Use "IE Proxy Settings" correctly on Windows in vcpkg.

include/vcpkg/base/system.proxy.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <vcpkg/base/optional.h>
+
+#include <string>
+
+/*
+ * This is a helper class. It reads IE Proxy settings.
+ * For coherence of vcpkg design "using HTTP(S)_PROXY not WPAD", it is a user-friendly design to manually
+ * read the IE Proxy settings on Windows, and set the environment variables HTTP(S)_PROXY to the same
+ * when starting an external program (like CMake, which file(DOWNLOAD) only accept proxy settings
+ * by HTTP(S)_PROXY variables).
+ */
+
+namespace vcpkg::System
+{
+    struct IEProxySetting
+    {
+        std::wstring server;
+        std::wstring bypass;
+    };
+
+    vcpkg::Optional<IEProxySetting> get_windows_ie_proxy_server();
+}

src/tls12-download.c

@@ -1,6 +1,7 @@
 #include <Windows.h>
 #include <process.h>
 #include <winhttp.h>
+
 /*
  * This program must be as small as possible, because it is committed in binary form to the
  * vcpkg github repo to enable downloading the main vcpkg program on Windows 7, where TLS 1.2 is
@@ -208,8 +209,6 @@ int __stdcall entry()
         abort_api_failure(std_out, L"GetEnvironmentVariableW");
     }
 
-    write_message(std_out, L"\r\n");
-
     const HANDLE out_file = CreateFileW(out_file_path, FILE_WRITE_DATA, 0, 0, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);
     if (out_file == INVALID_HANDLE_VALUE)
     {
@@ -223,6 +222,31 @@ int __stdcall entry()
         abort_api_failure(std_out, L"WinHttpOpen");
     }
 
+    // If HTTPS_PROXY not found, try use IE Proxy. This works on Windows 10 20H2, so there's no need to determine
+    // the OS version >= 8.1.
+    if (access_type == WINHTTP_ACCESS_TYPE_NO_PROXY)
+    {
+        WINHTTP_CURRENT_USER_IE_PROXY_CONFIG ieProxy;
+        if (WinHttpGetIEProxyConfigForCurrentUser(&ieProxy) && ieProxy.lpszProxy != NULL)
+        {
+            WINHTTP_PROXY_INFO proxy;
+            proxy.dwAccessType = WINHTTP_ACCESS_TYPE_NAMED_PROXY;
+            proxy.lpszProxy = ieProxy.lpszProxy;
+            proxy.lpszProxyBypass = ieProxy.lpszProxyBypass;
+            WinHttpSetOption(session, WINHTTP_OPTION_PROXY, &proxy, sizeof(proxy));
+
+            write_message(std_out, L" (using IE proxy: ");
+            write_message(std_out, proxy.lpszProxy);
+            write_message(std_out, L")");
+
+            GlobalFree(ieProxy.lpszProxy);
+            GlobalFree(ieProxy.lpszProxyBypass);
+            GlobalFree(ieProxy.lpszAutoConfigUrl);
+        }
+    }
+
+    write_message(std_out, L"\r\n");
+
     unsigned long secure_protocols = WINHTTP_FLAG_SECURE_PROTOCOL_TLS1_2;
     if (!WinHttpSetOption(session, WINHTTP_OPTION_SECURE_PROTOCOLS, &secure_protocols, sizeof(DWORD)))
     {

src/vcpkg/base/downloads.cpp

@@ -6,12 +6,9 @@
 #include <vcpkg/base/system.h>
 #include <vcpkg/base/system.print.h>
 #include <vcpkg/base/system.process.h>
+#include <vcpkg/base/system.proxy.h>
 #include <vcpkg/base/util.h>
 
