Check for NUL terminator in MemoryPool::findString()

extras/tests/Helpers/api/String.h

@@ -37,6 +37,12 @@ class String {
     return *this;
   }
 
+  char operator[](unsigned int index) const {
+    if (index >= _str.size())
+      return 0;
+    return _str[index];
+  }
+
   friend std::ostream& operator<<(std::ostream& lhs, const ::String& rhs) {
     lhs << rhs._str;
     return lhs;

src/ArduinoJson/Memory/MemoryPool.hpp

@@ -166,9 +166,21 @@ class MemoryPool {
 
 #if ARDUINOJSON_ENABLE_STRING_DEDUPLICATION
   template <typename TAdaptedString>
-  const char* findString(const TAdaptedString& str) {
-    for (char* next = _begin; next < _left; ++next) {
-      if (str.compare(next) == 0)
+  static bool stringEquals(const char* p, size_t n, const TAdaptedString& s) {
+    if (p[n])  // check terminator first
+      return false;
+    for (size_t i = 0; i < n; i++) {
+      if (p[i] != s[i])
+        return false;
+    }
+    return true;
+  }
+
+  template <typename TAdaptedString>
+  const char* findString(const TAdaptedString& str) const {
+    size_t n = str.size();
+    for (char* next = _begin; next + n < _left; ++next) {
+      if (stringEquals(next, n, str))
         return next;
 
       // jump to next terminator

src/ArduinoJson/Strings/Adapters/ArduinoStringAdapter.hpp

@@ -32,6 +32,11 @@ class StringAdapter< ::String> {
     return safe_strcmp(me, other);
   }
 
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(_str != 0);
+    return _str->operator[](static_cast<unsigned int>(i));
+  }
+
   size_t size() const {
     return _str->length();
   }

src/ArduinoJson/Strings/Adapters/ConstRamStringAdapter.hpp

@@ -7,6 +7,7 @@
 #include <stddef.h>  // size_t
 #include <string.h>  // strcmp
 
+#include <ArduinoJson/Polyfills/assert.hpp>
 #include <ArduinoJson/Polyfills/safe_strcmp.hpp>
 #include <ArduinoJson/Strings/StoragePolicy.hpp>
 #include <ArduinoJson/Strings/StringAdapter.hpp>
@@ -32,6 +33,12 @@ class StringAdapter<const char*> {
     return strlen(_str);
   }
 
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(_str != 0);
+    ARDUINOJSON_ASSERT(i <= size());
+    return _str[i];
+  }
+
   const char* data() const {
     return _str;
   }

src/ArduinoJson/Strings/Adapters/FlashStringAdapter.hpp

@@ -39,6 +39,13 @@ class StringAdapter<const __FlashStringHelper*> {
     return strlen_P(reinterpret_cast<const char*>(_str));
   }
 
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(_str != 0);
+    ARDUINOJSON_ASSERT(i <= size());
+    return static_cast<char>(
+        pgm_read_byte(reinterpret_cast<const char*>(_str) + i));
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private:

src/ArduinoJson/Strings/Adapters/SizedFlashStringAdapter.hpp

@@ -34,6 +34,14 @@ class StringAdapter<const __FlashStringHelper*, true> {
     memcpy_P(p, reinterpret_cast<const char*>(_str), n);
   }
 
+  // TODO: not covered by the tests
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(_str != 0);
+    ARDUINOJSON_ASSERT(i <= _size);
+    return static_cast<char>(
+        pgm_read_byte(reinterpret_cast<const char*>(_str) + i));
+  }
+
   size_t size() const {
     return _size;
   }

src/ArduinoJson/Strings/Adapters/SizedRamStringAdapter.hpp

@@ -33,6 +33,12 @@ class StringAdapter<TChar*, true> {
     return _size;
   }
 
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(_str != 0);
+    ARDUINOJSON_ASSERT(i <= _size);
+    return _str[i];
+  }
+
   typedef storage_policies::store_by_copy storage_policy;
 
  private:

src/ArduinoJson/Strings/Adapters/StdStringAdapter.hpp

@@ -33,6 +33,11 @@ class StringAdapter<std::basic_string<char, TCharTraits, TAllocator> > {
     return _str->compare(other);
   }
 
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(i <= size());
+    return _str->operator[](i);
+  }
+
   size_t size() const {
     return _str->size();
   }

src/ArduinoJson/Strings/Adapters/StringViewAdapter.hpp

@@ -31,6 +31,11 @@ class StringAdapter<std::string_view> {
     return _str.compare(other);
   }
 
+  char operator[](size_t i) const {
+    ARDUINOJSON_ASSERT(i <= size());
+    return _str[i];
+  }
+
   size_t size() const {
     return _str.size();
   }