#4759 introducing a general body limit to avoid big heap allocations

context.go

@@ -940,6 +940,7 @@ func (c *Context) ShouldBindUri(obj any) error {
 // ShouldBindWith binds the passed struct pointer using the specified binding engine.
 // See the binding package.
 func (c *Context) ShouldBindWith(obj any, b binding.Binding) error {
+	c.limitRequestBody()
 	return b.Bind(c.Request, obj)
 }
 
@@ -949,6 +950,7 @@ func (c *Context) ShouldBindWith(obj any, b binding.Binding) error {
 // NOTE: This method reads the body before binding. So you should use
 // ShouldBindWith for better performance if you need to call only once.
 func (c *Context) ShouldBindBodyWith(obj any, bb binding.BindingBody) (err error) {
+	c.limitRequestBody()
 	var body []byte
 	if cb, ok := c.Get(BodyBytesKey); ok {
 		if cbb, ok := cb.([]byte); ok {
@@ -965,6 +967,19 @@ func (c *Context) ShouldBindBodyWith(obj any, bb binding.BindingBody) (err error
 	return bb.BindBody(body, obj)
 }
 
+// limitRequestBody wraps c.Request.Body in place so that reading more than
+// c.engine.MaxRequestBodyBytes from it fails with *http.MaxBytesError, which
+// MustBindWith already maps to a 413 response.
+func (c *Context) limitRequestBody() {
+	if c.engine == nil || c.engine.MaxRequestBodyBytes <= 0 {
+		return
+	}
+	if c.Request == nil || c.Request.Body == nil {
+		return
+	}
+	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, c.engine.MaxRequestBodyBytes)
+}
+
 // ShouldBindBodyWithJSON is a shortcut for c.ShouldBindBodyWith(obj, binding.JSON).
 func (c *Context) ShouldBindBodyWithJSON(obj any) error {
 	return c.ShouldBindBodyWith(obj, binding.JSON)

gin.go

@@ -23,10 +23,11 @@ import (
 )
 
 const (
-	defaultMultipartMemory = 32 << 20 // 32 MB
-	escapedColon           = "\\:"
-	colon                  = ":"
-	backslash              = "\\"
+	defaultMultipartMemory     = 32 << 20  // 32 MB
+	defaultMaxRequestBodyBytes = 128 << 20 // 128 MiB
+	escapedColon               = "\\:"
+	colon                      = ":"
+	backslash                  = "\\"
 )
 
 var (
@@ -166,6 +167,13 @@ type Engine struct {
 	// method call.
 	MaxMultipartMemory int64
 
+	// MaxRequestBodyBytes limits how many bytes Context's Bind*/ShouldBind*/
+	// ShouldBindBodyWith* methods will read from a request body before failing
+	// with a 413. It protects against a client sending an oversized or
+	// malformed body that would otherwise be buffered into memory in full
+	// before being rejected. Set to <= 0 to disable and read bodies unbounded.
+	MaxRequestBodyBytes int64
+
 	// UseH2C enable h2c support.
 	UseH2C bool
 
@@ -219,6 +227,7 @@ func New(opts ...OptionFunc) *Engine {
 		RemoveExtraSlash:       false,
 		UnescapePathValues:     true,
 		MaxMultipartMemory:     defaultMultipartMemory,
+		MaxRequestBodyBytes:    defaultMaxRequestBodyBytes,
 		trees:                  make(methodTrees, 0, 9),
 		delims:                 render.Delims{Left: "{{", Right: "}}"},
 		secureJSONPrefix:       "while(1);",