fix SimpleString equality for content with embedded NUL bytes (#1230)

strncmp stops at the first NUL byte, so two different strings of equal length that agree up to an embedded NUL compared equal, while operator< ordered the same pair with memcmp. Embedded NUL bytes reach a blackboard string through ImportBlackboardFromJSON, where a JSON escape decodes to a real NUL, and the scripting == and != operators compare through SimpleString.

Author: aysha-afrah26

include/behaviortree_cpp/utils/simple_string.hpp

@@ -110,13 +110,16 @@ class SimpleString
   bool operator==(const SimpleString& other) const
   {
     const size_t N = size();
-    return other.size() == N && std::strncmp(data(), other.data(), N) == 0;
+    // memcmp, not strncmp: the content may hold embedded NUL bytes, and strncmp
+    // stops at the first one, reporting two different strings of equal length as
+    // equal. It is also what operator< below compares with.
+    return other.size() == N && std::memcmp(data(), other.data(), N) == 0;
   }
 
   bool operator!=(const SimpleString& other) const
   {
     const size_t N = size();
-    return other.size() != N || std::strncmp(data(), other.data(), N) != 0;
+    return other.size() != N || std::memcmp(data(), other.data(), N) != 0;
   }
 
   bool operator<=(const SimpleString& other) const

tests/gtest_simple_string.cpp

@@ -377,6 +377,31 @@ TEST(SimpleStringTest, EmptyStringComparison)
   EXPECT_TRUE(nonEmpty >= empty1);
 }
 
+// Test comparison of strings that hold embedded NUL bytes
+TEST(SimpleStringTest, ComparisonWithEmbeddedNull)
+{
+  const SimpleString s1(std::string("a\0b", 3));
+  const SimpleString s2(std::string("a\0c", 3));
+  const SimpleString s3(std::string("a\0b", 3));
+
+  EXPECT_FALSE(s1 == s2);
+  EXPECT_TRUE(s1 != s2);
+  EXPECT_TRUE(s1 < s2);
+  EXPECT_FALSE(s1 > s2);
+
+  EXPECT_TRUE(s1 == s3);
+  EXPECT_FALSE(s1 != s3);
+
+  // same thing with the heap representation
+  const SimpleString l1(std::string("0123456789abcdef\0b", 18));
+  const SimpleString l2(std::string("0123456789abcdef\0c", 18));
+
+  EXPECT_FALSE(l1.isSOO());
+  EXPECT_FALSE(l1 == l2);
+  EXPECT_TRUE(l1 != l2);
+  EXPECT_TRUE(l1 < l2);
+}
+
 // Test that SimpleString size is as expected (16 bytes)
 TEST(SimpleStringTest, SizeOfSimpleString)
 {