delphi – 假设InternetCloseHandle()不会失败,从而允许更清晰的

发布时间：2020-12-15 09:19:32 所属栏目：大数据来源：网络整理

导读：这是使用WinINet执行HTTP请求的例程,并返回获取的字符串或引发异常： function Request(const pConnection: HINTERNET; const localpath: string): string;var Buffer: packed Array[1..5000] of Char; BytesRead: Cardinal; pRequest: HINTERNET; sent: boo

这是使用WinINet执行HTTP请求的例程,并返回获取的字符串或引发异常：

function Request(const pConnection: HINTERNET; const localpath: string): string;
var Buffer: packed Array[1..5000] of Char; BytesRead: Cardinal; pRequest: HINTERNET;     sent: boolean;
begin
Result := '';
pRequest := HTTPOpenRequest(pConnection,'GET',pchar(localpath),nil,0);
if pRequest <> nil then
  begin
  sent := HTTPSendRequest(pRequest,0);
  if sent then
    while InternetReadFile(pRequest,@Buffer,SizeOf(Buffer)-1 {leave room for terminator},BytesRead) do
      begin
      Buffer[BytesRead+1] := #0;
      Result := Result + buffer;
      end;
  InternetCloseHandle(pRequest);
  if not sent then RaiseLastOSerror; // HTTPSendRequest failed
  end
else RaiseLastOSerror; // HTTPOpenRequest failed
end;

如果即使成功分配了pRequest,InternetCloseHandle(pRequest)也可能失败,GetLastError()将返回InternetCloseHandle()而不是HTTPSendRequest()的错误代码.修复需要以下代码：

function Request(const pConnection: HINTERNET; const localpath: string): string;
var Buffer: packed Array[1..5000] of Char; BytesRead: Cardinal; pRequest: HINTERNET;
begin
Result := '';
pRequest := HTTPOpenRequest(pConnection,0);
if pRequest <> nil then
  begin
  if HTTPSendRequest(pRequest,0) then
    while InternetReadFile(pRequest,BytesRead) do
      begin
      Buffer[BytesRead+1] := #0;
      Result := Result + buffer;
      end
  else
    begin
    InternetCloseHandle(pRequest);
    RaiseLastOSerror; // HTTPSendRequest failed
    end;
  InternetCloseHandle(pRequest);
  end
else RaiseLastOSerror; // HTTPOpenRequest failed
end;

但这看起来更加丑陋,乍一看更加令人困惑.

假设InternetCloseHandle()不会失败,从而允许更简单的代码是否安全？

解决方法

我认为你这是错误的方式.您应该只检查每个API调用的错误,并在遇到异常时立即引发异常.这样您就会得到适合于产生异常的错误的错误消息.您根本无法期望继续调用其他API函数,然后针对前一段时间发生的错误引发异常.

我想你想要这样的东西：

Result := '';
pRequest := HTTPOpenRequest(pConnection,0);
if pRequest=nil then
  RaiseLastOSerror;
try
  CheckWin32Error(HTTPSendRequest(pRequest,0));
  while InternetReadFile(pRequest,SizeOf(Buffer)-1,BytesRead) do begin
    Buffer[BytesRead+1] := #0;
    Result := Result + buffer;
  end;
  if GetLastError<>0 then
    RaiseLastOSerror;
finally
  CheckWin32Error(InternetCloseHandle(pRequest));
end;

请注意,您没有包含InternetReadFile的任何错误检查.我试图为你写.

（编辑：李大同）

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