Merge pull request #235 from ConsenSys/witness-public-api

feat: added witness.Public to return Public part of the witness vector

backend/witness/vector.go

@@ -43,3 +43,34 @@ func newVector(curveID ecc.ID) (Vector, error) {
 	}
 	return w, nil
 }
+
+func newFrom(from Vector, n int) (Vector, error) {
+	switch wt := from.(type) {
+	case *witness_bn254.Witness:
+		a := make(witness_bn254.Witness, n)
+		copy(a, *wt)
+		return &a, nil
+	case *witness_bls12377.Witness:
+		a := make(witness_bls12377.Witness, n)
+		copy(a, *wt)
+		return &a, nil
+	case *witness_bls12381.Witness:
+		a := make(witness_bls12381.Witness, n)
+		copy(a, *wt)
+		return &a, nil
+	case *witness_bw6761.Witness:
+		a := make(witness_bw6761.Witness, n)
+		copy(a, *wt)
+		return &a, nil
+	case *witness_bls24315.Witness:
+		a := make(witness_bls24315.Witness, n)
+		copy(a, *wt)
+		return &a, nil
+	case *witness_bw6633.Witness:
+		a := make(witness_bw6633.Witness, n)
+		copy(a, *wt)
+		return &a, nil
+	default:
+		return nil, errMissingCurveID
+	}
+}

backend/witness/witness.go

@@ -84,6 +84,25 @@ func New(curveID ecc.ID, schema *schema.Schema) (*Witness, error) {
 	}, nil
 }
 
+// Public extracts the public part of the witness and returns a new witness object
+func (w *Witness) Public() (*Witness, error) {
+	if w.Vector == nil {
+		return nil, fmt.Errorf("%w: empty witness", ErrInvalidWitness)
+	}
+	if w.Schema == nil {
+		return nil, errMissingSchema
+	}
+	v, err := newFrom(w.Vector, w.Schema.NbPublic)
+	if err != nil {
+		return nil, err
+	}
+	return &Witness{
+		CurveID: w.CurveID,
+		Vector:  v,
+		Schema:  w.Schema,
+	}, nil
+}
+
 // MarshalBinary implements encoding.BinaryMarshaler
 // Only the vector of field elements is marshalled: the curveID and the Schema are omitted.
 func (w *Witness) MarshalBinary() (data []byte, err error) {

backend/witness/witness_test.go

@@ -103,6 +103,32 @@ func TestMarshal(t *testing.T) {
 	roundTripMarshal(assert, assignment, Binary, false)
 }
 
+func TestPublic(t *testing.T) {
+	assert := require.New(t)
+
+	var assignment circuit
+	assignment.X = new(fr.Element).SetInt64(42)
+	assignment.Y = new(fr.Element).SetInt64(8000)
+	assignment.E = new(fr.Element).SetInt64(1)
+
+	w, err := New(ecc.BN254, nil)
+	assert.NoError(err)
+
+	w.Schema, err = w.Vector.FromAssignment(&assignment, tVariable, false)
+	assert.NoError(err)
+
+	publicW, err := w.Public()
+	assert.NoError(err)
+
+	assert.Equal(3, w.Vector.Len())
+	assert.Equal(2, publicW.Vector.Len())
+
+	wt := publicW.Vector.(*witness_bn254.Witness)
+
+	assert.Equal("42", (*wt)[0].String())
+	assert.Equal("8000", (*wt)[1].String())
+}
+
 var tVariable reflect.Type
 
 func init() {

go.sum

@@ -1,7 +1,5 @@
 github.com/consensys/bavard v0.1.8-0.20210915155054-088da2f7f54a h1:AEpwbXTjBGKoqxuQ6QAcBMEuK0+PtajQj0wJkhTnSd0=
 github.com/consensys/bavard v0.1.8-0.20210915155054-088da2f7f54a/go.mod h1:9ItSMtA/dXMAiL7BG6bqW2m3NdSEObYWoH223nGHukI=
-github.com/consensys/gnark-crypto v0.5.4-0.20211222202820-aee0c136fb9f h1:HT4hl58/L66zdhJi8wEbdoXceHv9AnIJij5lP1iOuQw=
-github.com/consensys/gnark-crypto v0.5.4-0.20211222202820-aee0c136fb9f/go.mod h1:PicAZJP763+7N9LZFfj+MquTXq98pwjD6l8Ry8WdHSU=
 github.com/consensys/gnark-crypto v0.6.1-0.20220110145513-493bb1c180d9 h1:NSmw/VuOS3KCClXAijCQ6dJVtCSMbTwK/M8ulvPCvmY=
 github.com/consensys/gnark-crypto v0.6.1-0.20220110145513-493bb1c180d9/go.mod h1:PicAZJP763+7N9LZFfj+MquTXq98pwjD6l8Ry8WdHSU=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=