net/PToString: do not resolve IPv6 scope ids to interface names

Lacking NI_NUMERICSCOPE, every getnameinfo() call causes three
additional system calls:

 socket(AF_UNIX, SOCK_DGRAM, 0)
 ioctl(SIOCGIFNAME)
 close()

This is a rather large price for something that is called pretty
often.

debian/changelog

@@ -4,6 +4,7 @@ cm4all-beng-proxy (19.2) unstable; urgency=low
   * http/server: receive using io_uring
   * was: reduce the number of epoll_ctl() system calls again
   * was: receive from control channel using io_uring
+  * do not resolve IPv6 scope ids to interface names
 
  --   
 

src/net/PToString.cxx

@@ -6,6 +6,76 @@
 #include "pool/pool.hxx"
 #include "net/SocketAddress.hxx"
 #include "net/FormatAddress.hxx"
+#include "net/IPv4Address.hxx"
+#include "net/IPv6Address.hxx"
+
+#include <fmt/core.h>
+
+#include <arpa/inet.h>
+#include <string.h>
+
+static bool
+V4HostToString(std::span<char> buffer, const IPv4Address &address) noexcept
+{
+	return inet_ntop(AF_INET, &address.GetAddress(), buffer.data(), buffer.size()) != nullptr;
+}
+
+static bool
+V4ToString(std::span<char> buffer, const IPv4Address &address) noexcept
+{
+	const auto port = address.GetPort();
+	if (port == 0)
+		return V4HostToString(buffer, address);
+
+	if (!V4HostToString(buffer.first(buffer.size() - 8), address))
+		return false;
+
+	buffer = buffer.subspan(strlen(buffer.data()));
+	*fmt::format_to(buffer.data(), ":{}", port) = '\0';
+	return true;
+}
+
+static bool
+V6HostToString(std::span<char> buffer, const IPv6Address &address) noexcept
+{
+	return inet_ntop(AF_INET6, &address.GetAddress(), buffer.data(), buffer.size()) != nullptr;
+}
+
+static bool
+V6HostWithScopeToString(std::span<char> buffer, const IPv6Address &address) noexcept
+{
+	const auto scope_id = address.GetScopeId();
+	if (scope_id == 0)
+		return V6HostToString(buffer, address);
+
+	if (!V6HostToString(buffer.first(buffer.size() - 8), address))
+		return false;
+
+	buffer = buffer.subspan(strlen(buffer.data()));
+	*fmt::format_to(buffer.data(), "%{}", scope_id) = '\0';
+	return true;
+}
+
+static bool
+V6ToString(std::span<char> buffer, const IPv6Address &address) noexcept
+{
+	const auto port = address.GetPort();
+	if (port == 0)
+		return V6HostWithScopeToString(buffer, address);
+
+	buffer.front() = '[';
+	buffer = buffer.subspan(1);
+
+	if (!V6HostWithScopeToString(buffer.first(buffer.size() - 8), address))
+		return false;
+
+	buffer = buffer.subspan(strlen(buffer.data()));
+	buffer.front() = ']';
+	buffer = buffer.subspan(1);
+
+	*fmt::format_to(buffer.data(), ":{}", port) = '\0';
+	return true;
+}
 
 const char *
 address_to_string(struct pool &pool, SocketAddress address)
@@ -14,9 +84,24 @@ address_to_string(struct pool &pool, SocketAddress address)
 		return nullptr;
 
 	char host[512];
-	bool success = ToString(host, address);
-	if (!success || *host == 0)
-		return nullptr;
+
+	/* optimizations for IPv4 and IPv6 because glibc does not have
+           NI_NUMERICSCOPE */
+	switch (address.GetFamily()) {
+	case AF_INET:
+		if (!V4ToString(std::span{host}, IPv4Address::Cast(address)))
+			return nullptr;
+		break;
+
+	case AF_INET6:
+		if (!V6ToString(std::span{host}, IPv6Address::Cast(address)))
+			return nullptr;
+		break;
+
+	default:
+		if (!ToString(host, address) || *host == 0)
+			return nullptr;
+	}
 
 	return p_strdup(&pool, host);
 }
@@ -28,9 +113,24 @@ address_to_host_string(struct pool &pool, SocketAddress address)
 		return nullptr;
 
 	char host[512];
-	bool success = HostToString(host, address);
-	if (!success || *host == 0)
-		return nullptr;
+
+	/* optimizations for IPv4 and IPv6 because glibc does not have
+           NI_NUMERICSCOPE */
+	switch (address.GetFamily()) {
+	case AF_INET:
+		if (!V4HostToString(std::span{host}, IPv4Address::Cast(address)))
+			return nullptr;
+		break;
+
+	case AF_INET6:
+		if (!V6HostWithScopeToString(std::span{host}, IPv6Address::Cast(address)))
+			return nullptr;
+		break;
+
+	default:
+		if (!HostToString(host, address) || *host == 0)
+			return nullptr;
+	}
 
 	return p_strdup(&pool, host);
 }