move request_builder into internal pkg (#304) (#329)

* move request_builder into internal pkg (#304)

* add some test for internal.RequestBuilder

* add a test for openai.GetEngine

internal/request_builder.go

@@ -0,0 +1,40 @@
+package openai
+
+import (
+	"bytes"
+	"context"
+	"net/http"
+)
+
+type RequestBuilder interface {
+	Build(ctx context.Context, method, url string, request any) (*http.Request, error)
+}
+
+type HTTPRequestBuilder struct {
+	marshaller Marshaller
+}
+
+func NewRequestBuilder() *HTTPRequestBuilder {
+	return &HTTPRequestBuilder{
+		marshaller: &JSONMarshaller{},
+	}
+}
+
+func (b *HTTPRequestBuilder) Build(ctx context.Context, method, url string, request any) (*http.Request, error) {
+	if request == nil {
+		return http.NewRequestWithContext(ctx, method, url, nil)
+	}
+
+	var reqBytes []byte
+	reqBytes, err := b.marshaller.Marshal(request)
+	if err != nil {
+		return nil, err
+	}
+
+	return http.NewRequestWithContext(
+		ctx,
+		method,
+		url,
+		bytes.NewBuffer(reqBytes),
+	)
+}