2 * Platform-independent bits of X11 forwarding.
14 #define GET_16BIT(endian, cp) \
15 (endian=='B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp))
17 #define PUT_16BIT(endian, cp, val) \
18 (endian=='B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val))
20 const char *const x11_authnames
[] = {
21 "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"
26 unsigned char clientid
[6];
30 const struct plug_function_table
*fn
;
31 /* the above variable absolutely *must* be the first in this structure */
32 unsigned char firstpkt
[12]; /* first X data packet */
33 struct X11Display
*disp
;
35 unsigned char *auth_data
;
36 int data_read
, auth_plen
, auth_psize
, auth_dlen
, auth_dsize
;
38 int throttled
, throttle_override
;
39 unsigned long peer_ip
;
41 void *c
; /* data used by ssh.c */
45 static int xdmseen_cmp(void *a
, void *b
)
47 struct XDMSeen
*sa
= a
, *sb
= b
;
48 return sa
->time
> sb
->time ?
1 :
49 sa
->time
< sb
->time ?
-1 :
50 memcmp(sa
->clientid
, sb
->clientid
, sizeof(sa
->clientid
));
53 /* Do-nothing "plug" implementation, used by x11_setup_display() when it
54 * creates a trial connection (and then immediately closes it).
55 * XXX: bit out of place here, could in principle live in a platform-
56 * independent network.c or something */
57 static void dummy_plug_log(Plug p
, int type
, SockAddr addr
, int port
,
58 const char *error_msg
, int error_code
) { }
59 static int dummy_plug_closing
60 (Plug p
, const char *error_msg
, int error_code
, int calling_back
)
62 static int dummy_plug_receive(Plug p
, int urgent
, char *data
, int len
)
64 static void dummy_plug_sent(Plug p
, int bufsize
) { }
65 static int dummy_plug_accepting(Plug p
, OSSocket sock
) { return 1; }
66 static const struct plug_function_table dummy_plug
= {
67 dummy_plug_log
, dummy_plug_closing
, dummy_plug_receive
,
68 dummy_plug_sent
, dummy_plug_accepting
71 struct X11Display
*x11_setup_display(char *display
, int authtype
,
74 struct X11Display
*disp
= snew(struct X11Display
);
78 if (!display
|| !*display
) {
79 localcopy
= platform_get_x_display();
80 if (!localcopy
|| !*localcopy
) {
82 localcopy
= dupstr(":0"); /* plausible default for any platform */
85 localcopy
= dupstr(display
);
88 * Parse the display name.
90 * We expect this to have one of the following forms:
92 * - the standard X format which looks like
93 * [ [ protocol '/' ] host ] ':' displaynumber [ '.' screennumber ]
94 * (X11 also permits a double colon to indicate DECnet, but
95 * that's not our problem, thankfully!)
97 * - only seen in the wild on MacOS (so far): a pathname to a
98 * Unix-domain socket, which will typically and confusingly
99 * end in ":0", and which I'm currently distinguishing from
100 * the standard scheme by noting that it starts with '/'.
102 if (localcopy
[0] == '/') {
103 disp
->unixsocketpath
= localcopy
;
104 disp
->unixdomain
= TRUE
;
105 disp
->hostname
= NULL
;
106 disp
->displaynum
= -1;
110 char *colon
, *dot
, *slash
;
111 char *protocol
, *hostname
;
113 colon
= strrchr(localcopy
, ':');
117 return NULL
; /* FIXME: report a specific error? */
121 dot
= strchr(colon
, '.');
125 disp
->displaynum
= atoi(colon
);
127 disp
->screennum
= atoi(dot
);
132 hostname
= localcopy
;
133 if (colon
> localcopy
) {
134 slash
= strchr(localcopy
, '/');
137 protocol
= localcopy
;
142 disp
->hostname
= *hostname ?
dupstr(hostname
) : NULL
;
145 disp
->unixdomain
= (!strcmp(protocol
, "local") ||
146 !strcmp(protocol
, "unix"));
147 else if (!*hostname
|| !strcmp(hostname
, "unix"))
148 disp
->unixdomain
= platform_uses_x11_unix_by_default
;
150 disp
->unixdomain
= FALSE
;
152 if (!disp
->hostname
&& !disp
->unixdomain
)
153 disp
->hostname
= dupstr("localhost");
155 disp
->unixsocketpath
= NULL
;
162 * Look up the display hostname, if we need to.
