有时候，我们须要读取一些数据，而无论这数据来源于磁盘上的数据文件，还是来源于网络上的数据。于是。就有了以下的 StringExtensions.cs：
1 using System;
2 using System.IO;
3 using System.Net;
4
5 namespace Skyiv
6 {
7 public static class StringExtensions
8 {
9 public static Stream GetInputStream(this string fileNameOrUri, string user = null, string password = null)
10 {
11 if (!Uri.IsWellFormedUriString(fileNameOrUri, UriKind.Absolute)) return File.OpenRead(fileNameOrUri);
12 var uri = new Uri(fileNameOrUri);
13 if (uri.Scheme == Uri.UriSchemeHttp || uri.Scheme == Uri.UriSchemeHttps) return uri.GetHttpStream();
14 if (uri.Scheme == Uri.UriSchemeFtp) return uri.GetFtpStream(user, password);
15 if (uri.Scheme == Uri.UriSchemeFile) return uri.GetFileStream();
16 throw new NotSupportedException("Notsupported uri scheme: " + uri.Scheme);
17 }
18
19 static Stream GetFtpStream(this Uri uri, string user = null, string password = null)
20 {
21 var ftp = (FtpWebRequest)WebRequest.Create(uri);
22 if (user != null && user != "anonymous" && user != "ftp")
23 ftp.Credentials = new NetworkCredential(user, password);
24 ftp.Method = WebRequestMethods.Ftp.DownloadFile;
25 return ((FtpWebResponse)ftp.GetResponse()).GetResponseStream();
26 }
27
28 static Stream GetHttpStream(this Uri uri)
29 {
30 return ((HttpWebResponse)((HttpWebRequest)WebRequest.Create(uri)).GetResponse()).GetResponseStream();
31 }
32
33 static Stream GetFileStream(this Uri uri)
34 {
35 return ((FileWebResponse)((FileWebRequest)WebRequest.Create(uri)).GetResponse()).GetResponseStream();
36 }
37 }
38 }
上述程序中：
- 第 9 到 17 行的 GetInputStream 扩展方法返回来读取的数据的输入流。
- 第 11 行调用 Uri 类的静态方法 IsWellFormedUriString 推断是否从网络上读取数据。如不是。则直接调用 File 类的静态方法 OpenRead 得到输入流。
- 第 12 行构造一个 Uri 类的实例。
- 第 13 行处理输入使用 http 或者 https 协议的情况。
- 第 14 行处理输入使用 ftp 协议的情况。
- 第 15 行处理输入使用 file 协议的情况。
- 第 16 行处理其它协议。就是直接抛出一个 NotSupportedException 异常。表示我们仅仅支持上述四种协议。
- 第 19 到 26 行的 GetFtpStream 扩展方法用于获得 FTP server上发送的响应数据的输入流。能够是匿名的。也能够是非匿名的。
- 第 28 到 31 行的 GetHttpStream 扩展方法用于获得使用 http 或者 https 协议的网络流。
- 第 33 到 36 行的 GetFileStream 扩展方法用于获得使用 file 协议的本地磁盘文件系统的数据流。
以下就是測试用的 CopyTester.cs：
1 using System.IO;
2
3 namespace Skyiv.Test
4 {
5 static class CopyTester
6 {
7 static void Main(string[] args)
8 {
9 args[0].GetInputStream().CopyTo(File.Create(args[1]));
10 }
11 }
12 }
这个測试程序的功能就是拷贝数据，须要两个命令行參数：
- 第一个命令行參数指定数据来源，能够是本地磁盘文件。也能够是网络数据，支持 https、http、ftp 和 file 协议，当然，file 协议实际上还是读取本地磁盘文件。
- 第二个命令行參数指定将要复制到的本地磁盘文件的名称。
上述測试程序实质内容就是第 9 行的语句：
- 使用第一个命令行參数 args[0] 调用 String 类的 GetInputStream 扩展方法得到输入流。
- 调用 Stream 类的 CopyTo 方法将输入流复制到输出流。
- 输出流是使用 File 类的静态方法 Create 得到的。
在 Windows 操作系统中编译和执行：
E:\work> csc CopyTester.cs StringExtensions.cs
Microsoft(R) Visual C# 2010 编译器 4.0.30319.1 版
版权全部(C) Microsoft Corporation。 保留全部权利。 E:\work> CopyTester https://github.com/mono/xsp/zipball/master mono-xsp.zip
E:\work> CopyTester http://mysql.ntu.edu.tw/Downloads/Connector-Net/mysql-connector-net-6.5.4-noinstall.zip mysql-connector.zip
