path: root/e-util/e-passwords.c

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*- */

/*
 * e-passwords.c
 *
 * Copyright (C) 2001 Ximian, Inc.
 */

/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 * USA.
 */

/*
 * This looks a lot more complicated than it is, and than you'd think
 * it would need to be.  There is however, method to the madness.
 *
 * The code most cope with being called from any thread at any time,
 * recursively from the main thread, and then serialising every
 * request so that sane and correct values are always returned, and
 * duplicate requests are never made.
 *
 * To this end, every call is marshalled and queued and a dispatch
 * method invoked until that request is satisfied.  If mainloop
 * recursion occurs, then the sub-call will necessarily return out of
 * order, but will not be processed out of order.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <string.h>
#include <libgnome/gnome-config.h>
#include <libgnome/gnome-i18n.h>
#include <gtk/gtkversion.h>
#include <gtk/gtkentry.h>
#include <gtk/gtkvbox.h>
#include <gtk/gtkcheckbutton.h>
#include <gtk/gtkmessagedialog.h>

#include "e-passwords.h"
#include "libedataserver/e-msgport.h"
#include "widgets/misc/e-error.h"

#ifndef ENABLE_THREADS
#define ENABLE_THREADS (1)
#endif

#ifdef ENABLE_THREADS
#include <pthread.h>

static pthread_t main_thread;
static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
#define LOCK() pthread_mutex_lock(&lock)
#define UNLOCK() pthread_mutex_unlock(&lock)
#else
#define LOCK()
#define UNLOCK()
#endif

struct _EPassMsg {
    EMsg msg;

    void (*dispatch)(struct _EPassMsg *);

    /* input */
    struct _GtkWindow *parent;  
    const char *component;
    const char *key;
    const char *title;
    const char *prompt;
    const char *oldpass;
    guint32 flags;

    /* output */
    gboolean *remember;
    char *password;

    /* work variables */
    GtkWidget *entry;
    GtkWidget *check;
    int ismain:1;
    int noreply:1;      /* supress replies; when calling
                 * dispatch functions from others */
};

typedef struct _EPassMsg EPassMsg;

static GHashTable *passwords = NULL;
static GtkDialog *password_dialog;
static EDList request_list = E_DLIST_INITIALISER(request_list);
static int idle_id;
static int ep_online_state = TRUE;

static char *decode_base64 (char *base64);
static int base64_encode_close(unsigned char *in, int inlen, gboolean break_lines, unsigned char *out, int *state, int *save);
static int base64_encode_step(unsigned char *in, int len, gboolean break_lines, unsigned char *out, int *state, int *save);

static gboolean
ep_idle_dispatch(void *data)
{
    EPassMsg *msg;

    /* As soon as a password window is up we stop; it will
       re-invoke us when it has been closed down */
    LOCK();
    while (password_dialog == NULL && (msg = (EPassMsg *)e_dlist_remhead(&request_list))) {
        UNLOCK();

        msg->dispatch(msg);

        LOCK();
    }

    idle_id = 0;
    UNLOCK();

    return FALSE;
}

static EPassMsg *
ep_msg_new(void (*dispatch)(EPassMsg *))
{
    EPassMsg *msg;

    e_passwords_init();

    msg = g_malloc0(sizeof(*msg));
    msg->dispatch = dispatch;
    msg->msg.reply_port = e_msgport_new();
#ifdef ENABLE_THREADS
    msg->ismain = pthread_self() == main_thread;
#else
    msg->ismain = TRUE;
#endif
    return msg;
}

static void
ep_msg_free(EPassMsg *msg)
{
    e_msgport_destroy(msg->msg.reply_port);
    g_free(msg->password);
    g_free(msg);
}

static void
ep_msg_send(EPassMsg *msg)
{
    int needidle = 0;

    LOCK();
    e_dlist_addtail(&request_list, (EDListNode *)&msg->msg);
    if (!idle_id) {
        if (!msg->ismain)
            idle_id = g_idle_add(ep_idle_dispatch, NULL);
        else
            needidle = 1;
    }
    UNLOCK();

    if (msg->ismain) {
        EPassMsg *m;

        if (needidle)
            ep_idle_dispatch(NULL);
        while ((m = (EPassMsg *)e_msgport_get(msg->msg.reply_port)) == NULL)
            g_main_context_iteration(NULL, TRUE);
        g_assert(m == msg);
    } else {
        e_msgport_wait(msg->msg.reply_port);
        g_assert(e_msgport_get(msg->msg.reply_port) == &msg->msg);
    }
}

