目前没有找到.Net框架内置的解析方法，理论上HttpClient等类在内部应该已经实现了解析，但不知为何没有公开这些处理方法。（亦或是我没找到）那么只能自己来解析这些数据了。 

public enum HTTPHeaderField
{
Accept = 0,
Accept_Charset = 1,
Accept_Encoding = 2,
Accept_Language = 3,
Accept_Ranges = 4,
Authorization = 5,
Cache_Control = 6,
Connection = 7,
Cookie = 8,
Content_Length = 9,
Content_Type = 10,
Date = 11,
Expect = 12,
From = 13,
Host = 14,
If_Match = 15,
If_Modified_Since = 16,
If_None_Match = 17,
If_Range = 18,
If_Unmodified_Since = 19,
Max_Forwards = 20,
Pragma = 21,
Proxy_Authorization = 22,
Range = 23,
Referer = 24,
TE = 25,
Upgrade = 26,
User_Agent = 27,
Via = 28,
Warn = 29,
Age = 30,
Allow = 31,
Content_Encoding = 32,
Content_Language = 33,
Content_Location = 34,
Content_Disposition = 35,
Content_MD5 = 36,
Content_Range = 37,
ETag = 38,
Expires = 39,
Last_Modified = 40,
Location = 41,
Proxy_Authenticate = 42,
Refresh = 43,
Retry_After = 44,
Server = 45,
Set_Cookie = 46,
Trailer = 47,
Transfer_Encoding = 48,
Vary = 49,
Warning = 50,
WWW_Authenticate = 51
};
class HTTPHeader
{
#region PROPERTIES
private string[] m_StrHTTPField = new string[52];
private byte[] m_byteData = http://www.mamicode.com/new byte[4096];
public string[] HTTPField
{
get { return m_StrHTTPField; }
set { m_StrHTTPField = value; }
}
public byte[] Data
{
get { return m_byteData; }
set { m_byteData = http://www.mamicode.com/value; }
}
#endregion
// convertion
System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
#region CONSTRUCTEUR
/// <summary>
/// Constructeur par défaut - non utilisé
/// </summary>
private HTTPHeader()
{ }
public HTTPHeader(byte[] ByteHTTPRequest)
{
string HTTPRequest = encoding.GetString(ByteHTTPRequest);
try
{
int IndexHeaderEnd;
string Header;
// Si la taille de requête est supérieur ou égale à 1460, alors toutes la chaine est l‘entête http
if (HTTPRequest.Length <= 1460)
Header = HTTPRequest;
else
{
IndexHeaderEnd = HTTPRequest.IndexOf("\r\n\r\n");
Header = HTTPRequest.Substring(0, IndexHeaderEnd);
Data = http://www.mamicode.com/ByteHTTPRequest.Skip(IndexHeaderEnd + 4).ToArray();
}
HTTPHeaderParse(Header);
}
catch (Exception)
{ }
}
#endregion
#region METHODES
private void HTTPHeaderParse(string Header)
{
#region HTTP HEADER REQUEST & RESPONSE
HTTPHeaderField HHField;
string HTTPfield, buffer;
int Index;
foreach (int IndexHTTPfield in Enum.GetValues(typeof(HTTPHeaderField)))
{
HHField = (HTTPHeaderField)IndexHTTPfield;
HTTPfield = "\n" + HHField.ToString().Replace(‘_‘, ‘-‘) + ": "; //Ajout de \n devant pour éviter les doublons entre cookie et set_cookie
// Si le champ n‘est pas présent dans la requête, on passe au champ suivant
Index = Header.IndexOf(HTTPfield);
if (Index == -1)
continue;
buffer = Header.Substring(Index + HTTPfield.Length);
Index = buffer.IndexOf("\r\n");
if (Index == -1)
m_StrHTTPField[IndexHTTPfield] = buffer.Trim();
else
m_StrHTTPField[IndexHTTPfield] = buffer.Substring(0, Index).Trim();
//Console.WriteLine("Index = " + IndexHTTPfield + " | champ = " + HTTPfield.Substring(1) + " " + m_StrHTTPField[IndexHTTPfield]);
}
// Affichage de tout les champs
/*for (int j = 0; j < m_StrHTTPField.Length; j++)
{
HHField = (HTTPHeaderField)j;
Console.WriteLine("m_StrHTTPField[" + j + "]; " + HHField + " = " + m_StrHTTPField[j]);
}
*/
#endregion
}
#endregion
}

编写以下代码以实现解析文件：

class Program
{
	static void Main(string[] args)
	{
		SRART: Console.WriteLine("输入待解析的HTTP报文数据文件完整路径：");
		var filename = Console.ReadLine();
		try
		{
			FileStream fs = new FileStream(filename, FileMode.Open);
			BinaryReader br = new BinaryReader(fs);
			var data = http://www.mamicode.com/br.ReadBytes((int)fs.Length);
			var header = new HTTPHeader(data);
			var x = 0;
			foreach (var f in header.HTTPField)
			{
				if (!String.IsNullOrEmpty(f))
				{
					Console.WriteLine($"[{x:00}] - {(HTTPHeaderField) x} : {f}");
				}
				x++;
			}
			Console.WriteLine($"总数据尺寸{fs.Length}字节，实际数据尺寸{header.Data.Length}字节");
			Console.WriteLine(Encoding.UTF8.GetString(header.Data));
			Console.WriteLine();
			br.Close();
			fs.Close();				
		}
		catch (Exception e)
		{
			Console.WriteLine(e);
		}
		goto SRART;
	}
}

这里还未实现gzip解压缩和字符解码，直接用UTF8解码输出的。（需要时再写吧，都是体力活儿~）

解析HTTP报文——C#