bindings/go: Add document-granularity streaming Index parser (#172)

bindings/go/scip/parse.go

@@ -0,0 +1,151 @@
+package scip
+
+import (
+	"io"
+
+	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/proto"
+
+	"github.com/sourcegraph/sourcegraph/lib/errors"
+)
+
+// IndexVisitor is a struct of functions rather than an interface since Go
+// doesn't support adding new functions to interfaces with default
+// implementations, so adding new functions here for new fields in
+// the SCIP schema would break clients. Individual functions may be nil.
+type IndexVisitor struct {
+	VisitMetadata       func(*Metadata)
+	VisitDocument       func(*Document)
+	VisitExternalSymbol func(*SymbolInformation)
+}
+
+// See https://protobuf.dev/programming-guides/encoding/#varints
+const maxVarintBytes = 10
+
+// ParseStreaming processes an index by incrementally reading input from the io.Reader.
+//
+// Parsing takes place at Document granularity for ease of use.
+func (pi *IndexVisitor) ParseStreaming(r io.Reader) error {
+	// The tag is encoded as a varint with value: (field_number << 3) | wire_type
+	// Varints < 128 fit in 1 byte, which means 4 bits are available for field
+	// numbers. The Index type has less than 15 fields, so the tag will fit in 1 byte.
+	tagBuf := make([]byte, 1)
+	lenBuf := make([]byte, 0, maxVarintBytes)
+	dataBuf := make([]byte, 0, 1024)
+
+	for {
+		numRead, err := r.Read(tagBuf)
+		if err == io.EOF {
+			return nil
+		}
+		if err != nil {
+			return errors.Wrapf(err, "failed to read from index reader: %w")
+		}
+		if numRead == 0 {
+			return errors.New("read 0 bytes from index")
+		}
+		fieldNumber, fieldType, errCode := protowire.ConsumeTag(tagBuf)
+		if errCode < 0 {
+			return errors.Wrap(protowire.ParseError(errCode), "failed to consume tag")
+		}
+		switch fieldNumber {
+		// As per scip.proto, all of Metadata, Document and SymbolInformation are sub-messages
+		case metadataFieldNumber, documentsFieldNumber, externalSymbolsFieldNumber:
+			if fieldType != protowire.BytesType {
+				return errors.Newf("expected LEN type tag for %s", indexFieldName(fieldNumber))
+			}
+			lenBuf = lenBuf[:0]
+			dataLen, err := readVarint(r, lenBuf)
+			if err != nil {
+				return errors.Wrapf(err, "failed to read length for %s", indexFieldName(fieldNumber))
+			}
+			if dataLen > uint64(cap(dataBuf)) {
+				dataBuf = make([]byte, dataLen)
+			} else {
+				dataBuf = dataBuf[:0]
+				for i := uint64(0); i < dataLen; i++ {
+					dataBuf = append(dataBuf, 0)
+				}
+			}
+			// Keep going when len == 0 instead of short-circuiting to preserve empty sub-messages
+			if dataLen > 0 {
+				numRead, err := r.Read(dataBuf)
+				if err != nil {
+					return errors.Wrapf(err, "failed to read data for %s", indexFieldName(fieldNumber))
+				}
+				if uint64(numRead) != dataLen {
+					return errors.Newf(
+						"expected to read %d bytes based on LEN but read %d bytes", dataLen, numRead)
+				}
+			}
+			if fieldNumber == metadataFieldNumber && pi.VisitMetadata != nil {
+				m := Metadata{}
+				if err := proto.Unmarshal(dataBuf, &m); err != nil {
+					return errors.Wrapf(err, "failed to read %s", indexFieldName(fieldNumber))
+				}
+				pi.VisitMetadata(&m)
+			} else if fieldNumber == documentsFieldNumber && pi.VisitDocument != nil {
+				d := Document{}
+				if err := proto.Unmarshal(dataBuf, &d); err != nil {
+					return errors.Wrapf(err, "failed to read %s", indexFieldName(fieldNumber))
+				}
+				pi.VisitDocument(&d)
+			} else if fieldNumber == externalSymbolsFieldNumber && pi.VisitExternalSymbol != nil {
+				s := SymbolInformation{}
+				if err := proto.Unmarshal(dataBuf, &s); err != nil {
+					return errors.Wrapf(err, "failed to read %s", indexFieldName(fieldNumber))
+				}
+				pi.VisitExternalSymbol(&s)
+			} else {
+				return errors.Newf("added new field in scip.Index but forgot to add unmarshaling code")
+			}
+		default:
+			return errors.Newf("added new field in scip.Index but forgot to update streaming parser")
+		}
+	}
+}
+
+const (
+	metadataFieldNumber        = 1
+	documentsFieldNumber       = 2
+	externalSymbolsFieldNumber = 3
+)
+
+// readVarint attempts to read a varint, using scratchBuf for temporary storage
+//
+// scratchBuf should be able to accommodate any varint size
+// based on its capacity, and be cleared before readVarint is called
+func readVarint(r io.Reader, scratchBuf []byte) (uint64, error) {
+	nextByteBuf := make([]byte, 1, 1)
+	for i := 0; i < cap(scratchBuf); i++ {
+		numRead, err := r.Read(nextByteBuf)
+		if err != nil {
+			return 0, errors.Wrapf(err, "failed to read %d-th byte of Varint. soFar: %v", i, scratchBuf)
+		}
+		if numRead == 0 {
+			return 0, errors.Newf("failed to read %d-th byte of Varint. soFar: %v", scratchBuf)
+		}
+		nextByte := nextByteBuf[0]
+		scratchBuf = append(scratchBuf, nextByte)
+		if nextByte <= 127 { // https://protobuf.dev/programming-guides/encoding/#varints
+			// Continuation bit is not set, so Varint must've ended
+			break
+		}
+	}
+	value, errCode := protowire.ConsumeVarint(scratchBuf)
+	if errCode < 0 {
+		return value, protowire.ParseError(errCode)
+	}
+	return value, nil
+}
+
+func indexFieldName(i protowire.Number) string {
+	if i == metadataFieldNumber {
+		return "metadata"
+	} else if i == documentsFieldNumber {
+		return "documents"
+	} else if i == externalSymbolsFieldNumber {
+		return "external_symbols"
+	}
+	return "<unknown>"
+}

