sftp session cache

src/cmd/sftpcache.c

@@ -0,0 +1,210 @@
+/*
+ * Multiplexor for sftp sessions.
+ * Assumes can parse session with sftp> prompts.
+ * Assumes clients are well-behaved and don't hang up the system.
+ *
+ * Stupid sftp bug: sftp invokes ssh, which always set O_NONBLOCK
+ * on 0, 1, and 2.  Ssh inherits sftp's 2, so we can't use the output pipe
+ * on fd 2, since it will get set O_NONBLOCK, sftp won't notice, and 
+ * writes will be lost.  So instead we use a separate pipe for errors
+ * and consult it after each command.  Assume the pipe buffer is 
+ * big enough to hold the error output.
+ */
+#include <u.h>
+#include <fcntl.h>
+#include <libc.h>
+#include <bio.h>
+
+#undef pipe
+
+int debug;
+#define dprint if(debug)print
+int sftpfd;
+int sftperr;
+Biobuf bin;
+
+void
+usage(void)
+{
+	fprint(2, "usage: sftpcache system\n");
+	exits("usage");
+}
+
+char*
+Brd(Biobuf *bin)
+{
+	static char buf[1000];
+	int c, tot;
+	
+	tot = 0;
+	while((c = Bgetc(bin)) >= 0 && tot<sizeof buf){
+		buf[tot++] = c;
+		if(c == '\n'){
+			buf[tot] = 0;
+			dprint("%s", buf);
+			return buf;
+		}
+		if(c == ' ' && tot == 6 && memcmp(buf, "sftp> ", 5) == 0){
+			buf[tot] = 0;
+			dprint("%s\n", buf);
+			return buf;
+		}
+	}
+	if(tot == sizeof buf)
+		sysfatal("response too long");
+	return nil;
+}
+
+int
+readstr(int fd, char *a, int n)
+{
+	int i;
+	
+	for(i=0; i<n; i++){
+		if(read(fd, a+i, 1) != 1)
+			return -1;
+		if(a[i] == '\n'){
+			a[i] = 0;
+			return i;
+		}
+	}
+	return n;
+}
+
+void
+doerrors(int fd)
+{
+	char buf[100];
+	int n;
+	
+	while((n = read(sftperr, buf, sizeof buf)) > 0){
+		if(debug)
+			write(1, buf, n);
+		write(fd, buf, n);
+	}
+}
+
+void
+bell(void *x, char *msg)
+{
+	if(strcmp(msg, "sys: child") == 0 || strcmp(msg, "sys: write on closed pipe") == 0)
+		sysfatal("sftp exited");
+	if(strcmp(msg, "alarm") == 0)
+		noted(NCONT);
+	noted(NDFLT);
+}
+
+void
+main(int argc, char **argv)
+{
+	char buf[200], cmd[1000], *q, *s;
+	char dir[100], ndir[100];
+	int p[2], px[2], pe[2], pid, ctl, nctl, fd, n;
+	
+	notify(bell);
+	fmtinstall('H', encodefmt);
+
+	ARGBEGIN{
+	case 'D':
+		debug = 1;
+		break;
+	default:
+		usage();
+	}ARGEND
+	
+	if(argc != 1)
+		usage();
+	
+	if(pipe(p) < 0 || pipe(px) < 0 || pipe(pe) < 0)
+		sysfatal("pipe: %r");
+	pid = fork();
+	if(pid < 0)
+		sysfatal("fork: %r");
+	if(pid == 0){
+		close(p[1]);
+		close(px[0]);
+		close(pe[0]);
+		dup(p[0], 0);
+		dup(px[1], 1);
+		dup(pe[1], 2);
+		if(p[0] > 2)
+			close(p[0]);
+		if(px[1] > 2)
+			close(px[1]);
+		if(pe[1] > 2)
+			close(pe[1]);
+		execl("sftp", "sftp", "-b", "/dev/stdin", argv[0], nil);
+		sysfatal("exec sftp: %r");
+	}
+
+	close(p[0]);
+	close(px[1]);
+	close(pe[1]);
+
+	sftpfd = p[1];
+	sftperr = pe[0];
+	Binit(&bin, px[0], OREAD);
+
+	fcntl(sftperr, F_SETFL, fcntl(sftperr, F_GETFL, 0)|O_NONBLOCK);
+
+	do
+		q = Brd(&bin);
+	while(q && strcmp(q, "sftp> ") != 0);
+	if(q == nil)
+		sysfatal("unexpected eof");
+
+	snprint(buf, sizeof buf, "unix!%s/%s.sftp", getns(), argv[0]);
+	ctl = announce(buf, dir);
+	if(ctl < 0)
+		sysfatal("announce %s: %r", buf);
+
+	pid = fork();
+	if(pid < 0)
+		sysfatal("fork");
+	if(pid != 0)
+		exits(nil);
+		
+	for(;;){
+		nctl = listen(dir, ndir);
+		if(nctl < 0)
+			sysfatal("listen %s: %r", buf);
+		fd = accept(ctl, ndir);
+		close(nctl);
+		if(fd < 0)
+			continue;
+		for(;;){
+		//	alarm(1000);
+			n = readstr(fd, cmd, sizeof cmd);
+		//	alarm(0);
+			if(n <= 0)
+				break;
+			dprint("CMD %s\n", cmd);
+			if(strcmp(cmd, "DONE") == 0)
+				break;
+			fprint(sftpfd, "%s\n", cmd);
+			q = Brd(&bin);
+			if(*q==0 || q[strlen(q)-1] != '\n')
+				sysfatal("unexpected response");
+			q[strlen(q)-1] = 0;
+			if(strcmp(q, cmd) != 0)
+				sysfatal("unexpected response");
+			while((q = Brd(&bin)) != nil){
+				if(strcmp(q, "sftp> ") == 0){
+					doerrors(fd);
+					break;
+				}
+				s = q+strlen(q);
+				while(s > q && (s[-1] == ' ' || s[-1] == '\n' || s[-1] == '\t' || s[-1] == '\r'))
+					s--;
+				*s = 0;
+				fprint(fd, "%s\n", q);
+			}
+			if(q == nil){
+				fprint(fd, "!!! unexpected eof\n");
+				sysfatal("unexpected eof");
+			}
+		}
+		close(fd);
+	}
+}
+