check: move from container

This package is not container specific, and widely used across the project.

Signed-off-by: Ophestra <cat@gensokyo.uk>

4 files changed, 594 insertions, 0 deletions

diff --git a/check/absolute.go b/check/absolute.go
new file mode 100644
index 00000000..d17d5e1a
--- /dev/null
+++ b/check/absolute.go
@@ -0,0 +1,132 @@
+// Package check provides types yielding values checked to meet a condition.
+package check
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"path"
+	"slices"
+	"strings"
+	"syscall"
+	"unique"
+)
+
+// AbsoluteError is returned by [NewAbs] and holds the invalid pathname.
+type AbsoluteError string
+
+func (e AbsoluteError) Error() string {
+	return fmt.Sprintf("path %q is not absolute", string(e))
+}
+
+func (e AbsoluteError) Is(target error) bool {
+	var ce AbsoluteError
+	if !errors.As(target, &ce) {
+		return errors.Is(target, syscall.EINVAL)
+	}
+	return e == ce
+}
+
+// Absolute holds a pathname checked to be absolute.
+type Absolute struct{ pathname unique.Handle[string] }
+
+// ok returns whether [Absolute] is not the zero value.
+func (a *Absolute) ok() bool { return a != nil && *a != (Absolute{}) }
+
+// unsafeAbs returns [check.Absolute] on any string value.
+func unsafeAbs(pathname string) *Absolute {
+	return &Absolute{unique.Make(pathname)}
+}
+
+// String returns the checked pathname.
+func (a *Absolute) String() string {
+	if !a.ok() {
+		panic("attempted use of zero Absolute")
+	}
+	return a.pathname.Value()
+}
+
+// Handle returns the underlying [unique.Handle].
+func (a *Absolute) Handle() unique.Handle[string] {
+	return a.pathname
+}
+
+// Is efficiently compares the underlying pathname.
+func (a *Absolute) Is(v *Absolute) bool {
+	if a == nil && v == nil {
+		return true
+	}
+	return a.ok() && v.ok() && a.pathname == v.pathname
+}
+
+// NewAbs checks pathname and returns a new [Absolute] if pathname is absolute.
+func NewAbs(pathname string) (*Absolute, error) {
+	if !path.IsAbs(pathname) {
+		return nil, AbsoluteError(pathname)
+	}
+	return unsafeAbs(pathname), nil
+}
+
+// MustAbs calls [NewAbs] and panics on error.
+func MustAbs(pathname string) *Absolute {
+	if a, err := NewAbs(pathname); err != nil {
+		panic(err)
+	} else {
+		return a
+	}
+}
+
+// Append calls [path.Join] with [Absolute] as the first element.
+func (a *Absolute) Append(elem ...string) *Absolute {
+	return unsafeAbs(path.Join(append([]string{a.String()}, elem...)...))
+}
+
+// Dir calls [path.Dir] with [Absolute] as its argument.
+func (a *Absolute) Dir() *Absolute { return unsafeAbs(path.Dir(a.String())) }
+
+// GobEncode returns the checked pathname.
+func (a *Absolute) GobEncode() ([]byte, error) {
+	return []byte(a.String()), nil
+}
+
+// GobDecode stores data if it represents an absolute pathname.
+func (a *Absolute) GobDecode(data []byte) error {
+	pathname := string(data)
+	if !path.IsAbs(pathname) {
+		return AbsoluteError(pathname)
+	}
+	a.pathname = unique.Make(pathname)
+	return nil
+}
+
+// MarshalJSON returns a JSON representation of the checked pathname.
+func (a *Absolute) MarshalJSON() ([]byte, error) {
+	return json.Marshal(a.String())
+}
+
+// UnmarshalJSON stores data if it represents an absolute pathname.
+func (a *Absolute) UnmarshalJSON(data []byte) error {
+	var pathname string
+	if err := json.Unmarshal(data, &pathname); err != nil {
+		return err
+	}
+	if !path.IsAbs(pathname) {
+		return AbsoluteError(pathname)
+	}
+	a.pathname = unique.Make(pathname)
+	return nil
+}
+
+// SortAbs calls [slices.SortFunc] for a slice of [Absolute].
+func SortAbs(x []*Absolute) {
+	slices.SortFunc(x, func(a, b *Absolute) int {
+		return strings.Compare(a.String(), b.String())
+	})
+}
+
+// CompactAbs calls [slices.CompactFunc] for a slice of [Absolute].
