Having created and used uxsel, it actually turns out to be

practically trivial to put all the pieces together and create a
working prototype of Unix PuTTY! It's missing a lot of things -
notably GUI request boxes for host keys and logfiles and so forth,
the Event Log, mid-session reconfiguration, session loading and
saving, sensible population of the character sets drop-down list and
probably other fiddly little things too - but it will put up a
config box and then create a GUI window containing an SSH connection
to the host you specified, so it's _basically_ there. Woo!

[originally from svn r3020]

unix/uxputty.c

@@ -0,0 +1,261 @@
+/*
+ * Unix PuTTY main program.
+ */
+
+#include <stdio.h>
+#include <assert.h>
+#include <termios.h>
+#include <unistd.h>
+
+#include "putty.h"
+#include "storage.h"
+
+/*
+ * FIXME: At least some of these functions should be replaced with
+ * GTK GUI error-box-type things.
+ * 
+ * In particular, all the termios-type things must go, and
+ * termios.h should disappear from the above #include list.
+ */
+void fatalbox(char *p, ...)
+{
+    va_list ap;
+    fprintf(stderr, "FATAL ERROR: ");
+    va_start(ap, p);
+    vfprintf(stderr, p, ap);
+    va_end(ap);
+    fputc('\n', stderr);
+    cleanup_exit(1);
+}
+void connection_fatal(void *frontend, char *p, ...)
+{
+    va_list ap;
+    fprintf(stderr, "FATAL ERROR: ");
+    va_start(ap, p);
+    vfprintf(stderr, p, ap);
+    va_end(ap);
+    fputc('\n', stderr);
+    cleanup_exit(1);
+}
+void cmdline_error(char *p, ...)
+{
+    va_list ap;
+    fprintf(stderr, "plink: ");
+    va_start(ap, p);
+    vfprintf(stderr, p, ap);
+    va_end(ap);
+    fputc('\n', stderr);
+    exit(1);
+}
+
+/*
+ * Clean up and exit.
+ */
+void cleanup_exit(int code)
+{
+    /*
+     * Clean up.
+     */
+    sk_cleanup();
+    random_save_seed();
+    exit(code);
+}
+
+void verify_ssh_host_key(void *frontend, char *host, int port, char *keytype,
+			 char *keystr, char *fingerprint)
+{
+    int ret;
+
+    static const char absentmsg[] =
+	"The server's host key is not cached. You have no guarantee\n"
+	"that the server is the computer you think it is.\n"
+	"The server's key fingerprint is:\n"
+	"%s\n"
+	"If you trust this host, enter \"y\" to add the key to\n"
+	"PuTTY's cache and carry on connecting.\n"
+	"If you want to carry on connecting just once, without\n"
+	"adding the key to the cache, enter \"n\".\n"
+	"If you do not trust this host, press Return to abandon the\n"
+	"connection.\n"
+	"Store key in cache? (y/n) ";
+
+    static const char wrongmsg[] =
+	"WARNING - POTENTIAL SECURITY BREACH!\n"
+	"The server's host key does not match the one PuTTY has\n"
+	"cached. This means that either the server administrator\n"
+	"has changed the host key, or you have actually connected\n"
+	"to another computer pretending to be the server.\n"
+	"The new key fingerprint is:\n"
+	"%s\n"
+	"If you were expecting this change and trust the new key,\n"
+	"enter \"y\" to update PuTTY's cache and continue connecting.\n"
+	"If you want to carry on connecting but without updating\n"
+	"the cache, enter \"n\".\n"
+	"If you want to abandon the connection completely, press\n"
+	"Return to cancel. Pressing Return is the ONLY guaranteed\n"
+	"safe choice.\n"
+	"Update cached key? (y/n, Return cancels connection) ";
+
+    static const char abandoned[] = "Connection abandoned.\n";
+
+    char line[32];
+
+    /*
+     * Verify the key.
+     */
+    ret = verify_host_key(host, port, keytype, keystr);
+
+    if (ret == 0)		       /* success - key matched OK */
+	return;
+
+    if (ret == 2) {		       /* key was different */
+	fprintf(stderr, wrongmsg, fingerprint);
+	fflush(stderr);
+    }
+    if (ret == 1) {		       /* key was absent */