/* the functions that actually do the work */
static void
ep_clear_passwords(EPassMsg *msg)
{
    char *path;

    path = g_strdup_printf ("/Evolution/Passwords-%s", msg->component);

    gnome_config_private_clean_section (path);
    gnome_config_private_sync_file ("/Evolution");

    g_free (path);

    if (!msg->noreply)
        e_msgport_reply(&msg->msg);
}

static gboolean
free_entry (gpointer key, gpointer value, gpointer user_data)
{
    g_free (key);
    memset (value, 0, strlen (value));
    g_free (value);
    return TRUE;
}

static void
ep_forget_passwords(EPassMsg *msg)
{
    void *it;
    char *key;

    it = gnome_config_private_init_iterator_sections("/Evolution");
    while ( (it = gnome_config_iterator_next(it, &key, NULL)) ) {
        if (0 == strncmp(key, "Passwords-", 10)) {
            char *section = g_strdup_printf("/Evolution/%s", key);

            gnome_config_private_clean_section (section);
            g_free(section);
        }
        g_free(key);
    }

    gnome_config_private_sync_file ("/Evolution");

    /* free up the session passwords */
    g_hash_table_foreach_remove (passwords, free_entry, NULL);

    if (!msg->noreply)
        e_msgport_reply(&msg->msg);
}

static char *
password_path (const char *component_name, const char *key)
{
    char *keycopy, *path;
    int i;
    keycopy = g_strdup (key);

    for (i = 0; i < strlen (keycopy); i ++)
        if (keycopy[i] == '/' || keycopy[i] =='=')
            keycopy[i] = '_';
    
    path = g_strdup_printf ("/Evolution/Passwords-%s/%s", component_name, keycopy);

    g_free (keycopy);

    return path;
}

static void
ep_remember_password(EPassMsg *msg)
{
    gpointer okey, value;
    char *path, *pass64;
    int len, state, save;

    if (g_hash_table_lookup_extended (passwords, msg->key, &okey, &value)) {
        /* add it to the on-disk cache of passwords */
        path = password_path (msg->component, okey);

        len = strlen (value);
        pass64 = g_malloc0 ((len + 2) * 4 / 3 + 1);
        state = save = 0;
        base64_encode_close (value, len, FALSE, pass64, &state, &save);

        gnome_config_private_set_string (path, pass64);
        g_free (path);
        g_free (pass64);

        /* now remove it from our session hash */
        g_hash_table_remove (passwords, msg->key);
        g_free (okey);
        g_free (value);

        gnome_config_private_sync_file ("/Evolution");
    }

    if (!msg->noreply)
        e_msgport_reply(&msg->msg);
}

static void
ep_forget_password (EPassMsg *msg)
{
    gpointer okey, value;
    char *path;

    if (g_hash_table_lookup_extended (passwords, msg->key, &okey, &value)) {
        g_hash_table_remove (passwords, msg->key);
        memset (value, 0, strlen (value));
        g_free (okey);
        g_free (value);
    }

    /* clear it in the on disk db */
    path = password_path (msg->component, msg->key);
    gnome_config_private_clean_key (path);
    gnome_config_private_sync_file ("/Evolution");
    g_free (path);
    
    if (!msg->noreply)
        e_msgport_reply(&msg->msg);
}

static void
ep_get_password (EPassMsg *msg)
{
    char *path, *passwd;
    char *encoded = NULL;

    passwd = g_hash_table_lookup (passwords, msg->key);
    if (passwd) {
        msg->password = g_strdup(passwd);
    } else {
        /* not part of the session hash, look it up in the on disk db */
        path = password_path (msg->component, msg->key);
        encoded = gnome_config_private_get_string_with_default (path, NULL);
        g_free (path);
        if (encoded) {
            msg->password = decode_base64 (encoded);
            g_free (encoded);
        }
    }

    if (!msg->noreply)
        e_msgport_reply(&msg->msg);
}

static void
ep_add_password (EPassMsg *msg)
{
    gpointer okey, value;

