mbfilter_utf7imap.c

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/*
 * "streamable kanji code filter and converter"
 * Copyright (c) 1998-2002 HappySize, Inc. All rights reserved.
 *
 * LICENSE NOTICES
 *
 * This file is part of "streamable kanji code filter and converter",
 * which is distributed under the terms of GNU Lesser General Public
 * License (version 2) as published by the Free Software Foundation.
 *
 * This software 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with "streamable kanji code filter and converter";
 * if not, write to the Free Software Foundation, Inc., 59 Temple Place,
 * Suite 330, Boston, MA  02111-1307  USA
 *
 * The author of this file:
 *
 */
/*
 * The source code included in this file was separated from mbfilter.c
 * by moriyoshi koizumi <moriyoshi@php.net> on 4 dec 2002.
 *
 */
 
/* Modified UTF-7 used for 'international mailbox names' in the IMAP protocol
 * Also known as mUTF-7
 * Defined in RFC 3501 5.1.3 (https://tools.ietf.org/html/rfc3501)
 *
 * Quoting from the RFC:
 *
 ***********************************************************************
 * In modified UTF-7, printable US-ASCII characters, except for "&",
 * represent themselves; that is, characters with octet values 0x20-0x25
 * and 0x27-0x7e. The character "&" (0x26) is represented by the
 * two-octet sequence "&-".
 *
 * All other characters (octet values 0x00-0x1f and 0x7f-0xff) are
 * represented in modified BASE64, with a further modification from
 * UTF-7 that "," is used instead of "/". Modified BASE64 MUST NOT be
 * used to represent any printing US-ASCII character which can represent
 * itself.
 *
 * "&" is used to shift to modified BASE64 and "-" to shift back to
 * US-ASCII. There is no implicit shift from BASE64 to US-ASCII, and
 * null shifts ("-&" while in BASE64; note that "&-" while in US-ASCII
 * means "&") are not permitted.  However, all names start in US-ASCII,
 * and MUST end in US-ASCII; that is, a name that ends with a non-ASCII
 * ISO-10646 character MUST end with a "-").
 ***********************************************************************
 *
 * The purpose of all this is: 1) to keep all parts of IMAP messages 7-bit clean,
 * 2) to avoid giving special treatment to +, /, \, and ~, since these are
 * commonly used in mailbox names, and 3) to ensure there is only one
 * representation of any mailbox name (vanilla UTF-7 does allow multiple
 * representations of the same string, by Base64-encoding characters which
 * could have been included as ASCII literals.)
 *
 * RFC 2152 also applies, since it defines vanilla UTF-7 (minus IMAP modifications)
 * The following paragraph is notable:
 *
 ***********************************************************************
 * Unicode is encoded using Modified Base64 by first converting Unicode
 * 16-bit quantities to an octet stream (with the most significant octet first).
 * Surrogate pairs (UTF-16) are converted by treating each half of the pair as
 * a separate 16 bit quantity (i.e., no special treatment). Text with an odd
 * number of octets is ill-formed. ISO 10646 characters outside the range
 * addressable via surrogate pairs cannot be encoded.
 ***********************************************************************
 *
 * So after reversing the modified Base64 encoding on an encoded section,
 * the contents are interpreted as UTF-16BE. */
 
#include "mbfilter.h"
#include "mbfilter_utf7imap.h"
#include "utf7_helper.h"
 
static int mbfl_filt_conv_wchar_utf7imap_flush(mbfl_convert_filter *filter);
static int mbfl_filt_conv_utf7imap_wchar_flush(mbfl_convert_filter *filter);
static size_t mb_utf7imap_to_wchar(unsigned char **in, size_t *in_len, uint32_t *buf, size_t bufsize, unsigned int *state);
static void mb_wchar_to_utf7imap(uint32_t *in, size_t len, mb_convert_buf *buf, bool end);
static bool mb_check_utf7imap(unsigned char *in, size_t in_len);
 
static const char *mbfl_encoding_utf7imap_aliases[] = {"mUTF-7", NULL};
 
const mbfl_encoding mbfl_encoding_utf7imap = {
    mbfl_no_encoding_utf7imap,
    "UTF7-IMAP",
    NULL,
    mbfl_encoding_utf7imap_aliases,
    NULL,
    0,
    &vtbl_utf7imap_wchar,
    &vtbl_wchar_utf7imap,
    mb_utf7imap_to_wchar,
    mb_wchar_to_utf7imap,
    mb_check_utf7imap,
    NULL,
};
 
