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?
82 Answers
Solved!!
I just had to put the sending process inside the parent rather than the child. In this way the CGI is executed immediately:
if (pipe(cgiPipe))
{ perror("pipe");
}
cgiPid = fork();
if (cgiPid == 0)
{ /* child */ /* piping the POST content... */ 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]); /* 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); } /* 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... */
}Thank you for your help!
And… let's hope to see a remote control for GNUNet as early as possble! :)
This can be achieved by replacing the file descriptor STDIN_FILENO with the opened socket using dup2(). You should also then close the original socket in the child process:
dup2(socket_fd, STDIN_FILENO);
close(socket_fd); ;
execve("cgi_process", args, env);The execve puts into execution another process whose STDIN is bound to socket_fd.
