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// Copyright 2022 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
/** Decodes arguments and formats them with the provided format string. */
import Long from 'long';
const SPECIFIER_REGEX =
/%(\.([0-9]+))?(hh|h|ll|l|j|z|t|L)?([%csdioxXufFeEaAgGnp])/g;
// Conversion specifiers by type; n is not supported.
const SIGNED_INT = 'di'.split('');
const UNSIGNED_INT = 'oxXup'.split('');
const FLOATING_POINT = 'fFeEaAgG'.split('');
enum DecodedStatusFlags {
// Status flags for a decoded argument. These values should match the
// DecodingStatus enum in pw_tokenizer/internal/decode.h.
OK = 0, // decoding was successful
MISSING = 1, // the argument was not present in the data
TRUNCATED = 2, // the argument was truncated during encoding
DECODE_ERROR = 4, // an error occurred while decoding the argument
SKIPPED = 8, // argument was skipped due to a previous error
}
interface DecodedArg {
size: number;
value: string | number | Long | null;
}
// ZigZag decode function from protobuf's wire_format module.
function zigzagDecode(value: Long, unsigned = false): Long {
// 64 bit math is:
// signmask = (zigzag & 1) ? -1 : 0;
// twosComplement = (zigzag >> 1) ^ signmask;
//
// To work with 32 bit, we can operate on both but "carry" the lowest bit
// from the high word by shifting it up 31 bits to be the most significant bit
// of the low word.
let bitsLow = value.low,
bitsHigh = value.high;
const signFlipMask = -(bitsLow & 1);
bitsLow = ((bitsLow >>> 1) | (bitsHigh << 31)) ^ signFlipMask;
bitsHigh = (bitsHigh >>> 1) ^ signFlipMask;
return new Long(bitsLow, bitsHigh, unsigned);
}
export class PrintfDecoder {
// Reads a unicode string from the encoded data.
private decodeString(args: Uint8Array): DecodedArg {
if (args.length === 0) return { size: 0, value: null };
let sizeAndStatus = args[0];
let status = DecodedStatusFlags.OK;
if (sizeAndStatus & 0x80) {
status |= DecodedStatusFlags.TRUNCATED;
sizeAndStatus &= 0x7f;
}
const rawData = args.slice(0, sizeAndStatus + 1);
const data = rawData.slice(1);
if (data.length < sizeAndStatus) {
status |= DecodedStatusFlags.DECODE_ERROR;
}
const decoded = new TextDecoder().decode(data);
return { size: rawData.length, value: decoded };
}
private decodeSignedInt(args: Uint8Array): DecodedArg {
return this._decodeInt(args);
}
private _decodeInt(args: Uint8Array, unsigned = false): DecodedArg {
if (args.length === 0) return { size: 0, value: null };
let count = 0;
let result = new Long(0);
let shift = 0;
for (count = 0; count < args.length; count++) {
const byte = args[count];
result = result.or(
Long.fromInt(byte, unsigned).and(0x7f).shiftLeft(shift),
);
if (!(byte & 0x80)) {
return { value: zigzagDecode(result, unsigned), size: count + 1 };
}
shift += 7;
if (shift >= 64) break;
}
return { size: 0, value: null };
}
private decodeUnsignedInt(
args: Uint8Array,
lengthSpecifier: string,
): DecodedArg {
const arg = this._decodeInt(args, true);
const bits = ['ll', 'j'].indexOf(lengthSpecifier) !== -1 ? 64 : 32;
// Since ZigZag encoding is used, unsigned integers must be masked off to
// their original bit length.
if (arg.value !== null) {
let num = arg.value as Long;
if (bits === 32) {
num = num.and(Long.fromInt(1).shiftLeft(bits).add(-1));
} else {
num = num.and(-1);
}
arg.value = num.toString();
}
return arg;
}
private decodeChar(args: Uint8Array): DecodedArg {
const arg = this.decodeSignedInt(args);
if (arg.value !== null) {
const num = arg.value as Long;
arg.value = String.fromCharCode(num.toInt());
}
return arg;
}
private decodeFloat(args: Uint8Array, precision: string): DecodedArg {
if (args.length < 4) return { size: 0, value: '' };
const floatValue = new DataView(args.buffer, args.byteOffset, 4).getFloat32(
0,
true,
);
if (precision)
return { size: 4, value: floatValue.toFixed(parseInt(precision)) };
return { size: 4, value: floatValue };
}
private format(
specifierType: string,
args: Uint8Array,
precision: string,
lengthSpecifier: string,
): DecodedArg {
if (specifierType == '%') return { size: 0, value: '%' }; // literal %
if (specifierType === 's') {
return this.decodeString(args);
}
if (specifierType === 'c') {
return this.decodeChar(args);
}
if (SIGNED_INT.indexOf(specifierType) !== -1) {
return this.decodeSignedInt(args);
}
if (UNSIGNED_INT.indexOf(specifierType) !== -1) {
return this.decodeUnsignedInt(args, lengthSpecifier);
}
if (FLOATING_POINT.indexOf(specifierType) !== -1) {
return this.decodeFloat(args, precision);
}
// Unsupported specifier, return as-is
return { size: 0, value: '%' + specifierType };
}
decode(formatString: string, args: Uint8Array): string {
return formatString.replace(
SPECIFIER_REGEX,
(
_specifier,
_precisionFull,
precision,
lengthSpecifier,
specifierType,
) => {
const decodedArg = this.format(
specifierType,
args,
precision,
lengthSpecifier,
);
args = args.slice(decodedArg.size);
if (decodedArg === null) return '';
return String(decodedArg.value);
},
);
}
}
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