    if (g_hash_table_lookup_extended (passwords, msg->key, &okey, &value)) {
        g_hash_table_remove (passwords, msg->key);
        g_free (okey);
        g_free (value);
    }

    g_hash_table_insert (passwords, g_strdup (msg->key), g_strdup (msg->oldpass));

    if (!msg->noreply)
        e_msgport_reply(&msg->msg);
}

static void ep_ask_password(EPassMsg *msg);

static void
pass_response(GtkDialog *dialog, int response, void *data)
{
    EPassMsg *msg = data;
    int type = msg->flags & E_PASSWORDS_REMEMBER_MASK;
    EDList pending = E_DLIST_INITIALISER(pending);
    EPassMsg *mw, *mn;

    if (response == GTK_RESPONSE_OK) {
        msg->password = g_strdup(gtk_entry_get_text((GtkEntry *)msg->entry));

        if (type != E_PASSWORDS_REMEMBER_NEVER) {
            int noreply = msg->noreply;

            *msg->remember = gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (msg->check));

            msg->noreply = 1;

            if (*msg->remember || type == E_PASSWORDS_REMEMBER_FOREVER) {
                msg->oldpass = msg->password;
                ep_add_password(msg);
            }

            if (*msg->remember && type == E_PASSWORDS_REMEMBER_FOREVER)
                ep_remember_password(msg);

            msg->noreply = noreply;
        }
    }

    gtk_widget_destroy((GtkWidget *)dialog);
    password_dialog = NULL;

    /* ok, here things get interesting, we suck up any pending
     * operations on this specific password, and return the same
     * result or ignore other operations */

    LOCK();
    mw = (EPassMsg *)request_list.head;
    mn = (EPassMsg *)mw->msg.ln.next;
    while (mn) {
        if ((mw->dispatch == ep_forget_password
             || mw->dispatch == ep_get_password
             || mw->dispatch == ep_ask_password)
            && (strcmp(mw->component, msg->component) == 0
            && strcmp(mw->key, msg->key) == 0)) {
            e_dlist_remove((EDListNode *)mw);
            mw->password = g_strdup(msg->password);
            e_msgport_reply(&mw->msg);
        }
        mw = mn;
        mn = (EPassMsg *)mn->msg.ln.next;
    }
    UNLOCK();

    if (!msg->noreply)
        e_msgport_reply(&msg->msg);

    ep_idle_dispatch(NULL);
}

static void
ep_ask_password(EPassMsg *msg)
{
    GtkWidget *vbox;
    int type = msg->flags & E_PASSWORDS_REMEMBER_MASK;
    int noreply = msg->noreply;
    AtkObject *a11y;

    msg->noreply = 1;

    /*password_dialog = (GtkDialog *)e_error_new(msg->parent, "mail:ask-session-password", msg->prompt, NULL);*/
    password_dialog = (GtkDialog *)gtk_message_dialog_new (msg->parent,
                                   0,
                                   GTK_MESSAGE_QUESTION,
                                   GTK_BUTTONS_OK_CANCEL,
                                   "%s", msg->prompt);
    gtk_window_set_title(GTK_WINDOW(password_dialog), msg->title);

#if !GTK_CHECK_VERSION (2,4,0)
    gtk_dialog_set_has_separator(password_dialog, FALSE);
#endif
    gtk_dialog_set_default_response(password_dialog, GTK_RESPONSE_OK);

    vbox = gtk_vbox_new (FALSE, 6);
    gtk_widget_show (vbox);
    gtk_box_pack_start (GTK_BOX (GTK_DIALOG (password_dialog)->vbox), vbox, TRUE, FALSE, 0);
    gtk_container_set_border_width((GtkContainer *)vbox, 6);
    
    msg->entry = gtk_entry_new ();

    a11y = gtk_widget_get_accessible (msg->entry);
    atk_object_set_description (a11y, msg->prompt);
    gtk_entry_set_visibility ((GtkEntry *)msg->entry, !(msg->flags & E_PASSWORDS_SECRET));
    gtk_entry_set_activates_default((GtkEntry *)msg->entry, TRUE);
    gtk_box_pack_start (GTK_BOX (vbox), msg->entry, TRUE, FALSE, 3);
    gtk_widget_show (msg->entry);
    gtk_widget_grab_focus (msg->entry);
    
    if ((msg->flags & E_PASSWORDS_REPROMPT)) {
        ep_get_password(msg);
        if (msg->password) {
            gtk_entry_set_text ((GtkEntry *) msg->entry, msg->password);
            g_free (msg->password);
            msg->password = NULL;
        }
    }

