Fix fmt function to handle empty strings and update make_prefix template parameters

Author: mutouyun

src/libipc/imp/fmt.cpp

@@ -199,6 +199,7 @@ void fmt_context::expend(std::size_t sz) noexcept {
 
 bool fmt_context::append(span<char const> const &str) noexcept {
   auto sz = str.size();
+  if (sz == 0) return true;
   if (str.back() == '\0') --sz;
   auto sbuf = buffer(sz);
   if (sbuf.size() < sz) {

src/libipc/memory/resource.h

@@ -46,9 +46,9 @@ inline std::string make_string(char const *str) {
 }
 
 /// \brief Combine prefix from a list of strings.
-template <typename... A>
-inline std::string make_prefix(std::string prefix, A &&...args) {
-  return ipc::fmt(prefix, "__IPC_SHM__", std::forward<A>(args)...);
+template <typename A1, typename... A>
+inline std::string make_prefix(A1 &&prefix, A &&...args) {
+  return ipc::fmt(std::forward<A1>(prefix), "__IPC_SHM__", std::forward<A>(args)...);
 }
 
 } // namespace ipc

test/imp/test_imp_fmt.cpp

@@ -110,6 +110,13 @@ TEST(fmt, fmt) {
   std::string test(4096, ' ');
   std::memcpy(&test[test.size() - sizeof(txt) + 1], txt, sizeof(txt) - 1);
   EXPECT_EQ(s, test);
+
+  EXPECT_EQ(ipc::fmt("", 1, "", '2', "", 3.0), "123.000000");
+  std::string empty;
+  EXPECT_EQ(ipc::fmt(empty, 1, "", '2', "", 3.0), "123.000000");
+  EXPECT_EQ(ipc::fmt(empty, 1, empty, '2', "", 3.0), "123.000000");
+  EXPECT_EQ(ipc::fmt("", 1, empty, '2', empty, 3.0), "123.000000");
+  EXPECT_EQ(ipc::fmt("", 1, "", '2', empty), "12");
 }
 
 namespace {