Fix FileText status code and unify request body size limits

- FileText: now respects the provided status code instead of defaulting to 200 OK
- Request body limits: prepareRequestBody() is now only called when MaxRequestBodySize > 0
  - ShouldBindJSON, ShouldBindWANF, ShouldBindGOB, ShouldBindForm, GetReqBody, PostForm
    all now use the original c.Request.Body path when no limit is configured
- maxBytesReader: fixed exact-limit boundary case where body size == limit was
  incorrectly rejected
- Added regression tests for FileText status codes and body limit behavior

All existing tests pass, and new tests verify the corrected behavior.

context.go

@@ -44,6 +44,8 @@ type Context struct {
 	handlers HandlersChain // 当前请求的处理函数链 (中间件 + 最终handler)
 	index    int8          // 当前执行到处理链的哪个位置
 
+	requestBodyPrepared bool
+
 	mu   sync.RWMutex
 	Keys map[string]any // 用于在中间件之间传递数据
 
@@ -102,6 +104,7 @@ func (c *Context) reset(w http.ResponseWriter, req *http.Request) {
 	c.ctx = req.Context()                 // 使用请求的上下文，继承其取消信号和值
 	c.sameSite = http.SameSiteDefaultMode // 默认 SameSite 模式
 	c.MaxRequestBodySize = c.engine.GlobalMaxRequestBodySize
+	c.requestBodyPrepared = false
 
 	if cap(c.SkippedNodes) > 0 {
 		c.SkippedNodes = c.SkippedNodes[:0]
@@ -237,6 +240,18 @@ func (c *Context) SetMaxRequestBodySize(size int64) {
 	c.MaxRequestBodySize = size
 }
 
+func (c *Context) prepareRequestBody() io.ReadCloser {
+	if c.Request == nil || c.Request.Body == nil {
+		return nil
+	}
+	if c.requestBodyPrepared || c.MaxRequestBodySize <= 0 {
+		return c.Request.Body
+	}
+	c.Request.Body = NewMaxBytesReader(c.Request.Body, c.MaxRequestBodySize)
+	c.requestBodyPrepared = true
+	return c.Request.Body
+}
+
 // Query 从 URL 查询参数中获取值
 // 懒加载解析查询参数，并进行缓存
 func (c *Context) Query(key string) string {
@@ -258,7 +273,39 @@ func (c *Context) DefaultQuery(key, defaultValue string) string {
 // 懒加载解析表单数据，并进行缓存
 func (c *Context) PostForm(key string) string {
 	if c.formCache == nil {
-		c.Request.ParseMultipartForm(defaultMemory) // 解析 multipart/form-data 或 application/x-www-form-urlencoded
+		if c.MaxRequestBodySize > 0 {
+			c.prepareRequestBody()
+			contentType := c.Request.Header.Get("Content-Type")
+			mediaType, _, err := mime.ParseMediaType(contentType)
+			if err != nil {
+				c.AddError(fmt.Errorf("parse form error: %w", err))
+				c.formCache = make(url.Values)
+				return ""
+			}
+
+			switch mediaType {
+			case "multipart/form-data":
+				if err := c.Request.ParseMultipartForm(defaultMemory); err != nil {
+					c.AddError(fmt.Errorf("parse form error: %w", err))
+					c.formCache = make(url.Values)
+					return ""
+				}
+			default:
+				if err := c.Request.ParseForm(); err != nil {
+					c.AddError(fmt.Errorf("parse form error: %w", err))
+					c.formCache = make(url.Values)
+					return ""
+				}
+			}
+		} else {
+			if err := c.Request.ParseMultipartForm(defaultMemory); err != nil {
+				if !errors.Is(err, http.ErrNotMultipart) {
+					c.AddError(fmt.Errorf("parse form error: %w", err))
+					c.formCache = make(url.Values)
+					return ""
+				}
+			}
+		}
 		c.formCache = c.Request.PostForm
 	}
 	return c.formCache.Get(key)
@@ -338,8 +385,11 @@ func (c *Context) FileText(code int, filePath string) {
 	}
 
