1 /*
2  * Multiplexor for sftp sessions.
3  * Assumes can parse session with sftp> prompts.
4  * Assumes clients are well-behaved and don't hang up the system.
5  *
6  * Stupid sftp bug: sftp invokes ssh, which always set O_NONBLOCK
7  * on 0, 1, and 2.  Ssh inherits sftp's 2, so we can't use the output pipe
8  * on fd 2, since it will get set O_NONBLOCK, sftp won't notice, and
9  * writes will be lost.  So instead we use a separate pipe for errors
10  * and consult it after each command.  Assume the pipe buffer is
11  * big enough to hold the error output.
12  */
13 #include <u.h>
14 #include <fcntl.h>
15 #include <libc.h>
16 #include <bio.h>
17 
18 #undef pipe
19 
20 int debug;
21 #define dprint if(debug)print
22 int sftpfd;
23 int sftperr;
24 Biobuf bin;
25 
26 void
27 usage(void)
28 {
29 	fprint(2, "usage: sftpcache system\n");
30 	exits("usage");
31 }
32 
33 char*
34 Brd(Biobuf *bin)
35 {
36 	static char buf[1000];
37 	int c, tot;
38 
39 	tot = 0;
40 	while((c = Bgetc(bin)) >= 0 && tot<sizeof buf){
41 		buf[tot++] = c;
42 		if(c == '\n'){
43 			buf[tot] = 0;
44 			dprint("OUT %s", buf);
45 			return buf;
46 		}
47 		if(c == ' ' && tot == 6 && memcmp(buf, "sftp> ", 5) == 0){
48 			buf[tot] = 0;
49 			dprint("OUT %s\n", buf);
50 			return buf;
51 		}
52 	}
53 	if(tot == sizeof buf)
54 		sysfatal("response too long");
55 	return nil;
56 }
57 
58 int
59 readstr(int fd, char *a, int n)
60 {
61 	int i;
62 
63 	for(i=0; i<n; i++){
64 		if(read(fd, a+i, 1) != 1)
65 			return -1;
66 		if(a[i] == '\n'){
67 			a[i] = 0;
68 			return i;
69 		}
70 	}
71 	return n;
72 }
73 
74 void
75 doerrors(int fd)
76 {
77 	char buf[100];
78 	int n, first;
79 
80 	first = 1;
81 	while((n = read(sftperr, buf, sizeof buf)) > 0){
82 		if(debug){
83 			if(first){
84 				first = 0;
85 				fprint(2, "OUT errors:\n");
86 			}
87 			write(1, buf, n);
88 		}
89 		write(fd, buf, n);
90 	}
91 }
92 
93 void
94 bell(void *x, char *msg)
95 {
96 	if(strcmp(msg, "sys: child") == 0 || strcmp(msg, "sys: write on closed pipe") == 0)
97 		sysfatal("sftp exited");
98 	if(strcmp(msg, "alarm") == 0)
99 		noted(NCONT);
100 	noted(NDFLT);
101 }
102 
103 void
104 main(int argc, char **argv)
105 {
106 	char buf[200], cmd[1000], *q, *s;
107 	char dir[100], ndir[100];
108 	int p[2], px[2], pe[2], pid, ctl, nctl, fd, n;
109 
110 	notify(bell);
111 	fmtinstall('H', encodefmt);
112 
113 	ARGBEGIN{
114 	case 'D':
115 		debug = 1;
116 		break;
117 	default:
118 		usage();
119 	}ARGEND
120 
121 	if(argc != 1)
122 		usage();
123 
124 	if(pipe(p) < 0 || pipe(px) < 0 || pipe(pe) < 0)
125 		sysfatal("pipe: %r");
126 	pid = fork();
127 	if(pid < 0)
128 		sysfatal("fork: %r");
129 	if(pid == 0){
130 		close(p[1]);
131 		close(px[0]);
132 		close(pe[0]);
133 		dup(p[0], 0);
134 		dup(px[1], 1);
135 		dup(pe[1], 2);
136 		if(p[0] > 2)
137 			close(p[0]);
138 		if(px[1] > 2)
139 			close(px[1]);
140 		if(pe[1] > 2)
141 			close(pe[1]);
142 		execl("sftp", "sftp", "-b", "/dev/stdin", argv[0], nil);
143 		sysfatal("exec sftp: %r");
144 	}
145 
146 	close(p[0]);
147 	close(px[1]);
148 	close(pe[1]);
149 
150 	sftpfd = p[1];
151 	sftperr = pe[0];
152 	Binit(&bin, px[0], OREAD);
153 
154 	fcntl(sftperr, F_SETFL, fcntl(sftperr, F_GETFL, 0)|O_NONBLOCK);
155 
156 	do
157 		q = Brd(&bin);
158 	while(q && strcmp(q, "sftp> ") != 0);
159 	if(q == nil)
160 		sysfatal("unexpected eof");
161 
162 	snprint(buf, sizeof buf, "unix!%s/%s.sftp", getns(), argv[0]);
163 	ctl = announce(buf, dir);
164 	if(ctl < 0)
165 		sysfatal("announce %s: %r", buf);
166 
167 	pid = fork();
168 	if(pid < 0)
169 		sysfatal("fork");
170 	if(pid != 0)
171 		exits(nil);
172 
173 	for(;;){
174 		nctl = listen(dir, ndir);
175 		if(nctl < 0)
176 			sysfatal("listen %s: %r", buf);
177 		fd = accept(ctl, ndir);
178 		close(nctl);
179 		if(fd < 0)
180 			continue;
181 		for(;;){
182 		/*	alarm(1000); */
183 			n = readstr(fd, cmd, sizeof cmd);
184 		/*	alarm(0); */
185 			if(n <= 0)
186 				break;
187 			dprint("CMD %s\n", cmd);
188 			if(strcmp(cmd, "DONE") == 0){
189 				fprint(fd, "DONE\n");
190 				break;
191 			}
192 			fprint(sftpfd, "-%s\n", cmd);
193 			q = Brd(&bin);
194 			if(*q==0 || q[strlen(q)-1] != '\n')
195 				sysfatal("unexpected response");
196 			q[strlen(q)-1] = 0;
197 			if(q[0] != '-' || strcmp(q+1, cmd) != 0)
198 				sysfatal("unexpected response");
199 			while((q = Brd(&bin)) != nil){
200 				if(strcmp(q, "sftp> ") == 0){
201 					doerrors(fd);
202 					break;
203 				}
204 				s = q+strlen(q);
205 				while(s > q && (s[-1] == ' ' || s[-1] == '\n' || s[-1] == '\t' || s[-1] == '\r'))
206 					s--;
207 				*s = 0;
208 				fprint(fd, "%s\n", q);
209 			}
210 			if(q == nil){
211 				fprint(fd, "!!! unexpected eof\n");
212 				sysfatal("unexpected eof");
213 			}
214 		}
215 		close(fd);
216 	}
217 }