Replace ipv4 inet_ntop with a handrolled function (#367)

kiroma · web-flow · commit f7a781f99338 · 2025-02-20T21:06:03.000+08:00
* Replace ipv4 inet_ntop with a handrolled function

* make iptos static

* Make codegen better behaved on msvc / gcc

For some reason gcc assumes that static constexpr array can be modified and does not attempt to zero init the string, reading from the array instead. Having the buffer be initialized in the function instead via a consteval seems to yield proper results.
MSVC just straight up doesn't understand static initialization and attempts to initialize the static buffer on every function call. Microsoft never fails to disappoint.
diff --git a/trantor/net/InetAddress.cc b/trantor/net/InetAddress.cc
@@ -196,16 +196,40 @@ bool InetAddress::isLoopbackIp() const
     return false;
 }
 
+static void byteToChars(std::string::iterator &dst, unsigned char byte)
+{
+    *dst = byte / 100 + '0';
+    dst += byte >= 100;
+    *dst = byte % 100 / 10 + '0';
+    dst += byte >= 10;
+    *dst = byte % 10 + '0';
+    ++dst;
+}
+
+static std::string iptos(unsigned inet_addr)
+{
+    // Initialize with a static buffer to force the constructor of string to get
+    // fully inlined
+    constexpr char stringInitBuffer[15]{};
+    std::string out(stringInitBuffer, 15);
+    std::string::iterator dst = out.begin();
+    byteToChars(dst, inet_addr >> 0 & 0xff);
+    *(dst++) = '.';
+    byteToChars(dst, inet_addr >> 8 & 0xff);
+    *(dst++) = '.';
+    byteToChars(dst, inet_addr >> 16 & 0xff);
+    *(dst++) = '.';
+    byteToChars(dst, inet_addr >> 24 & 0xff);
+    out.erase(dst, out.end());
+    return out;
+}
+
 std::string InetAddress::toIp() const
 {
-    char buf[64];
+    char buf[INET6_ADDRSTRLEN]{};
     if (addr_.sin_family == AF_INET)
     {
-#if defined _WIN32
-        ::inet_ntop(AF_INET, (PVOID)&addr_.sin_addr, buf, sizeof(buf));
-#else
-        ::inet_ntop(AF_INET, &addr_.sin_addr, buf, sizeof(buf));
-#endif
+        return iptos(addr_.sin_addr.s_addr);
     }
     else if (addr_.sin_family == AF_INET6)
     {
