具有多个范围的 HTTP 请求

Question

如果我想部分下载文件并在请求标头中定义单个范围，我会得到 响应正文中请求文件的字节流。

但如果我指定多个范围如下，我总是会为每个定义的范围额外 响应正文中损坏的响应标头（描述请求的范围） 下载的文件。

static void Main(string[] args)
{

    Console.Write("Please enter target File: ");
    string Target = Console.ReadLine();
    string Source = @"http://mozilla-mirror.3347.voxcdn.com/pub/mozilla.org/firefox/releases/3.6/win32/de/Firefox%20Setup%203.6.exe";

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Source);
    request.Credentials = CredentialCache.DefaultCredentials;

    // define multiple Ranges
    request.AddRange(      0, 1000000);
    request.AddRange(1000000, 2000000);

    HttpWebResponse response = (HttpWebResponse)request.GetResponse();

    using (Stream source = response.GetResponseStream())
    {
        using (FileStream target = File.Open(Target, FileMode.OpenOrCreate, FileAccess.Write, FileShare.ReadWrite))
        {
            byte[] buffer = new byte[4096];
            int BytesRead = 0;
            int TotalBytesRead = 0;

            while((BytesRead = source.Read(buffer, 0, buffer.Length)) > 0) 
            {
                target.Write(buffer, 0, BytesRead);
                TotalBytesRead += BytesRead;

                Console.WriteLine("{0}", TotalBytesRead);
            }
        }
    }

    Console.WriteLine("Downloading Finished!");
    Console.ReadLine();
}

请求如W​​ireshark所示：

http://img197.imageshack.us/img197/8199/requesty.png

Response Body 应该只包含文件的 Byte-Stream，但在每个定义 Range 的开头额外包含不需要的 Response-Header：

是否可以在不单独请求每个 Range 的情况下避免正文中额外的响应头？

或

是否有内置方法来过滤附加响应标头，其大小可能因 HTTP 服务器而异？

Answer 1

不，这就是 HTTP/1.1 中多个范围的工作方式。见RFC 2616, Section 19.2。

Answer 2

感谢您的帮助，如上面链接中所述，它是假定的 http 响应具有多个范围的请求的方式。

所以....

是否可以避免在正文中添加额外的响应头而不 分别请求每个范围？

=> 没有。

是否有内置方法来过滤附加响应标头，其大小 可能因 HTTP 服务器而异？

=> 我不知道，但是...

也许你们中的一些人可能会对以下代码块有一个批判性的看法 从文件数据中过滤标题：

public void DoDownload(Range[] Ranges)
    {

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(m_Source);
        request.Credentials = CredentialCache.DefaultCredentials;

        foreach (Range r in Ranges)
        {
            request.AddRange(r.From, r.To);
        }

        HttpWebResponse response = (HttpWebResponse)request.GetResponse();

        string boundary = "";
        Match m = Regex.Match(response.ContentType, @"^.*boundary=(?<boundary>.*)$");

        if (m.Success)
        {
            boundary = m.Groups["boundary"].Value;
        }
        else
        {
            throw new InvalidDataException("invalid packet data: no boundary specification found.");
        }


        using (Stream source = response.GetResponseStream())
        {
            using (FileStream target = File.Open(m_TargetFile, FileMode.OpenOrCreate, FileAccess.Write, FileShare.ReadWrite))
            {
                // buffer for payload
                byte[] buffer = new byte[4096];
                // buffer for current range header
                byte[] header = new byte[200];
                // next header after x bytes
                int NextHeader = 0;
                // current position in header[]
                int HeaderPosition = 0;
                // current position in buffer[]
                int BufferPosition = 0;
                // left data to proceed
                int BytesToProceed = 0;
                // total data written without range-headers
                long TotalBytesWritten = 0;
                // count of last data written to target file
                int BytesWritten = 0;
                // size of processed header data
                int HeaderSize = 0;
                // count of last data read from ResponseStream
                int BytesRead = 0;


                while ((BytesRead = source.Read(buffer, 0, buffer.Length)) > 0)
                {
                    BufferPosition = 0;
                    BytesToProceed = BytesRead;
                    HeaderSize = 0;

                    while (BytesToProceed > 0)
                    {
                        if (NextHeader == 0)
                        {
                            for (;HeaderPosition < header.Length; HeaderPosition++, BufferPosition++, HeaderSize++)
                            {
                                if (BytesToProceed > HeaderPosition && BufferPosition < BytesRead)
                                {
                                    header[HeaderPosition] = buffer[BufferPosition];

                                    if (HeaderPosition >= 4 &&
                                        header[HeaderPosition - 3] == 0x0d &&
                                        header[HeaderPosition - 2] == 0x0a &&
                                        header[HeaderPosition - 1] == 0x0d &&
                                        header[HeaderPosition] == 0x0a)
                                    {
                                        string RangeHeader = Encoding.ASCII.GetString(header, 0, HeaderPosition + 1);
                                        Match mm = Regex.Match(RangeHeader,
                                            @"^\r\n(--)?" + boundary + @".*?(?<from>\d+)\s*-\s*(?<to>\d+)/.*\r\n\r\n", RegexOptions.Singleline);

                                        if (mm.Success)
                                        {
                                            int RangeStart = Convert.ToInt32(mm.Groups["from"].Value);
                                            int RangeEnd = Convert.ToInt32(mm.Groups["to"].Value);

                                            NextHeader = (RangeEnd - RangeStart) + 1; 

                                            target.Seek(RangeStart, SeekOrigin.Begin);
                                            BufferPosition++;

                                            BytesToProceed -= HeaderSize + 1;

                                            HeaderPosition = 0;
                                            HeaderSize = 0;

                                            break;
                                        }
                                        else { throw new InvalidDataException("invalid header: missing range specification.");}
                                    }
                                }
                                else { goto READ_NEW; }
                            }

                            if (NextHeader == 0)
                                throw new InvalidDataException("invalid packet data: no range-header found.");
                        }

                        BytesWritten = (NextHeader > BytesToProceed) ? BytesToProceed : NextHeader;

                        target.Write(buffer, BufferPosition, BytesWritten);

                        BytesToProceed -= BytesWritten;
                        NextHeader -= BytesWritten;
                        BufferPosition += BytesWritten;

                        TotalBytesWritten += BytesWritten;
                    }

                READ_NEW:;
                }
            }
        }
    }

如果有另一种/更好的方法可以给我一些提示。

最好的问候 cap_Chap