Rewrite concat_string_ref

src/HttpServer.cc

@@ -1187,17 +1187,10 @@ void prepare_redirect_response(Stream *stream, Http2Handler *hd,
     authority = stream->header.host;
   }
 
-  size_t len = scheme.size() + str_size("://") + authority.size() + path.size();
-  auto iov = make_byte_ref(stream->balloc, len + 1);
-  auto p = iov.base;
-  p = std::copy(std::begin(scheme), std::end(scheme), p);
-  p = util::copy_lit(p, "://");
-  p = std::copy(std::begin(authority), std::end(authority), p);
-  p = std::copy(std::begin(path), std::end(path), p);
-  *p = '\0';
+  auto location = concat_string_ref(
+      stream->balloc, scheme, StringRef::from_lit("://"), authority, path);
 
-  auto headers =
-      HeaderRefs{{StringRef::from_lit("location"), StringRef{iov.base, p}}};
+  auto headers = HeaderRefs{{StringRef::from_lit("location"), location}};
 
   auto sessions = hd->get_sessions();
   auto status_page = sessions->get_server()->get_status_page(status);

src/allocator.h

@@ -120,31 +120,43 @@ StringRef make_string_ref(BlockAllocator &alloc, const StringRef &src) {
   return StringRef{dst, src.size()};
 }
 
-// Returns the string which is the concatenation of |a| and |b| in
-// this order.  The resulting string will be NULL-terminated.
-template <typename BlockAllocator>
-StringRef concat_string_ref(BlockAllocator &alloc, const StringRef &a,
-                            const StringRef &b) {
-  auto len = a.size() + b.size();
-  auto dst = static_cast<uint8_t *>(alloc.alloc(len + 1));
-  auto p = dst;
-  p = std::copy(std::begin(a), std::end(a), p);
-  p = std::copy(std::begin(b), std::end(b), p);
-  *p = '\0';
-  return StringRef{dst, len};
+// private function used in concat_string_ref.  this is the base
+// function of concat_string_ref_count().
+inline size_t concat_string_ref_count(size_t acc) { return acc; }
+
+// private function used in concat_string_ref.  This function counts
+// the sum of length of given arguments.  The calculated length is
+// accumulated, and passed to the next function.
+template <typename... Args>
+size_t concat_string_ref_count(size_t acc, const StringRef &value,
+                               Args &&... args) {
+  return concat_string_ref_count(acc + value.size(),
+                                 std::forward<Args>(args)...);
 }
 
-// Returns the string which is the concatenation of |a|, |b| and |c|
-// in this order.  The resulting string will be NULL-terminated.
-template <typename BlockAllocator>
-StringRef concat_string_ref(BlockAllocator &alloc, const StringRef &a,
-                            const StringRef &b, const StringRef &c) {
-  auto len = a.size() + b.size() + c.size();
+// private function used in concat_string_ref.  this is the base
+// function of concat_string_ref_copy().
+inline uint8_t *concat_string_ref_copy(uint8_t *p) { return p; }
+
+// private function used in concat_string_ref.  This function copies
+// given strings into |p|.  |p| is incremented by the copied length,
+// and returned.  In the end, return value points to the location one
+// beyond the last byte written.
+template <typename... Args>
+uint8_t *concat_string_ref_copy(uint8_t *p, const StringRef &value,
+                                Args &&... args) {
+  p = std::copy(std::begin(value), std::end(value), p);
+  return concat_string_ref_copy(p, std::forward<Args>(args)...);
+}
+
+// Returns the string which is the concatenation of |args| in the
+// given order.  The resulting string will be NULL-terminated.
+template <typename BlockAllocator, typename... Args>
+StringRef concat_string_ref(BlockAllocator &alloc, Args &&... args) {
+  size_t len = concat_string_ref_count(0, std::forward<Args>(args)...);
   auto dst = static_cast<uint8_t *>(alloc.alloc(len + 1));
   auto p = dst;
-  p = std::copy(std::begin(a), std::end(a), p);
-  p = std::copy(std::begin(b), std::end(b), p);
-  p = std::copy(std::begin(c), std::end(c), p);
+  p = concat_string_ref_copy(p, std::forward<Args>(args)...);
   *p = '\0';
   return StringRef{dst, len};
 }

src/shrpx_http.cc

@@ -48,20 +48,11 @@ StringRef create_error_html(BlockAllocator &balloc, unsigned int http_status) {
   auto status_string = http2::get_status_string(balloc, http_status);
   const auto &server_name = httpconf.server_name;
 