164 if (!disp
->unixdomain
) {
167 disp
->port
= 6000 + disp
->displaynum
;
168 disp
->addr
= name_lookup(disp
->hostname
, disp
->port
,
169 &disp
->realhost
, cfg
, ADDRTYPE_UNSPEC
);
171 if ((err
= sk_addr_error(disp
->addr
)) != NULL
) {
172 sk_addr_free(disp
->addr
);
173 sfree(disp
->hostname
);
174 sfree(disp
->unixsocketpath
);
175 return NULL
; /* FIXME: report an error */
180 * Try upgrading an IP-style localhost display to a Unix-socket
181 * display (as the standard X connection libraries do).
183 if (!disp
->unixdomain
&& sk_address_is_local(disp
->addr
)) {
184 SockAddr ux
= platform_get_x11_unix_address(NULL
, disp
->displaynum
);
185 const char *err
= sk_addr_error(ux
);
187 /* Create trial connection to see if there is a useful Unix-domain
189 const struct plug_function_table
*dummy
= &dummy_plug
;
190 Socket s
= sk_new(sk_addr_dup(ux
), 0, 0, 0, 0, 0, (Plug
)&dummy
);
191 err
= sk_socket_error(s
);
197 sk_addr_free(disp
->addr
);
198 disp
->unixdomain
= TRUE
;
200 /* Fill in the rest in a moment */
204 if (disp
->unixdomain
) {
206 disp
->addr
= platform_get_x11_unix_address(disp
->unixsocketpath
,
208 if (disp
->unixsocketpath
)
209 disp
->realhost
= dupstr(disp
->unixsocketpath
);
211 disp
->realhost
= dupprintf("unix:%d", disp
->displaynum
);
216 * Invent the remote authorisation details.
218 if (authtype
== X11_MIT
) {
219 disp
->remoteauthproto
= X11_MIT
;
221 /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
222 disp
->remoteauthdata
= snewn(16, unsigned char);
223 for (i
= 0; i
< 16; i
++)
224 disp
->remoteauthdata
[i
] = random_byte();
225 disp
->remoteauthdatalen
= 16;
227 disp
->xdmseen
= NULL
;
229 assert(authtype
== X11_XDM
);
230 disp
->remoteauthproto
= X11_XDM
;
232 /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
233 disp
->remoteauthdata
= snewn(16, unsigned char);
234 for (i
= 0; i
< 16; i
++)
235 disp
->remoteauthdata
[i
] = (i
== 8 ?
0 : random_byte());
236 disp
->remoteauthdatalen
= 16;
238 disp
->xdmseen
= newtree234(xdmseen_cmp
);
240 disp
->remoteauthprotoname
= dupstr(x11_authnames
[disp
->remoteauthproto
]);
241 disp
->remoteauthdatastring
= snewn(disp
->remoteauthdatalen
* 2 + 1, char);
242 for (i
= 0; i
< disp
->remoteauthdatalen
; i
++)
243 sprintf(disp
->remoteauthdatastring
+ i
*2, "%02x",
244 disp
->remoteauthdata
[i
]);
247 * Fetch the local authorisation details.
