preimage: preimage interface without geth dependency

preimage/go.mod

+module github.com/ethereum-optimism/cannon/preimage
+
+go 1.20
+
+require (
+	github.com/stretchr/testify v1.8.2
+	golang.org/x/crypto v0.8.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	golang.org/x/sys v0.7.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

preimage/go.sum

+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.2 h1:+h33VjcLVPDHtOdpUCuF+7gSuG3yGIftsP1YvFihtJ8=
+github.com/stretchr/testify v1.8.2/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
+golang.org/x/crypto v0.8.0 h1:pd9TJtTueMTVQXzk8E2XESSMQDj/U7OUu0PqJqPXQjQ=
+golang.org/x/crypto v0.8.0/go.mod h1:mRqEX+O9/h5TFCrQhkgjo2yKi0yYA+9ecGkdQoHrywE=
+golang.org/x/sys v0.7.0 h1:3jlCCIQZPdOYu1h8BkNvLz8Kgwtae2cagcG/VamtZRU=
+golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

preimage/hints.go

+package preimage
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+// HintWriter writes hints to an io.Writer (e.g. a special file descriptor, or a debug log),
+// for a pre-image oracle service to prepare specific pre-images.
+type HintWriter struct {
+	rw io.ReadWriter
+}
+
+var _ Hinter = (*HintWriter)(nil)
+
+func NewHintWriter(rw io.ReadWriter) *HintWriter {
+	return &HintWriter{rw: rw}
+}
+
+func (hw *HintWriter) Hint(v Hint) {
+	hint := v.Hint()
+	var hintBytes []byte
+	hintBytes = binary.BigEndian.AppendUint32(hintBytes, uint32(len(hint)))
+	hintBytes = append(hintBytes, []byte(hint)...)
+	_, err := hw.rw.Write(hintBytes)
+	if err != nil {
+		panic(fmt.Errorf("failed to write pre-image hint: %w", err))
+	}
+	_, err = hw.rw.Read([]byte{0})
+	if err != nil {
+		panic(fmt.Errorf("failed to read pre-image hint ack: %w", err))
+	}
+}
+
+// HintReader reads the hints of HintWriter and passes them to a router for preparation of the requested pre-images.
+// Onchain the written hints are no-op.
+type HintReader struct {
+	rw io.ReadWriter
+}
+
+func NewHintReader(rw io.ReadWriter) *HintReader {
+	return &HintReader{rw: rw}
+}
+
+func (hr *HintReader) NextHint(router func(hint string) error) error {
+	var length uint32
+	if err := binary.Read(hr.rw, binary.BigEndian, &length); err != nil {
+		if err == io.EOF {
+			return io.EOF
+		}
+		return fmt.Errorf("failed to read hint length prefix: %w", err)
+	}
+	payload := make([]byte, length)
+	if length > 0 {
+		if _, err := io.ReadFull(hr.rw, payload); err != nil {
+			return fmt.Errorf("failed to read hint payload (length %d): %w", length, err)
+		}
+	}
+	if err := router(string(payload)); err != nil {
+		// write back on error to unblock the HintWriter
+		_, _ = hr.rw.Write([]byte{0})
+		return fmt.Errorf("failed to handle hint: %w", err)
+	}
+	if _, err := hr.rw.Write([]byte{0}); err != nil {
+		return fmt.Errorf("failed to write trailing no-op byte to unblock hint writer: %w", err)
+	}
+	return nil
+}