-#if defined(_WIN32)
-#include <VersionHelpers.h>
-#endif
-
 namespace vcpkg::Downloads
 {
 #if defined(_WIN32)
@@ -92,12 +89,8 @@ namespace vcpkg::Downloads
     {
         static ExpectedS<WinHttpSession> make()
         {
-            auto h = WinHttpOpen(L"vcpkg/1.0",
-                                 IsWindows8Point1OrGreater() ? WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY
-                                                             : WINHTTP_ACCESS_TYPE_DEFAULT_PROXY,
-                                 WINHTTP_NO_PROXY_NAME,
-                                 WINHTTP_NO_PROXY_BYPASS,
-                                 0);
+            auto h = WinHttpOpen(
+                L"vcpkg/1.0", WINHTTP_ACCESS_TYPE_NO_PROXY, WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0);
             if (!h) return Strings::concat("WinHttpOpen() failed: ", GetLastError());
             WinHttpSession ret;
             ret.m_hSession.reset(h);
@@ -116,31 +109,19 @@ namespace vcpkg::Downloads
 
                 WinHttpSetOption(ret.m_hSession.get(), WINHTTP_OPTION_PROXY, &proxy, sizeof(proxy));
             }
-            // Win7 IE Proxy fallback
-            else if (IsWindows7OrGreater() && !IsWindows8Point1OrGreater())
+            // IE Proxy fallback, this works on Windows 10
+            else
             {
-                // First check if any proxy has been found automatically
-                WINHTTP_PROXY_INFO proxyInfo;
-                DWORD proxyInfoSize = sizeof(WINHTTP_PROXY_INFO);
-                auto noProxyFound =
-                    !WinHttpQueryOption(ret.m_hSession.get(), WINHTTP_OPTION_PROXY, &proxyInfo, &proxyInfoSize) ||
-                    proxyInfo.dwAccessType == WINHTTP_ACCESS_TYPE_NO_PROXY;
-
-                // If no proxy was found automatically, use IE's proxy settings, if any
-                if (noProxyFound)
+                // We do not use WPAD anymore
+                // Directly read IE Proxy setting
+                auto ieProxy = System::get_windows_ie_proxy_server();
+                if (ieProxy.has_value())
                 {
-                    WINHTTP_CURRENT_USER_IE_PROXY_CONFIG ieProxy;
-                    if (WinHttpGetIEProxyConfigForCurrentUser(&ieProxy) && ieProxy.lpszProxy != nullptr)
-                    {
-                        WINHTTP_PROXY_INFO proxy;
-                        proxy.dwAccessType = WINHTTP_ACCESS_TYPE_NAMED_PROXY;
-                        proxy.lpszProxy = ieProxy.lpszProxy;
-                        proxy.lpszProxyBypass = ieProxy.lpszProxyBypass;
-                        WinHttpSetOption(ret.m_hSession.get(), WINHTTP_OPTION_PROXY, &proxy, sizeof(proxy));
-                        GlobalFree(ieProxy.lpszProxy);
-                        GlobalFree(ieProxy.lpszProxyBypass);
-                        GlobalFree(ieProxy.lpszAutoConfigUrl);
-                    }
+                    WINHTTP_PROXY_INFO proxy;
+                    proxy.dwAccessType = WINHTTP_ACCESS_TYPE_NAMED_PROXY;
+                    proxy.lpszProxy = ieProxy.get()->server.data();
+                    proxy.lpszProxyBypass = ieProxy.get()->bypass.data();
+                    WinHttpSetOption(ret.m_hSession.get(), WINHTTP_OPTION_PROXY, &proxy, sizeof(proxy));
                 }
             }
 

src/vcpkg/base/system.proxy.cpp

@@ -0,0 +1,25 @@
+#include <vcpkg/base/system.proxy.h>
+
+vcpkg::Optional<vcpkg::System::IEProxySetting> vcpkg::System::get_windows_ie_proxy_server()
+{
+#if defined(_WIN32)
+    WINHTTP_CURRENT_USER_IE_PROXY_CONFIG ieProxy;
+    if (WinHttpGetIEProxyConfigForCurrentUser(&ieProxy) && ieProxy.lpszProxy != nullptr)
+    {
+        vcpkg::System::IEProxySetting ieProxySetting;
+
+        ieProxySetting.server = ieProxy.lpszProxy;
+
+        if (ieProxy.lpszProxyBypass != nullptr) ieProxySetting.bypass = ieProxy.lpszProxyBypass;
+
+        GlobalFree(ieProxy.lpszProxy);
+        GlobalFree(ieProxy.lpszProxyBypass);
+        GlobalFree(ieProxy.lpszAutoConfigUrl);
+
+        return ieProxySetting;
+    }
+    return vcpkg::Optional<vcpkg::System::IEProxySetting>();
+#else
+    return vcpkg::Optional<vcpkg::System::IEProxySetting>();
+#endif
+}