249 disp
->localauthproto
= X11_NO_AUTH
;
250 disp
->localauthdata
= NULL
;
251 disp
->localauthdatalen
= 0;
252 platform_get_x11_auth(disp
, cfg
);
257 void x11_free_display(struct X11Display
*disp
)
259 if (disp
->xdmseen
!= NULL
) {
260 struct XDMSeen
*seen
;
261 while ((seen
= delpos234(disp
->xdmseen
, 0)) != NULL
)
263 freetree234(disp
->xdmseen
);
265 sfree(disp
->hostname
);
266 sfree(disp
->unixsocketpath
);
267 if (disp
->localauthdata
)
268 memset(disp
->localauthdata
, 0, disp
->localauthdatalen
);
269 sfree(disp
->localauthdata
);
270 if (disp
->remoteauthdata
)
271 memset(disp
->remoteauthdata
, 0, disp
->remoteauthdatalen
);
272 sfree(disp
->remoteauthdata
);
273 sfree(disp
->remoteauthprotoname
);
274 sfree(disp
->remoteauthdatastring
);
275 sk_addr_free(disp
->addr
);
279 #define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */
281 static char *x11_verify(unsigned long peer_ip
, int peer_port
,
282 struct X11Display
*disp
, char *proto
,
283 unsigned char *data
, int dlen
)
285 if (strcmp(proto
, x11_authnames
[disp
->remoteauthproto
]) != 0)
286 return "wrong authorisation protocol attempted";
287 if (disp
->remoteauthproto
== X11_MIT
) {
288 if (dlen
!= disp
->remoteauthdatalen
)
289 return "MIT-MAGIC-COOKIE-1 data was wrong length";
290 if (memcmp(disp
->remoteauthdata
, data
, dlen
) != 0)
291 return "MIT-MAGIC-COOKIE-1 data did not match";
293 if (disp
->remoteauthproto
== X11_XDM
) {
297 struct XDMSeen
*seen
, *ret
;
300 return "XDM-AUTHORIZATION-1 data was wrong length";
302 return "cannot do XDM-AUTHORIZATION-1 without remote address data";
303 des_decrypt_xdmauth(disp
->remoteauthdata
+9, data
, 24);
304 if (memcmp(disp
->remoteauthdata
, data
, 8) != 0)
305 return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
306 if (GET_32BIT_MSB_FIRST(data
+8) != peer_ip
)
307 return "XDM-AUTHORIZATION-1 data failed check"; /* IP wrong */
308 if ((int)GET_16BIT_MSB_FIRST(data
+12) != peer_port
)
309 return "XDM-AUTHORIZATION-1 data failed check"; /* port wrong */
310 t
= GET_32BIT_MSB_FIRST(data
+14);
311 for (i
= 18; i
< 24; i
++)
312 if (data
[i
] != 0) /* zero padding wrong */
313 return "XDM-AUTHORIZATION-1 data failed check";
315 if (abs(t
- tim
) > XDM_MAXSKEW
)
316 return "XDM-AUTHORIZATION-1 time stamp was too far out";
317 seen
= snew(struct XDMSeen
);
319 memcpy(seen
->clientid
, data
+8, 6);
320 assert(disp
->xdmseen
!= NULL
);
321 ret
= add234(disp
->xdmseen
, seen
);
324 return "XDM-AUTHORIZATION-1 data replayed";
326 /* While we're here, purge entries too old to be replayed. */
328 seen
= index234(disp
->xdmseen
, 0);
329 assert(seen
!= NULL
);
330 if (t
- seen
->time
<= XDM_MAXSKEW
)
332 sfree(delpos234(disp
->xdmseen
, 0));
335 /* implement other protocols here if ever required */
339 void x11_get_auth_from_authfile(struct X11Display
*disp
,
340 const char *authfilename
)
343 char *buf
, *ptr
, *str
[4];
345 int family
, protocol
;
346 int ideal_match
= FALSE
;
347 char *ourhostname
= get_hostname();
350 * Normally we should look for precisely the details specified in
351 * `disp'. However, there's an oddity when the display is local:
352 * displays like "localhost:0" usually have their details stored
353 * in a Unix-domain-socket record (even if there isn't actually a
354 * real Unix-domain socket available, as with OpenSSH's proxy X11
357 * This is apparently a fudge to get round the meaninglessness of
358 * "localhost" in a shared-home-directory context -- xauth entries
359 * for Unix-domain sockets already disambiguate this by storing
360 * the *local* hostname in the conveniently-blank hostname field,
361 * but IP "localhost" records couldn't do this. So, typically, an
362 * IP "localhost" entry in the auth database isn't present and if
363 * it were it would be ignored.
365 * However, we don't entirely trust that (say) Windows X servers
366 * won't rely on a straight "localhost" entry, bad idea though
367 * that is; so if we can't find a Unix-domain-socket entry we'll
368 * fall back to an IP-based entry if we can find one.
