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Introduce utility class for encoding
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Joe-Abraham committed Apr 1, 2024
1 parent 865ba33 commit 4503a3a
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4 changes: 4 additions & 0 deletions velox/common/encode/CMakeLists.txt
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# See the License for the specific language governing permissions and
# limitations under the License.

if(${VELOX_BUILD_TESTING})
add_subdirectory(tests)
endif()

add_library(velox_encode Base64.cpp)
target_link_libraries(velox_encode PUBLIC Folly::folly)
128 changes: 128 additions & 0 deletions velox/common/encode/EncoderUtils.h
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/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* 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
*
* http://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.
*/
#pragma once

#include <exception>
#include <map>
#include <string>

#include <folly/Range.h>

namespace facebook::velox::encoding {

class EncoderException : public std::exception {
public:
explicit EncoderException(const char* msg) : msg_(msg) {}
const char* what() const noexcept override {
return msg_;
}

protected:
const char* msg_;
};

using Charset = std::array<char, 64>;
using ReverseIndex = std::array<uint8_t, 256>;

// Padding character used in encoding
constexpr static char kPadding = '=';

// Checks is there padding in encoded data
inline bool isPadded(const char* data, size_t len) {
return (len > 0 && data[len - 1] == kPadding) ? true : false;
}

// Counts the number of padding characters in encoded data.
inline size_t countPadding(const char* src, size_t len) {
size_t padding_count = 0;
while (len > 0 && src[len - 1] == kPadding) {
padding_count++;
len--;
}

return padding_count;
}

// Gets value corresponding to an encoded character
inline uint8_t
baseReverseLookup(int base, char p, const ReverseIndex& reverse_lookup) {
auto curr = reverse_lookup[(uint8_t)p];
// Value of encoded character shall be less than base.
if (curr >= base) {
throw EncoderException(
"decode() - invalid input string: invalid characters");
}

return curr;
}

// Validate the character in charset with ReverseIndex table
constexpr bool checkForwardIndex(
uint8_t idx,
const Charset& charset,
const ReverseIndex& table) {
for (uint8_t i = 0; i <= idx; ++i) {
if (!(table[static_cast<uint8_t>(charset[i])] == i)) {
return false;
}
}
return true;
}

/// Similar to strchr(), but for null-terminated const strings.
/// Another difference is that we do not consider "\0" to be present in the
/// string.
/// Returns true if "str" contains the character c.
constexpr bool findCharacterInCharSet(
const Charset& charset,
int base,
uint8_t idx,
const char c) {
while (idx < base) {
if (charset[idx] == c) {
return true;
}
idx++;
}
return false;
}

// Validate the value in ReverseIndex table with charset.
constexpr bool checkReverseIndex(
uint8_t idx,
const Charset& charset,
int base,
const ReverseIndex& table) {
for (uint8_t currentIdx = idx;; --currentIdx) {
if (table[currentIdx] == 255) {
if (findCharacterInCharSet(
charset, base, 0, static_cast<char>(currentIdx))) {
return false; // Character should not be found
}
} else {
if (!(charset[table[currentIdx]] == currentIdx)) {
return false; // Character at table index does not match currentIdx
}
}

if (currentIdx == 0) {
break; // Stop the loop when reaching 0 to avoid underflow
}
}
return true;
}

} // namespace facebook::velox::encoding
23 changes: 23 additions & 0 deletions velox/common/encode/tests/CMakeLists.txt
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# Copyright (c) Facebook, Inc. and its affiliates.
#
# 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
#
# http://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.

add_executable(velox_common_encode_test EncoderUtilsTests.cpp)
add_test(velox_common_encode_test velox_common_encode_test)
target_link_libraries(
velox_common_encode_test
PUBLIC Folly::folly
PRIVATE velox_encode
velox_exception
gtest
gtest_main)
77 changes: 77 additions & 0 deletions velox/common/encode/tests/EncoderUtilsTests.cpp
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/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* 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
*
* http://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.
*/

#include <gtest/gtest.h>
#include "velox/common/base/tests/GTestUtils.h"
#include "velox/common/encode/EncoderUtils.h"

namespace facebook::velox::encoding {
class EncoderUtilsTest : public ::testing::Test {};

TEST_F(EncoderUtilsTest, ChecksPadding) {
EXPECT_TRUE(isPadded("ABC=", 4));
EXPECT_FALSE(isPadded("ABC", 3));
}

TEST_F(EncoderUtilsTest, CountsPaddingCorrectly) {
EXPECT_EQ(0, countPadding("ABC", 3));
EXPECT_EQ(1, countPadding("ABC=", 4));
EXPECT_EQ(2, countPadding("AB==", 4));
}

constexpr Charset testCharset = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'};

constexpr ReverseIndex testReverseIndex = {
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 255,
255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255,
255, 255, 255, 255, 255, 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, 255, 255, 255, 255, 255, 255, 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, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255};

TEST_F(EncoderUtilsTest, HandlesLookupAndExceptions) {
int base = 64;
EXPECT_NO_THROW(baseReverseLookup(base, 'A', testReverseIndex));
EXPECT_THROW(
baseReverseLookup(base, '=', testReverseIndex), EncoderException);
}

TEST_F(EncoderUtilsTest, ValidatesCharsetWithReverseIndex) {
EXPECT_TRUE(checkForwardIndex(63, testCharset, testReverseIndex));
}

TEST_F(EncoderUtilsTest, ValidatesReverseIndexWithCharset) {
EXPECT_TRUE(checkReverseIndex(255, testCharset, 64, testReverseIndex));
}

} // namespace facebook::velox::encoding

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