-  size_t len = 256 + server_name.size() + status_string.size() * 2;
-
-  auto iov = make_byte_ref(balloc, len + 1);
-  auto p = iov.base;
-
-  p = util::copy_lit(p, R"(<!DOCTYPE html><html lang="en"><title>)");
-  p = std::copy(std::begin(status_string), std::end(status_string), p);
-  p = util::copy_lit(p, "</title><body><h1>");
-  p = std::copy(std::begin(status_string), std::end(status_string), p);
-  p = util::copy_lit(p, "</h1><footer>");
-  p = std::copy(std::begin(server_name), std::end(server_name), p);
-  p = util::copy_lit(p, "</footer></body></html>");
-  *p = '\0';
-  return StringRef{iov.base, p};
+  return concat_string_ref(
+      balloc, StringRef::from_lit(R"(<!DOCTYPE html><html lang="en"><title>)"),
+      status_string, StringRef::from_lit("</title><body><h1>"), status_string,
+      StringRef::from_lit("</h1><footer>"), server_name,
+      StringRef::from_lit("</footer></body></html>"));
 }
 
 StringRef create_forwarded(BlockAllocator &balloc, int params,

src/shrpx_https_upstream.cc

@@ -264,14 +264,8 @@ void rewrite_request_host_path_from_uri(BlockAllocator &balloc, Request &req,
       auto q = util::get_uri_field(uri.c_str(), u, UF_QUERY);
       path = StringRef{std::begin(path), std::end(q)};
     } else {
-      auto iov = make_byte_ref(balloc, path.size() + 1 + fdata.len + 1);
-      auto p = iov.base;
-
-      p = std::copy(std::begin(path), std::end(path), p);
-      *p++ = '?';
-      p = std::copy_n(&uri[fdata.off], fdata.len, p);
-      *p = '\0';
-      path = StringRef{iov.base, p};
+      path = concat_string_ref(balloc, path, StringRef::from_lit("?"),
+                               StringRef{&uri[fdata.off], fdata.len});
     }
   }
 

src/template.h

@@ -437,11 +437,11 @@ public:
     return StringRef(s);
   }
 
-  const_iterator begin() const { return base; };
-  const_iterator cbegin() const { return base; };
+  constexpr const_iterator begin() const { return base; };
+  constexpr const_iterator cbegin() const { return base; };
 
-  const_iterator end() const { return base + len; };
-  const_iterator cend() const { return base + len; };
+  constexpr const_iterator end() const { return base + len; };
+  constexpr const_iterator cend() const { return base + len; };
 
   const_reverse_iterator rbegin() const {
     return const_reverse_iterator{base + len};
@@ -453,10 +453,12 @@ public:
   const_reverse_iterator rend() const { return const_reverse_iterator{base}; }
   const_reverse_iterator crend() const { return const_reverse_iterator{base}; }
 
-  const char *c_str() const { return base; }
-  size_type size() const { return len; }
-  bool empty() const { return len == 0; }
-  const_reference operator[](size_type pos) const { return *(base + pos); }
+  constexpr const char *c_str() const { return base; }
+  constexpr size_type size() const { return len; }
+  constexpr bool empty() const { return len == 0; }
+  constexpr const_reference operator[](size_type pos) const {
+    return *(base + pos);
+  }
 
   std::string str() const { return std::string(base, len); }
   const uint8_t *byte() const {