370 int localhost
= !disp
->unixdomain
&& sk_address_is_local(disp
->addr
);
372 authfp
= fopen(authfilename
, "rb");
376 /* Records in .Xauthority contain four strings of up to 64K each */
377 buf
= snewn(65537 * 4, char);
379 while (!ideal_match
) {
380 int c
, i
, j
, match
= FALSE
;
382 #define GET do { c = fgetc(authfp); if (c == EOF) goto done; c = (unsigned char)c; } while (0)
383 /* Expect a big-endian 2-byte number giving address family */
385 GET
; family
= (family
<< 8) | c
;
386 /* Then expect four strings, each composed of a big-endian 2-byte
387 * length field followed by that many bytes of data */
389 for (i
= 0; i
< 4; i
++) {
391 GET
; len
[i
] = (len
[i
] << 8) | c
;
393 for (j
= 0; j
< len
[i
]; j
++) {
401 * Now we have a full X authority record in memory. See
402 * whether it matches the display we're trying to
405 * The details we've just read should be interpreted as
408 * - 'family' is the network address family used to
409 * connect to the display. 0 means IPv4; 6 means IPv6;
410 * 256 means Unix-domain sockets.
412 * - str[0] is the network address itself. For IPv4 and
413 * IPv6, this is a string of binary data of the
414 * appropriate length (respectively 4 and 16 bytes)
415 * representing the address in big-endian format, e.g.
416 * 7F 00 00 01 means IPv4 localhost. For Unix-domain
417 * sockets, this is the host name of the machine on
418 * which the Unix-domain display resides (so that an
419 * .Xauthority file on a shared file system can contain
420 * authority entries for Unix-domain displays on
421 * several machines without them clashing).
423 * - str[1] is the display number. I've no idea why
424 * .Xauthority stores this as a string when it has a
425 * perfectly good integer format, but there we go.
427 * - str[2] is the authorisation method, encoded as its
428 * canonical string name (i.e. "MIT-MAGIC-COOKIE-1",
429 * "XDM-AUTHORIZATION-1" or something we don't
432 * - str[3] is the actual authorisation data, stored in
436 if (disp
->displaynum
< 0 || disp
->displaynum
!= atoi(str
[1]))
437 continue; /* not the one */
439 for (protocol
= 1; protocol
< lenof(x11_authnames
); protocol
++)
440 if (!strcmp(str
[2], x11_authnames
[protocol
]))
442 if (protocol
== lenof(x11_authnames
))
443 continue; /* don't recognise this protocol, look for another */
447 if (!disp
->unixdomain
&&
448 sk_addrtype(disp
->addr
) == ADDRTYPE_IPV4
) {
450 sk_addrcopy(disp
->addr
, buf
);
451 if (len
[0] == 4 && !memcmp(str
[0], buf
, 4)) {
453 /* If this is a "localhost" entry, note it down
454 * but carry on looking for a Unix-domain entry. */
455 ideal_match
= !localhost
;
460 if (!disp
->unixdomain
&&
461 sk_addrtype(disp
->addr
) == ADDRTYPE_IPV6
) {
463 sk_addrcopy(disp
->addr
, buf
);
464 if (len
[0] == 16 && !memcmp(str
[0], buf
, 16)) {
466 ideal_match
= !localhost
;
470 case 256: /* Unix-domain / localhost */
471 if ((disp
->unixdomain
|| localhost
)
472 && ourhostname
&& !strcmp(ourhostname
, str
[0]))
473 /* A matching Unix-domain socket is always the best
475 match
= ideal_match
= TRUE
;
480 /* Current best guess -- may be overridden if !ideal_match */
481 disp
->localauthproto
= protocol
;
482 sfree(disp
->localauthdata
); /* free previous guess, if any */
483 disp
->localauthdata
= snewn(len
[3], unsigned char);
484 memcpy(disp
->localauthdata
, str
[3], len
[3]);
485 disp
->localauthdatalen
= len
[3];
491 memset(buf
, 0, 65537 * 4);
496 static void x11_log(Plug p
, int type
, SockAddr addr
, int port
,
497 const char *error_msg
, int error_code
)
499 /* We have no interface to the logging module here, so we drop these. */
502 static int x11_closing(Plug plug
, const char *error_msg
, int error_code
,
505 struct X11Private
*pr
= (struct X11Private
*) plug
;
508 * We have no way to communicate down the forwarded connection,
509 * so if an error occurred on the socket, we just ignore it
510 * and treat it like a proper close.