    /* static password, shouldn't be remembered between sessions,
       but will be remembered within the session beyond our control */
    if (type != E_PASSWORDS_REMEMBER_NEVER) {
        msg->check = gtk_check_button_new_with_mnemonic(type == E_PASSWORDS_REMEMBER_FOREVER
                                ? _("_Remember this password")
                                : _("_Remember this password for the remainder of this session"));
        gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (msg->check), *msg->remember);
        gtk_box_pack_start (GTK_BOX (vbox), msg->check, TRUE, FALSE, 3);
        gtk_widget_show (msg->check);
    }
    
    msg->noreply = noreply;

    g_signal_connect(password_dialog, "response", G_CALLBACK (pass_response), msg);
    gtk_widget_show((GtkWidget *)password_dialog);
}


/**
 * e_passwords_init:
 *
 * Initializes the e_passwords routines. Must be called before any other
 * e_passwords_* function.
 **/
void
e_passwords_init (void)
{
    LOCK();

    if (!passwords) {
        /* create the per-session hash table */
        passwords = g_hash_table_new (g_str_hash, g_str_equal);
#ifdef ENABLE_THREADS
        main_thread = pthread_self();
#endif
    }

    UNLOCK();
}

/**
 * e_passwords_cancel:
 * 
 * Cancel any outstanding password operations and close any dialogues
 * currently being shown.
 **/
void
e_passwords_cancel(void)
{
    EPassMsg *msg;

    LOCK();
    while ((msg = (EPassMsg *)e_dlist_remhead(&request_list)))
        e_msgport_reply(&msg->msg);
    UNLOCK();

    if (password_dialog)
        gtk_widget_destroy((GtkWidget *)password_dialog);
}

/**
 * e_passwords_shutdown:
 *
 * Cleanup routine to call before exiting.
 **/
void
e_passwords_shutdown (void)
{
    /* shouldn't need this really - everything is synchronous */
    gnome_config_private_sync_file ("/Evolution");

    e_passwords_cancel();

    if (passwords) {
        /* and destroy our per session hash */
        g_hash_table_foreach_remove (passwords, free_entry, NULL);
        g_hash_table_destroy (passwords);
        passwords = NULL;
    }
}

/**
 * e_passwords_set_online:
 * @state: 
 * 
 * Set the offline-state of the application.  This is a work-around
 * for having the backends fully offline aware, and returns a
 * cancellation response instead of prompting for passwords.
 *
 * FIXME: This is not a permanent api, review post 2.0.
 **/
void
e_passwords_set_online(int state)
{
    ep_online_state = state;
    /* TODO: we could check that a request is open and close it, or maybe who cares */
}

/**
 * e_passwords_forget_passwords:
 *
 * Forgets all cached passwords, in memory and on disk.
 **/
void
e_passwords_forget_passwords (void)
{
    EPassMsg *msg = ep_msg_new(ep_forget_passwords);

    ep_msg_send(msg);
    ep_msg_free(msg);
}

/**
 * e_passwords_clear_passwords:
 *
 * Forgets all disk cached passwords for the component.
 **/
void
e_passwords_clear_passwords (const char *component_name)
{
    EPassMsg *msg = ep_msg_new(ep_clear_passwords);

    msg->component = component_name;
    ep_msg_send(msg);
    ep_msg_free(msg);
}

/**
 * e_passwords_remember_password:
 * @key: the key
 *
 * Saves the password associated with @key to disk.
 **/
void
e_passwords_remember_password (const char *component_name, const char *key)
{
    EPassMsg *msg;

    g_return_if_fail(component_name != NULL);
    g_return_if_fail(key != NULL);

    msg = ep_msg_new(ep_remember_password);

    msg->component = component_name;
    msg->key = key;

    ep_msg_send(msg);
    ep_msg_free(msg);
}

/**
 * e_passwords_forget_password:
 * @key: the key
 *
 * Forgets the password associated with @key, in memory and on disk.
 **/
void
e_passwords_forget_password (const char *component_name, const char *key)
{
    EPassMsg *msg;

