chore: import upstream snapshot with attribution

core/dataloader/string_prefix_reader.go

@@ -0,0 +1,59 @@
+// Copyright 2024 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package dataloader
+
+import "io"
+
+// stringPrefixReader is an io.ReadCloser that reads from a string prefix before reading from
+// another io.Reader. This is used for reassembling partial records across multi-message
+// exchanges, since the end of a wire message does not typically line up with the end of a record.
+type stringPrefixReader struct {
+	prefix         string
+	prefixPosition uint
+	reader         io.Reader
+}
+
+var _ io.ReadCloser = (*stringPrefixReader)(nil)
+
+// NewStringPrefixReader creates a new stringPrefixReader that first returns the data in |prefix| and
+// then returns data from |reader|.
+func NewStringPrefixReader(prefix string, reader io.Reader) *stringPrefixReader {
+	return &stringPrefixReader{
+		prefix: prefix,
+		reader: reader,
+	}
+}
+
+// Read implements the io.Reader interface
+func (spr *stringPrefixReader) Read(p []byte) (n int, err error) {
+	if spr.prefixPosition < uint(len(spr.prefix)) {
+		n = copy(p, spr.prefix[spr.prefixPosition:])
+		spr.prefixPosition += uint(n)
+		if n == len(p) {
+			return n, nil
+		}
+	}
+
+	read, err := spr.reader.Read(p[n:])
+	return n + read, err
+}
+
+// Close implements the io.Closer interface
+func (spr *stringPrefixReader) Close() error {
+	if closer, ok := spr.reader.(io.Closer); ok {
+		return closer.Close()
+	}
+	return nil
+}