src/utils/SkBase64.cpp

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */


#include "SkBase64.h"

#define DecodePad -2
#define EncodePad 64

static const char default_encode[] = 
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz"
    "0123456789+/=";

static const signed char decodeData[] = {
    62, -1, -1, -1, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, DecodePad, -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
};

SkBase64::SkBase64() : fLength((size_t) -1), fData(NULL) {
}

#if defined _WIN32 && _MSC_VER >= 1300  // disable 'two', etc. may be used without having been initialized
#pragma warning ( push )
#pragma warning ( disable : 4701 )
#endif

SkBase64::Error SkBase64::decode(const void* srcPtr, size_t size, bool writeDestination) {
    unsigned char* dst = (unsigned char*) fData;
    const unsigned char* dstStart = (const unsigned char*) fData;
    const unsigned char* src = (const unsigned char*) srcPtr;
    bool padTwo = false;
    bool padThree = false;
    const unsigned char* end = src + size;
    while (src < end) {
        unsigned char bytes[4];
        int byte = 0;
        do {
            unsigned char srcByte = *src++;
            if (srcByte == 0)
                goto goHome;
            if (srcByte <= ' ')
                continue; // treat as white space
            if (srcByte < '+' || srcByte > 'z')
                return kBadCharError;
            signed char decoded = decodeData[srcByte - '+'];
            bytes[byte] = decoded;
            if (decoded < 0) {
                if (decoded == DecodePad) 
                    goto handlePad;
                return kBadCharError;
            } else
                byte++;
            if (*src)
                continue;
            if (byte == 0)
                goto goHome;
            if (byte == 4)
                break;
handlePad:
            if (byte < 2)
                return kPadError;
            padThree = true;
            if (byte == 2)
                padTwo = true;
            break;
        } while (byte < 4);
        int two = 0;
        int three = 0;
        if (writeDestination) {
            int one = (uint8_t) (bytes[0] << 2);
            two = bytes[1];
            one |= two >> 4;
            two = (uint8_t) (two << 4);
            three = bytes[2];
            two |= three >> 2;
            three = (uint8_t) (three << 6);
            three |= bytes[3];
            SkASSERT(one < 256 && two < 256 && three < 256);
            *dst = (unsigned char) one;
        }
        dst++;
        if (padTwo) 
            break;
        if (writeDestination)
            *dst = (unsigned char) two;
        dst++;
        if (padThree)
            break;
        if (writeDestination)
            *dst = (unsigned char) three;
        dst++;
    }
goHome:
    fLength = dst - dstStart;
    return kNoError;
}

#if defined _WIN32 && _MSC_VER >= 1300  
#pragma warning ( pop )
#endif

size_t SkBase64::Encode(const void* srcPtr, size_t length, void* dstPtr, const char* encodeMap) {
    const char* encode;
    if (NULL == encodeMap) {
        encode = default_encode;
    } else {
        encode = encodeMap;
    }
    const unsigned char* src = (const unsigned char*) srcPtr;
    unsigned char* dst = (unsigned char*) dstPtr;
    if (dst) {
        size_t remainder = length % 3;
        const unsigned char* end = &src[length - remainder];
        while (src < end) {
            unsigned a = *src++;
            unsigned b = *src++;
            unsigned c = *src++;
            int      d = c & 0x3F;
            c = (c >> 6 | b << 2) & 0x3F; 
            b = (b >> 4 | a << 4) & 0x3F;
            a = a >> 2;
            *dst++ = encode[a];
            *dst++ = encode[b];
            *dst++ = encode[c];
            *dst++ = encode[d];
        }
        if (remainder > 0) {
            int k1 = 0;
            int k2 = EncodePad;
            int a = (uint8_t) *src++;
            if (remainder == 2)
            {
                int b = *src++;
                k1 = b >> 4;
                k2 = (b << 2) & 0x3F;
            }
            *dst++ = encode[a >> 2];
            *dst++ = encode[(k1 | a << 4) & 0x3F];
            *dst++ = encode[k2];
            *dst++ = encode[EncodePad];
        }
    }
    return (length + 2) / 3 * 4;
}

SkBase64::Error SkBase64::decode(const char* src, size_t len) {
    Error err = decode(src, len, false);
    SkASSERT(err == kNoError);
    if (err != kNoError)
        return err;
    fData = new char[fLength];  // should use sk_malloc/sk_free
    decode(src, len, true);
    return kNoError;
}

#ifdef SK_SUPPORT_UNITTEST
void SkBase64::UnitTest() {
    signed char all[256];
    for (int index = 0; index < 256; index++)
        all[index] = (signed char) (index + 1);
    for (int offset = 0; offset < 6; offset++) {
        size_t length = 256 - offset;
        size_t encodeLength = Encode(all + offset, length, NULL);
        char* src = (char*)sk_malloc_throw(encodeLength + 1);
        Encode(all + offset, length, src);
        src[encodeLength] = '\0';
        SkBase64 tryMe;
        tryMe.decode(src, encodeLength);
        SkASSERT(length == tryMe.fLength);
        SkASSERT(strcmp((const char*) (all + offset), tryMe.fData) == 0);
        sk_free(src);
        delete[] tryMe.fData;
    }
}
#endif