Backends: notify ldisc when sendok becomes true. (NFC)

I've introduced a function ldisc_notify_sendok(), which backends
should call on their ldisc (if they have one) when anything changes
that might cause backend_sendok() to start returning true.

At the moment, the function does nothing. But in future, I'm going to
make ldisc start buffering typed-ahead input data not yet sent to the
backend, and then the effect of this function will be to trigger
flushing all that data into the backend.

Backends only have to call this function if sendok was previously
false: backends requiring no network connection stage (like pty and
serial) can safely return true from sendok, and in that case, they
don't also have to immediately call this function.

ldisc.c

@@ -139,6 +139,10 @@ void ldisc_echoedit_update(Ldisc *ldisc)
     seat_echoedit_update(ldisc->seat, ECHOING, EDITING);
 }
 
+void ldisc_check_sendok(Ldisc *ldisc)
+{
+}
+
 void ldisc_send(Ldisc *ldisc, const void *vbuf, int len, bool interactive)
 {
     const char *buf = (const char *)vbuf;

otherbackends/raw.c

@@ -17,6 +17,7 @@ struct Raw {
     size_t bufsize;
     Seat *seat;
     LogContext *logctx;
+    Ldisc *ldisc;
     bool sent_console_eof, sent_socket_eof, socket_connected;
 
     Conf *conf;
@@ -41,6 +42,8 @@ static void raw_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
                        error_code, raw->conf, raw->socket_connected);
     if (type == PLUGLOG_CONNECT_SUCCESS) {
         raw->socket_connected = true;
+        if (raw->ldisc)
+            ldisc_check_sendok(raw->ldisc);
         if (is_tempseat(raw->seat)) {
             Seat *ts = raw->seat;
             tempseat_flush(ts);
@@ -295,7 +298,8 @@ static bool raw_ldisc(Backend *be, int option)
 
 static void raw_provide_ldisc(Backend *be, Ldisc *ldisc)
 {
-    /* This is a stub. */
+    Raw *raw = container_of(be, Raw, backend);
+    raw->ldisc = ldisc;
 }
 
 static int raw_exitcode(Backend *be)

otherbackends/rlogin.c

@@ -22,6 +22,7 @@ struct Rlogin {
     int term_width, term_height;
     Seat *seat;
     LogContext *logctx;
+    Ldisc *ldisc;
 
     Conf *conf;
 
@@ -194,6 +195,8 @@ static void rlogin_startup(Rlogin *rlogin, int prompt_result,
     }
 
     rlogin->prompt = NULL;
+    if (rlogin->ldisc)
+        ldisc_check_sendok(rlogin->ldisc);
 }
 
 static const PlugVtable Rlogin_plugvt = {
@@ -413,7 +416,8 @@ static bool rlogin_ldisc(Backend *be, int option)
 
 static void rlogin_provide_ldisc(Backend *be, Ldisc *ldisc)
 {
-    /* This is a stub. */
+    Rlogin *rlogin = container_of(be, Rlogin, backend);
+    rlogin->ldisc = ldisc;
 }
 
 static int rlogin_exitcode(Backend *be)

otherbackends/supdup.c

@@ -71,6 +71,7 @@ struct supdup_tag
 
     Seat *seat;
     LogContext *logctx;
+    Ldisc *ldisc;
     int term_width, term_height;
 
     long long ttyopt;
@@ -565,6 +566,8 @@ static void supdup_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
                        supdup->conf, supdup->socket_connected);
     if (type == PLUGLOG_CONNECT_SUCCESS) {
         supdup->socket_connected = true;
+        if (supdup->ldisc)
+            ldisc_check_sendok(supdup->ldisc);
         if (is_tempseat(supdup->seat)) {
             Seat *ts = supdup->seat;
             tempseat_flush(ts);
@@ -893,6 +896,8 @@ static bool supdup_ldisc(Backend *be, int option)
 
 static void supdup_provide_ldisc(Backend *be, Ldisc *ldisc)
 {
+    Supdup *supdup = container_of(be, Supdup, backend);
+    supdup->ldisc = ldisc;
 }
 