preimage/hints_test.go

+package preimage
+
+import (
+	"bytes"
+	"crypto/rand"
+	"errors"
+	"io"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+type rawHint string
+
+func (rh rawHint) Hint() string {
+	return string(rh)
+}
+
+func TestHints(t *testing.T) {
+	// Note: pretty much every string is valid communication:
+	// length, payload, 0. Worst case you run out of data, or allocate too much.
+	testHint := func(hints ...string) {
+		a, b := bidirectionalPipe()
+		var wg sync.WaitGroup
+		wg.Add(2)
+
+		go func() {
+			hw := NewHintWriter(a)
+			for _, h := range hints {
+				hw.Hint(rawHint(h))
+			}
+			wg.Done()
+		}()
+
+		got := make(chan string, len(hints))
+		go func() {
+			defer wg.Done()
+			hr := NewHintReader(b)
+			for i := 0; i < len(hints); i++ {
+				err := hr.NextHint(func(hint string) error {
+					got <- hint
+					return nil
+				})
+				if err == io.EOF {
+					break
+				}
+				require.NoError(t, err)
+			}
+		}()
+		if waitTimeout(&wg) {
+			t.Error("hint read/write stuck")
+		}
+
+		require.Equal(t, len(hints), len(got), "got all hints")
+		for _, h := range hints {
+			require.Equal(t, h, <-got, "hints match")
+		}
+	}
+
+	t.Run("empty hint", func(t *testing.T) {
+		testHint("")
+	})
+	t.Run("hello world", func(t *testing.T) {
+		testHint("hello world")
+	})
+	t.Run("zero byte", func(t *testing.T) {
+		testHint(string([]byte{0}))
+	})
+	t.Run("many zeroes", func(t *testing.T) {
+		testHint(string(make([]byte, 1000)))
+	})
+	t.Run("random data", func(t *testing.T) {
+		dat := make([]byte, 1000)
+		_, _ = rand.Read(dat[:])
+		testHint(string(dat))
+	})
+	t.Run("multiple hints", func(t *testing.T) {
+		testHint("give me header a", "also header b", "foo bar")
+	})
+	t.Run("unexpected EOF", func(t *testing.T) {
+		var buf bytes.Buffer
+		hw := NewHintWriter(&buf)
+		hw.Hint(rawHint("hello"))
+		_, _ = buf.Read(make([]byte, 1)) // read one byte so it falls short, see if it's detected
+		hr := NewHintReader(&buf)
+		err := hr.NextHint(func(hint string) error { return nil })
+		require.ErrorIs(t, err, io.ErrUnexpectedEOF)
+	})
+	t.Run("cb error", func(t *testing.T) {
+		a, b := bidirectionalPipe()
+		var wg sync.WaitGroup
+		wg.Add(2)
+
+		go func() {
+			hw := NewHintWriter(a)
+			hw.Hint(rawHint("one"))
+			hw.Hint(rawHint("two"))
+			wg.Done()
+		}()
+		go func() {
+			defer wg.Done()
+			hr := NewHintReader(b)
+			cbErr := errors.New("fail")
+			err := hr.NextHint(func(hint string) error { return cbErr })
+			require.ErrorIs(t, err, cbErr)
+			var readHint string
+			err = hr.NextHint(func(hint string) error {
+				readHint = hint
+				return nil
+			})
+			require.NoError(t, err)
+			require.Equal(t, readHint, "two")
+		}()
+		if waitTimeout(&wg) {
+			t.Error("read/write hint stuck")
+		}
+	})
+}
+
+// waitTimeout returns true iff wg.Wait timed out
+func waitTimeout(wg *sync.WaitGroup) bool {
+	done := make(chan struct{})
+	go func() {
+		wg.Wait()
+		close(done)
+	}()
+	select {
+	case <-time.After(time.Second * 30):
+		return true
+	case <-done:
+		return false
+	}
+}

preimage/iface.go

+package preimage
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+)
+
+type Key interface {
+	// PreimageKey changes the Key commitment into a
+	// 32-byte type-prefixed preimage key.
+	PreimageKey() [32]byte
+}
+
+type Oracle interface {
+	// Get the full pre-image of a given pre-image key.
+	// This returns no error: the client state-transition
+	// is invalid if there is any missing pre-image data.
+	Get(key Key) []byte
+}
+
+type OracleFn func(key Key) []byte
+
+func (fn OracleFn) Get(key Key) []byte {
+	return fn(key)
+}
+
+// KeyType is the key-type of a pre-image, used to prefix the pre-image key with.
+type KeyType byte
+
+const (
+	// The zero key type is illegal to use, ensuring all keys are non-zero.
+	_ KeyType = 0
+	// LocalKeyType is for input-type pre-images, specific to the local program instance.
+	LocalKeyType KeyType = 1
+	// Keccak256KeyType is for keccak256 pre-images, for any global shared pre-images.
+	Keccak256KeyType KeyType = 2
+)
+
+// LocalIndexKey is a key local to the program, indexing a special program input.
+type LocalIndexKey uint64
+
+func (k LocalIndexKey) PreimageKey() (out [32]byte) {
+	out[0] = byte(LocalKeyType)
+	binary.BigEndian.PutUint64(out[24:], uint64(k))
+	return
+}
+
+// Keccak256Key wraps a keccak256 hash to use it as a typed pre-image key.
+type Keccak256Key [32]byte
+
+func (k Keccak256Key) PreimageKey() (out [32]byte) {
+	out = k                         // copy the keccak hash
+	out[0] = byte(Keccak256KeyType) // apply prefix
+	return
+}
+
+func (k Keccak256Key) String() string {
+	return "0x" + hex.EncodeToString(k[:])
+}
+
+func (k Keccak256Key) TerminalString() string {
+	return "0x" + hex.EncodeToString(k[:])
+}
+
+// Hint is an interface to enable any program type to function as a hint,
+// when passed to the Hinter interface, returning a string representation
+// of what data the host should prepare pre-images for.
+type Hint interface {
+	Hint() string
+}
+
+// Hinter is an interface to write hints to the host.
+// This may be implemented as a no-op or logging hinter
+// if the program is executing in a read-only environment
+// where the host is expected to have all pre-images ready.
+type Hinter interface {
+	Hint(v Hint)
+}
+
+type HinterFn func(v Hint)
+
+func (fn HinterFn) Hint(v Hint) {
+	fn(v)
+}

