Support splice in http blind tunnel

1. Add TS_USE_LINUX_SPLICE as a compilation option.
2. Make MIOBuffer and MIOBufferReader polymorphic classes making their member function virtual.
3. Create PipeIOBuffer and PipeIOBufferReader as derived classed, encapsulating Linux pipe.
4. Use dynamic_cast to enable logic switch in state machines and continuations.

CMakeLists.txt

@@ -428,6 +428,21 @@ list(APPEND CMAKE_REQUIRED_LIBRARIES pthread)
 check_symbol_exists(pthread_getname_np pthread.h HAVE_PTHREAD_GETNAME_NP)
 check_symbol_exists(pthread_get_name_np pthread.h HAVE_PTHREAD_GET_NAME_NP)
 
+option(USE_SPLICE "Enable the use of splice(2) for zero copy (default OFF) (linux only)" OFF)
+
+# Check for the splice function
+include(CheckFunctionExists)
+check_function_exists(splice HAVE_SPLICE)
+
+# Configure USE_SPLICE based on both availability and user option
+if(HAVE_SPLICE AND USE_SPLICE)
+  message(STATUS "splice is available and enabled.")
+  set(TS_USE_LINUX_SPLICE 1) # Use ON for true
+else()
+  message(STATUS "splice is either not available or disabled by the user.")
+  set(TS_USE_LINUX_SPLICE 0) # Use OFF for false
+endif()
+
 check_source_compiles(
   C "#include <pthread.h>
   void main() { pthread_setname_np(\"name\"); }" HAVE_PTHREAD_SETNAME_NP_1

CMakePresets.json

@@ -17,6 +17,19 @@
         "CMAKE_COMPILE_WARNING_AS_ERROR": "ON"
       }
     },
+    {
+      "name": "default-splice",
+      "displayName": "Default build with splice",
+      "description": "Default build using Ninja generator with splice",
+      "inherits": ["default"],
+      "binaryDir": "${sourceDir}/build-${presetName}",
+      "generator": "Ninja",
+      "cacheVariables": {
+        "CMAKE_COLOR_DIAGNOSTICS": "ON",
+        "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
+        "USE_SPLICE": "ON"
+      }
+    },
     {
       "name": "layout-defaults",
       "displayName": "Default install layout paths template",