Add Windows native IDN support

configure.ac

@@ -76,6 +76,10 @@ dnl Hashes: Configure hash functions to use
 AC_ARG_WITH([winhashes],
   [AS_HELP_STRING([--with-winhashes], [use windows native hash fucntions.])])
 
+dnl WinIDN: Use winidn explicitly
+AC_ARG_WITH([winidn],
+  [AS_HELP_STRING([--with-winidn], [use windows native idn fucntions.])])
+
 dnl Zlib: Configure use of zlib for compression
 AC_ARG_WITH([zlib],
   [AS_HELP_STRING([--without-zlib], [disable zlib.])])
@@ -851,6 +855,7 @@ AS_IF([test "X$iri" != "Xno"],[
 AC_ARG_WITH(libidn, AC_HELP_STRING([--with-libidn=[DIR]],
                                    [Support IDN2008/IRIs (needs GNU libidn2 + libunicode)]),
                                    libidn=$withval, libidn="")
+
 if test "X$iri" != "Xno"; then
   AS_IF([test "x$with_libidn2" != xno], [
     AC_SEARCH_LIBS(idn2_lookup_u8, idn2,
@@ -863,6 +868,13 @@ if test "X$iri" != "Xno"; then
 #        [iri=no; AC_MSG_WARN(*** LIBUNISTRING was not found. You will not be able to use IDN2008 support)])
 #    ])
   ])
+
+  AS_IF([test "x$with_libidn2" = xno && test "x$with_winidn" != xno
+        test "X$IS_WINDOWS" == "Xyes" && test "X$am_cv_func_iconv" == "Xyes" ],
+  [
+    iri=yes
+    AC_DEFINE([ENABLE_IRI], 1, [Define if IRI support is enabled.])
+  ])
 fi
 
 dnl

src/win-idn.c

@@ -0,0 +1,70 @@
+/* Windows native IDN support.
+   Copyright (C) 2020-2020 Free Software Foundation,
+   Inc.
+   Originally contributed by YX Hao.
+
+This file is part of GNU Wget.
+
+GNU Wget is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3 of the License, or
+(at your option) any later version.
+
+GNU Wget is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with Wget.  If not, see <http://www.gnu.org/licenses/>.
+
+Additional permission under GNU GPL version 3 section 7
+
+If you modify this program, or any covered work, by linking or
+combining it with the OpenSSL project's OpenSSL library (or a
+modified version of that library), containing parts covered by the
+terms of the OpenSSL or SSLeay licenses, the Free Software Foundation
+grants you additional permission to convey the resulting work.
+Corresponding Source for a non-source form of such a combination
+shall include the source code for the parts of OpenSSL used as well
+as that of the covered work.  */
+
+
+#include <winnls.h>
+
+/* Windows idn APIs are Unicode based
+    https://docs.microsoft.com/en-us/windows/win32/intl/nls--internationalized-domain-name--idn--conversion-sample
+*/
+#define IDN_MAX_LENGTH 254 // https://en.wikipedia.org/wiki/Hostname
+
+char *idn_encode(const char *encoding, const char *host) {
+    wchar_t *host_w = NULL;
+    wchar_t *punycode_w = NULL;
+    char *punycode = NULL;
+
+
+    if (!transcode("UTF-16LE", encoding, host, strlen(host), (char**) &host_w)) {
+        goto cleanup;
+    }
+
+    punycode_w = calloc(IDN_MAX_LENGTH, sizeof(wchar_t));
+    if (punycode_w == NULL) {
+        logprintf (LOG_VERBOSE, "calloc failed: 0x%08X\n", errno);
+        goto cleanup;
+    }
+
+    if (IdnToAscii(IDN_ALLOW_UNASSIGNED, host_w, -1, punycode_w, IDN_MAX_LENGTH) == 0) {
+        logprintf (LOG_VERBOSE, "IdnToAscii failed: 0x%08X\n", GetLastError());
+        goto cleanup;
+    }
+
+    transcode(encoding, "UTF-16LE", (char*) punycode_w, wcslen(punycode_w) * 2, &punycode);
+
+    DEBUGP (("WinIDN: host -> punycode: '%s'\n", punycode));
+
+cleanup:
+    free(punycode_w);
+    free(host_w);
+
+    return punycode;
+}