E:\work> CopyTester ftp://ftp.ntu.edu.tw/pub/MySQL/Downloads/Connector-Net/mysql-connector-net-6.5.4-noinstall.zip mysql-connector.2.zip
E:\work> CopyTester file:///E:/work/mysql-connector.zip mysql-connector.3.zip
E:\work> CopyTester mysql-connector.zip mysql-connector.4.zip
E:\work> dir *.zip
2012/03/11 09:35 468,024 mono-xsp.zip
2012/03/11 09:37 4,176,361 mysql-connector.2.zip
2012/03/11 09:38 4,176,361 mysql-connector.3.zip
2012/03/11 09:38 4,176,361 mysql-connector.4.zip
2012/03/11 09:36 4,176,361 mysql-connector.zip
上面分别測试了以 https、http、ftp、file 协议读取网络数据，以及从本地磁盘上读取数据。注意。file 协议实际上还是从本地磁盘读取数据。
在 Linux 操作系统中编译和执行：
ben@vbox:~/work> dmcs CopyTester.cs StringExtensions.cs
ben@vbox:~/work> mono CopyTester.exe http://mysql.ntu.edu.tw/Downloads/Connector-Net/mysql-connector-net-6.5.4-noinstall.zip mysql-connector.zip
ben@vbox:~/work> mono CopyTester.exe ftp://ftp.ntu.edu.tw/pub/MySQL/Downloads/Connector-Net/mysql-connector-net-6.5.4-noinstall.zip mysql-connector.2.zip
ben@vbox:~/work> mono CopyTester.exe file:///home/ben/work/mysql-connector.zip mysql-connector.3.zip
ben@vbox:~/work> mono CopyTester.exe mysql-connector.zip mysql-connector.4.zip
ben@vbox:~/work> ls -l *.zip
-rw-r--r-- 1 ben users 4176361 Mar 11 09:54 mysql-connector.2.zip
-rw-r--r-- 1 ben users 4176361 Mar 11 10:01 mysql-connector.3.zip
-rw-r--r-- 1 ben users 4176361 Mar 11 10:01 mysql-connector.4.zip
-rw-r--r-- 1 ben users 4176361 Mar 11 09:53 mysql-connector.zip
在 Windows 操作系统能够正常读取网络上的 https 数据流，在 Linux 操作系统中会失败：
ben@vbox:~/work> mono CopyTester.exe https://github.com/mono/xsp/zipball/master mono-xsp.zip Unhandled Exception: System.Net.WebException: Error getting response stream (Write: The authentication or decryption has failed.): SendFailure ---> System.IO.IOException: The authentication or decryption has failed. ---> Mono.Security.Protocol.Tls.TlsException: Invalid certificate received from server. Error code: 0xffffffff800b010a
at Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.validateCertificates (Mono.Security.X509.X509CertificateCollection certificates) [0x00000] in :0
at Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.ProcessAsTls1 () [0x00000] in :0
at Mono.Security.Protocol.Tls.Handshake.HandshakeMessage.Process () [0x00000] in :0
at (wrapper remoting-invoke-with-check) Mono.Security.Protocol.Tls.Handshake.HandshakeMessage:Process ()
at Mono.Security.Protocol.Tls.ClientRecordProtocol.ProcessHandshakeMessage (Mono.Security.Protocol.Tls.TlsStream handMsg) [0x00000] in :0
at Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult) [0x00000] in :0
--- End of inner exception stack trace ---
at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult) [0x00000] in :0
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult) [0x00000] in :0
at System.Net.HttpWebRequest.GetResponse () [0x00000] in :0
at Skyiv.StringExtensions.GetHttpStream (System.Uri uri) [0x00000] in :0
at Skyiv.StringExtensions.GetInputStream (System.String fileNameOrUri, System.String user, System.String password) [0x00000] in :0
