path: root/www/lib/localforage/src/utils/serializer.js

import createBlob from './createBlob';

// Sadly, the best way to save binary data in WebSQL/localStorage is serializing
// it to Base64, so this is how we store it to prevent very strange errors with less
// verbose ways of binary <-> string data storage.
var BASE_CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

var BLOB_TYPE_PREFIX = '~~local_forage_type~';
var BLOB_TYPE_PREFIX_REGEX = /^~~local_forage_type~([^~]+)~/;

var SERIALIZED_MARKER = '__lfsc__:';
var SERIALIZED_MARKER_LENGTH = SERIALIZED_MARKER.length;

// OMG the serializations!
var TYPE_ARRAYBUFFER = 'arbf';
var TYPE_BLOB = 'blob';
var TYPE_INT8ARRAY = 'si08';
var TYPE_UINT8ARRAY = 'ui08';
var TYPE_UINT8CLAMPEDARRAY = 'uic8';
var TYPE_INT16ARRAY = 'si16';
var TYPE_INT32ARRAY = 'si32';
var TYPE_UINT16ARRAY = 'ur16';
var TYPE_UINT32ARRAY = 'ui32';
var TYPE_FLOAT32ARRAY = 'fl32';
var TYPE_FLOAT64ARRAY = 'fl64';
var TYPE_SERIALIZED_MARKER_LENGTH = SERIALIZED_MARKER_LENGTH +
    TYPE_ARRAYBUFFER.length;

var toString = Object.prototype.toString;

function stringToBuffer(serializedString) {
    // Fill the string into a ArrayBuffer.
    var bufferLength = serializedString.length * 0.75;
    var len = serializedString.length;
    var i;
    var p = 0;
    var encoded1, encoded2, encoded3, encoded4;

    if (serializedString[serializedString.length - 1] === '=') {
        bufferLength--;
        if (serializedString[serializedString.length - 2] === '=') {
            bufferLength--;
        }
    }

    var buffer = new ArrayBuffer(bufferLength);
    var bytes = new Uint8Array(buffer);

    for (i = 0; i < len; i += 4) {
        encoded1 = BASE_CHARS.indexOf(serializedString[i]);
        encoded2 = BASE_CHARS.indexOf(serializedString[i + 1]);
        encoded3 = BASE_CHARS.indexOf(serializedString[i + 2]);
        encoded4 = BASE_CHARS.indexOf(serializedString[i + 3]);

        /*jslint bitwise: true */
        bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
        bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
        bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
    }
    return buffer;
}

// Converts a buffer to a string to store, serialized, in the backend
// storage library.
function bufferToString(buffer) {
    // base64-arraybuffer
    var bytes = new Uint8Array(buffer);
    var base64String = '';
    var i;

    for (i = 0; i < bytes.length; i += 3) {
        /*jslint bitwise: true */
        base64String += BASE_CHARS[bytes[i] >> 2];
        base64String += BASE_CHARS[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
        base64String += BASE_CHARS[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
        base64String += BASE_CHARS[bytes[i + 2] & 63];
    }

    if ((bytes.length % 3) === 2) {
        base64String = base64String.substring(0, base64String.length - 1) + '=';
    } else if (bytes.length % 3 === 1) {
        base64String = base64String.substring(0, base64String.length - 2) + '==';
    }

    return base64String;
}

// Serialize a value, afterwards executing a callback (which usually
// instructs the `setItem()` callback/promise to be executed). This is how
// we store binary data with localStorage.
function serialize(value, callback) {
    var valueType = '';
    if (value) {
        valueType = toString.call(value);
    }

    // Cannot use `value instanceof ArrayBuffer` or such here, as these
    // checks fail when running the tests using casper.js...
    //
    // TODO: See why those tests fail and use a better solution.
    if (value && (valueType === '[object ArrayBuffer]' ||
        value.buffer &&
        toString.call(value.buffer) === '[object ArrayBuffer]')) {
        // Convert binary arrays to a string and prefix the string with
        // a special marker.
        var buffer;
        var marker = SERIALIZED_MARKER;

        if (value instanceof ArrayBuffer) {
            buffer = value;
            marker += TYPE_ARRAYBUFFER;
        } else {
            buffer = value.buffer;

