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Implement Go's varint 64 bit integer decoding in binary decoder #1589

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Jul 11, 2023
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Implement Go's varint 64 bit integer decoding in binary decoder #1589

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Implement Go's varint 64 bit integer decoding in binary decoder
ddelnano Jun 28, 2023
11d1d05
Add additional test cases and ensure empty buffer returns 0 rather th…
ddelnano Jun 28, 2023
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31 changes: 31 additions & 0 deletions src/stirling/utils/binary_decoder.h
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,8 @@
namespace px {
namespace stirling {

constexpr int kMaxVarintLen64 = 10;

/**
* Provides functions to extract bytes from a bytes buffer.
*/
Expand Down Expand Up @@ -60,6 +62,35 @@ class BinaryDecoder {
return val;
}

// Extract UVarInt encoded value and return result as uint64_t. The details of this encoding's
// specification can be see in the following link:
// https://cs.opensource.google/go/go/+/refs/tags/go1.20.5:src/encoding/binary/varint.go;l=7-25
StatusOr<uint64_t> ExtractUVarInt() {
uint64_t x = 0;
uint bits = 0;
int i = 0;

while (buf_.size() >= 1 && i < kMaxVarintLen64) {
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uint8_t b = buf_[0];
buf_.remove_prefix(1);

if (b < 0x80) {
if (i == kMaxVarintLen64 - 1 && b > 1) {
return error::ResourceUnavailable("Insufficient number of bytes.");
}
return x | uint64_t(b) << bits;
}

x |= uint64_t(b & 0x7f) << bits;
bits += 7;
i++;
}
if (i == kMaxVarintLen64) {
return error::ResourceUnavailable("Insufficient number of bytes.");
}
return 0;
}

template <typename TCharType = char>
StatusOr<std::basic_string_view<TCharType>> ExtractString(size_t len) {
static_assert(sizeof(TCharType) == 1);
Expand Down
44 changes: 44 additions & 0 deletions src/stirling/utils/binary_decoder_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@
#include "src/stirling/utils/binary_decoder.h"

#include <string>
#include <utility>
#include <vector>

#include <gmock/gmock.h>
#include <gtest/gtest.h>
Expand Down Expand Up @@ -51,6 +53,48 @@ TEST(BinaryDecoderTest, ExtractInt) {
EXPECT_EQ(0, bin_decoder.BufSize());
}

TEST(BinaryDecoderTest, ExtractUVarInt) {
std::vector<std::pair<std::vector<uint8_t>, uint64_t>> uVarInts = {
{{}, 0},
{{0x01}, 1},
{{0x02}, 2},
{{0x7f}, 127},
{{0x80, 0x01}, 128},
{{0xff, 0x01}, 255},
{{0x80, 0x02}, 256},
{{0x80, 0x80, 0x02}, 32768},
{{0x80, 0x80, 0x80, 0x02}, 4194304},
{{0x80, 0x80, 0x80, 0x80, 0x02}, 536870912},
{{0x80, 0x80, 0x80, 0x80, 0x80, 0x02}, 68719476736},
{{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x02}, 8796093022208},
{{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x02}, 1125899906842624},
{{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x02}, 144115188075855872},
{{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x00}, 0},
{{0xd7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x01}, 18446744073709551575UL},
};
for (auto& p : uVarInts) {
auto data = p.first;
std::string_view s(reinterpret_cast<char*>(data.data()), data.size());
BinaryDecoder bin_decoder(s);
ASSERT_OK_AND_EQ(bin_decoder.ExtractUVarInt(), p.second);
EXPECT_EQ(0, bin_decoder.BufSize());
}
}

TEST(BinaryDecoderTest, ExtractUVarIntOverflow) {
std::vector<std::vector<uint8_t>> uVarInts = {
{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x02},
{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x02},
{0xd7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x01},
{0xd7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f},
};
for (auto& data : uVarInts) {
std::string_view s(reinterpret_cast<char*>(data.data()), data.size());
BinaryDecoder bin_decoder(s);
EXPECT_NOT_OK(bin_decoder.ExtractUVarInt());
}
}

TEST(BinaryDecoderTest, ExtractString) {
std::string_view data("abc123");
BinaryDecoder bin_decoder(data);
Expand Down