HttpWebRequest.AddRange 支持long类型

很久很久以前，在哪个FAT32格式还流行的年代，文件大小普遍还没超过4G的年代，.Net已经出来了。

而那时候.Net实现的HTTP断点续传协议，还没预料到如此普及(我猜的)。那时候的HttpWebRequest.AddRange 还仅限于 int(Int32)类型。。。

虽然在.Net 4.0 以后，HttpWebRequest的 AddRange 方法已经默认支持 long类型(Int64)。但是相对于比较旧的版本上，应该如何支持呢？特别是Unity3D 这些N久还在用Mono 2.6(相当于 .Net 3.5)的时候。

当然网上也有相应的解决方案：

 MethodInfo method = typeof(WebHeaderCollection).GetMethod("AddWithoutValidate", BindingFlags.Instance | BindingFlags.NonPublic);

 HttpWebRequest request = (HttpWebRequest)WebRequest.Create ("http://www.example.com/file.exe");

 long start = int32.MaxValue;
 long end = int32.MaxValue +  ;

 string key = "Range";
 string val = string.Format ("bytes={0}-{1}", start, end);

 method.Invoke (request.Headers, new object[] { key, val });

也有一个不需要反射(Reflection)的继承版本，当然这个做法不可行，因为HttpWebRequest.set Headers时候内部是重新构造了WebHeaderCollection 对象，而且并没有将 "Range" 头信息添加进去

 //错误版本
 public class InheritWebHeaders : WebHeaderCollection
 {
     /*
     define your properties & methods here. -- by Mitchell Chu
     */
     public void AddHeaderWithoutValidate(
         string name
         , string value)
     {
         base.AddWithoutValidate(name, value);
     }
 }

 // usage:
 HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://blog.useasp.net/");
 InheritWebHeaders headers = new InheritWebHeaders();
 headers.AddHeaderWithoutValidate("Referrer", "http://blog.useasp.net/tag/.net");
 // other HTTP Headers
 request.Headers = headers;
 /// do more here...

所以 还是只能反射来支持long类型了，使用ILSpy 查看一下 System.dll(2.0.0.0) 中HttpWebRequest.AddRange的实现：

 public void AddRange(int from, int to)
 {
     this.AddRange("bytes", from, to);
 }
 public void AddRange(int range)
 {
     this.AddRange("bytes", range);
 }

 public void AddRange(string rangeSpecifier, int from, int to)
 {
     if (rangeSpecifier == null)
     {
         throw new ArgumentNullException("rangeSpecifier");
     }
     if (from <  || to < )
     {
         throw new ArgumentOutOfRangeException(SR.GetString("net_rangetoosmall"));
     }
     if (from > to)
     {
         throw new ArgumentOutOfRangeException(SR.GetString("net_fromto"));
     }
     if (!WebHeaderCollection.IsValidToken(rangeSpecifier))
     {
         throw new ArgumentException(SR.GetString("net_nottoken"), "rangeSpecifier");
     }
     if (!this.AddRange(rangeSpecifier, from.ToString(NumberFormatInfo.InvariantInfo), to.ToString(NumberFormatInfo.InvariantInfo)))
     {
         throw new InvalidOperationException(SR.GetString("net_rangetype"));
     }
 }

 public void AddRange(string rangeSpecifier, int range)
 {
     if (rangeSpecifier == null)
     {
         throw new ArgumentNullException("rangeSpecifier");
     }
     if (!WebHeaderCollection.IsValidToken(rangeSpecifier))
     {
         throw new ArgumentException(SR.GetString("net_nottoken"), "rangeSpecifier");
     }
     if (!this.AddRange(rangeSpecifier, range.ToString(NumberFormatInfo.InvariantInfo), (range >= ) ? "" : null))
     {
         throw new InvalidOperationException(SR.GetString("net_rangetype"));
     }
 }

 private bool AddRange(string rangeSpecifier, string from, string to)
 {
     string text = this._HttpRequestHeaders["Range"];
     if (text == null || text.Length == )
     {
         text = rangeSpecifier + "=";
     }
     else
     {
         if (string.Compare(text.Substring(, text.IndexOf('=')), rangeSpecifier, StringComparison.OrdinalIgnoreCase) != )
         {
             return false;
         }
         text = string.Empty;
     }
     text += from.ToString();
     if (to != null)
     {
         text = text + "-" + to;
     }
     this._HttpRequestHeaders.SetAddVerified("Range", text);
     return true;
 }

由此看出 AddRange 方法最终实现是 AddRange(string rangeSpecifier, string from, string to)

这样做的好处是有扩展性，哪怕以后文件大到Int128，Int256 也是可以支持的。但是至于为何不公开，应该是为了防止某些程序员乱写FromTo的参数吧，万一写成了非整型类型呢~