preimage/oracle.go

+package preimage
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+// OracleClient implements the Oracle by writing the pre-image key to the given stream,
+// and reading back a length-prefixed value.
+type OracleClient struct {
+	rw io.ReadWriter
+}
+
+func NewOracleClient(rw io.ReadWriter) *OracleClient {
+	return &OracleClient{rw: rw}
+}
+
+var _ Oracle = (*OracleClient)(nil)
+
+func (o *OracleClient) Get(key Key) []byte {
+	h := key.PreimageKey()
+	if _, err := o.rw.Write(h[:]); err != nil {
+		panic(fmt.Errorf("failed to write key %s (%T) to pre-image oracle: %w", key, key, err))
+	}
+
+	var length uint64
+	if err := binary.Read(o.rw, binary.BigEndian, &length); err != nil {
+		panic(fmt.Errorf("failed to read pre-image length of key %s (%T) from pre-image oracle: %w", key, key, err))
+	}
+	payload := make([]byte, length)
+	if _, err := io.ReadFull(o.rw, payload); err != nil {
+		panic(fmt.Errorf("failed to read pre-image payload (length %d) of key %s (%T) from pre-image oracle: %w", length, key, key, err))
+	}
+
+	return payload
+}
+
+// OracleServer serves the pre-image requests of the OracleClient, implementing the same protocol as the onchain VM.
+type OracleServer struct {
+	rw io.ReadWriter
+}
+
+func NewOracleServer(rw io.ReadWriter) *OracleServer {
+	return &OracleServer{rw: rw}
+}
+
+func (o *OracleServer) NextPreimageRequest(getPreimage func(key [32]byte) ([]byte, error)) error {
+	var key [32]byte
+	if _, err := io.ReadFull(o.rw, key[:]); err != nil {
+		if err == io.EOF {
+			return io.EOF
+		}
+		return fmt.Errorf("failed to read requested pre-image key: %w", err)
+	}
+	value, err := getPreimage(key)
+	if err != nil {
+		return fmt.Errorf("failed to serve pre-image %s request: %w", key, err)
+	}
+
+	if err := binary.Write(o.rw, binary.BigEndian, uint64(len(value))); err != nil {
+		return fmt.Errorf("failed to write length-prefix %d: %w", len(value), err)
+	}
+	if len(value) == 0 {
+		return nil
+	}
+	if _, err := o.rw.Write(value); err != nil {
+		return fmt.Errorf("failed to write pre-image value (%d long): %w", len(value), err)
+	}
+	return nil
+}

preimage/oracle_test.go

+package preimage
+
+import (
+	"bytes"
+	"crypto/rand"
+	"fmt"
+	"io"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/crypto/sha3"
+)
+
+func keccak256(v []byte) (out [32]byte) {
+	s := sha3.NewLegacyKeccak256()
+	s.Write(v)
+	s.Sum(out[:0])
+	return
+}
+
+type readWritePair struct {
+	io.Reader
+	io.Writer
+}
+
+func bidirectionalPipe() (a, b io.ReadWriter) {
+	ar, bw := io.Pipe()
+	br, aw := io.Pipe()
+	return readWritePair{Reader: ar, Writer: aw}, readWritePair{Reader: br, Writer: bw}
+}
+
+func TestOracle(t *testing.T) {
+	testPreimage := func(preimages ...[]byte) {
+		a, b := bidirectionalPipe()
+		cl := NewOracleClient(a)
+		srv := NewOracleServer(b)
+
+		preimageByHash := make(map[[32]byte][]byte)
+		for _, p := range preimages {
+			k := Keccak256Key(keccak256(p))
+			preimageByHash[k.PreimageKey()] = p
+		}
+		for _, p := range preimages {
+			k := Keccak256Key(keccak256(p))
+
+			var wg sync.WaitGroup
+			wg.Add(2)
+
+			go func(k Key, p []byte) {
+				result := cl.Get(k)
+				wg.Done()
+				expected := preimageByHash[k.PreimageKey()]
+				require.True(t, bytes.Equal(expected, result), "need correct preimage %x, got %x", expected, result)
+			}(k, p)
+
+			go func() {
+				err := srv.NextPreimageRequest(func(key [32]byte) ([]byte, error) {
+					dat, ok := preimageByHash[key]
+					if !ok {
+						return nil, fmt.Errorf("cannot find %s", key)
+					}
+					return dat, nil
+				})
+				wg.Done()
+				require.NoError(t, err)
+			}()
+			wg.Wait()
+		}
+	}
+	t.Run("empty preimage", func(t *testing.T) {
+		testPreimage([]byte{})
+	})
+	t.Run("nil preimage", func(t *testing.T) {
+		testPreimage(nil)
+	})
+	t.Run("zero", func(t *testing.T) {
+		testPreimage([]byte{0})
+	})
+	t.Run("multiple", func(t *testing.T) {
+		testPreimage([]byte("tx from alice"), []byte{0x13, 0x37}, []byte("tx from bob"))
+	})
+	t.Run("zeroes", func(t *testing.T) {
+		testPreimage(make([]byte, 1000))
+	})
+	t.Run("random", func(t *testing.T) {
+		dat := make([]byte, 1000)
+		_, _ = rand.Read(dat[:])
+		testPreimage(dat)
+	})
+}