Code review changes.

bson/bsonrw/value_reader.go

@@ -739,7 +739,7 @@ func (vr *valueReader) ReadValue() (ValueReader, error) {
  return nil, ErrEOA
  }
 
- if err := vr.consumeCString(); err != nil {
+ if err := vr.skipCString(); err != nil {
  return nil, err
  }
 
@@ -793,7 +793,7 @@ func (vr *valueReader) readByte() (byte, error) {
  return vr.d[vr.offset-1], nil
 }
 
-func (vr *valueReader) consumeCString() error {
+func (vr *valueReader) skipCString() error {
  idx := bytes.IndexByte(vr.d[vr.offset:], 0x00)
  if idx < 0 {
  return io.EOF

bson/bsonrw/value_writer.go

@@ -255,7 +255,6 @@ func (vw *valueWriter) writeElementHeader(t bsontype.Type, destination mode, cal
  }
  vw.appendHeader(t, key)
  case mValue:
- // TODO: Do this with a cache of the first 1000 or so array keys.
  vw.appendIntHeader(t, frame.arrkey)
  default:
  modes := []mode{mElement, mValue}
@@ -611,6 +610,12 @@ func (vw *valueWriter) writeLength() error {
 }
 
 func isValidCString(cs string) bool {
+ // Disallow the zero byte in a cstring because the zero byte is used as the
+ // terminating character. It's safe to check bytes instead of runes because
+ // all multibyte UTF-8 code points start with "11xxxxxx" or "10xxxxxx", so
+ // "00000000" will never be part of a multibyte UTF-8 code point.
+ //
+ // See https://en.wikipedia.org/wiki/UTF-8#Encoding for details.
  return strings.IndexByte(cs, 0) == -1
 }
 

bson/marshal.go

@@ -171,7 +171,24 @@ var bufPool = sync.Pool{
 // See [Encoder] for more examples.
 func MarshalAppendWithContext(ec bsoncodec.EncodeContext, dst []byte, val interface{}) ([]byte, error) {
  sw := bufPool.Get().(*bytes.Buffer)
- defer bufPool.Put(sw)
+ defer func() {
+ // Proper usage of a sync.Pool requires each entry to have approximately
+ // the same memory cost. To obtain this property when the stored type
+ // contains a variably-sized buffer, we add a hard limit on the maximum
+ // buffer to place back in the pool. We limit the size to 16MiB because
+ // that's the maximum wire message size supported by any current MongoDB
+ // server.
+ //
+ // Comment based on
+ // https://cs.opensource.google/go/go/+/refs/tags/go1.19:src/fmt/print.go;l=147
+ //
+ // Recycle byte slices that are smaller than 16MiB and at least half
+ // occupied.
+ if sw.Cap() < 16*1024*1024 && sw.Cap()/2 < sw.Len() {
+ bufPool.Put(sw)
+ }
+ }()
+
  sw.Reset()
  vw := bvwPool.Get(sw)
  defer bvwPool.Put(vw)