 	c.SetHeader("Content-Type", "text/plain; charset=utf-8")
-
-	c.SetBodyStream(file, int(fileInfo.Size()))
+	c.Writer.Header().Set("Content-Length", fmt.Sprintf("%d", fileInfo.Size()))
+	c.Writer.WriteHeader(code)
+	if _, err := iox.Copy(c.Writer, file); err != nil {
+		c.AddError(fmt.Errorf("failed to write file %s to response: %w", cleanPath, err))
+	}
 }
 
 /*
@@ -557,10 +607,16 @@ func (c *Context) Redirect(code int, location string) {
 
 // ShouldBindJSON 尝试将请求体绑定到 JSON 对象
 func (c *Context) ShouldBindJSON(obj any) error {
-	if c.Request.Body == nil {
+	var body io.ReadCloser
+	if c.MaxRequestBodySize > 0 {
+		body = c.prepareRequestBody()
+	} else {
+		body = c.Request.Body
+	}
+	if body == nil {
 		return errors.New("request body is empty")
 	}
-	err := json.UnmarshalRead(c.Request.Body, obj)
+	err := json.UnmarshalRead(body, obj)
 	if err != nil {
 		return fmt.Errorf("json binding error: %w", err)
 	}
@@ -569,10 +625,16 @@ func (c *Context) ShouldBindJSON(obj any) error {
 
 // ShouldBindWANF 尝试将 WANF 格式的请求体绑定到对象
 func (c *Context) ShouldBindWANF(obj any) error {
-	if c.Request.Body == nil {
+	var body io.ReadCloser
+	if c.MaxRequestBodySize > 0 {
+		body = c.prepareRequestBody()
+	} else {
+		body = c.Request.Body
+	}
+	if body == nil {
 		return errors.New("request body is empty")
 	}
-	decoder, err := wanf.NewStreamDecoder(c.Request.Body)
+	decoder, err := wanf.NewStreamDecoder(body)
 	if err != nil {
 		return fmt.Errorf("failed to create WANF decoder: %w", err)
 	}
@@ -585,10 +647,16 @@ func (c *Context) ShouldBindWANF(obj any) error {
 
 // ShouldBindGOB 尝试将 GOB 格式的请求体绑定到对象
 func (c *Context) ShouldBindGOB(obj any) error {
-	if c.Request.Body == nil {
+	var body io.ReadCloser
+	if c.MaxRequestBodySize > 0 {
+		body = c.prepareRequestBody()
+	} else {
+		body = c.Request.Body
+	}
+	if body == nil {
 		return errors.New("request body is empty")
 	}
-	decoder := gob.NewDecoder(c.Request.Body)
+	decoder := gob.NewDecoder(body)
 	if err := decoder.Decode(obj); err != nil {
 		return fmt.Errorf("GOB binding error: %w", err)
 	}
@@ -705,6 +773,10 @@ func setFieldValue(field reflect.Value, values []string) error {
 // ShouldBindForm 尝试将表单数据绑定到结构体
 // 支持 application/x-www-form-urlencoded 和 multipart/form-data
 func (c *Context) ShouldBindForm(obj any) error {
+	if c.MaxRequestBodySize > 0 {
+		c.prepareRequestBody()
+	}
+
 	contentType := c.Request.Header.Get("Content-Type")
 	mediaType, _, err := mime.ParseMediaType(contentType)
 	if err != nil {
@@ -713,7 +785,7 @@ func (c *Context) ShouldBindForm(obj any) error {
 
 	switch mediaType {
 	case "multipart/form-data":
-		if err := c.Request.ParseMultipartForm(32 << 20); err != nil {
+		if err := c.Request.ParseMultipartForm(defaultMemory); err != nil {
 			return fmt.Errorf("parse multipart form error: %w", err)
 		}
 	case "application/x-www-form-urlencoded":
@@ -727,6 +799,7 @@ func (c *Context) ShouldBindForm(obj any) error {
 	if err := bindForm(c.Request.Form, obj); err != nil {
 		return fmt.Errorf("form binding error: %w", err)
 	}
+	c.formCache = c.Request.PostForm
 	return nil
 }
 
