[SKV-627] feat(utils): add an utility function to find string prefix …

…by separator (apache#1338)

src/rdsn/include/dsn/utility/strings.h

@@ -81,5 +81,9 @@ char *trim_string(char *s);
 
 // calculate the md5 checksum of buffer
 std::string string_md5(const char *buffer, unsigned int length);
+
+// splits the "input" string by the only character "separator" to get the string prefix.
+// if there is no prefix or the first character is "separator", it will return "".
+std::string find_string_prefix(const std::string &input, char separator);
 } // namespace utils
 } // namespace dsn

src/rdsn/src/utils/strings.cpp

@@ -219,5 +219,14 @@ std::string string_md5(const char *buffer, unsigned length)
 
     return result;
 }
+
+std::string find_string_prefix(const std::string &input, char separator)
+{
+    auto current = input.find(separator);
+    if (current == 0 || current == std::string::npos) {
+        return std::string();
+    }
+    return input.substr(0, current);
+}
 } // namespace utils
 } // namespace dsn

src/rdsn/src/utils/test/utils.cpp

@@ -212,6 +212,28 @@ TEST(core, dlink)
     EXPECT_TRUE(count == 0);
 }
 
+TEST(core, find_string_prefix)
+{
+    struct test_case
+    {
+        std::string input;
+        char separator;
+        std::string expected_prefix;
+    } tests[] = {{"", ' ', ""},
+                 {"abc.def", ' ', ""},
+                 {"abc.def", '.', "abc"},
+                 {"ab.cd.ef", '.', "ab"},
+                 {"abc...def", '.', "abc"},
+                 {".abc.def", '.', ""},
+                 {" ", ' ', ""},
+                 {"..", '.', ""},
+                 {". ", ' ', "."}};
+    for (const auto &test : tests) {
+        auto actual_output = find_string_prefix(test.input, test.separator);
+        EXPECT_EQ(actual_output, test.expected_prefix);
+    }
+}
+
 class foo : public ::dsn::ref_counter
 {
 public: