1 files changed, 70 insertions, 0 deletions
diff --git a/internal/sys/interface.go b/internal/sys/interface.go
new file mode 100644
index 00000000..80a07ae6
--- /dev/null
+++ b/internal/sys/interface.go
@@ -0,0 +1,70 @@
+package sys
+
+import (
+	"io/fs"
+	"os/user"
+	"path"
+	"strconv"
+
+	"git.gensokyo.uk/security/fortify/internal/fmsg"
+)
+
+// State provides safe interaction with operating system state.
+type State 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)
+	// MustExecutable provides [proc.MustExecutable].
+	MustExecutable() string
+	// LookupGroup provides [user.LookupGroup].
+	LookupGroup(name string) (*user.Group, 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)
+	// EvalSymlinks provides [filepath.EvalSymlinks]
+	EvalSymlinks(path string) (string, error)
+	// Exit provides [os.Exit].
+	Exit(code int)
+
+	// Paths returns a populated [Paths] struct.
+	Paths() Paths
+	// Uid invokes fsu and returns target uid.
+	// Any errors returned by Uid is already wrapped [fmsg.BaseError].
+	Uid(aid int) (int, error)
+}
+
+// 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 State, v *Paths) {
+	v.SharePath = path.Join(os.TempDir(), "fortify."+strconv.Itoa(os.Geteuid()))
+
+	fmsg.Verbosef("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.Verbosef("runtime directory at %q", v.RunDirPath)
+}