Make new_error_socket() into a printf-style function.

Almost all the call sites were doing a cumbersome dupprintf-use-free
cycle to get a formatted message into an ErrorSocket anyway, so it
seems more sensible to give them an easier way of doing so.

The few call sites that were passing a constant string literal
_shouldn't_ have been - they'll be all the better for adding a
strerror suffix to the message they were previously giving!

Recipe

@@ -270,7 +270,7 @@ MISC     = misc marshal
 MISCNET  = timing callback MISC version settings tree234 proxy CONF be_misc
 WINMISC  = MISCNET winstore winnet winhandl cmdline windefs winmisc winproxy
          + wintime winhsock errsock winsecur winucs miscucs
-UXMISC   = MISCNET uxstore uxsel uxnet uxpeer uxmisc uxproxy time
+UXMISC   = MISCNET uxstore uxsel uxnet uxpeer uxmisc uxproxy errsock time
 
 # import.c and dependencies, for PuTTYgen-like utilities that have to
 # load foreign key files.

errsock.c

@@ -56,11 +56,23 @@ static const SocketVtable ErrorSocket_sockvt = {
     sk_error_peer_info,
 };
 
-Socket *new_error_socket(const char *errmsg, Plug *plug)
+static Socket *new_error_socket_internal(char *errmsg, Plug *plug)
 {
     ErrorSocket *es = snew(ErrorSocket);
     es->sock.vt = &ErrorSocket_sockvt;
     es->plug = plug;
-    es->error = dupstr(errmsg);
+    es->error = errmsg;
     return &es->sock;
 }
+
+Socket *new_error_socket_fmt(Plug *plug, const char *fmt, ...)
+{
+    va_list ap;
+    char *msg;
+
+    va_start(ap, fmt);
+    msg = dupvprintf(fmt, ap);
+    va_end(ap);
+
+    return new_error_socket_internal(msg, plug);
+}

network.h

@@ -220,7 +220,7 @@ char *get_hostname(void);
  * Trivial socket implementation which just stores an error. Found in
  * errsock.c.
  */
-Socket *new_error_socket(const char *errmsg, Plug *plug);
+Socket *new_error_socket_fmt(Plug *plug, const char *fmt, ...);
 
 /*
  * Trivial plug that does absolutely nothing. Found in nullplug.c.

windows/winnpc.c

@@ -23,7 +23,6 @@ Socket *new_named_pipe_client(const char *pipename, Plug *plug)
     HANDLE pipehandle;
     PSID usersid, pipeowner;
     PSECURITY_DESCRIPTOR psd;
-    char *err;
     Socket *ret;
 
     assert(strncmp(pipename, "\\\\.\\pipe\\", 9) == 0);
@@ -38,11 +37,9 @@ Socket *new_named_pipe_client(const char *pipename, Plug *plug)
             break;
 
         if (GetLastError() != ERROR_PIPE_BUSY) {
-            err = dupprintf("Unable to open named pipe '%s': %s",
-                            pipename, win_strerror(GetLastError()));
-            ret = new_error_socket(err, plug);
-            sfree(err);
-            return ret;
+            return new_error_socket_fmt(
+                plug, "Unable to open named pipe '%s': %s",
+                pipename, win_strerror(GetLastError()));
         }
 
         /*
@@ -53,41 +50,33 @@ Socket *new_named_pipe_client(const char *pipename, Plug *plug)
          * take excessively long.)
          */
         if (!WaitNamedPipe(pipename, NMPWAIT_USE_DEFAULT_WAIT)) {
-            err = dupprintf("Error waiting for named pipe '%s': %s",
-                            pipename, win_strerror(GetLastError()));
-            ret = new_error_socket(err, plug);
-            sfree(err);
-            return ret;
+            return new_error_socket_fmt(
+                plug, "Error waiting for named pipe '%s': %s",
+                pipename, win_strerror(GetLastError()));
         }
     }
 
     if ((usersid = get_user_sid()) == NULL) {
         CloseHandle(pipehandle);
-        err = dupprintf("Unable to get user SID");
-        ret = new_error_socket(err, plug);
-        sfree(err);
-        return ret;
+        return new_error_socket_fmt(
+            plug, "Unable to get user SID: %s", win_strerror(GetLastError()));
     }
 
     if (p_GetSecurityInfo(pipehandle, SE_KERNEL_OBJECT,
                           OWNER_SECURITY_INFORMATION,
                           &pipeowner, NULL, NULL, NULL,
                           &psd) != ERROR_SUCCESS) {
-        err = dupprintf("Unable to get named pipe security information: %s",
-                        win_strerror(GetLastError()));
-        ret = new_error_socket(err, plug);
-        sfree(err);
         CloseHandle(pipehandle);
-        return ret;
+        return new_error_socket_fmt(
+            plug, "Unable to get named pipe security information: %s",
+            win_strerror(GetLastError()));
     }
 
     if (!EqualSid(pipeowner, usersid)) {
-        err = dupprintf("Owner of named pipe '%s' is not us", pipename);
-        ret = new_error_socket(err, plug);
-        sfree(err);
         CloseHandle(pipehandle);
         LocalFree(psd);
-        return ret;
+        return new_error_socket_fmt(
+            plug, "Owner of named pipe '%s' is not us", pipename);
     }
 
     LocalFree(psd);

windows/winproxy.c

@@ -50,30 +50,30 @@ Socket *platform_new_connection(SockAddr *addr, const char *hostname,
     sa.lpSecurityDescriptor = NULL;    /* default */
     sa.bInheritHandle = TRUE;
     if (!CreatePipe(&us_from_cmd, &cmd_to_us, &sa, 0)) {
-	Socket *ret =
-            new_error_socket("Unable to create pipes for proxy command", plug);
         sfree(cmd);
-	return ret;
+	return new_error_socket_fmt(
+            plug, "Unable to create pipes for proxy command: %s",
+            win_strerror(GetLastError()));
     }
 
     if (!CreatePipe(&cmd_from_us, &us_to_cmd, &sa, 0)) {
-	Socket *ret =
-            new_error_socket("Unable to create pipes for proxy command", plug);
         sfree(cmd);
 	CloseHandle(us_from_cmd);
 	CloseHandle(cmd_to_us);
-	return ret;
+	return new_error_socket_fmt(
+            plug, "Unable to create pipes for proxy command: %s",
+            win_strerror(GetLastError()));
     }
 
     if (!CreatePipe(&us_from_cmd_err, &cmd_err_to_us, &sa, 0)) {
-        Socket *ret = new_error_socket
-            ("Unable to create pipes for proxy command", plug);
         sfree(cmd);
         CloseHandle(us_from_cmd);
         CloseHandle(cmd_to_us);
         CloseHandle(us_to_cmd);
         CloseHandle(cmd_from_us);
-        return ret;
+        return new_error_socket_fmt(
+            plug, "Unable to create pipes for proxy command: %s",
+            win_strerror(GetLastError()));
     }
 
     SetHandleInformation(us_to_cmd, HANDLE_FLAG_INHERIT, 0);