 static int supdup_exitcode(Backend *be)

otherbackends/telnet.c

@@ -628,6 +628,8 @@ static void telnet_log(Plug *plug, PlugLogType type, SockAddr *addr, int port,
                        telnet->socket_connected);
     if (type == PLUGLOG_CONNECT_SUCCESS) {
         telnet->socket_connected = true;
+        if (telnet->ldisc)
+            ldisc_check_sendok(telnet->ldisc);
         if (is_tempseat(telnet->seat)) {
             Seat *ts = telnet->seat;
             tempseat_flush(ts);

pscp.c

@@ -58,6 +58,7 @@ const char *const appname = "PSCP";
 #define MAX_SCP_BUFSIZE 16384
 
 void ldisc_echoedit_update(Ldisc *ldisc) { }
+void ldisc_check_sendok(Ldisc *ldisc) { }
 
 static size_t pscp_output(Seat *, bool is_stderr, const void *, size_t);
 static bool pscp_eof(Seat *);

psftp.c

@@ -2448,6 +2448,7 @@ int do_sftp(int mode, int modeflags, char *batchfile)
 static bool verbose = false;
 
 void ldisc_echoedit_update(Ldisc *ldisc) { }
+void ldisc_check_sendok(Ldisc *ldisc) { }
 
 /*
  * Receive a block of data from the SSH link. Block until all data

putty.h

@@ -2055,6 +2055,7 @@ void ldisc_configure(Ldisc *, Conf *);
 void ldisc_free(Ldisc *);
 void ldisc_send(Ldisc *, const void *buf, int len, bool interactive);
 void ldisc_echoedit_update(Ldisc *);
+void ldisc_check_sendok(Ldisc *);
 
 /*
  * Exports from sshrand.c.

ssh.h

@@ -397,6 +397,7 @@ LogContext *ssh_get_logctx(Ssh *ssh);
 void ssh_throttle_conn(Ssh *ssh, int adjust);
 void ssh_got_exitcode(Ssh *ssh, int status);
 void ssh_ldisc_update(Ssh *ssh);
+void ssh_check_sendok(Ssh *ssh);
 void ssh_got_fallback_cmd(Ssh *ssh);
 bool ssh_is_bare(Ssh *ssh);
 

ssh/connection1.c

@@ -775,6 +775,8 @@ static void ssh1_set_wants_user_input(ConnectionLayer *cl, bool wanted)
 
     s->want_user_input = wanted;
     s->finished_setup = true;
+    if (wanted)
+        ssh_check_sendok(s->ppl.ssh);
 }
 
 static bool ssh1_connection_want_user_input(PacketProtocolLayer *ppl)

ssh/connection2.c

@@ -1709,6 +1709,8 @@ static void ssh2_set_wants_user_input(ConnectionLayer *cl, bool wanted)
         container_of(cl, struct ssh2_connection_state, cl);
 
     s->want_user_input = wanted;
+    if (wanted)
+        ssh_check_sendok(s->ppl.ssh);
 }
 
 static bool ssh2_connection_want_user_input(PacketProtocolLayer *ppl)

ssh/server.c

@@ -244,6 +244,8 @@ Conf *make_ssh_server_conf(void)
     return conf;
 }
 
+void ssh_check_sendok(Ssh *ssh) {}
+
 static const PlugVtable ssh_server_plugvt = {
     .log = server_socket_log,
     .closing = server_closing,

ssh/ssh.c

@@ -1156,6 +1156,14 @@ static bool ssh_sendok(Backend *be)
     return ssh->base_layer && ssh_ppl_want_user_input(ssh->base_layer);
 }
 
+void ssh_check_sendok(Ssh *ssh)
+{
+    /* Called when the connection layer might have caused ssh_sendok
+     * to start returning true */
+    if (ssh->ldisc)
+        ldisc_check_sendok(ssh->ldisc);
+}
+
 void ssh_ldisc_update(Ssh *ssh)
 {
     /* Called when the connection layer wants to propagate an update