            if (valueType === '[object Int8Array]') {
                marker += TYPE_INT8ARRAY;
            } else if (valueType === '[object Uint8Array]') {
                marker += TYPE_UINT8ARRAY;
            } else if (valueType === '[object Uint8ClampedArray]') {
                marker += TYPE_UINT8CLAMPEDARRAY;
            } else if (valueType === '[object Int16Array]') {
                marker += TYPE_INT16ARRAY;
            } else if (valueType === '[object Uint16Array]') {
                marker += TYPE_UINT16ARRAY;
            } else if (valueType === '[object Int32Array]') {
                marker += TYPE_INT32ARRAY;
            } else if (valueType === '[object Uint32Array]') {
                marker += TYPE_UINT32ARRAY;
            } else if (valueType === '[object Float32Array]') {
                marker += TYPE_FLOAT32ARRAY;
            } else if (valueType === '[object Float64Array]') {
                marker += TYPE_FLOAT64ARRAY;
            } else {
                callback(new Error('Failed to get type for BinaryArray'));
            }
        }

        callback(marker + bufferToString(buffer));
    } else if (valueType === '[object Blob]') {
        // Conver the blob to a binaryArray and then to a string.
        var fileReader = new FileReader();

        fileReader.onload = function() {
            // Backwards-compatible prefix for the blob type.
            var str = BLOB_TYPE_PREFIX + value.type + '~' +
                bufferToString(this.result);

            callback(SERIALIZED_MARKER + TYPE_BLOB + str);
        };

        fileReader.readAsArrayBuffer(value);
    } else {
        try {
            callback(JSON.stringify(value));
        } catch (e) {
            console.error("Couldn't convert value into a JSON string: ",
                value);

            callback(null, e);
        }
    }
}

// Deserialize data we've inserted into a value column/field. We place
// special markers into our strings to mark them as encoded; this isn't
// as nice as a meta field, but it's the only sane thing we can do whilst
// keeping localStorage support intact.
//
// Oftentimes this will just deserialize JSON content, but if we have a
// special marker (SERIALIZED_MARKER, defined above), we will extract
// some kind of arraybuffer/binary data/typed array out of the string.
function deserialize(value) {
    // If we haven't marked this string as being specially serialized (i.e.
    // something other than serialized JSON), we can just return it and be
    // done with it.
    if (value.substring(0,
            SERIALIZED_MARKER_LENGTH) !== SERIALIZED_MARKER) {
        return JSON.parse(value);
    }

    // The following code deals with deserializing some kind of Blob or
    // TypedArray. First we separate out the type of data we're dealing
    // with from the data itself.
    var serializedString = value.substring(TYPE_SERIALIZED_MARKER_LENGTH);
    var type = value.substring(SERIALIZED_MARKER_LENGTH,
        TYPE_SERIALIZED_MARKER_LENGTH);

    var blobType;
    // Backwards-compatible blob type serialization strategy.
    // DBs created with older versions of localForage will simply not have the blob type.
    if (type === TYPE_BLOB && BLOB_TYPE_PREFIX_REGEX.test(serializedString)) {
        var matcher = serializedString.match(BLOB_TYPE_PREFIX_REGEX);
        blobType = matcher[1];
        serializedString = serializedString.substring(matcher[0].length);
    }
    var buffer = stringToBuffer(serializedString);

    // Return the right type based on the code/type set during
    // serialization.
    switch (type) {
        case TYPE_ARRAYBUFFER:
            return buffer;
        case TYPE_BLOB:
            return createBlob([buffer], {type: blobType});
        case TYPE_INT8ARRAY:
            return new Int8Array(buffer);
        case TYPE_UINT8ARRAY:
            return new Uint8Array(buffer);
        case TYPE_UINT8CLAMPEDARRAY:
            return new Uint8ClampedArray(buffer);
        case TYPE_INT16ARRAY:
            return new Int16Array(buffer);
        case TYPE_UINT16ARRAY:
            return new Uint16Array(buffer);
        case TYPE_INT32ARRAY:
            return new Int32Array(buffer);
        case TYPE_UINT32ARRAY:
            return new Uint32Array(buffer);
        case TYPE_FLOAT32ARRAY:
            return new Float32Array(buffer);
        case TYPE_FLOAT64ARRAY:
            return new Float64Array(buffer);
        default:
            throw new Error('Unkown type: ' + type);
    }
}

var localforageSerializer = {
    serialize: serialize,
    deserialize: deserialize,
    stringToBuffer: stringToBuffer,
    bufferToString: bufferToString
};

export default localforageSerializer;