I want to create a remote control for GNUNet, so I started writing a self-made multithreaded-generical-purpose webserver for the GNU OS, able to authenticate users (reading from the system user database) and able to execute generic CGI programs/scripts. I started from scratch and it's just a draft for now. However, everything seems to work fine.
I have just a question.
As you know, a CGI programs/scripts read the POST string from the STDIN and send their content to the STDOUT. The following is (part of) the code I wrote. And it seems to work.
if (pipe(cgiPipe))
{
perror("pipe");
}
cgiPid = fork();
if (cgiPid == 0)
{
/* child */
/* piping the POST content... */
/* first, send the truncated part of the POST string contained within the request string... */
if (nPOSTLength && (nSentChrs = write(cgiPipe[1], sPOSTSegment,
nReqLen + requestString - sPOSTSegment)) > 0)
{
nPOSTLength -= nSentChrs;
/* after, read and send the rest of the POST string not received yet... */
while (nPOSTLength > 0 && (nReadChrs = read(nRemote, reservedBuffer,
BUFFER_SIZE_PER_USER)) > 0 && (nSentChrs = write(cgiPipe[1], reservedBuffer,
nReadChrs)) > 0 && nReadChrs == nSentChrs)
{
nPOSTLength -= nReadChrs;
}
if (nReadChrs < 0)
{
printf("Error reading POST string.\n");
goto closeThread;
}
if (nSentChrs < 0)
{
printf("Error sending POST string.\n");
goto closeThread;
}
}
else
{
write(cgiPipe[1], "(null)", 6);
}
close(cgiPipe[1]);
/* redirecting the output of the pipe to the STDIN of the child process */
dup2(cgiPipe[0], STDIN_FILENO);
/* redirecting STDOUT of the child process to the remote client */
dup2(nRemote, STDOUT_FILENO);
setuid(nUserID);
if (execve(sLocalPath, NULL, aCGIEnv))
{
/* unable to execute CGI... */
perror("execve");
sendString(nRemote,
"HTTP/1.1 200 OK\r\n"
"Content-length: 97\r\n"
"Content-Type: text/html\r\n\r\n"
"<!doctype html><html><head><title>CGI Error</title></head><body><h1>CGI Error.</h1></body></html>\r\n"
);
}
goto closeThread;
}
else if (cgiPid > 0)
{
/* parent */
close(cgiPipe[0]);
/* wait for child process. */
if (waitpid(cgiPid, NULL, 0) == -1)
{
perror("wait");
}
goto closeThread;
}
else
{
/* parent */
perror("fork");
/* let's try to send it as normal file, if the user has the right permissions... */
}
As you can see, before executing the CGI program, the whole POST string is received from the client and piped (first the truncated part of it contained within the request string – usually few bytes – and then the rest). Then, the CGI program is executed.
And now my question…
If I try to upload a file of several MBs, several MBs are piped before the invocation of the CGI: is there any way to redirect the socket directly to the STDIN of the new process, in order to not read it before? But, for sure, I have to send the read truncated part of the POST string, before. So, I can schematize what I would like to do in this way:
- piping a string (few bytes) to the STDIN, then
- redirecting the socket (the client) to the STDIN, then
- executing an external process (the CGI program)
Is it possible? Can you show me how?
Solved!!
I just had to put the sending process inside the parent rather than the child. In this way the CGI is executed immediately:
Thank you for your help!
And… let's hope to see a remote control for GNUNet as early as possble! :)