Address PR comments.

values/decoding/dictionary_based_string_iterator.go

@@ -11,7 +11,8 @@ import (
 // dictionaryBasedStringIterator iterates over a
 // dict encoded stream of string data.
 type dictionaryBasedStringIterator struct {
-	reader xio.SimpleReadCloser
+	reader     xio.SimpleReadCloser
+	byteReader io.ByteReader // Same as `reader` but has the proper type to save interface conversions in `Next`
 	// extDict is passed externally from the string decoder
 	// and should not be mutated during iteration.
 	extDict []string
@@ -25,8 +26,9 @@ func newDictionaryBasedStringIterator(
 	extDict []string,
 ) *dictionaryBasedStringIterator {
 	return &dictionaryBasedStringIterator{
-		reader:  reader,
-		extDict: extDict,
+		reader:     reader,
+		byteReader: reader,
+		extDict:    extDict,
 	}
 }
 
@@ -38,7 +40,7 @@ func (it *dictionaryBasedStringIterator) Next() bool {
 	}
 
 	var idx int64
-	idx, it.err = binary.ReadVarint(it.reader)
+	idx, it.err = binary.ReadVarint(it.byteReader)
 	if it.err != nil {
 		return false
 	}
@@ -69,4 +71,5 @@ func (it *dictionaryBasedStringIterator) Close() {
 	it.err = nil
 	it.reader.Close()
 	it.reader = nil
+	it.byteReader = nil
 }

values/decoding/raw_size_string_iterator.go

@@ -17,7 +17,8 @@ const (
 // raw size encoded string data.
 // TODO(xichen): Get the buffer from bytes pool.
 type rawSizeStringIterator struct {
-	reader xio.SimpleReadCloser
+	reader     xio.SimpleReadCloser
+	byteReader io.ByteReader // Same as `reader` but has the proper type to save interface conversions in `Next`
 
 	curr string
 	err  error
@@ -28,8 +29,9 @@ func newRawSizeStringIterator(
 	reader xio.SimpleReadCloser,
 ) *rawSizeStringIterator {
 	return &rawSizeStringIterator{
-		reader: reader,
-		buf:    make([]byte, defaultInitialStringBufferCapacity),
+		reader:     reader,
+		byteReader: reader,
+		buf:        make([]byte, defaultInitialStringBufferCapacity),
 	}
 }
 
@@ -40,7 +42,7 @@ func (it *rawSizeStringIterator) Next() bool {
 	}
 
 	var rawSizeBytes int64
-	rawSizeBytes, it.err = binary.ReadVarint(it.reader)
+	rawSizeBytes, it.err = binary.ReadVarint(it.byteReader)
 	if it.err != nil {
 		return false
 	}
@@ -74,4 +76,5 @@ func (it *rawSizeStringIterator) Close() {
 	it.err = nil
 	it.reader.Close()
 	it.reader = nil
+	it.byteReader = nil
 }

values/decoding/varint_int_iterator.go

@@ -10,15 +10,19 @@ import (
 // varintIntIterator iterates over a stream of
 // varint encoded int data.
 type varintIntIterator struct {
-	reader xio.SimpleReadCloser
+	reader     xio.SimpleReadCloser
+	byteReader io.ByteReader // Same as `reader` but has the proper type to save interface conversions in `Next`
 
 	closed bool
 	curr   int
 	err    error
 }
 
 func newVarintIntIterator(reader xio.SimpleReadCloser) *varintIntIterator {
-	return &varintIntIterator{reader: reader}
+	return &varintIntIterator{
+		reader:     reader,
+		byteReader: reader,
+	}
 }
 
 // Next iteration.
@@ -28,7 +32,7 @@ func (it *varintIntIterator) Next() bool {
 	}
 
 	var curr int64
-	curr, it.err = binary.ReadVarint(it.reader)
+	curr, it.err = binary.ReadVarint(it.byteReader)
 	if it.err != nil {
 		return false
 	}
@@ -55,4 +59,5 @@ func (it *varintIntIterator) Close() {
 	it.err = nil
 	it.reader.Close()
 	it.reader = nil
+	it.byteReader = nil
 }

values/encoding/string_encode.go

@@ -12,6 +12,7 @@ import (
 	"github.com/xichen2020/eventdb/x/proto"
 	"github.com/xichen2020/eventdb/x/unsafe"
 
+	xerrors "github.com/m3db/m3x/errors"
 	"github.com/valyala/gozstd"
 )
 
@@ -109,27 +110,24 @@ func (enc *stringEncoder) Encode(strVals values.StringValues, writer io.Writer)
 	}
 	defer valuesIt.Close()
 
+	var multiErr xerrors.MultiError
 	switch metaProto.Encoding {
 	case encodingpb.EncodingType_RAW_SIZE:
-		if err := enc.rawSizeEncode(valuesIt, writer); err != nil {
-			return err
-		}
+		multiErr.Add(enc.rawSizeEncode(valuesIt, writer))
 	case encodingpb.EncodingType_DICTIONARY:
-		if err := enc.dictionaryEncode(valuesIt, dictionary, writer); err != nil {
-			return err
-		}
+		multiErr.Add(enc.dictionaryEncode(valuesIt, dictionary, writer))
 	default:
-		return fmt.Errorf("invalid encoding type: %v", metaProto.Encoding)
+		multiErr.Add(fmt.Errorf("invalid encoding type: %v", metaProto.Encoding))
 	}
 
 	// Close the compressWriter if its present.
 	if compressWriter != nil {
 		// NB(xichen): Close flushes and closes the compressed writer but doesn't
 		// close the writer wrapped by the compressed writer.
-		return compressWriter.Close()
+		multiErr.Add(compressWriter.Close())
 	}
 
-	return nil
+	return multiErr.FinalError()
 }
 
 func (enc *stringEncoder) reset() {