+	fprintf(stderr, absentmsg, fingerprint);
+	fflush(stderr);
+    }
+
+    {
+	struct termios oldmode, newmode;
+	tcgetattr(0, &oldmode);
+	newmode = oldmode;
+	newmode.c_lflag |= ECHO | ISIG | ICANON;
+	tcsetattr(0, TCSANOW, &newmode);
+	line[0] = '\0';
+	read(0, line, sizeof(line) - 1);
+	tcsetattr(0, TCSANOW, &oldmode);
+    }
+
+    if (line[0] != '\0' && line[0] != '\r' && line[0] != '\n') {
+	if (line[0] == 'y' || line[0] == 'Y')
+	    store_host_key(host, port, keytype, keystr);
+    } else {
+	fprintf(stderr, abandoned);
+	cleanup_exit(0);
+    }
+}
+
+/*
+ * Ask whether the selected cipher is acceptable (since it was
+ * below the configured 'warn' threshold).
+ * cs: 0 = both ways, 1 = client->server, 2 = server->client
+ */
+void askcipher(void *frontend, char *ciphername, int cs)
+{
+    static const char msg[] =
+	"The first %scipher supported by the server is\n"
+	"%s, which is below the configured warning threshold.\n"
+	"Continue with connection? (y/n) ";
+    static const char abandoned[] = "Connection abandoned.\n";
+
+    char line[32];
+
+    fprintf(stderr, msg,
+	    (cs == 0) ? "" :
+	    (cs == 1) ? "client-to-server " : "server-to-client ",
+	    ciphername);
+    fflush(stderr);
+
+    {
+	struct termios oldmode, newmode;
+	tcgetattr(0, &oldmode);
+	newmode = oldmode;
+	newmode.c_lflag |= ECHO | ISIG | ICANON;
+	tcsetattr(0, TCSANOW, &newmode);
+	line[0] = '\0';
+	read(0, line, sizeof(line) - 1);
+	tcsetattr(0, TCSANOW, &oldmode);
+    }
+
+    if (line[0] == 'y' || line[0] == 'Y') {
+	return;
+    } else {
+	fprintf(stderr, abandoned);
+	cleanup_exit(0);
+    }
+}
+
+void old_keyfile_warning(void)
+{
+    static const char message[] =
+	"You are loading an SSH 2 private key which has an\n"
+	"old version of the file format. This means your key\n"
+	"file is not fully tamperproof. Future versions of\n"
+	"PuTTY may stop supporting this private key format,\n"
+	"so we recommend you convert your key to the new\n"
+	"format.\n"
+	"\n"
+	"Once the key is loaded into PuTTYgen, you can perform\n"
+	"this conversion simply by saving it again.\n";
+
+    fputs(message, stderr);
+}
+
+/*
+ * Another bunch of temporary stub functions. These ones will want
+ * removing by means of implementing them properly: libcharset
+ * should invent its own sensible format for codepage names and a
+ * means of enumerating them, and printer_enum needs to be dealt
+ * with somehow or other too.
+ */
+
+char *cp_name(int codepage)
+{
+    return "";
+}
+char *cp_enumerate(int index)
+{
+    return NULL;
+}
+int decode_codepage(char *cp_name)
+{
+    return -2;
+}
+
+printer_enum *printer_start_enum(int *nprinters_ptr) {
+    *nprinters_ptr = 0;
+    return NULL;
+}
+char *printer_get_name(printer_enum *pe, int i) { return NULL;
+}
+void printer_finish_enum(printer_enum *pe) { }
+
+Backend *select_backend(Config *cfg)
+{
+    int i;
+    Backend *back = NULL;
+    for (i = 0; backends[i].backend != NULL; i++)
+	if (backends[i].protocol == cfg->protocol) {
+	    back = backends[i].backend;
+	    break;
+	}
+    assert(back != NULL);
+    return back;
+}
+
+int cfgbox(Config *cfg)
+{
+    extern int do_config_box(const char *title, Config *cfg);
+    return do_config_box("PuTTY Configuration", cfg);
+}
+
+int main(int argc, char **argv)
+{
+    extern int pt_main(int argc, char **argv);
+    sk_init();
+    flags = FLAG_VERBOSE | FLAG_INTERACTIVE;
+    default_protocol = be_default_protocol;
+    /* Find the appropriate default port. */
+    {
+	int i;
+	default_port = 0; /* illegal */
+	for (i = 0; backends[i].backend != NULL; i++)
+	    if (backends[i].protocol == default_protocol) {
+		default_port = backends[i].backend->default_port;
+		break;
+	    }
+    }
+    return pt_main(argc, argv);
+}