const struct mbfl_convert_vtbl vtbl_utf7imap_wchar = {
    mbfl_no_encoding_utf7imap,
    mbfl_no_encoding_wchar,
    mbfl_filt_conv_common_ctor,
    NULL,
    mbfl_filt_conv_utf7imap_wchar,
    mbfl_filt_conv_utf7imap_wchar_flush,
    NULL,
};
 
const struct mbfl_convert_vtbl vtbl_wchar_utf7imap = {
    mbfl_no_encoding_wchar,
    mbfl_no_encoding_utf7imap,
    mbfl_filt_conv_common_ctor,
    NULL,
    mbfl_filt_conv_wchar_utf7imap,
    mbfl_filt_conv_wchar_utf7imap_flush,
    NULL,
};
 
#define CK(statement)   do { if ((statement) < 0) return (-1); } while (0)
 
int mbfl_filt_conv_utf7imap_wchar(int c, mbfl_convert_filter *filter)
{
    int s, n = -1;
 
    if (filter->status != 0) { /* Modified Base64 */
        if (c >= 'A' && c <= 'Z') {
            n = c - 65;
        } else if (c >= 'a' && c <= 'z') {
            n = c - 71;
        } else if (c >= '0' && c <= '9') {
            n = c + 4;
        } else if (c == '+') {
            n = 62;
        } else if (c == ',') {
            n = 63;
        }
 
        if (n < 0 || n > 63) {
            if (c == '-') {
                if (filter->status == 1) { /* "&-" -> "&" */
                    filter->cache = filter->status = 0;
                    CK((*filter->output_function)('&', filter->data));
                } else if (filter->cache) {
                    /* Base64-encoded section ended abruptly, with partially encoded characters,
                     * or it could be that it ended on the first half of a surrogate pair */
                    filter->cache = filter->status = 0;
                    CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
                } else {
                    /* Base64-encoded section properly terminated by - */
                    filter->cache = filter->status = 0;
                }
            } else { /* illegal character */
                filter->cache = filter->status = 0;
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
            return 0;
        }
    }
 
    switch (filter->status) {
    /* directly encoded characters */
    case 0:
        if (c == '&') { /* shift character */
            filter->status++;
        } else if (c >= 0x20 && c <= 0x7E) { /* ASCII */
            CK((*filter->output_function)(c, filter->data));
        } else { /* illegal character */
            CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
        }
        break;
 
    /* decode Modified Base64 */
    case 1:
    case 2:
        filter->cache |= n << 10;
        filter->status = 3;
        break;
    case 3:
        filter->cache |= n << 4;
        filter->status = 4;
        break;
    case 4:
        s = ((n >> 2) & 0xf) | (filter->cache & 0xffff);
        n = (n & 0x3) << 14;
        filter->status = 5;
        if (s >= 0xd800 && s < 0xdc00) {
            /* 1st part of surrogate pair */
            s = (((s & 0x3ff) << 16) + 0x400000) | n;
            filter->cache = s;
        } else if (s >= 0xdc00 && s < 0xe000) {
            /* 2nd part of surrogate pair */
            if (filter->cache & 0xfff0000) {
                s &= 0x3ff;
                s |= (filter->cache & 0xfff0000) >> 6;
                filter->cache = n;
                CK((*filter->output_function)(s, filter->data));
            } else { /* illegal character */
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
        } else {
            filter->cache = n;
            /* Characters which can be expressed as literal, ASCII characters
             * should not be Base64-encoded */
            if (s < 0x20 || s > 0x7E || s == '&') {
                CK((*filter->output_function)(s, filter->data));
            } else {
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
        }
        break;
 
    case 5:
        filter->cache |= n << 8;
        filter->status = 6;
        break;
    case 6:
        filter->cache |= n << 2;
        filter->status = 7;
        break;
    case 7:
        s = ((n >> 4) & 0x3) | (filter->cache & 0xffff);
        n = (n & 0xf) << 12;
        filter->status = 8;
        if (s >= 0xd800 && s < 0xdc00) {
            s = (((s & 0x3ff) << 16) + 0x400000) | n;
            filter->cache = s;
        } else if (s >= 0xdc00 && s < 0xe000) {
            if (filter->cache & 0xfff0000) {
                s &= 0x3ff;
                s |= (filter->cache & 0xfff0000) >> 6;
                filter->cache = n;
                CK((*filter->output_function)(s, filter->data));
            } else { /* illegal character */
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
        } else {
            filter->cache = n;
            /* Characters which can be expressed as literal, ASCII characters
             * should not be Base64-encoded */
            if (s < 0x20 || s > 0x7E || s == '&') {
                CK((*filter->output_function)(s, filter->data));
            } else {
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
        }
        break;
 
