encode.c

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/*-------------------------------------------------------------------------
 *
 * encode.c
 *    Various data encoding/decoding things.
 *
 * Copyright (c) 2001-2020, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/encode.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <ctype.h>

#include "utils/builtins.h"
#include "utils/memutils.h"


/*
 * Encoding conversion API.
 * encode_len() and decode_len() compute the amount of space needed, while
 * encode() and decode() perform the actual conversions.  It is okay for
 * the _len functions to return an overestimate, but not an underestimate.
 * (Having said that, large overestimates could cause unnecessary errors,
 * so it's better to get it right.)  The conversion routines write to the
 * buffer at *res and return the true length of their output.
 */
struct pg_encoding
{
    uint64      (*encode_len) (const char *data, size_t dlen);
    uint64      (*decode_len) (const char *data, size_t dlen);
    uint64      (*encode) (const char *data, size_t dlen, char *res);
    uint64      (*decode) (const char *data, size_t dlen, char *res);
};

static const struct pg_encoding *pg_find_encoding(const char *name);

/*
 * SQL functions.
 */

Datum
binary_encode(PG_FUNCTION_ARGS)
{
    bytea      *data = PG_GETARG_BYTEA_PP(0);
    Datum       name = PG_GETARG_DATUM(1);
    text       *result;
    char       *namebuf;
    char       *dataptr;
    size_t      datalen;
    uint64      resultlen;
    uint64      res;
    const struct pg_encoding *enc;

    namebuf = TextDatumGetCString(name);

    enc = pg_find_encoding(namebuf);
    if (enc == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("unrecognized encoding: \"%s\"", namebuf)));

    dataptr = VARDATA_ANY(data);
    datalen = VARSIZE_ANY_EXHDR(data);

    resultlen = enc->encode_len(dataptr, datalen);

    /*
     * resultlen possibly overflows uint32, therefore on 32-bit machines it's
     * unsafe to rely on palloc's internal check.
     */
    if (resultlen > MaxAllocSize - VARHDRSZ)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("result of encoding conversion is too large")));

    result = palloc(VARHDRSZ + resultlen);

    res = enc->encode(dataptr, datalen, VARDATA(result));

    /* Make this FATAL 'cause we've trodden on memory ... */
    if (res > resultlen)
        elog(FATAL, "overflow - encode estimate too small");

    SET_VARSIZE(result, VARHDRSZ + res);

    PG_RETURN_TEXT_P(result);
}

Datum
binary_decode(PG_FUNCTION_ARGS)
{
    text       *data = PG_GETARG_TEXT_PP(0);
    Datum       name = PG_GETARG_DATUM(1);
    bytea      *result;
    char       *namebuf;
    char       *dataptr;
    size_t      datalen;
    uint64      resultlen;
    uint64      res;
    const struct pg_encoding *enc;

    namebuf = TextDatumGetCString(name);

    enc = pg_find_encoding(namebuf);
    if (enc == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("unrecognized encoding: \"%s\"", namebuf)));

    dataptr = VARDATA_ANY(data);
    datalen = VARSIZE_ANY_EXHDR(data);

    resultlen = enc->decode_len(dataptr, datalen);

    /*
     * resultlen possibly overflows uint32, therefore on 32-bit machines it's
     * unsafe to rely on palloc's internal check.
     */
    if (resultlen > MaxAllocSize - VARHDRSZ)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("result of decoding conversion is too large")));

    result = palloc(VARHDRSZ + resultlen);

    res = enc->decode(dataptr, datalen, VARDATA(result));

    /* Make this FATAL 'cause we've trodden on memory ... */
    if (res > resultlen)
        elog(FATAL, "overflow - decode estimate too small");

    SET_VARSIZE(result, VARHDRSZ + res);