+func CompactAbs(s []*Absolute) []*Absolute {
+	return slices.CompactFunc(s, func(a *Absolute, b *Absolute) bool {
+		return a.Is(b)
+	})
+}
diff --git a/check/absolute_test.go b/check/absolute_test.go
new file mode 100644
index 00000000..445ff2e2
--- /dev/null
+++ b/check/absolute_test.go
@@ -0,0 +1,401 @@
+package check_test
+
+import (
+	"bytes"
+	"encoding/gob"
+	"encoding/json"
+	"errors"
+	"reflect"
+	"strings"
+	"syscall"
+	"testing"
+	_ "unsafe" // for go:linkname
+
+	. "hakurei.app/check"
+)
+
+// unsafeAbs returns check.Absolute on any string value.
+//
+//go:linkname unsafeAbs hakurei.app/check.unsafeAbs
+func unsafeAbs(pathname string) *Absolute
+
+func TestAbsoluteError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+
+		err error
+		cmp error
+		ok  bool
+	}{
+		{"EINVAL", new(AbsoluteError), syscall.EINVAL, true},
+		{"not EINVAL", new(AbsoluteError), syscall.EBADE, false},
+		{"ne val", new(AbsoluteError), AbsoluteError("etc"), false},
+		{"equals", AbsoluteError("etc"), AbsoluteError("etc"), true},
+	}
+
+	for _, tc := range testCases {
+		if got := errors.Is(tc.err, tc.cmp); got != tc.ok {
+			t.Errorf("Is: %v, want %v", got, tc.ok)
+		}
+	}
+
+	t.Run("string", func(t *testing.T) {
+		t.Parallel()
+
+		want := `path "etc" is not absolute`
+		if got := (AbsoluteError("etc")).Error(); got != want {
+			t.Errorf("Error: %q, want %q", got, want)
+		}
+	})
+}
+
+func TestNewAbs(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+
+		pathname string
+		want     *Absolute
+		wantErr  error
+	}{
+		{"good", "/etc", MustAbs("/etc"), nil},
+		{"not absolute", "etc", nil, AbsoluteError("etc")},
+		{"zero", "", nil, AbsoluteError("")},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := NewAbs(tc.pathname)
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("NewAbs: %#v, want %#v", got, tc.want)
+			}
+			if !errors.Is(err, tc.wantErr) {
+				t.Errorf("NewAbs: error = %v, want %v", err, tc.wantErr)
+			}
+		})
+	}
+
+	t.Run("must", func(t *testing.T) {
+		t.Parallel()
+
+		defer func() {
+			wantPanic := AbsoluteError("etc")
+
+			if r := recover(); !reflect.DeepEqual(r, wantPanic) {
+				t.Errorf("MustAbs: panic = %v; want %v", r, wantPanic)
+			}
+		}()
+
+		MustAbs("etc")
+	})
+}
+
+func TestAbsoluteString(t *testing.T) {
+	t.Run("passthrough", func(t *testing.T) {
+		t.Parallel()
+
+		pathname := "/etc"
+		if got := unsafeAbs(pathname).String(); got != pathname {
+			t.Errorf("String: %q, want %q", got, pathname)
+		}
+	})
+
+	t.Run("zero", func(t *testing.T) {
+		t.Parallel()
+
+		defer func() {
+			wantPanic := "attempted use of zero Absolute"
+
+			if r := recover(); r != wantPanic {
+				t.Errorf("String: panic = %v, want %v", r, wantPanic)
+			}
+		}()
+
+		panic(new(Absolute).String())
+	})
+}
+
+func TestAbsoluteIs(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		a, v *Absolute
+		want bool
+	}{
+		{"nil", (*Absolute)(nil), (*Absolute)(nil), true},
+		{"nil a", (*Absolute)(nil), MustAbs("/"), false},
+		{"nil v", MustAbs("/"), (*Absolute)(nil), false},
+		{"zero", new(Absolute), new(Absolute), false},
+		{"zero a", new(Absolute), MustAbs("/"), false},
+		{"zero v", MustAbs("/"), new(Absolute), false},
+		{"equals", MustAbs("/"), MustAbs("/"), true},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.a.Is(tc.v); got != tc.want {
+				t.Errorf("Is: %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+type sCheck struct {
+	Pathname *Absolute `json:"val"`
+	Magic    uint64    `json:"magic"`
+}
+
+func TestCodecAbsolute(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		a    *Absolute
+
+		wantErr error
+
+		gob, sGob   string
+		json, sJson string
+	}{
+		{"nil", nil, nil,
+			"\x00", "\x00",
+			`null`, `{"val":null,"magic":3236757504}`},
+
+		{"good", MustAbs("/etc"),
+			nil,
+			"\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\b\xff\x80\x00\x04/etc",
+			",\xff\x83\x03\x01\x01\x06sCheck\x01\xff\x84\x00\x01\x02\x01\bPathname\x01\xff\x80\x00\x01\x05Magic\x01\x06\x00\x00\x00\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\x0f\xff\x84\x01\x04/etc\x01\xfc\xc0\xed\x00\x00\x00",
