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Add decoding and encoding of BitString ASN.1 records (#1850)
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‎Packet++/header/Asn1Codec.h

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@@ -6,6 +6,7 @@
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#include <stdexcept>
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#include <sstream>
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#include <chrono>
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#include <bitset>
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#include "PointerVector.h"
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/// @file
@@ -747,4 +748,59 @@ namespace pcpp
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Asn1GeneralizedTimeRecord() = default;
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std::string m_Timezone;
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};
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/// @class Asn1BitStringRecord
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/// Represents an ASN.1 record with a value of type BitString
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class Asn1BitStringRecord : public Asn1PrimitiveRecord
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{
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friend class Asn1Record;
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public:
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/// A constructor to create a record of type BitString
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/// @param value A bit string to set as the record value
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/// @throw std::invalid_argument if the string is not a valid bit string
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explicit Asn1BitStringRecord(const std::string& value);
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/// @return The bit string value of this record
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std::string getValue()
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{
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decodeValueIfNeeded();
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return m_Value.toString();
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};
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protected:
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void decodeValue(uint8_t* data, bool lazy) override;
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std::vector<uint8_t> encodeValue() const override;
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std::vector<std::string> toStringList() override;
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private:
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class BitSet
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{
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public:
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BitSet() = default;
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explicit BitSet(const std::string& value);
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BitSet(const uint8_t* data, size_t numBits);
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BitSet& operator=(const std::string& value);
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size_t sizeInBytes() const;
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std::string toString() const;
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std::vector<uint8_t> toBytes() const;
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size_t getNumBits() const
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{
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return m_NumBits;
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}
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private:
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void initFromString(const std::string& value);
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std::vector<std::bitset<8>> m_Data;
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size_t m_NumBits = 0;
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};
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Asn1BitStringRecord() = default;
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BitSet m_Value;
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};
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} // namespace pcpp

‎Packet++/src/Asn1Codec.cpp

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Original file line numberDiff line numberDiff line change
@@ -338,6 +338,11 @@ namespace pcpp
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newRecord = new Asn1BooleanRecord();
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break;
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}
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case Asn1UniversalTagType::BitString:
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{
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newRecord = new Asn1BitStringRecord();
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break;
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}
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case Asn1UniversalTagType::Null:
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{
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newRecord = new Asn1NullRecord();
@@ -1203,4 +1208,110 @@ namespace pcpp
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auto timeString = osstream.str();
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return { timeString.begin(), timeString.end() };
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}
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void Asn1BitStringRecord::BitSet::initFromString(const std::string& value)
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{
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m_NumBits = value.length();
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size_t numBytes = (m_NumBits + 7) / 8;
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m_Data.clear();
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m_Data.reserve(numBytes);
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size_t i = 0;
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while (i < value.length())
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{
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std::string curByteString = value.substr(i, 8);
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curByteString.append(8 - curByteString.length(), '0');
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try
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{
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std::bitset<8> bs(curByteString);
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m_Data.push_back(bs);
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i += 8;
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}
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catch (const std::invalid_argument&)
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{
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throw std::invalid_argument("Invalid bit string");
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}
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}
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}
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Asn1BitStringRecord::BitSet::BitSet(const std::string& value)
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{
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initFromString(value);
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}
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Asn1BitStringRecord::BitSet::BitSet(const uint8_t* data, size_t numBits) : m_NumBits(numBits)
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{
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if (!data || !numBits)
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{
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throw std::invalid_argument("Provided data is null or num of bits is 0");
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}
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size_t requiredBytes = (m_NumBits + 7) / 8;
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m_Data.resize(requiredBytes);
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std::copy_n(data, requiredBytes, m_Data.begin());
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}
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Asn1BitStringRecord::BitSet& Asn1BitStringRecord::BitSet::operator=(const std::string& value)
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{
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initFromString(value);
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return *this;
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}
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std::string Asn1BitStringRecord::BitSet::toString() const
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{
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std::string result;
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result.reserve(m_Data.size() * 8);
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for (const auto bs : m_Data)
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{
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result += bs.to_string();
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}
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result.resize(m_NumBits);
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return result;
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}
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std::vector<uint8_t> Asn1BitStringRecord::BitSet::toBytes() const
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{
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std::vector<uint8_t> result;
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result.reserve(m_Data.size());
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for (const auto& bs : m_Data)
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{
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result.push_back(static_cast<uint8_t>(bs.to_ulong()));
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}
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return result;
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}
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size_t Asn1BitStringRecord::BitSet::sizeInBytes() const
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{
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return m_Data.size();
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}
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Asn1BitStringRecord::Asn1BitStringRecord(const std::string& value)
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: Asn1PrimitiveRecord(Asn1UniversalTagType::BitString)
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{
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m_Value = value;
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m_ValueLength = m_Value.sizeInBytes() + 1;
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m_TotalLength = m_ValueLength + 2;
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}
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void Asn1BitStringRecord::decodeValue(uint8_t* data, bool lazy)
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{
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auto numBits = (m_ValueLength - 1) * 8 - static_cast<size_t>(data[0]);
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m_Value = BitSet(data + 1, numBits);
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}
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std::vector<uint8_t> Asn1BitStringRecord::encodeValue() const
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{
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auto result = m_Value.toBytes();
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size_t unusedBits = m_Value.sizeInBytes() * 8 - m_Value.getNumBits();
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result.insert(result.begin(), static_cast<uint8_t>(unusedBits));
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return result;
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}
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std::vector<std::string> Asn1BitStringRecord::toStringList()
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{
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return { Asn1Record::toStringList().front() + ", Value: " + m_Value.toString() };
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}
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} // namespace pcpp