at Skyiv.Test.CopyTester.Main (System.String[] args) [0x00000] in :0
[ERROR] FATAL UNHANDLED EXCEPTION: System.Net.WebException: Error getting response stream (Write: The authentication or decryption has failed.): SendFailure ---> System.IO.IOException: The authentication or decryption has failed. ---> Mono.Security.Protocol.Tls.TlsException: Invalid certificate received from server. Error code: 0xffffffff800b010a
at Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.validateCertificates (Mono.Security.X509.X509CertificateCollection certificates) [0x00000] in :0
at Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.ProcessAsTls1 () [0x00000] in :0
at Mono.Security.Protocol.Tls.Handshake.HandshakeMessage.Process () [0x00000] in :0
at (wrapper remoting-invoke-with-check) Mono.Security.Protocol.Tls.Handshake.HandshakeMessage:Process ()
at Mono.Security.Protocol.Tls.ClientRecordProtocol.ProcessHandshakeMessage (Mono.Security.Protocol.Tls.TlsStream handMsg) [0x00000] in :0
at Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult) [0x00000] in :0
--- End of inner exception stack trace ---
at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult) [0x00000] in :0
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult) [0x00000] in :0
at System.Net.HttpWebRequest.GetResponse () [0x00000] in :0
at Skyiv.StringExtensions.GetHttpStream (System.Uri uri) [0x00000] in :0
at Skyiv.StringExtensions.GetInputStream (System.String fileNameOrUri, System.String user, System.String password) [0x00000] in :0
at Skyiv.Test.CopyTester.Main (System.String[] args) [0x00000] in :0
不知道是不是我的 openSUSE 12.1 操作系统或者是 Mono 2.10.6 执行环境还须要进行一些配置，以便满足 https 的安全验证要求。可是我在 Windows 操作系统中也没有进行特别的配置。并且在 Linux 操作系统中使用 wget 命令也可下面载 https 协议的数据：
ben@vbox:~/work> wget https://github.com/mono/xsp/zipball/master
asking libproxy about url 'https://github.com/mono/xsp/zipball/master'
libproxy suggest to use 'direct://'
--2012-03-11 13:48:32-- https://github.com/mono/xsp/zipball/master
Resolving github.com (github.com)... 207.97.227.239
Connecting to github.com (github.com)|207.97.227.239|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://nodeload.github.com/mono/xsp/zipball/master [following]
asking libproxy about url 'https://nodeload.github.com/mono/xsp/zipball/master'
libproxy suggest to use 'direct://'
--2012-03-11 13:48:34-- https://nodeload.github.com/mono/xsp/zipball/master
Resolving nodeload.github.com (nodeload.github.com)... 207.97.227.252
Connecting to nodeload.github.com (nodeload.github.com)|207.97.227.252|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 468024 (457K) [application/octet-stream]
Saving to: `master' 100%[======================================>] 468,024 46.5K/s in 17s 2012-03-11 13:48:54 (27.0 KB/s) - `master' saved [468024/468024] ben@vbox:~/work> mv master mono-xsp.zip
这样看来。Mono 环境的 HttpWebRequest 类可能须要进行一些设置才干读取 https 协议的数据。
假设有哪位园友知道的话，请在本文的评论里告诉我，谢谢。