517 static int x11_receive(Plug plug
, int urgent
, char *data
, int len
)
519 struct X11Private
*pr
= (struct X11Private
*) plug
;
521 if (sshfwd_write(pr
->c
, data
, len
) > 0) {
523 sk_set_frozen(pr
->s
, 1);
529 static void x11_sent(Plug plug
, int bufsize
)
531 struct X11Private
*pr
= (struct X11Private
*) plug
;
533 sshfwd_unthrottle(pr
->c
, bufsize
);
537 * When setting up X forwarding, we should send the screen number
538 * from the specified local display. This function extracts it from
539 * the display string.
541 int x11_get_screen_number(char *display
)
545 n
= strcspn(display
, ":");
548 n
= strcspn(display
, ".");
551 return atoi(display
+ n
+ 1);
555 * Called to set up the raw connection.
557 * Returns an error message, or NULL on success.
558 * also, fills the SocketsStructure
560 extern const char *x11_init(Socket
*s
, struct X11Display
*disp
, void *c
,
561 const char *peeraddr
, int peerport
,
564 static const struct plug_function_table fn_table
= {
573 struct X11Private
*pr
;
578 pr
= snew(struct X11Private
);
580 pr
->auth_protocol
= NULL
;
584 pr
->throttled
= pr
->throttle_override
= 0;
587 pr
->s
= *s
= new_connection(sk_addr_dup(disp
->addr
),
588 disp
->realhost
, disp
->port
,
589 0, 1, 0, 0, (Plug
) pr
, cfg
);
590 if ((err
= sk_socket_error(*s
)) != NULL
) {
596 * See if we can make sense of the peer address we were given.
601 4 == sscanf(peeraddr
, "%d.%d.%d.%d", i
+0, i
+1, i
+2, i
+3)) {
602 pr
->peer_ip
= (i
[0] << 24) | (i
[1] << 16) | (i
[2] << 8) | i
[3];
603 pr
->peer_port
= peerport
;
610 sk_set_private_ptr(*s
, pr
);
614 void x11_close(Socket s
)
616 struct X11Private
*pr
;
619 pr
= (struct X11Private
*) sk_get_private_ptr(s
);
620 if (pr
->auth_protocol
) {
621 sfree(pr
->auth_protocol
);
622 sfree(pr
->auth_data
);
630 void x11_unthrottle(Socket s
)
632 struct X11Private
*pr
;
635 pr
= (struct X11Private
*) sk_get_private_ptr(s
);
638 sk_set_frozen(s
, pr
->throttled
|| pr
->throttle_override
);
641 void x11_override_throttle(Socket s
, int enable
)
643 struct X11Private
*pr
;
646 pr
= (struct X11Private
*) sk_get_private_ptr(s
);
648 pr
->throttle_override
= enable
;
649 sk_set_frozen(s
, pr
->throttled
|| pr
->throttle_override
);
653 * Called to send data down the raw connection.
655 int x11_send(Socket s
, char *data
, int len
)
657 struct X11Private
*pr
;
660 pr
= (struct X11Private
*) sk_get_private_ptr(s
);
663 * Read the first packet.
665 while (len
> 0 && pr
->data_read
< 12)
666 pr
->firstpkt
[pr
->data_read
++] = (unsigned char) (len
--, *data
++);
667 if (pr
->data_read
< 12)
671 * If we have not allocated the auth_protocol and auth_data
672 * strings, do so now.
674 if (!pr
->auth_protocol
) {
675 pr
->auth_plen
= GET_16BIT(pr
->firstpkt
[0], pr
->firstpkt
+ 6);
676 pr
->auth_dlen
= GET_16BIT(pr
->firstpkt
[0], pr
->firstpkt
+ 8);
677 pr
->auth_psize
= (pr
->auth_plen
+ 3) & ~3;
678 pr
->auth_dsize
= (pr
->auth_dlen
+ 3) & ~3;
679 /* Leave room for a terminating zero, to make our lives easier. */
680 pr
->auth_protocol
= snewn(pr
->auth_psize
+ 1, char);
681 pr
->auth_data
= snewn(pr
->auth_dsize
, unsigned char);
685 * Read the auth_protocol and auth_data strings.