‎Tests/Packet++Test/Tests/Asn1Tests.cpp

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@@ -372,6 +372,36 @@ PTF_TEST_CASE(Asn1DecodingTest)
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}
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}
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// BitString with 0 unused bytes
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{
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uint8_t data[20];
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auto dataLen = pcpp::hexStringToByteArray("030300a3b5", data, 20);
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auto record = pcpp::Asn1Record::decode(data, dataLen);
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PTF_ASSERT_EQUAL(record->getTagClass(), pcpp::Asn1TagClass::Universal, enumclass);
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PTF_ASSERT_FALSE(record->isConstructed());
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PTF_ASSERT_EQUAL(record->getUniversalTagType(), pcpp::Asn1UniversalTagType::BitString, enumclass);
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PTF_ASSERT_EQUAL(record->getTotalLength(), 5);
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PTF_ASSERT_EQUAL(record->getValueLength(), 3);
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PTF_ASSERT_EQUAL(record->castAs<pcpp::Asn1BitStringRecord>()->getValue(), "1010001110110101");
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PTF_ASSERT_EQUAL(record->toString(), "BitString, Length: 2+3, Value: 1010001110110101");
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}
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// BitString with unused bytes
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{
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uint8_t data[20];
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auto dataLen = pcpp::hexStringToByteArray("030306b2c0", data, 20);
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auto record = pcpp::Asn1Record::decode(data, dataLen);
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PTF_ASSERT_EQUAL(record->getTagClass(), pcpp::Asn1TagClass::Universal, enumclass);
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PTF_ASSERT_FALSE(record->isConstructed());
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PTF_ASSERT_EQUAL(record->getUniversalTagType(), pcpp::Asn1UniversalTagType::BitString, enumclass);
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PTF_ASSERT_EQUAL(record->getTotalLength(), 5);
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PTF_ASSERT_EQUAL(record->getValueLength(), 3);
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PTF_ASSERT_EQUAL(record->castAs<pcpp::Asn1BitStringRecord>()->getValue(), "1011001011");
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PTF_ASSERT_EQUAL(record->toString(), "BitString, Length: 2+3, Value: 1011001011");
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}
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// Sequence
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{
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uint8_t data[20];
@@ -979,6 +1009,35 @@ PTF_TEST_CASE(Asn1EncodingTest)
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"Invalid timezone format. Use 'Z' or '+/-HHMM'.");
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}
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// BitString with 0 unused bytes
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{
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pcpp::Asn1BitStringRecord record("1010001110110101");
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uint8_t data[20];
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auto dataLen = pcpp::hexStringToByteArray("030300a3b5", data, 20);
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auto encodedValue = record.encode();
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PTF_ASSERT_EQUAL(encodedValue.size(), dataLen);
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PTF_ASSERT_BUF_COMPARE(encodedValue.data(), data, dataLen)
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}
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// BitString with unused bytes
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{
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pcpp::Asn1BitStringRecord record("1011001011");
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uint8_t data[20];
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auto dataLen = pcpp::hexStringToByteArray("030306b2c0", data, 20);
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auto encodedValue = record.encode();
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PTF_ASSERT_EQUAL(encodedValue.size(), dataLen);
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PTF_ASSERT_BUF_COMPARE(encodedValue.data(), data, dataLen)
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}
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// BitString invalid value
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{
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PTF_ASSERT_RAISES(pcpp::Asn1BitStringRecord record("0011invalid"), std::invalid_argument, "Invalid bit string");
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}
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// Sequence
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{
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pcpp::Asn1OctetStringRecord octestStringRecord("abcd");

‎cppcheckSuppressions.txt

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@@ -9,6 +9,7 @@ unusedStructMember:*
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noExplicitConstructor:Common++/header/IpAddress.h
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noExplicitConstructor:Common++/header/MacAddress.h
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useStlAlgorithm:Packet++/src/Asn1Codec.cpp
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noExplicitConstructor:Pcap++/header/PcapFileDevice.h
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missingOverride:Pcap++/*

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