    PG_RETURN_BYTEA_P(result);
}


/*
 * HEX
 */

static const char hextbl[] = "0123456789abcdef";

static const int8 hexlookup[128] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};

uint64
hex_encode(const char *src, size_t len, char *dst)
{
    const char *end = src + len;

    while (src < end)
    {
        *dst++ = hextbl[(*src >> 4) & 0xF];
        *dst++ = hextbl[*src & 0xF];
        src++;
    }
    return (uint64) len * 2;
}

static inline char
get_hex(char c)
{
    int         res = -1;

    if (c > 0 && c < 127)
        res = hexlookup[(unsigned char) c];

    if (res < 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid hexadecimal digit: \"%c\"", c)));

    return (char) res;
}

uint64
hex_decode(const char *src, size_t len, char *dst)
{
    const char *s,
               *srcend;
    char        v1,
                v2,
               *p;

    srcend = src + len;
    s = src;
    p = dst;
    while (s < srcend)
    {
        if (*s == ' ' || *s == '\n' || *s == '\t' || *s == '\r')
        {
            s++;
            continue;
        }
        v1 = get_hex(*s++) << 4;
        if (s >= srcend)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid hexadecimal data: odd number of digits")));

        v2 = get_hex(*s++);
        *p++ = v1 | v2;
    }

    return p - dst;
}

static uint64
hex_enc_len(const char *src, size_t srclen)
{
    return (uint64) srclen << 1;
}

static uint64
hex_dec_len(const char *src, size_t srclen)
{
    return (uint64) srclen >> 1;
}

/*
 * BASE64
 */

static const char _base64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static const int8 b64lookup[128] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
    -1, 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, -1, -1, -1, -1, -1,
    -1, 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, -1, -1, -1, -1, -1,
};

static uint64
pg_base64_encode(const char *src, size_t len, char *dst)
{
    char       *p,
               *lend = dst + 76;
    const char *s,
               *end = src + len;
    int         pos = 2;
    uint32      buf = 0;

    s = src;
    p = dst;

    while (s < end)
    {
        buf |= (unsigned char) *s << (pos << 3);
        pos--;
        s++;

        /* write it out */
        if (pos < 0)
        {
            *p++ = _base64[(buf >> 18) & 0x3f];
            *p++ = _base64[(buf >> 12) & 0x3f];
            *p++ = _base64[(buf >> 6) & 0x3f];
            *p++ = _base64[buf & 0x3f];

            pos = 2;
            buf = 0;
        }
        if (p >= lend)
        {
            *p++ = '\n';
            lend = p + 76;
        }
    }
    if (pos != 2)
    {
        *p++ = _base64[(buf >> 18) & 0x3f];
        *p++ = _base64[(buf >> 12) & 0x3f];
        *p++ = (pos == 0) ? _base64[(buf >> 6) & 0x3f] : '=';
        *p++ = '=';
    }

    return p - dst;
}

static uint64
pg_base64_decode(const char *src, size_t len, char *dst)
{
    const char *srcend = src + len,
               *s = src;
    char       *p = dst;
    char        c;
    int         b = 0;
    uint32      buf = 0;
    int         pos = 0,
                end = 0;

    while (s < srcend)
    {
        c = *s++;

        if (c == ' ' || c == '\t' || c == '\n' || c == '\r')
            continue;

        if (c == '=')
        {
            /* end sequence */
            if (!end)
            {
                if (pos == 2)
                    end = 1;
                else if (pos == 3)
                    end = 2;
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("unexpected \"=\" while decoding base64 sequence")));
            }
            b = 0;
        }
        else
        {
            b = -1;
            if (c > 0 && c < 127)
                b = b64lookup[(unsigned char) c];
            if (b < 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("invalid symbol \"%c\" while decoding base64 sequence", (int) c)));
        }
        /* add it to buffer */
        buf = (buf << 6) + b;
        pos++;
        if (pos == 4)
        {
            *p++ = (buf >> 16) & 255;
            if (end == 0 || end > 1)
                *p++ = (buf >> 8) & 255;
            if (end == 0 || end > 2)
                *p++ = buf & 255;
            buf = 0;
            pos = 0;
        }
    }

    if (pos != 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid base64 end sequence"),
                 errhint("Input data is missing padding, is truncated, or is otherwise corrupted.")));

    return p - dst;
}


static uint64
pg_base64_enc_len(const char *src, size_t srclen)
{
    /* 3 bytes will be converted to 4, linefeed after 76 chars */
    return ((uint64) srclen + 2) * 4 / 3 + (uint64) srclen / (76 * 3 / 4);
}

static uint64
pg_base64_dec_len(const char *src, size_t srclen)
{
    return ((uint64) srclen * 3) >> 2;
}

