Merge 'sstring: add more accessors' from Kefu Chai

in this series, more accessors are added to `seastar::sstring`. the goal is to make sstring more standard compliant, so that it can be used in lieu of `std::string` when appropriate.

Closes #1755

* https://github.com/scylladb/seastar:
  sstring: add sstring::contains()
  sstring: add sstring::ends_with()
  sstring: add sstring::starts_with()
  sstring: add sstring::front()
  sstring: add sstring::find() overloads

include/seastar/core/sstring.hh

@@ -256,20 +256,18 @@ public:
  return npos;
  }
 
- size_t find(const basic_sstring& s, size_t pos = 0) const noexcept {
- const char_type* it = str() + pos;
- const char_type* end = str() + size();
- const char_type* c_str = s.str();
-
+ size_t find(const char_type* c_str, size_t pos, size_t len2) const noexcept {
+ assert(c_str != nullptr || len2 == 0);
  if (pos > size()) {
  return npos;
  }
 
- const size_t len2 = s.size();
  if (len2 == 0) {
  return pos;
  }
 
+ const char_type* it = str() + pos;
+ const char_type* end = str() + size();
  size_t len1 = end - it;
  if (len1 < len2) {
  return npos;
@@ -296,6 +294,23 @@ public:
  }
  }
 
+ constexpr size_t find(const char_type* s, size_t pos = 0) const noexcept {
+ return find(s, pos, traits_type::length(s));
+ }
+
+ size_t find(const basic_sstring& s, size_t pos = 0) const noexcept {
+ return find(s.str(), pos, s.size());
+ }
+
+ template<class StringViewLike,
+ std::enable_if_t<std::is_convertible_v<StringViewLike,
+ std::basic_string_view<char_type, traits_type>>,
+ int> = 0>
+ size_t find(const StringViewLike& sv_like, size_type pos = 0) const noexcept {
+ std::basic_string_view<char_type, traits_type> sv = sv_like;
+ return find(sv.data(), pos, sv.size());
+ }
+
  /**
  * find_last_of find the last occurrence of c in the string.
  * When pos is specified, the search only includes characters
@@ -446,6 +461,29 @@ public:
  replace(p, p, beg, end);
  }
 
+
+ /**
+ * Returns a read/write reference to the data at the first
+ * element of the string.
+ * This function shall not be called on empty strings.
+ */
+ reference
+ front() noexcept {
+ assert(!empty());
+ return *str();
+ }
+
+ /**
+ * Returns a read-only (constant) reference to the data at the first
+ * element of the string.
+ * This function shall not be called on empty strings.
+ */
+ const_reference
+ front() const noexcept {
+ assert(!empty());
+ return *str();
+ }
+
  /**
  * Returns a read/write reference to the data at the last
  * element of the string.
@@ -558,6 +596,42 @@ public:
  }
  }
 
+ constexpr bool starts_with(std::basic_string_view<char_type, traits_type> sv) const noexcept {
+ return size() > sv.size() && compare(0, sv.size(), sv) == 0;
+ }
+
+ constexpr bool starts_with(char_type c) const noexcept {
+ return !empty() && traits_type::eq(front(), c);
+ }
+
+ constexpr bool starts_with(const char_type* s) const noexcept {
+ return starts_with(std::basic_string_view<char_type, traits_type>(s));
+ }
+
+ constexpr bool ends_with(std::basic_string_view<char_type, traits_type> sv) const noexcept {
+ return size() > sv.size() && compare(size() - sv.size(), npos, sv) == 0;
+ }
+
+ constexpr bool ends_with(char_type c) const noexcept {
+ return !empty() && traits_type::eq(back(), c);
+ }
+
+ constexpr bool ends_with(const char_type* s) const noexcept {
+ return ends_with(std::basic_string_view<char_type, traits_type>(s));
+ }
+
+ constexpr bool contains(std::basic_string_view<char_type, traits_type> sv) const noexcept {
+ return find(sv) != npos;
+ }
+
+ constexpr bool contains(char_type c) const noexcept {
+ return find(c) != npos;
+ }
+
+ constexpr bool contains(const char_type* s) const noexcept {
+ return find(s) != npos;
+ }
+
  void swap(basic_sstring& x) noexcept {
  contents tmp;
  tmp = x.u;

tests/unit/sstring_test.cc

@@ -25,6 +25,7 @@
 #include <seastar/core/sstring.hh>
 #include <list>
 
+using namespace std::literals;
 using namespace seastar;
 