bindings/go/scip/parse_test.go

@@ -0,0 +1,48 @@
+package scip
+
+import (
+	"bytes"
+	"regexp"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/gofuzz"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/encoding/protojson"
+	"google.golang.org/protobuf/proto"
+)
+
+func TestFuzz(t *testing.T) {
+	pat := regexp.MustCompile("^(state|sizeCache|unknownFields|SignatureDocumentation)$")
+	f := fuzz.New().NumElements(0, 2).SkipFieldsWithPattern(pat)
+	for i := 0; i < 100; i++ {
+		index := Index{}
+		f.Fuzz(&index)
+
+		indexBytes, err := proto.Marshal(&index)
+		require.NoError(t, err)
+		bytesReader := bytes.NewReader(indexBytes)
+		parsedIndex := Index{}
+
+		indexVisitor := IndexVisitor{func(metadata *Metadata) {
+			parsedIndex.Metadata = metadata
+		}, func(document *Document) {
+			parsedIndex.Documents = append(parsedIndex.Documents, document)
+		}, func(extSym *SymbolInformation) {
+			parsedIndex.ExternalSymbols = append(parsedIndex.ExternalSymbols, extSym)
+		}}
+
+		if err := indexVisitor.ParseStreaming(bytesReader); err != nil {
+			t.Fatalf("failed to parse index: %s\ngot error: %v",
+				protojson.MarshalOptions{Multiline: true}.Format(&index), err)
+		}
+
+		if !proto.Equal(&index, &parsedIndex) {
+			want := protojson.MarshalOptions{Multiline: true}.Format(&index)
+			got := protojson.MarshalOptions{Multiline: true}.Format(&parsedIndex)
+			diff := cmp.Diff(want, got)
+			require.NotEqual(t, diff, "")
+			t.Fatalf("index (-want, +got): %s", diff)
+		}
+	}
+}