    g_return_if_fail(component_name != NULL);
    g_return_if_fail(key != NULL);

    msg = ep_msg_new(ep_forget_password);

    msg->component = component_name;
    msg->key = key;

    ep_msg_send(msg);
    ep_msg_free(msg);
}

/**
 * e_passwords_get_password:
 * @key: the key
 *
 * Return value: the password associated with @key, or %NULL.  Caller
 * must free the returned password.
 **/
char *
e_passwords_get_password (const char *component_name, const char *key)
{
    EPassMsg *msg;
    char *passwd;

    g_return_val_if_fail(component_name != NULL, NULL);
    g_return_val_if_fail(key != NULL, NULL);

    msg = ep_msg_new(ep_get_password);

    msg->component = component_name;
    msg->key = key;

    ep_msg_send(msg);

    passwd = msg->password;
    msg->password = NULL;
    ep_msg_free(msg);

    return passwd;
}

/**
 * e_passwords_add_password:
 * @key: a key
 * @passwd: the password for @key
 *
 * This stores the @key/@passwd pair in the current session's password
 * hash.
 **/
void
e_passwords_add_password (const char *key, const char *passwd)
{
    EPassMsg *msg;

    g_return_if_fail(key != NULL);
    g_return_if_fail(passwd != NULL);

    msg = ep_msg_new(ep_add_password);
    msg->key = key;
    msg->oldpass = passwd;

    ep_msg_send(msg);
    ep_msg_free(msg);
}

/**
 * e_passwords_ask_password:
 * @title: title for the password dialog
 * @component_name: the name of the component for which we're storing
 * the password (e.g. Mail, Addressbook, etc.)
 * @key: key to store the password under
 * @prompt: prompt string
 * @secret: whether or not the password text should be ***ed out
 * @remember_type: whether or not to offer to remember the password,
 * and for how long.
 * @remember: on input, the default state of the remember checkbox.
 * on output, the state of the checkbox when the dialog was closed.
 * @parent: parent window of the dialog, or %NULL
 *
 * Asks the user for a password.
 *
 * Return value: the password, which the caller must free, or %NULL if
 * the user cancelled the operation. *@remember will be set if the
 * return value is non-%NULL and @remember_type is not
 * E_PASSWORDS_DO_NOT_REMEMBER.
 **/
char *
e_passwords_ask_password (const char *title, const char *component_name,
              const char *key,
              const char *prompt,
              EPasswordsRememberType type,
              gboolean *remember,
              GtkWindow *parent)
{
    char *passwd;
    EPassMsg *msg = ep_msg_new(ep_ask_password);

    if ((type & E_PASSWORDS_ONLINE) && !ep_online_state)
        return NULL;

    msg->title = title;
    msg->component = component_name;
    msg->key = key;
    msg->prompt = prompt;
    msg->flags = type;
    msg->remember = remember;
    msg->parent = parent;

    ep_msg_send(msg);
    passwd = msg->password;
    msg->password = NULL;
    ep_msg_free(msg);
    
    return passwd;
}



static char *base64_alphabet =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static unsigned char camel_mime_base64_rank[256] = {
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255, 62,255,255,255, 63,
     52, 53, 54, 55, 56, 57, 58, 59, 60, 61,255,255,255,  0,255,255,
    255,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
     15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,255,255,255,255,255,
    255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
     41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
};

/* call this when finished encoding everything, to
   flush off the last little bit */
static int
base64_encode_close(unsigned char *in, int inlen, gboolean break_lines, unsigned char *out, int *state, int *save)
{
    int c1, c2;
    unsigned char *outptr = out;

    if (inlen>0)
        outptr += base64_encode_step(in, inlen, break_lines, outptr, state, save);

    c1 = ((unsigned char *)save)[1];
    c2 = ((unsigned char *)save)[2];
    
    switch (((char *)save)[0]) {
    case 2:
        outptr[2] = base64_alphabet[ ( (c2 &0x0f) << 2 ) ];
        g_assert(outptr[2] != 0);
        goto skip;
    case 1:
        outptr[2] = '=';
    skip:
        outptr[0] = base64_alphabet[ c1 >> 2 ];
        outptr[1] = base64_alphabet[ c2 >> 4 | ( (c1&0x3) << 4 )];
        outptr[3] = '=';
        outptr += 4;
        break;
    }
    if (break_lines)
        *outptr++ = '\n';

