Base64.cc

// See the file "COPYING" in the main distribution directory for copyright.

#include "zeek/Base64.h"

#include "zeek/zeek-config.h"

#include <cmath>

#include "zeek/Conn.h"
#include "zeek/Reporter.h"
#include "zeek/ZeekString.h"

namespace zeek::detail {

int Base64Converter::default_base64_table[256];
const std::string Base64Converter::default_alphabet =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

void Base64Converter::Encode(int len, const unsigned char* data, int* pblen, char** pbuf) {
    int blen;
    char* buf;

    if ( ! pbuf )
        reporter->InternalError("nil pointer to encoding result buffer");

    if ( *pbuf && (*pblen % 4 != 0) )
        reporter->InternalError("Base64 encode buffer not a multiple of 4");

    if ( *pbuf ) {
        buf = *pbuf;
        blen = *pblen;
    }
    else {
        blen = (int)(4 * ceil((double)len / 3));
        *pbuf = buf = new char[blen];
        *pblen = blen;
    }

    for ( int i = 0, j = 0; (i < len) && (j < blen); ) {
        uint32_t bit32 = data[i++] << 16;
        bit32 += (i++ < len ? data[i - 1] : 0) << 8;
        bit32 += i++ < len ? data[i - 1] : 0;

        buf[j++] = alphabet[(bit32 >> 18) & 0x3f];
        buf[j++] = alphabet[(bit32 >> 12) & 0x3f];
        buf[j++] = (i == (len + 2)) ? '=' : alphabet[(bit32 >> 6) & 0x3f];
        buf[j++] = (i >= (len + 1)) ? '=' : alphabet[bit32 & 0x3f];
    }
}

int* Base64Converter::InitBase64Table(const std::string& alphabet) {
    assert(alphabet.size() == 64);

    static bool default_table_initialized = false;

    if ( alphabet == default_alphabet && default_table_initialized )
        return default_base64_table;

    int* base64_table = nullptr;

    if ( alphabet == default_alphabet ) {
        base64_table = default_base64_table;
        default_table_initialized = true;
    }
    else
        base64_table = new int[256];

    int i;
    for ( i = 0; i < 256; ++i )
        base64_table[i] = -1;

    for ( i = 0; i < 26; ++i ) {
        base64_table[int(alphabet[0 + i])] = i;
        base64_table[int(alphabet[26 + i])] = i + 26;
    }

    for ( i = 0; i < 10; ++i )
        base64_table[int(alphabet[52 + i])] = i + 52;

    // Casts to avoid compiler warnings.
    base64_table[int(alphabet[62])] = 62;
    base64_table[int(alphabet[63])] = 63;
    base64_table[int('=')] = 0;

    return base64_table;
}

Base64Converter::Base64Converter(Connection* arg_conn, const std::string& arg_alphabet) {
    if ( arg_alphabet.size() > 0 ) {
        assert(arg_alphabet.size() == 64);
        alphabet = arg_alphabet;
    }
    else {
        alphabet = default_alphabet;
    }

    base64_table = nullptr;
    base64_group_next = 0;
    base64_padding = base64_after_padding = 0;
    errored = 0;
    conn = arg_conn;
}

Base64Converter::~Base64Converter() {
    if ( base64_table != default_base64_table )
        delete[] base64_table;
}

int Base64Converter::Decode(int len, const char* data, int* pblen, char** pbuf) {
    int blen;
    char* buf;

