OSS-Fuzz: Add new fuzzer targets datetime processing

fuzz/CMakeLists.txt

@@ -2,6 +2,7 @@ INCLUDE_DIRECTORIES(${WT_SOURCE_DIR}/src)
 
 ADD_EXECUTABLE(fuzz-cgi  fuzz-cgi.C)
 ADD_EXECUTABLE(fuzz-css  fuzz-css.C)
+ADD_EXECUTABLE(fuzz-datetime fuzz-datetime.C)
 ADD_EXECUTABLE(fuzz-eval fuzz-eval.C)
 ADD_EXECUTABLE(fuzz-http fuzz-http.C)
 ADD_EXECUTABLE(fuzz-json fuzz-json.C)
@@ -10,6 +11,7 @@ ADD_EXECUTABLE(fuzz-xml  fuzz-xml.C)
 
 TARGET_LINK_LIBRARIES(fuzz-cgi  PRIVATE wt $ENV{LIB_FUZZING_ENGINE})
 TARGET_LINK_LIBRARIES(fuzz-css  PRIVATE wt $ENV{LIB_FUZZING_ENGINE})
+TARGET_LINK_LIBRARIES(fuzz-datetime PRIVATE wt $ENV{LIB_FUZZING_ENGINE})
 TARGET_LINK_LIBRARIES(fuzz-eval PRIVATE wt $ENV{LIB_FUZZING_ENGINE})
 TARGET_LINK_LIBRARIES(fuzz-http PRIVATE wt wthttp $ENV{LIB_FUZZING_ENGINE})
 TARGET_LINK_LIBRARIES(fuzz-json PRIVATE wt $ENV{LIB_FUZZING_ENGINE})

fuzz/fuzz-datetime.C

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2026 Emweb bv, Herent, Belgium.
+ *
+ * See the LICENSE file for terms of use.
+ */
+
+#include <stdint.h>
+#include <stddef.h>
+#include <string>
+
+#include "Wt/WString.h"
+#include "Wt/WDate.h"
+#include "Wt/WTime.h"
+#include "Wt/WDateTime.h"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+  if (size < 1)
+    return 0;
+
+  // First byte splits the remaining bytes into a format string and a value
+  // string, so both the format parser and the value parser get fuzzed.
+  std::size_t formatLen = data[0] % size;
+  std::string format(reinterpret_cast<const char*>(data + 1), formatLen);
+  std::string value(reinterpret_cast<const char*>(data + 1 + formatLen),
+                    size - 1 - formatLen);
+
+  Wt::WString f = Wt::WString::fromUTF8(format);
+  Wt::WString v = Wt::WString::fromUTF8(value);
+
+  try { Wt::WDateTime::fromString(v, f); } catch (...) {}
+  try { Wt::WDate::fromString(v, f); } catch (...) {}
+  try { Wt::WTime::fromString(v, f); } catch (...) {}
+  try { Wt::WDateTime::fromString(v); } catch (...) {}
+
+  return 0;
+}