* Add Aes128Key::from_hex method.

* Remove commented out variables from `hdlc_decoder.cpp`

Author: PolarGoose

src/dlms_parser/decryption/aes_128_gcm_decryptor.h

@@ -1,10 +1,12 @@
 #pragma once
 
+#include <charconv>
 #include <cstdint>
 #include <cstring>
 #include <optional>
 #include <array>
 #include <span>
+#include <string_view>
 
 namespace dlms_parser {
 
@@ -23,6 +25,16 @@ class Aes128Key final {
     return Aes128Key(arr);
   }
 
+  [[nodiscard]] static std::optional<Aes128Key> from_hex(std::string_view hex) {
+    if (hex.size() != 32) return std::nullopt;
+    std::array<uint8_t, 16> arr{};
+    for (size_t i = 0; i < 16; ++i) {
+      auto [ptr, ec] = std::from_chars(hex.data() + i * 2, hex.data() + i * 2 + 2, arr[i], 16);
+      if (ec != std::errc{}) return std::nullopt;
+    }
+    return Aes128Key(arr);
+  }
+
   [[nodiscard]] const uint8_t* data() const { return key.data(); }
 
 private:

src/dlms_parser/hdlc_decoder.cpp

@@ -59,10 +59,8 @@ static size_t address_length(std::span<const uint8_t> p) {
   return 0;
 }
 
-static constexpr uint8_t HDLC_FLAG       = 0x7E;
-// static constexpr uint8_t HDLC_ESCAPE     = 0x7D;   // byte-stuffing disabled, see decode_one_()
-// static constexpr uint8_t HDLC_ESCAPE_XOR = 0x20;
-static constexpr uint8_t HDLC_SEG_BIT    = 0x08;  // bit 3 of frame-type byte: "more frames follow"
+static constexpr uint8_t HDLC_FLAG    = 0x7E;
+static constexpr uint8_t HDLC_SEG_BIT = 0x08;  // bit 3 of frame-type byte: "more frames follow"
 
 // ---------------------------------------------------------------------------
 // check() — stateless frame completeness check