    case 8:
        filter->cache |= n << 6;
        filter->status = 9;
        break;
    case 9:
        s = n | (filter->cache & 0xffff);
        filter->status = 2;
        if (s >= 0xd800 && s < 0xdc00) {
            s = (((s & 0x3ff) << 16) + 0x400000);
            filter->cache = s;
        } else if (s >= 0xdc00 && s < 0xe000) {
            if (filter->cache & 0xfff0000) {
                s &= 0x3ff;
                s |= (filter->cache & 0xfff0000) >> 6;
                filter->cache = 0;
                CK((*filter->output_function)(s, filter->data));
            } else { /* illegal character */
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
        } else {
            filter->cache = 0;
            /* Characters which can be expressed as literal, ASCII characters
             * should not be Base64-encoded */
            if (s < 0x20 || s > 0x7E || s == '&') {
                CK((*filter->output_function)(s, filter->data));
            } else {
                CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
            }
        }
        break;
 
        EMPTY_SWITCH_DEFAULT_CASE();
    }
 
    return 0;
}
 
static int mbfl_filt_conv_utf7imap_wchar_flush(mbfl_convert_filter *filter)
{
    if (filter->status) {
        /* It is illegal for a UTF-7 IMAP string to end in a Base-64 encoded
         * section. It should always change back to ASCII before the end. */
        (*filter->output_function)(MBFL_BAD_INPUT, filter->data);
        filter->status = 0;
    }
 
    if (filter->flush_function) {
        (*filter->flush_function)(filter->data);
    }
 
    return 0;
}
 
static const unsigned char mbfl_utf7imap_base64_table[] =
{
 /* 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', */
   0x41,0x42,0x43,0x44,0x45,0x46,0x47,0x48,0x49,0x4a,0x4b,0x4c,0x4d,
 /* 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', */
   0x4e,0x4f,0x50,0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58,0x59,0x5a,
 /* 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', */
   0x61,0x62,0x63,0x64,0x65,0x66,0x67,0x68,0x69,0x6a,0x6b,0x6c,0x6d,
 /* 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', */
   0x6e,0x6f,0x70,0x71,0x72,0x73,0x74,0x75,0x76,0x77,0x78,0x79,0x7a,
 /* '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', ',', '\0' */
   0x30,0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x2b,0x2c,0x00
};
 
int mbfl_filt_conv_wchar_utf7imap(int c, mbfl_convert_filter *filter)
{
    int n = 0, s;
 
    if (c == '&') {
        n = 1;
    } else if ((c >= 0x20 && c <= 0x7e) || c == 0) {
        n = 2;
    } else if (c >= 0 && c < MBFL_WCSPLANE_UCS2MAX) {
        ;
    } else if (c >= MBFL_WCSPLANE_SUPMIN && c < MBFL_WCSPLANE_SUPMAX) {
        s = ((c >> 10) - 0x40) | 0xd800;
        CK((*filter->filter_function)(s, filter));
        s = (c & 0x3ff) | 0xdc00;
        CK((*filter->filter_function)(s, filter));
        return 0;
    } else {
        CK(mbfl_filt_conv_illegal_output(c, filter));
        return 0;
    }
 
    switch (filter->status) {
    case 0:
        if (n != 0) {  /* directly encode characters */
            CK((*filter->output_function)(c, filter->data));
            if (n == 1) {
                CK((*filter->output_function)(0x2d, filter->data));        /* '-' */
            }
        } else {    /* Modified Base64 */
            CK((*filter->output_function)(0x26, filter->data));        /* '&' */
            filter->status = 1;
            filter->cache = c;
        }
        break;
 