687 while (len
> 0 && pr
->data_read
< 12 + pr
->auth_psize
)
688 pr
->auth_protocol
[pr
->data_read
++ - 12] = (len
--, *data
++);
689 while (len
> 0 && pr
->data_read
< 12 + pr
->auth_psize
+ pr
->auth_dsize
)
690 pr
->auth_data
[pr
->data_read
++ - 12 -
691 pr
->auth_psize
] = (unsigned char) (len
--, *data
++);
692 if (pr
->data_read
< 12 + pr
->auth_psize
+ pr
->auth_dsize
)
696 * If we haven't verified the authorisation, do so now.
701 pr
->auth_protocol
[pr
->auth_plen
] = '\0'; /* ASCIZ */
702 err
= x11_verify(pr
->peer_ip
, pr
->peer_port
,
703 pr
->disp
, pr
->auth_protocol
,
704 pr
->auth_data
, pr
->auth_dlen
);
707 * If authorisation failed, construct and send an error
708 * packet, then terminate the connection.
713 unsigned char *reply
;
715 message
= dupprintf("%s X11 proxy: %s", appname
, err
);
716 msglen
= strlen(message
);
717 reply
= snewn(8 + msglen
+1 + 4, unsigned char); /* include zero */
718 msgsize
= (msglen
+ 3) & ~3;
719 reply
[0] = 0; /* failure */
720 reply
[1] = msglen
; /* length of reason string */
721 memcpy(reply
+ 2, pr
->firstpkt
+ 2, 4); /* major/minor proto vsn */
722 PUT_16BIT(pr
->firstpkt
[0], reply
+ 6, msgsize
>> 2);/* data len */
723 memset(reply
+ 8, 0, msgsize
);
724 memcpy(reply
+ 8, message
, msglen
);
725 sshfwd_write(pr
->c
, (char *)reply
, 8 + msgsize
);
734 * Now we know we're going to accept the connection. Strip
735 * the fake auth data, and optionally put real auth data in
739 char realauthdata
[64];
741 int authstrlen
= strlen(x11_authnames
[pr
->disp
->localauthproto
]);
742 int buflen
= 0; /* initialise to placate optimiser */
743 static const char zeroes
[4] = { 0,0,0,0 };
746 if (pr
->disp
->localauthproto
== X11_MIT
) {
747 assert(pr
->disp
->localauthdatalen
<= lenof(realauthdata
));
748 realauthlen
= pr
->disp
->localauthdatalen
;
749 memcpy(realauthdata
, pr
->disp
->localauthdata
, realauthlen
);
750 } else if (pr
->disp
->localauthproto
== X11_XDM
&&
751 pr
->disp
->localauthdatalen
== 16 &&
752 ((buf
= sk_getxdmdata(s
, &buflen
))!=0)) {
754 realauthlen
= (buflen
+12+7) & ~7;
755 assert(realauthlen
<= lenof(realauthdata
));
756 memset(realauthdata
, 0, realauthlen
);
757 memcpy(realauthdata
, pr
->disp
->localauthdata
, 8);
758 memcpy(realauthdata
+8, buf
, buflen
);
760 PUT_32BIT_MSB_FIRST(realauthdata
+8+buflen
, t
);
761 des_encrypt_xdmauth(pr
->disp
->localauthdata
+9,
762 (unsigned char *)realauthdata
,
766 /* implement other auth methods here if required */
768 PUT_16BIT(pr
->firstpkt
[0], pr
->firstpkt
+ 6, authstrlen
);
769 PUT_16BIT(pr
->firstpkt
[0], pr
->firstpkt
+ 8, realauthlen
);
771 sk_write(s
, (char *)pr
->firstpkt
, 12);
774 sk_write(s
, x11_authnames
[pr
->disp
->localauthproto
],
776 sk_write(s
, zeroes
, 3 & (-authstrlen
));
779 sk_write(s
, realauthdata
, realauthlen
);
780 sk_write(s
, zeroes
, 3 & (-realauthlen
));
787 * After initialisation, just copy data simply.
790 return sk_write(s
, data
, len
);