+
+			`"/etc"`, `{"val":"/etc","magic":3236757504}`},
+		{"not absolute", nil,
+			AbsoluteError("etc"),
+			"\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\a\xff\x80\x00\x03etc",
+			",\xff\x83\x03\x01\x01\x06sCheck\x01\xff\x84\x00\x01\x02\x01\bPathname\x01\xff\x80\x00\x01\x05Magic\x01\x06\x00\x00\x00\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\x0f\xff\x84\x01\x03etc\x01\xfb\x01\x81\xda\x00\x00\x00",
+
+			`"etc"`, `{"val":"etc","magic":3236757504}`},
+		{"zero", nil,
+			new(AbsoluteError),
+			"\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\x04\xff\x80\x00\x00",
+			",\xff\x83\x03\x01\x01\x06sCheck\x01\xff\x84\x00\x01\x02\x01\bPathname\x01\xff\x80\x00\x01\x05Magic\x01\x06\x00\x00\x00\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\f\xff\x84\x01\x00\x01\xfb\x01\x81\xda\x00\x00\x00",
+			`""`, `{"val":"","magic":3236757504}`},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			t.Run("gob", func(t *testing.T) {
+				if tc.gob == "\x00" && tc.sGob == "\x00" {
+					// these values mark the current test to skip gob
+					return
+				}
+				t.Parallel()
+
+				t.Run("encode", func(t *testing.T) {
+					t.Parallel()
+
+					// encode is unchecked
+					if errors.Is(tc.wantErr, syscall.EINVAL) {
+						return
+					}
+
+					{
+						buf := new(bytes.Buffer)
+						err := gob.NewEncoder(buf).Encode(tc.a)
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Encode: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							goto checkSEncode
+						}
+						if buf.String() != tc.gob {
+							t.Errorf("Encode:\n%q\nwant:\n%q", buf.String(), tc.gob)
+						}
+					}
+
+				checkSEncode:
+					{
+						buf := new(bytes.Buffer)
+						err := gob.NewEncoder(buf).Encode(&sCheck{tc.a, syscall.MS_MGC_VAL})
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Encode: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							return
+						}
+						if buf.String() != tc.sGob {
+							t.Errorf("Encode:\n%q\nwant:\n%q", buf.String(), tc.sGob)
+						}
+					}
+				})
+
+				t.Run("decode", func(t *testing.T) {
+					t.Parallel()
+
+					{
+						var gotA *Absolute
+						err := gob.NewDecoder(strings.NewReader(tc.gob)).Decode(&gotA)
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Decode: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							goto checkSDecode
+						}
+						if !reflect.DeepEqual(tc.a, gotA) {
+							t.Errorf("Decode: %#v, want %#v", tc.a, gotA)
+						}
+					}
+
+				checkSDecode:
+					{
+						var gotSCheck sCheck
+						err := gob.NewDecoder(strings.NewReader(tc.sGob)).Decode(&gotSCheck)
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Decode: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							return
+						}
+						want := sCheck{tc.a, syscall.MS_MGC_VAL}
+						if !reflect.DeepEqual(gotSCheck, want) {
+							t.Errorf("Decode: %#v, want %#v", gotSCheck, want)
+						}
+					}
+				})
+
+			})
+
+			t.Run("json", func(t *testing.T) {
+				t.Parallel()
+
+				t.Run("marshal", func(t *testing.T) {
+					t.Parallel()
+
+					// marshal is unchecked
+					if errors.Is(tc.wantErr, syscall.EINVAL) {
+						return
+					}
+
+					{
+						d, err := json.Marshal(tc.a)
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Marshal: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							goto checkSMarshal
+						}
+						if string(d) != tc.json {
+							t.Errorf("Marshal:\n%s\nwant:\n%s", string(d), tc.json)
+						}
+					}
+
+				checkSMarshal:
+					{
+						d, err := json.Marshal(&sCheck{tc.a, syscall.MS_MGC_VAL})
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Marshal: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							return
+						}
+						if string(d) != tc.sJson {
+							t.Errorf("Marshal:\n%s\nwant:\n%s", string(d), tc.sJson)
+						}
+					}
+				})
+
+				t.Run("unmarshal", func(t *testing.T) {
+					t.Parallel()
+
+					{
