fix: return read error when ErrorResponse has nil Error field

stream_reader.go

@@ -64,7 +64,7 @@ func (stream *streamReader[T]) processLines() ([]byte, error) {
 		rawLine, readErr := stream.reader.ReadBytes('\n')
 		if readErr != nil || hasErrorPrefix {
 			respErr := stream.unmarshalError()
-			if respErr != nil {
+			if respErr != nil && respErr.Error != nil {
 				return nil, fmt.Errorf("error, %w", respErr.Error)
 			}
 			return nil, readErr

stream_reader_test.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"bytes"
 	"errors"
+	"io"
 	"testing"
 
 	utils "github.com/sashabaranov/go-openai/internal"
@@ -76,3 +77,33 @@ func TestStreamReaderRecvRaw(t *testing.T) {
 		t.Fatalf("Did not return raw line: %v", string(rawLine))
 	}
 }
+
+// TestStreamReaderReturnsReadErrWhenErrorResponseHasNilError tests that when
+// unmarshalError returns an ErrorResponse with a nil Error field (e.g., when
+// unmarshaling an empty JSON object "{}"), the original read error is returned
+// instead of "error, <nil>". This fixes issue #1060.
+func TestStreamReaderReturnsReadErrWhenErrorResponseHasNilError(t *testing.T) {
+	// Create a stream that will return io.EOF on read (simulating context cancellation)
+	// with an error accumulator that contains an empty JSON object
+	stream := &streamReader[ChatCompletionStreamResponse]{
+		reader:         bufio.NewReader(bytes.NewReader([]byte{})), // empty reader returns io.EOF
+		errAccumulator: utils.NewErrorAccumulator(),
+		unmarshaler:    &utils.JSONUnmarshaler{},
+	}
+
+	// Write an empty JSON object to the error accumulator
+	// This will unmarshal to ErrorResponse{Error: nil}
+	err := stream.errAccumulator.Write([]byte("{}"))
+	if err != nil {
+		t.Fatalf("Failed to write to error accumulator: %v", err)
+	}
+
+	// Call processLines which should return io.EOF, not "error, <nil>"
+	_, err = stream.processLines()
+	if err == nil {
+		t.Fatal("Expected error but got nil")
+	}
+	if !errors.Is(err, io.EOF) {
+		t.Fatalf("Expected io.EOF but got: %v", err)
+	}
+}