string) ([]os.DirEntry, error) { return os.ReadDir(name) }
+func (s *Std) Stat(name string) (fs.FileInfo, error)      { return os.Stat(name) }
+func (s *Std) Open(name string) (fs.File, error)          { return os.Open(name) }
+func (s *Std) Exit(code int)                              { fmsg.Exit(code) }
+
+const xdgRuntimeDir = "XDG_RUNTIME_DIR"
+
+func (s *Std) FshimPath() string {
+	s.fshimOnce.Do(func() {
+		p, ok := internal.Path(internal.Fshim)
+		if !ok {
+			fmsg.Fatal("invalid fshim path, this copy of fortify is not compiled correctly")
+		}
+		s.fshim = p
+	})
+
+	return s.fshim
+}
+
+func (s *Std) Paths() Paths {
+	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths) })
+	return s.paths
+}
+
+func (s *Std) SdBooted() bool {
+	s.sdBootedOnce.Do(func() { s.sdBooted = copySdBooted() })
+	return s.sdBooted
+}
+
+const systemdCheckPath = "/run/systemd/system"
+
+func copySdBooted() bool {
+	if v, err := sdBooted(); err != nil {
+		fmsg.Println("cannot read systemd marker:", err)
+		return false
+	} else {
+		return v
+	}
+}
+
+func sdBooted() (bool, error) {
+	_, err := os.Stat(systemdCheckPath)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			err = nil
+		}
+		return false, err
+	}
+
+	return true, nil
+}