+						var gotA *Absolute
+						err := json.Unmarshal([]byte(tc.json), &gotA)
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Unmarshal: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							goto checkSUnmarshal
+						}
+						if !reflect.DeepEqual(tc.a, gotA) {
+							t.Errorf("Unmarshal: %#v, want %#v", tc.a, gotA)
+						}
+					}
+
+				checkSUnmarshal:
+					{
+						var gotSCheck sCheck
+						err := json.Unmarshal([]byte(tc.sJson), &gotSCheck)
+						if !errors.Is(err, tc.wantErr) {
+							t.Errorf("Unmarshal: error = %v, want %v", err, tc.wantErr)
+						}
+						if tc.wantErr != nil {
+							return
+						}
+						want := sCheck{tc.a, syscall.MS_MGC_VAL}
+						if !reflect.DeepEqual(gotSCheck, want) {
+							t.Errorf("Unmarshal: %#v, want %#v", gotSCheck, want)
+						}
+					}
+				})
+			})
+		})
+	}
+
+	t.Run("json passthrough", func(t *testing.T) {
+		t.Parallel()
+
+		wantErr := "invalid character ':' looking for beginning of value"
+		if err := new(Absolute).UnmarshalJSON([]byte(":3")); err == nil || err.Error() != wantErr {
+			t.Errorf("UnmarshalJSON: error = %v, want %s", err, wantErr)
+		}
+	})
+}
+
+func TestAbsoluteWrap(t *testing.T) {
+	t.Parallel()
+
+	t.Run("join", func(t *testing.T) {
+		t.Parallel()
+
+		want := "/etc/nix/nix.conf"
+		if got := MustAbs("/etc").Append("nix", "nix.conf"); got.String() != want {
+			t.Errorf("Append: %q, want %q", got, want)
+		}
+	})
+
+	t.Run("dir", func(t *testing.T) {
+		t.Parallel()
+
+		want := "/"
+		if got := MustAbs("/etc").Dir(); got.String() != want {
+			t.Errorf("Dir: %q, want %q", got, want)
+		}
+	})
+
+	t.Run("sort", func(t *testing.T) {
+		t.Parallel()
+
+		want := []*Absolute{MustAbs("/etc"), MustAbs("/proc"), MustAbs("/sys")}
+		got := []*Absolute{MustAbs("/proc"), MustAbs("/sys"), MustAbs("/etc")}
+		SortAbs(got)
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("SortAbs: %#v, want %#v", got, want)
+		}
+	})
+
+	t.Run("compact", func(t *testing.T) {
+		t.Parallel()
+
+		want := []*Absolute{MustAbs("/etc"), MustAbs("/proc"), MustAbs("/sys")}
+		if got := CompactAbs([]*Absolute{MustAbs("/etc"), MustAbs("/proc"), MustAbs("/proc"), MustAbs("/sys")}); !reflect.DeepEqual(got, want) {
+			t.Errorf("CompactAbs: %#v, want %#v", got, want)
+		}
+	})
+}
diff --git a/check/overlay.go b/check/overlay.go
new file mode 100644
index 00000000..fbbcd1e6
--- /dev/null
+++ b/check/overlay.go
@@ -0,0 +1,30 @@
+package check
+
+import "strings"
+
+const (
+	// SpecialOverlayEscape is the escape string for overlay mount options.
+	SpecialOverlayEscape = `\`
+	// SpecialOverlayOption is the separator string between overlay mount options.
+	SpecialOverlayOption = ","
+	// SpecialOverlayPath is the separator string between overlay paths.
+	SpecialOverlayPath = ":"
+)
+
+// EscapeOverlayDataSegment escapes a string for formatting into the data
+// argument of an overlay mount system call.
+func EscapeOverlayDataSegment(s string) string {
+	if s == "" {
+		return ""
+	}
+
+	if f := strings.SplitN(s, "\x00", 2); len(f) > 0 {
+		s = f[0]
+	}
+
+	return strings.NewReplacer(
+		SpecialOverlayEscape, SpecialOverlayEscape+SpecialOverlayEscape,
+		SpecialOverlayOption, SpecialOverlayEscape+SpecialOverlayOption,
+		SpecialOverlayPath, SpecialOverlayEscape+SpecialOverlayPath,
+	).Replace(s)
+}
diff --git a/check/overlay_test.go b/check/overlay_test.go
new file mode 100644
index 00000000..9b32dbcb
--- /dev/null
+++ b/check/overlay_test.go
@@ -0,0 +1,31 @@
+package check_test
+
+import (
+	"testing"
+
+	"hakurei.app/check"
+)
+
+func TestEscapeOverlayDataSegment(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		s    string
+		want string
+	}{
+		{"zero", "", ""},
+		{"multi", `\\\:,:,\\\`, `\\\\\\\:\,\:\,\\\\\\`},
+		{"bwrap", `/path :,\`, `/path \:\,\\`},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := check.EscapeOverlayDataSegment(tc.s); got != tc.want {
+				t.Errorf("escapeOverlayDataSegment: %s, want %s", got, tc.want)
+			}
+		})
+	}
+}