Implement resize function for String

rosidl_runtime_c/include/rosidl_runtime_c/string_functions.h

@@ -117,6 +117,20 @@ bool
 rosidl_runtime_c__String__assign(
   rosidl_runtime_c__String * str, const char * value);
 
+/// Resize the char pointer.
+/**
+ * This function resize the input value pointer.
+ *
+ * \param[inout] str a pointer to a rosidl_runtime_c__String structure
+ * \param[in] n the new size of the internal buffer
+ * \return true if successful, false if the passed string pointer is null
+ *   or if the size is higher than SIZE_MAX or if the memory reallocation failed.
+ */
+ROSIDL_GENERATOR_C_PUBLIC
+bool
+rosidl_runtime_c__String__resize(
+  rosidl_runtime_c__String * str, size_t n);
+
 /// Initialize a rosidl_runtime_c__String__Sequence__init structure.
 /**
  * The rosidl_runtime_c__String__Sequence is initialized with the size passed to the function.

rosidl_runtime_c/src/string_functions.c

@@ -143,6 +143,29 @@ rosidl_runtime_c__String__copy(
     output, input->data, input->size);
 }
 
+bool
+rosidl_runtime_c__String__resize(
+  rosidl_runtime_c__String *str, size_t n)
+{
+  if(!str) {
+    return false;
+  }
+  // check valid range of n before allocating n + 1 characters
+  if(n > SIZE_MAX / sizeof(char) - 1) {
+    return false;
+  }
+  rcutils_allocator_t allocator = rcutils_get_default_allocator();
+  char * data = allocator.reallocate(str->data, (n + 1) * sizeof(char), allocator.state);
+  if(!data) {
+    return false;
+  }
+  data[n] = 0;
+  str->data = data;
+  str->size = n;
+  str->capacity = n + 1;
+  return true;
+}
+
 bool
 rosidl_runtime_c__String__Sequence__init(
   rosidl_runtime_c__String__Sequence * sequence, size_t size)

rosidl_runtime_c/test/test_string_functions.cpp

@@ -78,6 +78,18 @@ TEST(string_functions, resize_assignn) {
   EXPECT_TRUE(rosidl_runtime_c__String__init(&s));
   EXPECT_TRUE(rosidl_runtime_c__String__init(&t));
 
+  EXPECT_FALSE(rosidl_runtime_c__String__resize(nullptr, s_size));
+
+  // If you're here because this test crashed your computer, it might be because it just tried
+  // to allocate SIZE_MAX * 2 bytes, which means someone removed an important check.
+  EXPECT_FALSE(rosidl_runtime_c__String__resize(nullptr, SIZE_MAX * 2));
+
+  EXPECT_TRUE(rosidl_runtime_c__String__resize(&s, s_size));
+  EXPECT_EQ(s.size, s_size);
+  EXPECT_EQ(s.capacity, s_size + 1u);
+  EXPECT_NE(s.data, nullptr);
+  EXPECT_EQ(s.data[s_size], 0);
+
   EXPECT_FALSE(rosidl_runtime_c__String__assign(nullptr, nullptr));
   EXPECT_FALSE(rosidl_runtime_c__String__assignn(nullptr, nullptr, 0));
   EXPECT_FALSE(rosidl_runtime_c__String__assignn(&s, nullptr, 0));