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三、CGI编程实例
本节将用VB编写一个处理主页客户留言簿的CGI程序。除了要调用本文前面所介绍的Win32API函数外，程序中还调用了Win32API函数GetTempFileName()来获得一个唯一的临时文件名。程序中的函数UrlDecode()用来对客户端的输入进行URL译码。函数GetCgiValue()则用来分解字符串，根据表单元素的NAME属性获取其VALUE值，并调用UrlDecode()函数对其进行URL译码。
本程序要求在留言簿文件guests.html中使用一个定位串“<! ENDHEAD >”，将文件的开始部分和具体的客户留言部分分开。CGI程序将在“<! ENDHEAD >”所在的位置插入客户新的留言。guests.html应具有如下所示的样式：
<html>
<head><title>DHTML Zone </title></head>
<body bgcolor="#FFFFFF" text="#00000" vlink="#990000" link="#333399">
<! ENDHEAD >
<!---客户的留言部分从这开始-->
<P>……………………….
<!---客户的留言部分结束于此-->
</body></html>
这种样式将保证最后的留言出现在留言簿的最前面。如果要想使最后的留言出现在留言簿的最后面，则只需将留言簿文件中的定位字符串“<! ENDHEAD >”移到留言簿文件中客户留言部分和HTML文件结尾部分之间的位置就行了。整个程序的完整代码如下所示：
''guestbook.bas
Declare Function GetStdHandle Lib "kernel32" (ByVal nStdHandle As Long) As Long
Declare Function ReadFile Lib "kernel32" (ByVal hFile As Long, lpBuffer As Any,ByVal nNumberOfBytesToRead As Long, lpNumberOfBytesRead As Long, lpOverlapped As Any) As Long
Declare Function WriteFile Lib "kernel32" (ByVal hFile As Long,ByVal lpBuffer As String, ByVal nNumberOfBytesToWrite As Long,lpNumberOfBytesWritten As Long, lpOverlapped As Any) As Long
Declare Function GetTempFileName Lib "kernel32" Alias "GetTempFileNameA"(ByVal lpszPath As String, ByVal lpPrefixString As String, ByVal wUnique As Long, ByVal lpTempFileName As String) As Long
Public Const STD_INPUT_HANDLE = -10&
Public Const STD_OUTPUT_HANDLE = -11&
Public Const FILE_BEGIN = 0&
Public hStdIn As Long '' 标准输入文件句柄
Public hStdOut As Long '' 标准输出文件句柄
Public sFormData As String '' 用于存储没有经过URL译码的用户输入数据
Public lContentLength As Long
Public CGI_RequestMethod As String
Sub Main()
Dim CGI_ContentLength As String, CGI_QueryString As String, sBuff As String, chinesetail As String
Dim lBytesRead As Long， rc As Long，I As Long
Dim sEmail As String, sName As String, sURL As String, sfrom As String, tempstring As String
Dim sComment As String, tempFileName As String, guestbook As String
''CGI程序的初始化工作
hStdIn = GetStdHandle(STD_INPUT_HANDLE)
hStdOut = GetStdHandle(STD_OUTPUT_HANDLE)
CGI_RequestMethod = Environ("REQUEST_METHOD")
CGI_QueryString = Environ("QUERY_STRING")
CGI_ContentLength = Environ("CONTENT_LENGTH")
lContentLength = Val(CGI_ContentLength)
sBuff = String(lContentLength, Chr$(0))
OutPut "Content-type: text/html" & vbCrLf '' 输出MIME类型
OutPut "<FONT SIZE=""+2"">"
If CGI_RequestMethod = "POST" Then
sBuff = String(lContentLength, Chr$(0))
rc = ReadFile(hStdIn, ByVal sBuff, lContentLength, lBytesRead, ByVal 0&)
sFormData = Left$(sBuff, lBytesRead)
ElseIf CGI_RequestMethod = "GET" Then
sFormData = CGI_QueryString
Else
OutPut "Unknow Form Method !"
