fix: stream return EOF when openai return error (#184)

* fix: stream return EOF when openai return error

* perf: add error accumulator

* fix: golangci-lint

* fix: unmarshal error possibly null

* fix: error accumulator

* test: error accumulator use interface and add test code

* test: error accumulator add test code

* refactor: use stream reader to re-use stream code

* refactor: stream reader use generics

error_accumulator.go

@@ -0,0 +1,51 @@
+package openai
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+type errorAccumulator interface {
+	write(p []byte) error
+	unmarshalError() (*ErrorResponse, error)
+}
+
+type errorBuffer interface {
+	io.Writer
+	Len() int
+	Bytes() []byte
+}
+
+type errorAccumulate struct {
+	buffer      errorBuffer
+	unmarshaler unmarshaler
+}
+
+func newErrorAccumulator() errorAccumulator {
+	return &errorAccumulate{
+		buffer:      &bytes.Buffer{},
+		unmarshaler: &jsonUnmarshaler{},
+	}
+}
+
+func (e *errorAccumulate) write(p []byte) error {
+	_, err := e.buffer.Write(p)
+	if err != nil {
+		return fmt.Errorf("error accumulator write error, %w", err)
+	}
+	return nil
+}
+
+func (e *errorAccumulate) unmarshalError() (*ErrorResponse, error) {
+	var err error
+	if e.buffer.Len() > 0 {
+		var errRes ErrorResponse
+		err = e.unmarshaler.unmarshal(e.buffer.Bytes(), &errRes)
+		if err != nil {
+			return nil, err
+		}
+		return &errRes, nil
+	}
+	return nil, err
+}