    /* encode Modified Base64 */
    case 1:
        s = filter->cache;
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 10) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 4) & 0x3f], filter->data));
        if (n != 0) {
            CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s << 2) & 0x3c], filter->data));
            CK((*filter->output_function)('-', filter->data));
            CK((*filter->output_function)(c, filter->data));
            if (n == 1) {
                CK((*filter->output_function)('-', filter->data));
            }
            filter->status = 0;
        } else {
            filter->status = 2;
            filter->cache = ((s & 0xf) << 16) | c;
        }
        break;
 
    case 2:
        s = filter->cache;
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 14) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 8) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 2) & 0x3f], filter->data));
        if (n != 0) {
            CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s << 4) & 0x30], filter->data));
            CK((*filter->output_function)('-', filter->data));
            CK((*filter->output_function)(c, filter->data));
            if (n == 1) {
                CK((*filter->output_function)('-', filter->data));
            }
            filter->status = 0;
        } else {
            filter->status = 3;
            filter->cache = ((s & 0x3) << 16) | c;
        }
        break;
 
    case 3:
        s = filter->cache;
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 12) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(s >> 6) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[s & 0x3f], filter->data));
        if (n != 0) {
            CK((*filter->output_function)('-', filter->data));
            CK((*filter->output_function)(c, filter->data));
            if (n == 1) {
                CK((*filter->output_function)('-', filter->data));
            }
            filter->status = 0;
        } else {
            filter->status = 1;
            filter->cache = c;
        }
        break;
 
        EMPTY_SWITCH_DEFAULT_CASE();
    }
 
    return 0;
}
 
static int mbfl_filt_conv_wchar_utf7imap_flush(mbfl_convert_filter *filter)
{
    int status = filter->status, cache = filter->cache;
    filter->status = filter->cache = 0;
 
    /* flush fragments */
    switch (status) {
    case 1:
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 10) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 4) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache << 2) & 0x3c], filter->data));
        CK((*filter->output_function)('-', filter->data));
        break;
 
    case 2:
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 14) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 8) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 2) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache << 4) & 0x30], filter->data));
        CK((*filter->output_function)('-', filter->data));
        break;
 
    case 3:
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 12) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[(cache >> 6) & 0x3f], filter->data));
        CK((*filter->output_function)(mbfl_utf7imap_base64_table[cache & 0x3f], filter->data));
        CK((*filter->output_function)('-', filter->data));
        break;
    }
 
    return 0;
}
 
static inline bool is_base64_end(unsigned char c)
{
    return c >= DASH;
}
 
static unsigned char decode_base64(unsigned char c)
{
    if (c >= 'A' && c <= 'Z') {
        return c - 65;
    } else if (c >= 'a' && c <= 'z') {
        return c - 71;
    } else if (c >= '0' && c <= '9') {
        return c + 4;
    } else if (c == '+') {
        return 62;
    } else if (c == ',') {
        return 63;
    } else if (c == '-') {
        return DASH;
    }
    return ILLEGAL;
}
 
static uint32_t* handle_utf16_cp(uint16_t cp, uint32_t *out, uint16_t *surrogate1)
{
retry:
    if (*surrogate1) {
        if (cp >= 0xDC00 && cp <= 0xDFFF) {
            *out++ = ((*surrogate1 & 0x3FF) << 10) + (cp & 0x3FF) + 0x10000;
            *surrogate1 = 0;
        } else {
            *out++ = MBFL_BAD_INPUT;
            *surrogate1 = 0;
            goto retry;
        }
    } else if (cp >= 0xD800 && cp <= 0xDBFF) {
        *surrogate1 = cp;
    } else if (cp >= 0xDC00 && cp <= 0xDFFF) {
        /* 2nd part of surrogate pair came unexpectedly */
        *out++ = MBFL_BAD_INPUT;
    } else if (cp >= 0x20 && cp <= 0x7E && cp != '&') {
        *out++ = MBFL_BAD_INPUT;
    } else {
        *out++ = cp;
    }
    return out;
}
 
static uint32_t* handle_base64_end(unsigned char n, uint32_t *out, bool *base64, bool abrupt, uint16_t *surrogate1)
{
    if (abrupt || n == ILLEGAL || *surrogate1) {
        *out++ = MBFL_BAD_INPUT;
        *surrogate1 = 0;
    }
 
    *base64 = false;
    return out;
}
 
static size_t mb_utf7imap_to_wchar(unsigned char **in, size_t *in_len, uint32_t *buf, size_t bufsize, unsigned int *state)
{
    ZEND_ASSERT(bufsize >= 5); /* This function will infinite-loop if called with a tiny output buffer */
 