所以，相应地我们可以用反射写一个工具类(网上找的)：HttpWebRequest.AddRange support for long values

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Net;
 using System.Reflection;

 namespace HttpHelper
 {
     public static class HttpHelper
     {
         private static MethodInfo _addRangeMethodInfo = null;
         private static void GetMethodInfo()
         {
             if (_addRangeMethodInfo == null)
             {
                 Type t = typeof(HttpWebRequest);
                 MethodInfo[] methodInfoArray = t.GetMethods(BindingFlags.Instance | BindingFlags.NonPublic);
                 foreach (MethodInfo mi in methodInfoArray)
                     if (mi.Name == "AddRange")
                     {
                         _addRangeMethodInfo = mi;
                         return;
                     }
                 throw new Exception("HttpWebRequest type is missing the private AddRange method");
             }
         }

         public static void AddRange(this HttpWebRequest req, long from, long to)
         {
             GetMethodInfo();

             string rangeSpecifier = "bytes";
             string fromString = from.ToString();
             string toString = to.ToString();

             object[] args = new object[];

             args[] = rangeSpecifier;
             args[] = fromString;
             args[] = toString;

             _addRangeMethodInfo.Invoke(req, args);
         }

         public static void AddRange(this HttpWebRequest req, long from)
         {
             GetMethodInfo();

             string rangeSpecifier = "bytes";
             string fromString = from.ToString();
             string toString = "";

             object[] args = new object[];

             args[] = rangeSpecifier;
             args[] = fromString;
             args[] = toString;

             _addRangeMethodInfo.Invoke(req, args);
         }
     }
 }

当然事情还没结束，因为我们要支持的是还在使用老旧Mono版本的Unity3D，而Mono的HttpWebRequest内部实现 又和.Net的实现不同，所以上述的方法在U3D上根本不Work。

照版煮碗，我们先看一下U3D种 System.dll 的实现(如果找不到System.dll，可以先将工程Build一个出来，然后在工程文件内部(Xxx_Data/Managed/System.dll)即可找到。

我目前使用的是Unity4.6.4(项目需要，目前一直在使用此版本), 找到的System.dll版本为 2.0.5.0

public void AddRange(int range)
{
    this.AddRange("bytes", range);
}

public void AddRange(int from, int to)
{
    this.AddRange("bytes", from, to);
}

public void AddRange(string rangeSpecifier, int range)
{
    if (rangeSpecifier == null)
    {
        throw new ArgumentNullException("rangeSpecifier");
    }
    string text = this.webHeaders["Range"];
    if (text == null || text.Length == )
    {
        text = rangeSpecifier + "=";
    }
    else
    {
        if (!text.ToLower().StartsWith(rangeSpecifier.ToLower() + "="))
        {
            throw new InvalidOperationException("rangeSpecifier");
        }
        text += ",";
    }
    this.webHeaders.RemoveAndAdd("Range", text + range + "-");
}

public void AddRange(string rangeSpecifier, int from, int to)
{
    if (rangeSpecifier == null)
    {
        throw new ArgumentNullException("rangeSpecifier");
    }
    if (from <  || to <  || from > to)
    {
        throw new ArgumentOutOfRangeException();
    }
    string text = this.webHeaders["Range"];
    if (text == null || text.Length == )
    {
        text = rangeSpecifier + "=";
    }
    else
    {
        if (!text.ToLower().StartsWith(rangeSpecifier.ToLower() + "="))
        {
            throw new InvalidOperationException("rangeSpecifier");
        }
        text += ",";
    }
    this.webHeaders.RemoveAndAdd("Range", string.Concat(new object[]
    {
        text,
        from,
        "-",
        to
    }));
}

//顺道看一下 Headers的实现

public override WebHeaderCollection Headers
{
    get
    {
        return this.webHeaders;
    }
    set
    {
        this.CheckRequestStarted();
        WebHeaderCollection webHeaderCollection = new WebHeaderCollection(true);
        int count = value.Count;
        for (int i = ; i < count; i++)
        {
            webHeaderCollection.Add(value.GetKey(i), value.Get(i));
        }
        this.webHeaders = webHeaderCollection;
    }
}

我们可以针对U3D也做一个版本，但是这样反而觉得比较麻烦。 所以可以先给Helper添加默认的AddRange方法，然后通过外部可以覆盖原来的AddRange方法。

以下是代码：

 using System;
 using System.Net;
 using System.Reflection;

 namespace MyDownloader.Extension.Common
 {
     public static class HttpWebRequestHelper
     {

         public delegate void AddRangeFromToHandler(HttpWebRequest request, long from, long to);
         public delegate void AddRangeFromHandler(HttpWebRequest request, long from);

         static MethodInfo _addRangeMethodInfo = null;
         static AddRangeFromHandler addRangeFrom = null;
         static AddRangeFromToHandler addRangeFromTo = null;

         static HttpWebRequestHelper()
         {
             SetAddRange(AddRangeInternal, AddRangeInternal);
         }

         static void GetMethodInfo()
         {
             if (_addRangeMethodInfo != null)
             {
                 return;
             }
             Type t = typeof(HttpWebRequest);
             MethodInfo[] methodInfoArray = t.GetMethods(BindingFlags.Instance | BindingFlags.NonPublic);
             foreach (MethodInfo mi in methodInfoArray)
             {
                 if (mi.Name == "AddRange")
                 {
                     _addRangeMethodInfo = mi;
                     return;
                 }
             }
             throw new NotSupportedException("HttpWebRequest type is missing the private AddRange method");
         }