/*
 * Escape
 * Minimally escape bytea to text.
 * De-escape text to bytea.
 *
 * We must escape zero bytes and high-bit-set bytes to avoid generating
 * text that might be invalid in the current encoding, or that might
 * change to something else if passed through an encoding conversion
 * (leading to failing to de-escape to the original bytea value).
 * Also of course backslash itself has to be escaped.
 *
 * De-escaping processes \\ and any \### octal
 */

#define VAL(CH)         ((CH) - '0')
#define DIG(VAL)        ((VAL) + '0')

static uint64
esc_encode(const char *src, size_t srclen, char *dst)
{
    const char *end = src + srclen;
    char       *rp = dst;
    uint64      len = 0;

    while (src < end)
    {
        unsigned char c = (unsigned char) *src;

        if (c == '\0' || IS_HIGHBIT_SET(c))
        {
            rp[0] = '\\';
            rp[1] = DIG(c >> 6);
            rp[2] = DIG((c >> 3) & 7);
            rp[3] = DIG(c & 7);
            rp += 4;
            len += 4;
        }
        else if (c == '\\')
        {
            rp[0] = '\\';
            rp[1] = '\\';
            rp += 2;
            len += 2;
        }
        else
        {
            *rp++ = c;
            len++;
        }

        src++;
    }

    return len;
}

static uint64
esc_decode(const char *src, size_t srclen, char *dst)
{
    const char *end = src + srclen;
    char       *rp = dst;
    uint64      len = 0;

    while (src < end)
    {
        if (src[0] != '\\')
            *rp++ = *src++;
        else if (src + 3 < end &&
                 (src[1] >= '0' && src[1] <= '3') &&
                 (src[2] >= '0' && src[2] <= '7') &&
                 (src[3] >= '0' && src[3] <= '7'))
        {
            int         val;

            val = VAL(src[1]);
            val <<= 3;
            val += VAL(src[2]);
            val <<= 3;
            *rp++ = val + VAL(src[3]);
            src += 4;
        }
        else if (src + 1 < end &&
                 (src[1] == '\\'))
        {
            *rp++ = '\\';
            src += 2;
        }
        else
        {
            /*
             * One backslash, not followed by ### valid octal. Should never
             * get here, since esc_dec_len does same check.
             */
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                     errmsg("invalid input syntax for type %s", "bytea")));
        }

        len++;
    }

    return len;
}

static uint64
esc_enc_len(const char *src, size_t srclen)
{
    const char *end = src + srclen;
    uint64      len = 0;

    while (src < end)
    {
        if (*src == '\0' || IS_HIGHBIT_SET(*src))
            len += 4;
        else if (*src == '\\')
            len += 2;
        else
            len++;

        src++;
    }

    return len;
}

static uint64
esc_dec_len(const char *src, size_t srclen)
{
    const char *end = src + srclen;
    uint64      len = 0;

    while (src < end)
    {
        if (src[0] != '\\')
            src++;
        else if (src + 3 < end &&
                 (src[1] >= '0' && src[1] <= '3') &&
                 (src[2] >= '0' && src[2] <= '7') &&
                 (src[3] >= '0' && src[3] <= '7'))
        {
            /*
             * backslash + valid octal
             */
            src += 4;
        }
        else if (src + 1 < end &&
                 (src[1] == '\\'))
        {
            /*
             * two backslashes = backslash
             */
            src += 2;
        }
        else
        {
            /*
             * one backslash, not followed by ### valid octal
             */
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                     errmsg("invalid input syntax for type %s", "bytea")));
        }

        len++;
    }
    return len;
}

/*
 * Common
 */

static const struct
{
    const char *name;
    struct pg_encoding enc;
}           enclist[] =

{
    {
        "hex",
        {
            hex_enc_len, hex_dec_len, hex_encode, hex_decode
        }
    },
    {
        "base64",
        {
            pg_base64_enc_len, pg_base64_dec_len, pg_base64_encode, pg_base64_decode
        }
    },
    {
        "escape",
        {
            esc_enc_len, esc_dec_len, esc_encode, esc_decode
        }
    },
    {
        NULL,
        {
            NULL, NULL, NULL, NULL
        }
    }
};

static const struct pg_encoding *
pg_find_encoding(const char *name)
{
    int         i;

    for (i = 0; enclist[i].name; i++)
        if (pg_strcasecmp(enclist[i].name, name) == 0)
            return &enclist[i].enc;

    return NULL;
}