    /* Why does this require a minimum output buffer size of 5?
     * See comment in mb_utf7_to_wchar; the worst case for this function is similar,
     * though not exactly the same. */
 
    unsigned char *p = *in, *e = p + *in_len;
    /* Always leave one empty space in output buffer in case the string ends while
     * in Base64 mode and we need to emit an error marker */
    uint32_t *out = buf, *limit = buf + bufsize - 1;
 
    bool base64 = *state & 1;
    uint16_t surrogate1 = (*state >> 1); /* First half of a surrogate pair */
 
    while (p < e && out < limit) {
        if (base64) {
            /* Base64 section */
            if ((limit - out) < 4) {
                break;
            }
 
            unsigned char n1 = decode_base64(*p++);
            if (is_base64_end(n1)) {
                out = handle_base64_end(n1, out, &base64, false, &surrogate1);
                continue;
            } else if (p == e) {
                out = handle_base64_end(n1, out, &base64, true, &surrogate1);
                continue;
            }
            unsigned char n2 = decode_base64(*p++);
            if (is_base64_end(n2) || p == e) {
                out = handle_base64_end(n2, out, &base64, true, &surrogate1);
                continue;
            }
            unsigned char n3 = decode_base64(*p++);
            if (is_base64_end(n3)) {
                out = handle_base64_end(n3, out, &base64, true, &surrogate1);
                continue;
            }
            out = handle_utf16_cp((n1 << 10) | (n2 << 4) | ((n3 & 0x3C) >> 2), out, &surrogate1);
            if (p == e) {
                /* It is an error if trailing padding bits are not zeroes or if we were
                 * expecting the 2nd part of a surrogate pair when Base64 section ends */
                if ((n3 & 0x3) || surrogate1)
                    *out++ = MBFL_BAD_INPUT;
                break;
            }
 
            unsigned char n4 = decode_base64(*p++);
            if (is_base64_end(n4)) {
                out = handle_base64_end(n4, out, &base64, n3 & 0x3, &surrogate1);
                continue;
            } else if (p == e) {
                out = handle_base64_end(n4, out, &base64, true, &surrogate1);
                continue;
            }
            unsigned char n5 = decode_base64(*p++);
            if (is_base64_end(n5) || p == e) {
                out = handle_base64_end(n5, out, &base64, true, &surrogate1);
                continue;
            }
            unsigned char n6 = decode_base64(*p++);
            if (is_base64_end(n6)) {
                out = handle_base64_end(n6, out, &base64, true, &surrogate1);
                continue;
            }
            out = handle_utf16_cp((n3 << 14) | (n4 << 8) | (n5 << 2) | ((n6 & 0x30) >> 4), out, &surrogate1);
            if (p == e) {
                if ((n6 & 0xF) || surrogate1)
                    *out++ = MBFL_BAD_INPUT;
                break;
            }
 
            unsigned char n7 = decode_base64(*p++);
            if (is_base64_end(n7)) {
                out = handle_base64_end(n7, out, &base64, n6 & 0xF, &surrogate1);
                continue;
            } else if (p == e) {
                out = handle_base64_end(n7, out, &base64, true, &surrogate1);
                continue;
            }
            unsigned char n8 = decode_base64(*p++);
            if (is_base64_end(n8)) {
                out = handle_base64_end(n8, out, &base64, true, &surrogate1);
                continue;
            }
            out = handle_utf16_cp((n6 << 12) | (n7 << 6) | n8, out, &surrogate1);
        } else {
            unsigned char c = *p++;
 
            if (c == '&') {
                if (p < e && *p == '-') {
                    *out++ = '&';
                    p++;
                } else {
                    base64 = true;
                }
            } else if (c >= 0x20 && c <= 0x7E) {
                *out++ = c;
            } else {
                *out++ = MBFL_BAD_INPUT;
            }
        }
    }
 
    if (p == e && base64) {
        /* UTF7-IMAP doesn't allow strings to end in Base64 mode
         * One space in output buffer was reserved just for this */
        ZEND_ASSERT(out < limit);
        *out++ = MBFL_BAD_INPUT;
    }
 
    *state = (surrogate1 << 1) | base64;
    *in_len = e - p;
    *in = p;
    return out - buf;
}
 
