hst/instance: define instance state

This is now part of the hst API. This change also improves identifier generation and serialisation.

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

3 files changed, 198 insertions, 1 deletions

diff --git a/hst/hst.go b/hst/hst.go
index 7fd7619c..bdff19f8 100644
--- a/hst/hst.go
+++ b/hst/hst.go
@@ -16,7 +16,7 @@ type AppError struct {
 	// A user-facing description of where the error occurred.
 	Step string `json:"step"`
 	// The underlying error value.
-	Err error
+	Err error `json:"err"`
 	// An arbitrary error message, overriding the return value of Message if not empty.
 	Msg string `json:"message,omitempty"`
 }
diff --git a/hst/instance.go b/hst/instance.go
new file mode 100644
index 00000000..5d15df6b
--- /dev/null
+++ b/hst/instance.go
@@ -0,0 +1,84 @@
+package hst
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"time"
+)
+
+// An ID is a unique identifier held by a running hakurei container.
+type ID [16]byte
+
+// ErrIdentifierLength is returned when encountering a [hex] representation of [ID] with unexpected length.
+var ErrIdentifierLength = errors.New("identifier string has unexpected length")
+
+// IdentifierDecodeError is returned by [ID.UnmarshalText] to provide relevant error descriptions.
+type IdentifierDecodeError struct{ Err error }
+
+func (e IdentifierDecodeError) Unwrap() error { return e.Err }
+func (e IdentifierDecodeError) Error() string {
+	var invalidByteError hex.InvalidByteError
+	switch {
+	case errors.As(e.Err, &invalidByteError):
+		return fmt.Sprintf("got invalid byte %#U in identifier", rune(invalidByteError))
+	case errors.Is(e.Err, hex.ErrLength):
+		return "odd length identifier hex string"
+
+	default:
+		return e.Err.Error()
+	}
+}
+
+// String returns the [hex] string representation of [ID].
+func (a *ID) String() string { return hex.EncodeToString(a[:]) }
+
+// CreationTime returns the point in time [ID] was created.
+func (a *ID) CreationTime() time.Time {
+	return time.Unix(0, int64(binary.BigEndian.Uint64(a[:8]))).UTC()
+}
+
+// NewInstanceID creates a new unique [ID].
+func NewInstanceID(id *ID) error { return newInstanceID(id, uint64(time.Now().UnixNano())) }
+
+// newInstanceID creates a new unique [ID] with the specified timestamp.
+func newInstanceID(id *ID, p uint64) error {
+	binary.BigEndian.PutUint64(id[:8], p)
+	_, err := rand.Read(id[8:])
+	return err
+}
+
+// MarshalText encodes the [hex] representation of [ID].
+func (a *ID) MarshalText() (text []byte, err error) {
+	text = make([]byte, hex.EncodedLen(len(a)))
+	hex.Encode(text, a[:])
+	return
+}
+
+// UnmarshalText decodes a [hex] representation of [ID].
+func (a *ID) UnmarshalText(text []byte) error {
+	dl := hex.DecodedLen(len(text))
+	if dl != len(a) {
+		return IdentifierDecodeError{ErrIdentifierLength}
+	}
+	_, err := hex.Decode(a[:], text)
+	if err == nil {
+		return nil
+	}
+	return IdentifierDecodeError{err}
+}
+
+// A State describes a running hakurei container.
+type State struct {
+	// Unique instance id, created by [NewInstanceID].
+	ID ID `json:"instance"`
+	// Shim process pid. Runs as the target user.
+	PID int `json:"pid"`
+	// Configuration used to start the container.
+	Config *Config `json:"config"`
+
+	// Point in time the shim process was created.
+	Time time.Time `json:"time"`
+}
diff --git a/hst/instance_test.go b/hst/instance_test.go
new file mode 100644
index 00000000..5be9fc8b
--- /dev/null
+++ b/hst/instance_test.go
@@ -0,0 +1,113 @@
+package hst_test
+
+import (
+	"encoding/hex"
+	"errors"
+	"reflect"
+	"testing"
+	"time"
+	_ "unsafe"
+
+	"hakurei.app/hst"
+)
+
+//go:linkname newInstanceID hakurei.app/hst.newInstanceID
+func newInstanceID(id *hst.ID, p uint64) error
+
+func TestIdentifierDecodeError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"invalid byte", hst.IdentifierDecodeError{Err: hex.InvalidByteError(0)},
+			"got invalid byte U+0000 in identifier"},
+		{"odd length", hst.IdentifierDecodeError{Err: hex.ErrLength},
+			"odd length identifier hex string"},
+		{"passthrough", hst.IdentifierDecodeError{Err: hst.ErrIdentifierLength},
+			hst.ErrIdentifierLength.Error()},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.err.Error(); got != tc.want {
+				t.Errorf("Error: %q, want %q", got, tc.want)
+			}
+		})
+	}
+
+	t.Run("unwrap", func(t *testing.T) {
+		t.Parallel()
+
+		err := hst.IdentifierDecodeError{Err: hst.ErrIdentifierLength}
+		if !errors.Is(err, hst.ErrIdentifierLength) {
+			t.Errorf("Is unexpected false")
+		}
+	})
+}
+
+func TestID(t *testing.T) {
+	t.Parallel()
+
+	var randomID hst.ID
+	if err := hst.NewInstanceID(&randomID); err != nil {
+		t.Fatalf("NewInstanceID: error = %v", err)
+	}
+
+	testCases := []struct {
+		name string
+		data string
+		want hst.ID
+		err  error
+	}{
+		{"bad length", "meow", hst.ID{},
+			hst.IdentifierDecodeError{Err: hst.ErrIdentifierLength}},
+		{"invalid byte", "02bc7f8936b2af6\x00\x00e2535cd71ef0bb7", hst.ID{},
+			hst.IdentifierDecodeError{Err: hex.InvalidByteError(0)}},
+
+		{"zero", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", hst.ID{}, nil},
+		{"random", randomID.String(), randomID, nil},
+		{"sample", "ba21c9bd33d9d37917288281a2a0d239", hst.ID{
+			0xba, 0x21, 0xc9, 0xbd,
+			0x33, 0xd9, 0xd3, 0x79,
+			0x17, 0x28, 0x82, 0x81,
+			0xa2, 0xa0, 0xd2, 0x39}, nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			var got hst.ID
+			if err := got.UnmarshalText([]byte(tc.data)); !reflect.DeepEqual(err, tc.err) {
+				t.Errorf("UnmarshalText: error = %#v, want %#v", err, tc.err)
+			}
+
+			if tc.err == nil {
+				if gotString := got.String(); gotString != tc.data {
+					t.Errorf("String: %q, want %q", gotString, tc.data)
+				}
+				if gotData, _ := got.MarshalText(); string(gotData) != tc.data {
+					t.Errorf("MarshalText: %q, want %q", string(gotData), tc.data)
+				}
+			}
+		})
+	}
+
+	t.Run("time", func(t *testing.T) {
+		t.Parallel()
+		var id hst.ID
+
+		now := time.Now()
+		if err := newInstanceID(&id, uint64(now.UnixNano())); err != nil {
+			t.Fatalf("newInstanceID: error = %v", err)
+		}
+
+		got := id.CreationTime()
+		if !got.Equal(now) {
+			t.Fatalf("CreationTime(%q): %s, want %s", id.String(), got, now)
+		}
+	})
+}