Add null_safe_string_view(const char*, std::size_t)

[why]
There are use cases for constructing a string_view with a specified size
that is still protected against null pointers. This is different from
safe_string_view(const char*, std::size_t) which terminates the string
at a null byte.

Signed-off-by: Lars Froehlich <lars.froehlich@desy.de>

Author: alt-graph

include/gul17/string_util.h

@@ -256,7 +256,8 @@ std::string null_safe_string(const char* char_ptr);
  * auto c = safe_string_view("AB\0CD"); // c == "AB"sv
  * \endcode
  *
- * \param char_ptr  Pointer to a null-terminated string or a null pointer
+ * \param char_ptr  Pointer to a string that has at least \c length accessible bytes, or a
+ *                  null pointer
  *
  * \see safe_string_view(), null_safe_string()
  *
@@ -265,6 +266,30 @@ std::string null_safe_string(const char* char_ptr);
 GUL_EXPORT
 std::string_view null_safe_string_view(const char* char_ptr);
 
+/**
+ * Safely construct a string_view from a char pointer and a length.
+ *
+ * If the pointer is null, an empty string_view is constructed. Otherwise, the function
+ * constructs a std::string_view with the specified length from it. Zero bytes in the
+ * input range do not terminate the string_view.
+ *
+ * \code
+ * auto a = safe_string_view(nullptr, 10); // a == ""sv
+ * auto b = safe_string_view("ABC", 4);    // b == "ABC\0"sv
+ * auto c = safe_string_view("AB\0CD", 4); // c == "AB\0C"sv
+ * \endcode
+ *
+ * \param char_ptr  Pointer to a string with at least \c length accessible bytes, or a
+ *                  null pointer
+ * \param length    Length of the generated string_view (unless the pointer is null)
+ *
+ * \see safe_string_view(), null_safe_string()
+ *
+ * \since version UNRELEASED
+ */
+GUL_EXPORT
+std::string_view null_safe_string_view(const char* char_ptr, std::size_t length);
+
 /**
  * Repeat a string N times.
  * \code

src/string_util.cc

@@ -50,6 +50,16 @@ std::string_view null_safe_string_view(const char* char_ptr)
     return result;
 }
 
+std::string_view null_safe_string_view(const char* char_ptr, std::size_t length)
+{
+    std::string_view result;
+
+    if (char_ptr)
+        result = std::string_view(char_ptr, length);
+
+    return result;
+}
+
 std::string repeat(std::string_view str, std::size_t n)
 {
     std::string result;

tests/test_string_util.cc

@@ -134,6 +134,20 @@ TEST_CASE("null_safe_string_view(const char*)", "[string_util]")
     REQUIRE(null_safe_string_view("hi\0there") == "hi"sv);
 }
 
+TEST_CASE("null_safe_string_view(const char*, std::size_t)", "[string_util]")
+{
+    using gul17::null_safe_string_view;
+
+    REQUIRE(null_safe_string_view(nullptr, 0ull) == std::string_view{});
+    REQUIRE(null_safe_string_view(nullptr, 10ull) == std::string_view{});
+    REQUIRE(null_safe_string_view("", 0ull) == ""sv);
+    REQUIRE(null_safe_string_view("", 1ull) == "\0"sv);
+    REQUIRE(null_safe_string_view("hello", 5ull) == "hello"sv);
+    REQUIRE(null_safe_string_view("hello", 2ull) == "he"sv);
+    REQUIRE(null_safe_string_view("hi\0there", 2ull) == "hi"sv);
+    REQUIRE(null_safe_string_view("hi\0there", 4ull) == "hi\0t"sv);
+}
+
 TEST_CASE("repeat()", "[string_util]")
 {
     REQUIRE(repeat("du", 3) == "dududu");