    // Initialization of table on first_time call of Decode.
    if ( ! base64_table )
        base64_table = InitBase64Table(alphabet);

    if ( ! pbuf )
        reporter->InternalError("nil pointer to decoding result buffer");

    if ( *pbuf ) {
        buf = *pbuf;
        blen = *pblen;
    }
    else {
        // Estimate the maximal number of 3-byte groups needed,
        // plus 1 byte for the optional ending NUL.
        blen = int((len + base64_group_next + 3) / 4) * 3 + 1;
        *pbuf = buf = new char[blen];
    }

    int dlen = 0;

    while ( true ) {
        if ( base64_group_next == 4 ) {
            // For every group of 4 6-bit numbers,
            // write the decoded 3 bytes to the buffer.
            if ( base64_after_padding ) {
                if ( ++errored == 1 )
                    IllegalEncoding("extra base64 groups after '=' padding are ignored");
                base64_group_next = 0;
                continue;
            }

            int num_octets = 3 - base64_padding;

            if ( buf + num_octets > *pbuf + blen )
                break;

            uint32_t bit32 = ((base64_group[0] & 0x3f) << 18) | ((base64_group[1] & 0x3f) << 12) |
                             ((base64_group[2] & 0x3f) << 6) | ((base64_group[3] & 0x3f));

            if ( --num_octets >= 0 )
                *buf++ = char((bit32 >> 16) & 0xff);

            if ( --num_octets >= 0 )
                *buf++ = char((bit32 >> 8) & 0xff);

            if ( --num_octets >= 0 )
                *buf++ = char((bit32) & 0xff);

            if ( base64_padding > 0 )
                base64_after_padding = 1;

            base64_group_next = 0;
            base64_padding = 0;
        }

        if ( dlen >= len )
            break;

        unsigned char c = (unsigned char)data[dlen];
        if ( c == '=' )
            ++base64_padding;

        int k = base64_table[c];
        if ( k >= 0 )
            base64_group[base64_group_next++] = k;
        else {
            if ( ++errored == 1 )
                IllegalEncoding(util::fmt("character %d ignored by Base64 decoding", (int)c));
        }

        ++dlen;
    }

    *pblen = buf - *pbuf;
    return dlen;
}

int Base64Converter::Done(int* pblen, char** pbuf) {
    const char* padding = "===";

    if ( base64_group_next != 0 ) {
        if ( base64_group_next < 4 )
            IllegalEncoding(
                util::fmt("incomplete base64 group, padding with %d bits of 0", (4 - base64_group_next) * 6));
        Decode(4 - base64_group_next, padding, pblen, pbuf);
        return -1;
    }

    if ( pblen )
        *pblen = 0;

    return 0;
}

void Base64Converter::IllegalEncoding(const char* msg) {
    // strncpy(error_msg, msg, sizeof(error_msg));
    if ( conn )
        conn->Weird("base64_illegal_encoding", msg);
    else
        reporter->Error("%s", msg);
}

String* decode_base64(const String* s, const String* a, Connection* conn) {
    if ( a && a->Len() != 0 && a->Len() != 64 ) {
        reporter->Error("base64 decoding alphabet is not 64 characters: %s", a->CheckString());
        return nullptr;
    }

    int buf_len = int((s->Len() + 3) / 4) * 3 + 1;
    int rlen2, rlen = buf_len;
    char *rbuf2, *rbuf = new char[rlen];

    Base64Converter dec(conn, a ? a->CheckString() : "");
    dec.Decode(s->Len(), (const char*)s->Bytes(), &rlen, &rbuf);

    if ( dec.Errored() )
        goto err;

    rlen2 = buf_len - rlen;
    rbuf2 = rbuf + rlen;
    // Done() returns -1 if there isn't enough padding, but we just ignore
    // it.
    dec.Done(&rlen2, &rbuf2);
    rlen += rlen2;

    rbuf[rlen] = '\0';
    return new String(true, (u_char*)rbuf, rlen);

err:
    delete[] rbuf;
    return nullptr;
}

String* encode_base64(const String* s, const String* a, Connection* conn) {
    if ( a && a->Len() != 0 && a->Len() != 64 ) {
        reporter->Error("base64 alphabet is not 64 characters: %s", a->CheckString());
        return nullptr;
    }

    char* outbuf = nullptr;
    int outlen = 0;
    Base64Converter enc(conn, a ? a->CheckString() : "");
    enc.Encode(s->Len(), (const unsigned char*)s->Bytes(), &outlen, &outbuf);

    return new String(true, (u_char*)outbuf, outlen);
}

} // namespace zeek::detail