/* vi: set sw=4 ts=4: */
/*
 * Copyright 2003, Glenn McGrath
 * Copyright 2006, Rob Landley <rob@landley.net>
 * Copyright 2010, Denys Vlasenko
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
#include "libbb.h"

/* Conversion table.  for base 64 */
const char bb_uuenc_tbl_base64[65 + 1] ALIGN1 = {
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
        'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
        'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
        'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
        'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
        'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
        'w', 'x', 'y', 'z', '0', '1', '2', '3',
        '4', '5', '6', '7', '8', '9', '+', '/',
        '=' /* termination character */,
        '\0' /* needed for uudecode.c only */
};

const char bb_uuenc_tbl_std[65] ALIGN1 = {
        '`', '!', '"', '#', '$', '%', '&', '\'',
        '(', ')', '*', '+', ',', '-', '.', '/',
        '0', '1', '2', '3', '4', '5', '6', '7',
        '8', '9', ':', ';', '<', '=', '>', '?',
        '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
        'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
        'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
        'X', 'Y', 'Z', '[', '\\', ']', '^', '_',
        '`' /* termination character */
};

/*
 * Encode bytes at S of length LENGTH to uuencode or base64 format and place it
 * to STORE.  STORE will be 0-terminated, and must point to a writable
 * buffer of at least 1+BASE64_LENGTH(length) bytes.
 * where BASE64_LENGTH(len) = (4 * ((LENGTH + 2) / 3))
 */
void FAST_FUNC bb_uuencode(char *p, const void *src, int length, const char *tbl)
{
        const unsigned char *s = src;

        /* Transform the 3x8 bits to 4x6 bits */
        while (length > 0) {
                unsigned s1, s2;

                /* Are s[1], s[2] valid or should be assumed 0? */
                s1 = s2 = 0;
                length -= 3; /* can be >=0, -1, -2 */
                if (length >= -1) {
                        s1 = s[1];
                        if (length >= 0)
                                s2 = s[2];
                }
                *p++ = tbl[s[0] >> 2];
                *p++ = tbl[((s[0] & 3) << 4) + (s1 >> 4)];
                *p++ = tbl[((s1 & 0xf) << 2) + (s2 >> 6)];
                *p++ = tbl[s2 & 0x3f];
                s += 3;
        }
        /* Zero-terminate */
        *p = '\0';
        /* If length is -2 or -1, pad last char or two */
        while (length) {
                *--p = tbl[64];
                length++;
        }
}

/*
 * Decode base64 encoded string. Stops on '\0'.
 *
 * Returns: pointer to the undecoded part of source.
 * If points to '\0', then the source was fully decoded.
 * (*pp_dst): advanced past the last written byte.
 */
const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
{
        char *dst = *pp_dst;
        const char *src_tail;

        while (1) {
                unsigned char six_bit[4];
                int count = 0;

                /* Fetch up to four 6-bit values */
                src_tail = src;
                while (count < 4) {
                        char *table_ptr;
                        int ch;

                        /* Get next _valid_ character.
                         * bb_uuenc_tbl_base64[] contains this string:
                         *  0         1         2         3         4         5         6
                         *  01234567890123456789012345678901234567890123456789012345678901234
                         * "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
                         */
                        do {
                                ch = *src;
                                if (ch == '\0') {
                                        if (count == 0) {
                                                /* Example:
                                                 * If we decode "QUJD <NUL>", we want
                                                 * to return ptr to NUL, not to ' ',
                                                 * because we did fully decode
                                                 * the string (to "ABC").
                                                 */
                                                src_tail = src;
                                        }
                                        goto ret;
                                }
                                src++;
                                table_ptr = strchr(bb_uuenc_tbl_base64, ch);
//TODO: add BASE64_FLAG_foo to die on bad char?
                        } while (!table_ptr);

                        /* Convert encoded character to decimal */
                        ch = table_ptr - bb_uuenc_tbl_base64;

                        /* ch is 64 if char was '=', otherwise 0..63 */
                        if (ch == 64)
                                break;
                        six_bit[count] = ch;
                        count++;
                }

                /* Transform 6-bit values to 8-bit ones.
                 * count can be < 4 when we decode the tail:
                 * "eQ==" -> "y", not "y NUL NUL".
                 * Note that (count > 1) is always true,
                 * "x===" encoding is not valid:
                 * even a single zero byte encodes as "AA==".
                 * However, with current logic we come here with count == 1
                 * when we decode "==" tail.
                 */
                if (count > 1)
                        *dst++ = six_bit[0] << 2 | six_bit[1] >> 4;
                if (count > 2)
                        *dst++ = six_bit[1] << 4 | six_bit[2] >> 2;
                if (count > 3)
                        *dst++ = six_bit[2] << 6 | six_bit[3];
                /* Note that if we decode "AA==" and ate first '=',
                 * we just decoded one char (count == 2) and now we'll
                 * do the loop once more to decode second '='.
                 */
        } /* while (1) */
 ret:
        *pp_dst = dst;
        return src_tail;
}

/*
 * Decode base64 encoded stream.
 * Can stop on EOF, specified char, or on uuencode-style "====" line:
 * flags argument controls it.
 */
void FAST_FUNC read_base64(FILE *src_stream, FILE *dst_stream, int flags)
{
/* Note that EOF _can_ be passed as exit_char too */
#define exit_char    ((int)(signed char)flags)
#define uu_style_end (flags & BASE64_FLAG_UU_STOP)

        /* uuencoded files have 61 byte lines. Use 64 byte buffer
         * to process line at a time.
         */
        enum { BUFFER_SIZE = 64 };

        char in_buf[BUFFER_SIZE + 2];
        char out_buf[BUFFER_SIZE / 4 * 3 + 2];
        char *out_tail;
        const char *in_tail;
        int term_seen = 0;
        int in_count = 0;

        while (1) {
                while (in_count < BUFFER_SIZE) {
                        int ch = fgetc(src_stream);
                        if (ch == exit_char) {
                                if (in_count == 0)
                                        return;
                                term_seen = 1;
                                break;
                        }
                        if (ch == EOF) {
                                term_seen = 1;
                                break;
                        }
                        /* Prevent "====" line to be split: stop if we see '\n'.
                         * We can also skip other whitespace and skirt the problem
                         * of files with NULs by stopping on any control char or space:
                         */
                        if (ch <= ' ')
                                break;
                        in_buf[in_count++] = ch;
                }
                in_buf[in_count] = '\0';

                /* Did we encounter "====" line? */
                if (uu_style_end && strcmp(in_buf, "====") == 0)
                        return;

                out_tail = out_buf;
                in_tail = decode_base64(&out_tail, in_buf);

                fwrite(out_buf, (out_tail - out_buf), 1, dst_stream);

                if (term_seen) {
                        /* Did we consume ALL characters? */
                        if (*in_tail == '\0')
                                return;
                        /* No */
                        bb_error_msg_and_die("truncated base64 input");
                }

                /* It was partial decode */
                in_count = strlen(in_tail);
                memmove(in_buf, in_tail, in_count);
        }
}