         //默认调用
         internal static void AddRangeInternal(HttpWebRequest req, long from, long to)
         {
             GetMethodInfo();

             string rangeSpecifier = "bytes";
             string fromString = from.ToString();
             string toString = to.ToString();

             object[] args = new object[];

             args[] = rangeSpecifier;
             args[] = fromString;
             args[] = toString;

             _addRangeMethodInfo.Invoke(req, args);
         }

         internal static void AddRangeInternal(HttpWebRequest req, long from)
         {
             GetMethodInfo();

             string rangeSpecifier = "bytes";
             string fromString = from.ToString();
             string toString = "";

             object[] args = new object[];

             args[] = rangeSpecifier;
             args[] = fromString;
             args[] = toString;

             _addRangeMethodInfo.Invoke(req, args);
         }

         public static void SetAddRange(AddRangeFromHandler fromOnly, AddRangeFromToHandler fromTo)
         {
             if (fromOnly == null || fromTo == null)
                 throw new ArgumentNullException();
             addRangeFrom = fromOnly;
             addRangeFromTo = fromTo;
         }

         public static void AddRange(HttpWebRequest request, long from)
         {
             addRangeFrom(request, from);
         }

         public static void AddRange(HttpWebRequest request, long from, long to)
         {
             addRangeFromTo(request, from, to);
         }
     }
 }

在U3D中使用(TEST VERSION)：

public class HttpWebRequestHelperUnityTest{

    public void TEST()
    {
        var http = new MyDownloader.Extension.Protocols.HttpFtpProtocolExtension();

        HttpWebRequestHelper.SetAddRange(AddRange, AddRange);
        DownloadManager.Instance.DownloadEnded += (s, e) => { print(e.Downloader.LocalFile); };
    }

    public void AddRange(HttpWebRequest req, long range)
    {
        AddRange(req, "bytes", range);
    }

    public void AddRange(HttpWebRequest req, long from, long to)
    {
        AddRange(req, "bytes", from, to);
    }

    public void AddRange(HttpWebRequest req, string rangeSpecifier, long range)
    {
        if (rangeSpecifier == null)
        {
            throw new ArgumentNullException("rangeSpecifier");
        }
        string text = req.Headers["Range"];
        if (text == null || text.Length == )
        {
            text = rangeSpecifier + "=";
        }
        else
        {
            if (!text.ToLower().StartsWith(rangeSpecifier.ToLower() + "="))
            {
                throw new InvalidOperationException("rangeSpecifier");
            }
            text += ",";
        }
        HeadersRemoveAndAdd(req.Headers, "Range", text + range + "-");
    }

    public void AddRange(HttpWebRequest req, string rangeSpecifier, long from, long to)
    {
        if (rangeSpecifier == null)
        {
            throw new ArgumentNullException("rangeSpecifier");
        }
        if (from <  || to <  || from > to)
        {
            throw new ArgumentOutOfRangeException();
        }
        string text = req.Headers["Range"];
        if (text == null || text.Length == )
        {
            text = rangeSpecifier + "=";
        }
        else
        {
            if (!text.ToLower().StartsWith(rangeSpecifier.ToLower() + "="))
            {
                throw new InvalidOperationException("rangeSpecifier");
            }
            text += ",";
        }
        HeadersRemoveAndAdd(req.Headers, "Range", string.Concat(new object[]
        {
                text,
                from,
                "-",
                to
        }));
    }

    static void HeadersRemoveAndAdd(WebHeaderCollection headers, string name, string value)
    {
        GetMethodInfo();
        removeAndAddRangeMethodInfo.Invoke(headers, new object[] { name, value });
    }

    static MethodInfo removeAndAddRangeMethodInfo = null;
    static void GetMethodInfo()
    {
        if (removeAndAddRangeMethodInfo != null)
            return;

        Type t = typeof(WebHeaderCollection);
        MethodInfo[] methodInfoArray = t.GetMethods(BindingFlags.Instance | BindingFlags.NonPublic);
        foreach (MethodInfo mi in methodInfoArray)
        {
            if (mi.Name == "RemoveAndAdd")
            {
                removeAndAddRangeMethodInfo = mi;
                return;
            }
        }
        throw new NotSupportedException("WebHeaderCollection type is missing the private RemoveAndAdd method");
    }
}