server: set maximum allowed request body. (#3324)

This patch sets the value as 5GiB + 64MiB.  5GiB is the maximum
allowed object size and 64MiB is for form data fields and headers.

cmd/generic-handlers.go

@@ -42,9 +42,13 @@ func registerHandlers(mux *router.Router, handlerFns ...HandlerFunc) http.Handle
 
 // Adds limiting body size middleware
 
-// Set the body size limit to 6 Gb = Maximum object size + other possible data
-// in the same request
-const requestMaxBodySize = (5 + 1) * humanize.GiByte
+// Maximum allowed form data field values. 64MiB is a guessed practical value
+// which is more than enough to accommodate any form data fields and headers.
+const requestFormDataSize = 64 * humanize.MiByte
+
+// For any HTTP request, request body should be not more than 5GiB + requestFormDataSize
+// where, 5GiB is the maximum allowed object size for object upload.
+const requestMaxBodySize = 5*humanize.GiByte + requestFormDataSize
 
 type requestSizeLimitHandler struct {
 	handler     http.Handler