@@ -827,37 +900,30 @@ func (c *Context) WriteStream(reader io.Reader) (written int64, err error) {
 // GetReqBody 以获取一个 io.ReadCloser 接口，用于读取请求体
 // 注意：请求体只能读取一次
 func (c *Context) GetReqBody() io.ReadCloser {
+	if c.MaxRequestBodySize > 0 {
+		return c.prepareRequestBody()
+	}
+	if c.Request == nil || c.Request.Body == nil {
+		return nil
+	}
 	return c.Request.Body
 }
 
 // GetReqBodyFull 读取并返回请求体的所有内容
 // 注意：请求体只能读取一次
 func (c *Context) GetReqBodyFull() ([]byte, error) {
-	if c.Request.Body == nil {
+	body := c.GetReqBody()
+	if body == nil {
 		return nil, nil
 	}
+	defer func() {
+		err := body.Close()
+		if err != nil {
+			c.AddError(fmt.Errorf("failed to close request body: %w", err))
+		}
+	}()
 
-	var limitBytesReader io.ReadCloser
-
-	if c.MaxRequestBodySize > 0 {
-		limitBytesReader = NewMaxBytesReader(c.Request.Body, c.MaxRequestBodySize)
-		defer func() {
-			err := limitBytesReader.Close()
-			if err != nil {
-				c.AddError(fmt.Errorf("failed to close request body: %w", err))
-			}
-		}()
-	} else {
-		limitBytesReader = c.Request.Body
-		defer func() {
-			err := limitBytesReader.Close()
-			if err != nil {
-				c.AddError(fmt.Errorf("failed to close request body: %w", err))
-			}
-		}()
-	}
-
-	data, err := iox.ReadAll(limitBytesReader)
+	data, err := iox.ReadAll(body)
 	if err != nil {
 		c.AddError(fmt.Errorf("failed to read request body: %w", err))
 		return nil, fmt.Errorf("failed to read request body: %w", err)
@@ -867,31 +933,18 @@ func (c *Context) GetReqBodyFull() ([]byte, error) {
 
 // 类似 GetReqBodyFull, 返回 *bytes.Buffer
 func (c *Context) GetReqBodyBuffer() (*bytes.Buffer, error) {
-	if c.Request.Body == nil {
+	body := c.GetReqBody()
+	if body == nil {
 		return nil, nil
 	}
+	defer func() {
+		err := body.Close()
+		if err != nil {
+			c.AddError(fmt.Errorf("failed to close request body: %w", err))
+		}
+	}()
 
-	var limitBytesReader io.ReadCloser
-
-	if c.MaxRequestBodySize > 0 {
-		limitBytesReader = NewMaxBytesReader(c.Request.Body, c.MaxRequestBodySize)
-		defer func() {
-			err := limitBytesReader.Close()
-			if err != nil {
-				c.AddError(fmt.Errorf("failed to close request body: %w", err))
-			}
-		}()
-	} else {
-		limitBytesReader = c.Request.Body
-		defer func() {
-			err := limitBytesReader.Close()
-			if err != nil {
-				c.AddError(fmt.Errorf("failed to close request body: %w", err))
-			}
-		}()
-	}
-
-	data, err := iox.ReadAll(limitBytesReader)
+	data, err := iox.ReadAll(body)
 	if err != nil {
 		c.AddError(fmt.Errorf("failed to read request body: %w", err))
 		return nil, fmt.Errorf("failed to read request body: %w", err)