Improve socket error handling so that a socket error isn't an

automatic fatalbox(). Instead, the error is passed to the receiver
routine, which can decide just how fatal the problem really is.

[originally from svn r894]

network.h

@@ -8,10 +8,6 @@
  * send data without having to worry about blocking. The stuff
  * behind the abstraction takes care of selects and nonblocking
  * writes and all that sort of painful gubbins.
- * 
- * If urgent data comes in on a socket, the back end will read and
- * discard up to the urgent pointer, then read the urgent byte and
- * send _that_ to the receiver function with `urgent' set.
  */
 
 #ifndef PUTTY_NETWORK_H
@@ -19,6 +15,24 @@
 
 typedef struct Socket_tag *Socket;
 typedef struct SockAddr_tag *SockAddr;
+
+/*
+ * This is the function a client must register with each socket, to
+ * receive data coming in on that socket. The parameter `urgent'
+ * decides the meaning of `data' and `len':
+ * 
+ *  - urgent==0. `data' points to `len' bytes of perfectly ordinary
+ *    data.
+ * 
+ *  - urgent==1. `data' points to `len' bytes of data, which were
+ *    read from before an Urgent pointer.
+ * 
+ *  - urgent==2. `data' points to `len' bytes of data, the first of
+ *    which was the one at the Urgent mark.
+ * 
+ *  - urgent==3. An error has occurred on the socket. `data' points
+ *    to an error string, and `len' points to an error code.
+ */
 typedef int (*sk_receiver_t)(Socket s, int urgent, char *data, int len);
 
 void sk_init(void);		       /* called once at program startup */

raw.c

@@ -25,6 +25,11 @@ static void c_write (char *buf, int len) {
 }
 
 static int raw_receive (Socket s, int urgent, char *data, int len) {
+    if (urgent==3) {
+        /* A socket error has occurred. */
+        connection_fatal(data);
+        len = 0;
+    }
     if (!len) {
 	/* Connection has closed. */
 	sk_close(s);

rlogin.c

@@ -25,6 +25,11 @@ static void c_write (char *buf, int len) {
 }
 
 static int rlogin_receive (Socket s, int urgent, char *data, int len) {
+    if (urgent==3) {
+        /* A socket error has occurred. */
+        connection_fatal(data);
+        len = 0;
+    }
     if (!len) {
 	/* Connection has closed. */
 	sk_close(s);

ssh.c

@@ -1148,6 +1148,11 @@ static void ssh_gotdata(unsigned char *data, int datalen)
 }
 
 static int ssh_receive(Socket skt, int urgent, char *data, int len) {
+    if (urgent==3) {
+        /* A socket error has occurred. */
+        connection_fatal(data);
+        len = 0;
+    }
     if (!len) {
 	/* Connection has closed. */
 	ssh_state = SSH_STATE_CLOSED;

telnet.c

@@ -461,6 +461,11 @@ static void do_telnet_read (char *buf, int len) {
 }
 
 static int telnet_receive(Socket s, int urgent, char *data, int len) {
+    if (urgent==3) {
+        /* A socket error has occurred. */
+        connection_fatal(data);
+        len = 0;
+    }
     if (!len) {
 	/* Connection has closed. */
 	sk_close(s);

winnet.c

@@ -569,7 +569,11 @@ int select_result(WPARAM wParam, LPARAM lParam) {
 	return 1;		       /* boggle */
 
     if ((err = WSAGETSELECTERROR(lParam)) != 0) {
-	fatalbox(winsock_error_string(err));
+        /*
+         * An error has occurred on this socket. Pass it to the
+         * receiver function.
+         */
+        return s->receiver(s, 3, winsock_error_string(err), err);
     }
 
     noise_ultralight(lParam);
@@ -584,7 +588,7 @@ int select_result(WPARAM wParam, LPARAM lParam) {
 	    }
 	}
 	if (ret < 0) {
-	    fatalbox(winsock_error_string(err));
+	    return s->receiver(s, 3, winsock_error_string(err), err);
 	} else {
             int type = s->in_oob ? 2 : 0;
             s->in_oob = FALSE;

x11fwd.c

@@ -106,6 +106,14 @@ static int x11_verify(char *proto, unsigned char *data, int dlen) {
 static int x11_receive (Socket s, int urgent, char *data, int len) {
     struct X11Private *pr = (struct X11Private *)sk_get_private_ptr(s);
 
+    if (urgent==3) {
+        /*
+         * A socket error has occurred. We have no way to
+         * communicate this down the forwarded connection, so we'll
+         * just treat it like a proper close.
+         */
+        len = 0;
+    }
     if (!len) {
 	/* Connection has closed. */
         sshfwd_close(pr->c);