 BOOST_AUTO_TEST_CASE(test_make_sstring) {
@@ -51,6 +52,12 @@ BOOST_AUTO_TEST_CASE(test_add_literal_to_sstring) {
  BOOST_REQUIRE_EQUAL("x" + sstring("y"), sstring("xy"));
 }
 
+BOOST_AUTO_TEST_CASE(test_front) {
+ sstring s("abcde");
+ BOOST_CHECK_EQUAL(s.front(), 'a');
+ BOOST_CHECK_EQUAL(std::as_const(s).front(), 'a');
+}
+
 BOOST_AUTO_TEST_CASE(test_find_sstring) {
  BOOST_REQUIRE_EQUAL(sstring("abcde").find('b'), 1u);
  BOOST_REQUIRE_EQUAL(sstring("babcde").find('b',1), 2u);
@@ -99,6 +106,52 @@ BOOST_AUTO_TEST_CASE(test_str_not_find_sstring) {
  BOOST_REQUIRE_EQUAL(sstring("abc").find("abcde"), sstring::npos);
 }
 
+BOOST_AUTO_TEST_CASE(test_str_starts_with) {
+ BOOST_CHECK(sstring("abcdefg").starts_with("ab"sv));
+ BOOST_CHECK(sstring("abcde").starts_with('a'));
+ BOOST_CHECK(sstring("abcde").starts_with("ab"));
+ BOOST_CHECK(sstring("abcdefg").starts_with(""));
+
+ BOOST_CHECK(!sstring("abcde").starts_with("cde"));
+ BOOST_CHECK(!sstring("abcde").starts_with('b'));
+ BOOST_CHECK(!sstring("abcdefg").starts_with("cde"sv));
+ BOOST_CHECK(!sstring("abcdefg").starts_with("ab\0"sv));
+}
+
+BOOST_AUTO_TEST_CASE(test_str_ends_with) {
+ BOOST_CHECK(sstring("abcdefg").ends_with("efg"sv));
+ BOOST_CHECK(sstring("abcde").ends_with('e'));
+ BOOST_CHECK(sstring("abcde").ends_with("de"));
+ BOOST_CHECK(sstring("abcdefg").ends_with(""));
+
+ BOOST_CHECK(!sstring("abcde").ends_with("abc"));
+ BOOST_CHECK(!sstring("abcde").ends_with('b'));
+ BOOST_CHECK(!sstring("abcdefg").ends_with("abc"sv));
+ BOOST_CHECK(!sstring("abcdefg").ends_with("efg\0"sv));
+}
+
+BOOST_AUTO_TEST_CASE(test_str_contains) {
+ BOOST_CHECK(sstring("abcde").starts_with("ab"sv));
+ BOOST_CHECK(sstring("abcde").starts_with('a'));
+ BOOST_CHECK(sstring("abcde").starts_with("ab"));
+ BOOST_CHECK(sstring("abcde").starts_with(""));
+
+ BOOST_CHECK(sstring("abcde").contains("bc"sv));
+ BOOST_CHECK(sstring("abcde").contains("bc"));
+ BOOST_CHECK(sstring("abcde").contains('c'));
+
+ BOOST_CHECK(sstring("abcde").contains("de"sv));
+ BOOST_CHECK(sstring("abcde").contains("de"));
+
+ BOOST_CHECK(!sstring("abcde").contains("bad"));
+ BOOST_CHECK(!sstring("abcde").contains("bce"));
+ BOOST_CHECK(!sstring("abcde").contains("x"));
+ BOOST_CHECK(!sstring("abcde").contains('x'));
+ BOOST_CHECK(!sstring("abcde").contains("ab\0"sv));
+ BOOST_CHECK(!sstring("abcde").contains("bc\0"sv));
+ BOOST_CHECK(!sstring("abcde").contains("de\0"sv));
+}
+
 BOOST_AUTO_TEST_CASE(test_substr_sstring) {
  BOOST_REQUIRE_EQUAL(sstring("abcde").substr(1,2), "bc");
  BOOST_REQUIRE_EQUAL(sstring("abc").substr(1,2), "bc");