Optimize bytesToHex function to reuse string and use single definition

lib/libpcsc-cpp/include/pcsc-cpp/pcsc-cpp.hpp

@@ -82,7 +82,9 @@ constexpr uint16_t toSW(byte_type sw1, byte_type sw2) noexcept
 }
 
 /** Convert bytes to hex string. */
-std::string bytes2hexstr(const byte_vector& bytes);
+std::ostream& operator<<(std::ostream& os, const pcsc_cpp::byte_vector& data);
+
+std::string operator+(std::string lhs, const byte_vector& rhs);
 
 /** Struct that wraps response APDUs. */
 struct ResponseApdu
@@ -129,7 +131,7 @@ struct ResponseApdu
 
     friend std::string operator+(std::string&& lhs, const ResponseApdu& rhs)
     {
-        return lhs + pcsc_cpp::bytes2hexstr(rhs.data) + pcsc_cpp::bytes2hexstr({rhs.sw1, rhs.sw2});
+        return lhs + rhs.data + byte_vector {rhs.sw1, rhs.sw2};
     }
 };
 

lib/libpcsc-cpp/src/utils.cpp

@@ -36,11 +36,11 @@ using namespace std::string_literals;
 #undef LOBYTE
 #endif
 
-constexpr byte_type HIBYTE(size_t w)
+constexpr byte_type HIBYTE(size_t w) noexcept
 {
     return static_cast<byte_type>((w >> 8) & 0xff);
 }
-constexpr byte_type LOBYTE(size_t w)
+constexpr byte_type LOBYTE(size_t w) noexcept
 {
     return static_cast<byte_type>(w & 0xff);
 }
@@ -57,10 +57,9 @@ class UnexpectedResponseError : public Error
     explicit UnexpectedResponseError(const CommandApdu& command, const ResponseApdu& response,
                                      const char* file, const int line,
                                      const char* callerFunctionName) :
-        Error("transmitApduWithExpectedResponse(): Unexpected response to command '"s
-              + bytes2hexstr(command) + "' - expected '9000', got '"s + response + "' in "
-              + removeAbsolutePathPrefix(file) + ':' + std::to_string(line) + ':'
-              + callerFunctionName)
+        Error("transmitApduWithExpectedResponse(): Unexpected response to command '"s + command
+              + "' - expected '9000', got '"s + response + "' in " + removeAbsolutePathPrefix(file)
+              + ':' + std::to_string(line) + ':' + callerFunctionName)
     {
     }
 };
@@ -70,15 +69,19 @@ class UnexpectedResponseError : public Error
 namespace pcsc_cpp
 {
 
-std::string bytes2hexstr(const byte_vector& bytes)
+std::ostream& operator<<(std::ostream& os, const pcsc_cpp::byte_vector& data)
 {
-    std::ostringstream hexStringBuilder;
-
-    hexStringBuilder << std::setfill('0') << std::hex;
-
-    for (const auto byte : bytes)
-        hexStringBuilder << std::setw(2) << short(byte);
+    os << std::setfill('0') << std::hex;
+    for (const auto byte : data)
+        os << std::setw(2) << short(byte);
+    return os;
+}
 
+std::string operator+(std::string lhs, const byte_vector& rhs)
+{
+    lhs.reserve(lhs.size() + rhs.size() * 2);
+    std::ostringstream hexStringBuilder(std::move(lhs));
+    hexStringBuilder << rhs;
     return hexStringBuilder.str();
 }
 
@@ -103,8 +106,8 @@ size_t readDataLengthFromAsn1(const SmartCard& card)
     if (response.data[0] != DER_SEQUENCE_TYPE_TAG) {
         // TODO: more specific exception
         THROW(Error,
-              "readDataLengthFromAsn1(): First byte must be SEQUENCE (0x30), but is 0x"s
-                  + bytes2hexstr({response.data[0]}));
+              "readDataLengthFromAsn1(): First byte must be SEQUENCE (0x30), but is "s
+                  + int2hexstr(response.data[0]));
     }
 
     // TODO: support other lenghts besides 2.
@@ -113,8 +116,8 @@ size_t readDataLengthFromAsn1(const SmartCard& card)
         // TODO: more specific exception
         THROW(Error,
               "readDataLengthFromAsn1(): Second byte must be two-byte length indicator "s
-              "(0x82), but is 0x"s
-                  + bytes2hexstr({response.data[1]}));
+              "(0x82), but is "s
+                  + int2hexstr(response.data[1]));
     }
 
     // Read 2-byte length field at offset 2 and 3 and add the 4 DER length bytes.

src/electronic-id.cpp

@@ -213,19 +213,6 @@ const std::vector<MaskedATREntry> MASKED_ATRS = {
      constructor<ElectronicID::Type::LuxEID>},
 };
 
-std::string byteVectorToHexString(const byte_vector& bytes)
-{
-    std::ostringstream hexStringBuilder;
-
-    hexStringBuilder << std::setfill('0') << std::hex;
-
-    for (const auto byte : bytes) {
-        hexStringBuilder << std::setw(2) << static_cast<short>(byte);
-    }
-
-    return hexStringBuilder.str();
-}
-
 const auto SUPPORTED_ALGORITHMS = std::map<std::string, HashAlgorithm> {
     {"SHA-224"s, HashAlgorithm::SHA224},    {"SHA-256"s, HashAlgorithm::SHA256},
     {"SHA-384"s, HashAlgorithm::SHA384},    {"SHA-512"s, HashAlgorithm::SHA512},
@@ -270,8 +257,7 @@ ElectronicID::ptr getElectronicID(const pcsc_cpp::Reader& reader)
 
     // It should be verified that the card is supported with isCardSupported() before
     // calling getElectronicID(), so it is a programming error to reach this point.
-    THROW(ProgrammingError,
-          "Card with ATR '" + byteVectorToHexString(reader.cardAtr) + "' is not supported");
+    THROW(ProgrammingError, "Card with ATR '" + reader.cardAtr + "' is not supported");
 }
 
 bool ElectronicID::isSupportedSigningHashAlgorithm(const HashAlgorithm hashAlgo) const

tests/common/selectcard.hpp

@@ -14,8 +14,3 @@ inline electronic_id::CardInfo::ptr autoSelectSupportedCard() {
 
     return  cardList[0];
 }
-
-inline std::ostream &operator<<(std::ostream &os, const pcsc_cpp::byte_vector &data)
-{
-    return os << pcsc_cpp::bytes2hexstr(data);
-}

tests/integration/test-get-certificate.cpp

@@ -26,6 +26,8 @@
 
 #include <iostream>
 
+using namespace pcsc_cpp;
+
 TEST(electronic_id_test, getCertificate)
 {
     using namespace electronic_id;