如何读取Windows自动配置脚本地址并为CefSharp设置代理？

Got it, let's sort this out properly. You're right that the usual approaches fall short here—WebRequest.GetSystemWebProxy doesn't expose the raw PAC URL, CefSharp's built-in proxy handling skips auto-config scripts, and registry reads are fragile. The correct way is to use the WinINet API properly with the right option flag, which is what Windows itself uses to retrieve these settings. Here's a robust implementation:

Why Other Methods Fail #

• WebRequest.GetSystemWebProxy: This is built for .NET's internal web request handling; it resolves proxy settings per-request instead of returning the raw PAC script address directly.
• CefSharp's ProxyConfig: As you noted, it only supports static proxy configurations, not PAC-based auto-config.
• Registry Reading: Unreliable because Microsoft can change registry paths across Windows versions, and it won't pick up policy-enforced settings that aren't stored in the registry.

Correct WinINet Implementation #

We'll use P/Invoke to call WinINet's InternetQueryOption with the INTERNET_OPTION_AUTOCONFIG_URL flag, which is the official way to get the auto-config script URL.

using System;
using System.Runtime.InteropServices;
using System.ComponentModel;

public static class SystemProxyHelper
{
    // WinINet API imports
    [DllImport("wininet.dll", SetLastError = true, CharSet = CharSet.Auto)]
    private static extern IntPtr InternetOpen(string lpszAgent, int dwAccessType, string lpszProxyName, string lpszProxyBypass, int dwFlags);

    [DllImport("wininet.dll", SetLastError = true, CharSet = CharSet.Auto)]
    private static extern bool InternetQueryOption(IntPtr hInternet, int dwOption, IntPtr lpBuffer, ref int lpdwBufferLength);

    [DllImport("wininet.dll", SetLastError = true)]
    private static extern bool InternetCloseHandle(IntPtr hInternet);

    // Option flag to retrieve the auto-config URL
    private const int INTERNET_OPTION_AUTOCONFIG_URL = 59;

    /// <summary>
    /// Gets the system's auto-config proxy (PAC) URL, if set
    /// </summary>
    /// <returns>The PAC URL, or null if no auto-config is set</returns>
    public static string GetAutoConfigProxyUrl()
    {
        IntPtr internetHandle = IntPtr.Zero;
        try
        {
            // Initialize a WinINet context (no actual internet connection needed)
            internetHandle = InternetOpen("CefSharpProxyDetector", 1, null, null, 0);
            if (internetHandle == IntPtr.Zero)
            {
                throw new Win32Exception(Marshal.GetLastWin32Error());
            }

            // First call to get the required buffer size
            int bufferSize = 0;
            InternetQueryOption(internetHandle, INTERNET_OPTION_AUTOCONFIG_URL, IntPtr.Zero, ref bufferSize);
            
            if (bufferSize == 0)
            {
                return null; // No auto-config URL configured
            }

            // Allocate buffer and retrieve the URL
            IntPtr buffer = Marshal.AllocHGlobal(bufferSize);
            try
            {
                if (InternetQueryOption(internetHandle, INTERNET_OPTION_AUTOCONFIG_URL, buffer, ref bufferSize))
                {
                    return Marshal.PtrToStringAuto(buffer);
                }
                else
                {
                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }
            }
            finally
            {
                Marshal.FreeHGlobal(buffer);
            }
        }
        finally
        {
            // Clean up the WinINet handle
            if (internetHandle != IntPtr.Zero)
            {
                InternetCloseHandle(internetHandle);
            }
        }
    }
}

Apply to CefSharp #

Now use the helper method to set the PAC URL in your CefSharp settings:

// Initialize CefSharp settings
var cefSettings = new CefSettings();

// Get the system auto-config proxy URL
string pacProxyUrl = SystemProxyHelper.GetAutoConfigProxyUrl();

if (!string.IsNullOrEmpty(pacProxyUrl))
{
    // Add the PAC URL to CefSharp's command line arguments
    cefSettings.CefCommandLineArgs.Add("proxy-pac-url", pacProxyUrl);
    
    // Optional: Disable auto-detection if you only want to use the configured PAC
    // cefSettings.CefCommandLineArgs.Add("proxy-auto-detect", "false");
}

// Initialize CefSharp with the configured settings
Cef.Initialize(cefSettings);

Key Notes #

• WinINet Initialization: You must call InternetOpen first to create a valid WinINet context; InternetQueryOption won't work without it.
• Resource Cleanup: Always release the WinINet handle and allocated buffer to avoid memory leaks.
• Official Support: This method uses the same API Windows uses to retrieve proxy settings, so it's reliable across Windows versions and respects group policies.

内容的提问来源于stack exchange，提问作者Martin Andersen