#define SAVE_CONVERSION_STATE() buf->state = (cache << 4) | (nbits << 1) | base64
#define RESTORE_CONVERSION_STATE() base64 = (buf->state & 1); nbits = (buf->state >> 1) & 0x7; cache = (buf->state >> 4)
 
static const unsigned char mbfl_base64_table[] = {
 /* 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', */
   0x41,0x42,0x43,0x44,0x45,0x46,0x47,0x48,0x49,0x4a,0x4b,0x4c,0x4d,
 /* 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', */
   0x4e,0x4f,0x50,0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58,0x59,0x5a,
 /* 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', */
   0x61,0x62,0x63,0x64,0x65,0x66,0x67,0x68,0x69,0x6a,0x6b,0x6c,0x6d,
 /* 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', */
   0x6e,0x6f,0x70,0x71,0x72,0x73,0x74,0x75,0x76,0x77,0x78,0x79,0x7a,
 /* '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', ',', '\0' */
   0x30,0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x2b,0x2c,0x00
};
 
static void mb_wchar_to_utf7imap(uint32_t *in, size_t len, mb_convert_buf *buf, bool end)
{
    unsigned char *out, *limit;
    MB_CONVERT_BUF_LOAD(buf, out, limit);
    MB_CONVERT_BUF_ENSURE(buf, out, limit, len);
 
    bool base64;
    unsigned char nbits, cache; /* `nbits` is the number of cached bits; either 0, 2, or 4 */
    RESTORE_CONVERSION_STATE();
 
    while (len--) {
        uint32_t w = *in++;
        if (base64) {
            if (w >= 0x20 && w <= 0x7E) {
                /* End of Base64 section. Drain buffered bits (if any), close Base64 section
                 * Leave enough space in the output buffer such that even if the remainder of
                 * the input string is ASCII, we can output the whole thing without having to
                 * check for output buffer space again */
                base64 = false;
                in--; len++; /* Unconsume codepoint; it will be handled by 'ASCII section' code below */
                MB_CONVERT_BUF_ENSURE(buf, out, limit, len + 2);
                if (nbits) {
                    out = mb_convert_buf_add(out, mbfl_base64_table[(cache << (6 - nbits)) & 0x3F]);
                }
                nbits = cache = 0;
                out = mb_convert_buf_add(out, '-');
            } else if (w >= MBFL_WCSPLANE_UTF32MAX) {
                /* Make recursive call to add an error marker character */
                SAVE_CONVERSION_STATE();
                MB_CONVERT_ERROR(buf, out, limit, w, mb_wchar_to_utf7imap);
                MB_CONVERT_BUF_ENSURE(buf, out, limit, len);
                RESTORE_CONVERSION_STATE();
            } else {
                /* Encode codepoint, preceded by any cached bits, as Base64
                 * Make enough space in the output buffer to hold both any bytes that
                 * we emit right here, plus any finishing byte which might need to
                 * be emitted if the input string ends abruptly */
                uint64_t bits;
                if (w >= MBFL_WCSPLANE_SUPMIN) {
                    /* Must use surrogate pair */
                    MB_CONVERT_BUF_ENSURE(buf, out, limit, 7);
                    w -= 0x10000;
                    bits = ((uint64_t)cache << 32) | 0xD800DC00L | ((w & 0xFFC00) << 6) | (w & 0x3FF);
                    nbits += 32;
                } else {
                    MB_CONVERT_BUF_ENSURE(buf, out, limit, 4);
                    bits = (cache << 16) | w;
                    nbits += 16;
                }
 
                while (nbits >= 6) {
                    out = mb_convert_buf_add(out, mbfl_base64_table[(bits >> (nbits - 6)) & 0x3F]);
                    nbits -= 6;
                }
                cache = bits;
            }
        } else {
            /* ASCII section */
            if (w == '&') {
                MB_CONVERT_BUF_ENSURE(buf, out, limit, len + 2);
                out = mb_convert_buf_add2(out, '&', '-');
            } else if (w >= 0x20 && w <= 0x7E) {
                out = mb_convert_buf_add(out, w);
            } else if (w >= MBFL_WCSPLANE_UTF32MAX) {
                buf->state = 0;
                MB_CONVERT_ERROR(buf, out, limit, w, mb_wchar_to_utf7imap);
                MB_CONVERT_BUF_ENSURE(buf, out, limit, len);
                RESTORE_CONVERSION_STATE();
            } else {
                out = mb_convert_buf_add(out, '&');
                base64 = true;
                in--; len++; /* Unconsume codepoint; it will be handled by Base64 code above */
            }
        }
    }
 