End If
chinesetail = String(400, " ")
''为了在页面上正确显示中文，生成一个空格串以获取客户端用户的输入
sName = GetCgiValue("name")
sEmail = GetCgiValue("email")
sURL = GetCgiValue("URL")
sfrom = GetCgiValue("from")
sComment = GetCgiValue("URL_Comment")
''对客户端用户的输入进行检查
If Len(sName) = 0 Then
OutPut "<P>非常抱歉！您还没有填写姓名！" & chinesetail
Exit Sub
End If
If Len(sComment) = 0 Then
OutPut "<P>非常抱歉！您还没有提出建议！" & chinesetail
Exit Sub
End If
''获取唯一的临时文件名和留言簿文件并打开它们
tempFileName = TempFile("c:\windows\temp", "gbk")
guestbook = "e:\netscape\server\docs\guests.html"
Open tempFileName For Output As #1
Open guestbook For Input As #2
Do ''本循环体用于将留言簿中字符串"<! ENDHEAD >"前面的内容写入临时文件
Line Input #2, tempstring
Print #1, tempstring
Loop While tempstring <> "<! ENDHEAD >" And Not EOF(2)
''向临时文件中插入客户端用户的留言
Print #1, "<hr>" & vbCrLf
Print #1, "<ul>" & vbCrLf
Print #1, "<li><b>留言时间</b>：" & Date$ & " " & Time$ & vbCrLf
Print #1, "<li><b>姓名: </b>" & sName & vbCrLf
If Len(sEmail) <> 0 Then
Print #1, "<li><b>E-mail: </b><a href=""mailto:" & sEmail & """ >" & sEmail & "</a>" & vbCrLf
End If
If Len(sURL) <> 0 Then
Print #1, "<li><b>我的主页: </b> <a href=""" & sURL & """ >" & sURL & "</a>" & vbCrLf
End If
If Len(sfrom) <> 0 Then
Print #1, "<li><b>我来自: </b>" & sfrom & vbCrLf
End If
Print #1, "<li><b>我的建议: </b>" & vbCrLf
Print #1, sComment & vbCrLf
Print #1, "</ul>" & vbCrLf
Do ''本循环体用于将留言簿剩余的东西写入留言簿
Line Input #2, tempstring
Print #1, tempstring
Loop While Not EOF(2)
Close #1
Close #2
Kill guestbook ''删除旧的留言簿
Name tempFileName As guestbook ''将临时文件改成新的留言簿
OutPut "<P>非常感谢您的留言!" & chinesetail
OutPut "<P>欢迎您经常光顾本主页！" & chinesetail
OutPut "</FONT>"
End Sub
Sub OutPut(s As String) '' 本子程序用于向标准输出写信息
Dim lBytesWritten As Long
s = s & vbCrLf
WriteFile hStdOut, s, Len(s), lBytesWritten, ByVal 0&
End Sub
Public Function GetCgiValue(cgiName As String) As String
'' 本子程序可以获取表单上某一元素的数据
Dim delim2 As Long '' position of "="
Dim delim1 As Long '' position of "&"
Dim n As Integer
Dim pointer1 As Long，pointer2 As Long，length As Long，length1 As Long
Dim tmpstring1 As String，tmpstring2 As String
pointer1 = 1
pointer2 = 1
delim2 = InStr(pointer2, sFormData, "=")
pointer2 = delim2 + 1
Do
length = delim2 - pointer1
tmpstring1 = Mid(sFormData, pointer1, length)
delim1 = InStr(pointer1, sFormData, "&")
pointer1 = delim1 + 1
length1 = delim1 - pointer2
If delim1 = 0 Then length1 = lContentLength + 1 - pointer2
If tmpstring1 = cgiName Then
tmpstring2 = Mid$(sFormData, pointer2, length1)
GetCgiValue = UrlDecode(tmpstring2)
Exit Do
End If
If delim1 = 0 Then
Exit Do
End If
delim2 = InStr(pointer2, sFormData, "=")
pointer2 = delim2 + 1
Loop
End Function
Public Function UrlDecode(ByVal sEncoded As String) As String
'' 本函数可以对用户输入的数据进行URL解码
Dim pointer As Long '' sEncoded position pointer
Dim pos As Long '' position of InStr target
Dim temp As String
If sEncoded = "" Then Exit Function
pointer = 1
Do ''本循环体用于将"+"转换成空格
pos = InStr(pointer, sEncoded, "+")
If pos = 0 Then Exit Do
Mid$(sEncoded, pos, 1) = " "
pointer = pos + 1
Loop
pointer = 1
Do
''本循环体用于将%XX转换成字符。对于两个连续的%XX，如果第一个%XX不是某些特指的Web系统保留字符，将把它们转换成汉字
pos = InStr(pointer, sEncoded, "%")
If pos = 0 Then Exit Do
temp = Chr$("&H" & (Mid$(sEncoded, pos + 1, 2)))
If Mid(sEncoded, pos + 3, 1) = "%" And (temp <> ":") And (temp <> "/") _
And (temp <> "(") And (temp <> ")") And (temp <> ".") And (temp <> ",") _
And (temp <> ";") And (temp <> "%") Then
Mid$(sEncoded, pos, 2) = Chr$("&H" & (Mid$(sEncoded, pos + 1, 2)) _
& (Mid$(sEncoded, pos + 4, 2)))
sEncoded = Left$(sEncoded, pos) & Mid$(sEncoded, pos + 6)
pointer = pos + 1
Else
Mid$(sEncoded, pos, 1) = temp
sEncoded = Left$(sEncoded, pos) & Mid$(sEncoded, pos + 3)
pointer = pos + 1
End If
Loop
UrlDecode = sEncoded
Exit Function
End Function
Public Function TempFile(sPath As String, sPrefix As String) As String
''本函数可以获得一个唯一的临时文件名
Dim x As Long，rc As Long
TempFile = String(127, Chr$(0))
rc = GetTempFileName(sPath, sPrefix, ByVal 0&, TempFile)
x = InStr(TempFile, Chr$(0))
If x > 0 Then TempFile = Left$(TempFile, x - 1)
End Function
CGI程序guestbook.bas所要处理的表单如下所示：
<html><head><title>贵宾留言簿</title></head>
<body>
<h3>贵宾留言簿测试</h3>
<form action="/cgi-bin/guest.exe" method="post">
您的姓名: <input type="text" name="name"><br>
您的Email信箱: <input type="text" name="email"><br>
您的主页的URL: <input type="text" name="URL"><br>
您的建议:<br> <textarea name="URL_Comment" rows=4 cols=30></textarea><br>
您来自: <input type="text" name="from"><br>
<input type="submit" value=" 留言 ">
</form>
</body></html>
虽然目前已经有很多可以取代CGI且其性能较CGI要高的技术（例如ASP、ISAPI、NSAPI等），但使用它们时需要用到专门的知识和工具，并且利用这些技术所编制的程序只适用于特定的Web服务器或系统平台。考虑到CGI编程具有易用易学性、跨服务器平台特性等优点，因此，CGI程序还将在WWW上占有一席之地。
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