c++ - 使用管道从子进程重定向 I/O - winapi

Question

我正在使用一个提供 api 的应用程序，以便更轻松地编写脚本。基本上，当您编写有效输入时，它会输出一个答案。我想使用该输出来发送更多输入，例如:

Input: <nodes>
Output: 1, 56, 23
Input <56>
Output: "Apple"

我想要做的是一个写入目标进程 STDIN，然后从它的 STDOUT 读取输出的程序。为此，我主要从那里获取代码:

Creating a Child Process with Redirected Input and Output (Windows) - MSDN

唯一的问题是，为了从子进程读取，我首先需要关闭用于写入它的父进程的句柄，这意味着我不能使用子进程的输出来写入更多的东西。

这是从 msdn 中提取的简化代码:

#include <Windows.h>
#include <string>

using std::string;

HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;

#define BUFSIZE 4096

void WriteToPipe(string msg); 
void ReadFromPipe(void); 

int main()
{
    /*
     * CREATE PIPES
    */

    SECURITY_ATTRIBUTES saAttr;

    // Set the bInheritHandle flag so pipe handles are inherited.
    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
    saAttr.bInheritHandle = TRUE;
    saAttr.lpSecurityDescriptor = NULL;

    // Create pipes for the child process's STDOUT and STDIN,
    // ensures both handle are not inherited
    CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0);
    SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0);

    CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0);
    SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0);

    /*
     * CREATE CHILD PROCESS
    */

    TCHAR szCmdline[]=TEXT("target.exe");
    STARTUPINFO siStartInfo;
    PROCESS_INFORMATION piProcInfo;

    // Set up members of the PROCESS_INFORMATION structure.
    ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION) );

    // Set up members of the STARTUPINFO structure.
    // This structure specifies the STDIN and STDOUT handles for redirection.
    ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
    siStartInfo.cb = sizeof(STARTUPINFO);
    siStartInfo.hStdError  = g_hChildStd_OUT_Wr;
    siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
    siStartInfo.hStdInput  = g_hChildStd_IN_Rd;
    siStartInfo.dwFlags |= STARTF_USESTDHANDLES;

    CreateProcess(NULL, szCmdline, NULL, NULL, TRUE, 0,
                  NULL,  NULL, &siStartInfo, &piProcInfo);

    // Close handles to the child process and its primary thread.
    // Some applications might keep these handles to monitor the status
    // of the child process, for example. 
    CloseHandle(g_hChildStd_OUT_Wr);
    CloseHandle(g_hChildStd_IN_Rd);
    CloseHandle(piProcInfo.hProcess);
    CloseHandle(piProcInfo.hThread);

    /*
     * ACTUAL APPLICATION
    */

    WriteToPipe("<nodes>\n");

    // Need to close the handle before reading
    CloseHandle(g_hChildStd_IN_Wr); // PROBLEM HERE

    ReadFromPipe();

    WriteToPipe("<56>\n"); // I can't, as I have released the handle already

    system("pause");

    return 0;
}

void WriteToPipe(string msg)
{
    WriteFile(g_hChildStd_IN_Wr, msg.c_str(), msg.size(), NULL, NULL);
}

void ReadFromPipe(void)
{
    DWORD dwRead, dwWritten;
    CHAR chBuf[BUFSIZE];
    BOOL bSuccess = FALSE;
    HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);

    for (;;)
    {
        bSuccess = ReadFile(g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
        if( ! bSuccess || dwRead == 0 ) break;

        bSuccess = WriteFile(hParentStdOut, chBuf, dwRead, &dwWritten, NULL);
        if (! bSuccess ) break;
    }
}

问题来自行:

CloseHandle(g_hChildStd_IN_Wr);

要么我把它留在那里，我将无法在读取一次后写入我的子进程，要么我删除它然后 ReadFromPipe 陷入死锁。

如有任何帮助，我们将不胜感激，谢谢!

Answer 1

ReadFile(..., BUFSIZE) 意思是“等到程序写入 BUFSIZE 字节，或者关闭它的管道末端”。该程序只写入少量字节，然后等待您未提供的更多输入。如果关闭写入管道，它知道没有更多输入并退出，此时您的 ReadFile 知道没有更多输入并返回。您需要找到一种方法来只读取管道中的字节数。

这里的魔力是PeekNamedPipe ，它告诉您程序输出了多少数据，因此您可以在不阻塞的情况下读取多少数据。请注意，您必须每隔一段时间继续检查一次，以查看自上次检查以来程序是否写入了更多字节。