    *save = 0;
    *state = 0;

    return outptr-out;
}

/*
  performs an 'encode step', only encodes blocks of 3 characters to the
  output at a time, saves left-over state in state and save (initialise to
  0 on first invocation).
*/
static int
base64_encode_step(unsigned char *in, int len, gboolean break_lines, unsigned char *out, int *state, int *save)
{
    register unsigned char *inptr, *outptr;

    if (len<=0)
        return 0;

    inptr = in;
    outptr = out;

    if (len + ((char *)save)[0] > 2) {
        unsigned char *inend = in+len-2;
        register int c1, c2, c3;
        register int already;

        already = *state;

        switch (((char *)save)[0]) {
        case 1: c1 = ((unsigned char *)save)[1]; goto skip1;
        case 2: c1 = ((unsigned char *)save)[1];
            c2 = ((unsigned char *)save)[2]; goto skip2;
        }
        
        /* yes, we jump into the loop, no i'm not going to change it, it's beautiful! */
        while (inptr < inend) {
            c1 = *inptr++;
        skip1:
            c2 = *inptr++;
        skip2:
            c3 = *inptr++;
            *outptr++ = base64_alphabet[ c1 >> 2 ];
            *outptr++ = base64_alphabet[ c2 >> 4 | ( (c1&0x3) << 4 ) ];
            *outptr++ = base64_alphabet[ ( (c2 &0x0f) << 2 ) | (c3 >> 6) ];
            *outptr++ = base64_alphabet[ c3 & 0x3f ];
            /* this is a bit ugly ... */
            if (break_lines && (++already)>=19) {
                *outptr++='\n';
                already = 0;
            }
        }

        ((char *)save)[0] = 0;
        len = 2-(inptr-inend);
        *state = already;
    }

    if (len>0) {
        register char *saveout;

        /* points to the slot for the next char to save */
        saveout = & (((char *)save)[1]) + ((char *)save)[0];

        /* len can only be 0 1 or 2 */
        switch(len) {
        case 2: *saveout++ = *inptr++;
        case 1: *saveout++ = *inptr++;
        }
        ((char *)save)[0]+=len;
    }

    return outptr-out;
}


/**
 * base64_decode_step: decode a chunk of base64 encoded data
 * @in: input stream
 * @len: max length of data to decode
 * @out: output stream
 * @state: holds the number of bits that are stored in @save
 * @save: leftover bits that have not yet been decoded
 *
 * Decodes a chunk of base64 encoded data
 **/
static int
base64_decode_step(unsigned char *in, int len, unsigned char *out, int *state, unsigned int *save)
{
    register unsigned char *inptr, *outptr;
    unsigned char *inend, c;
    register unsigned int v;
    int i;

    inend = in+len;
    outptr = out;

    /* convert 4 base64 bytes to 3 normal bytes */
    v=*save;
    i=*state;
    inptr = in;
    while (inptr<inend) {
        c = camel_mime_base64_rank[*inptr++];
        if (c != 0xff) {
            v = (v<<6) | c;
            i++;
            if (i==4) {
                *outptr++ = v>>16;
                *outptr++ = v>>8;
                *outptr++ = v;
                i=0;
            }
        }
    }

    *save = v;
    *state = i;

    /* quick scan back for '=' on the end somewhere */
    /* fortunately we can drop 1 output char for each trailing = (upto 2) */
    i=2;
    while (inptr>in && i) {
        inptr--;
        if (camel_mime_base64_rank[*inptr] != 0xff) {
            if (*inptr == '=')
                outptr--;
            i--;
        }
    }

    /* if i!= 0 then there is a truncation error! */
    return outptr-out;
}

static char *
decode_base64 (char *base64)
{
    char *plain, *pad = "==";
    int len, out, state, save;
    
    len = strlen (base64);
    plain = g_malloc0 (len);
    state = save = 0;
    out = base64_decode_step (base64, len, plain, &state, &save);
    if (len % 4) {
        base64_decode_step (pad, 4 - len % 4, plain + out,
                    &state, &save);
    }
    
    return plain;
}