src/vcpkg/build.cpp

@@ -8,6 +8,7 @@
 #include <vcpkg/base/system.debug.h>
 #include <vcpkg/base/system.print.h>
 #include <vcpkg/base/system.process.h>
+#include <vcpkg/base/system.proxy.h>
 #include <vcpkg/base/util.h>
 
 #include <vcpkg/binarycaching.h>
@@ -396,6 +397,69 @@ namespace vcpkg::Build
                 if (auto p_val = val.get()) env.emplace(var, *p_val);
             }
 
+            /*
+             * On Windows 10 (>= 8.1) it is a user-friendly way to automatically set HTTP_PROXY and HTTPS_PROXY
+             * environment variables by reading proxy settings via WinHttpGetIEProxyConfigForCurrentUser, preventing
+             * users set and unset these variables manually (which is not a decent way). It is common in China or any
+             * other regions that needs an proxy software (v2ray, shadowsocks, etc.), which sets the IE Proxy Settings,
+             * but not setting environment variables. This will make vcpkg easier to use, specially when use vcpkg in
+             * Visual Studio, we even cannot set HTTP(S)_PROXY in CLI, if we want to open or close Proxy we need to
+             * restart VS.
+             */
+            auto ieProxy = System::get_windows_ie_proxy_server();
+            if (ieProxy.has_value())
+            {
+                std::string server = Strings::to_utf8(ieProxy.get()->server);
+
+                // Separate settings in IE Proxy Settings, which is rare?
+                // Python implementation:
+                // https://github.com/python/cpython/blob/7215d1ae25525c92b026166f9d5cac85fb1defe1/Lib/urllib/request.py#L2655
+                if (Strings::contains(server, "="))
+                {
+                    auto proxy_settings = Strings::split(server, ';');
+                    for (auto& s : proxy_settings)
+                    {
+                        auto kvp = Strings::split(s, '=');
+                        if (kvp.size() == 2)
+                        {
+                            auto protocol = kvp[0];
+                            auto address = kvp[1];
+                            if (!Strings::contains(address, "://"))
+                            {
+                                address = Strings::concat(protocol, "://", address);
+                            }
+                            protocol = Strings::concat(Strings::ascii_to_uppercase(protocol.c_str()), "_PROXY");
+                            env.emplace(protocol, address);
+                            System::print2("-- Setting ", protocol, " environment variables to ", address, "\n");
+                        }
+                    }
+                }
+                // Specified http:// prefix
+                else if (Strings::starts_with(server, "http://"))
+                {
+                    System::print2("-- Setting HTTP_PROXY environment variables to ", server, "\n");
+                    env.emplace("HTTP_PROXY", server);
+                }
+                // Specified https:// prefix
+                else if (Strings::starts_with(server, "https://"))
+                {
+                    System::print2("-- Setting HTTPS_PROXY environment variables to ", server, "\n");
+                    env.emplace("HTTPS_PROXY", server);
+                }
+                // Most common case: "ip:port" style, apply to HTTP and HTTPS proxies.
+                // An HTTP(S)_PROXY means https requests go through that, it can be:
+                // http:// prefixed: the request go through an HTTP proxy without end-to-end security.
+                // https:// prefixed: the request go through an HTTPS proxy with end-to-end security.
+                // Nothing prefixed: don't know the default behaviour, seems considering HTTP proxy as default.
+                // We simply set "ip:port" to HTTP(S)_PROXY variables because it works on most common cases.
+                else
+                {
+                    System::print2("-- Automatically setting HTTP(S)_PROXY environment variables to ", server, "\n");
+
+                    env.emplace("HTTP_PROXY", server.c_str());
+                    env.emplace("HTTPS_PROXY", server.c_str());
+                }
+            }
             return {env};
         });