    if (end) {
        if (nbits) {
            out = mb_convert_buf_add(out, mbfl_base64_table[(cache << (6 - nbits)) & 0x3F]);
        }
        if (base64) {
            MB_CONVERT_BUF_ENSURE(buf, out, limit, 1);
            out = mb_convert_buf_add(out, '-');
        }
    } else {
        SAVE_CONVERSION_STATE();
    }
 
    MB_CONVERT_BUF_STORE(buf, out, limit);
}
 
static bool is_utf16_cp_valid(uint16_t cp, bool is_surrogate)
{
    if (is_surrogate) {
        return cp >= 0xDC00 && cp <= 0xDFFF;
    } else if (cp >= 0xDC00 && cp <= 0xDFFF) {
        /* 2nd part of surrogate pair came unexpectedly */
        return false;
    } else if (cp >= 0x20 && cp <= 0x7E && cp != '&') {
        return false;
    }
    return true;
}
 
static bool mb_check_utf7imap(unsigned char *in, size_t in_len)
{
    unsigned char *p = in, *e = p + in_len;
    bool base64 = false;
    bool is_surrogate = false;
 
    while (p < e) {
        if (base64) {
            /* Base64 section */
            unsigned char n1 = decode_base64(*p++);
            if (is_base64_end(n1)) {
                if (!is_base64_end_valid(n1, false, is_surrogate)) {
                    return false;
                }
                base64 = false;
                continue;
            } else if (p == e) {
                return false;
            }
            unsigned char n2 = decode_base64(*p++);
            if (is_base64_end(n2) || p == e) {
                return false;
            }
            unsigned char n3 = decode_base64(*p++);
            if (is_base64_end(n3)) {
                return false;
            }
            uint16_t cp1 = (n1 << 10) | (n2 << 4) | ((n3 & 0x3C) >> 2);
            if (!is_utf16_cp_valid(cp1, is_surrogate)) {
                return false;
            }
            is_surrogate = has_surrogate(cp1, is_surrogate);
            if (p == e) {
                return false;
            }
 
            unsigned char n4 = decode_base64(*p++);
            if (is_base64_end(n4)) {
                if (!is_base64_end_valid(n4, n3 & 0x3, is_surrogate)) {
                    return false;
                }
                base64 = false;
                continue;
            } else if (p == e) {
                return false;
            }
            unsigned char n5 = decode_base64(*p++);
            if (is_base64_end(n5) || p == e) {
                return false;
            }
            unsigned char n6 = decode_base64(*p++);
            if (is_base64_end(n6)) {
                return false;
            }
            uint16_t cp2 = (n3 << 14) | (n4 << 8) | (n5 << 2) | ((n6 & 0x30) >> 4);
            if (!is_utf16_cp_valid(cp2, is_surrogate)) {
                return false;
            }
            is_surrogate = has_surrogate(cp2, is_surrogate);
            if (p == e) {
                return false;
            }
 
            unsigned char n7 = decode_base64(*p++);
            if (is_base64_end(n7)) {
                if (!is_base64_end_valid(n7, n6 & 0xF, is_surrogate)) {
                    return false;
                }
                base64 = false;
                continue;
            } else if (p == e) {
                return false;
            }
            unsigned char n8 = decode_base64(*p++);
            if (is_base64_end(n8)) {
                return false;
            }
            uint16_t cp3 = (n6 << 12) | (n7 << 6) | n8;
            if (!is_utf16_cp_valid(cp3, is_surrogate)) {
                return false;
            }
            is_surrogate = has_surrogate(cp3, is_surrogate);
        } else {
            /* ASCII text section */
            unsigned char c = *p++;
 
            if (c == '&') {
                if (p == e) {
                    return false;
                }
                unsigned char n = decode_base64(*p);
                if (n == DASH) {
                    p++;
                } else if (n == ILLEGAL) {
                    return false;
                } else {
                    base64 = true;
                }
            } else if (c >= 0x20 && c <= 0x7E) {
                continue;
            } else {
                return false;
            }
        }
    }
    return !base64;
}