`devp2p enrdump`: 1 extra prefix byte added for hex representation.

[nalepae]

System information

./devp2p --version
devp2p version 1.14.0-unstable-d8e0807d-20240306

OS & Version: OSX
Commit hash : d8e0807

Expected behaviour

Test vector: https://eips.ethereum.org/EIPS/eip-778#test-vectors

./devp2p enrdump enr:-IS4QHCYrYZbAKWCBRlAy5zzaDZXJBGkcnh4MHcBFZntXNFrdvJjX04jRzjzCBOonrkTfj499SZuOh8R33Ls8RRcy5wBgmlkgnY0gmlwhH8AAAGJc2VjcDI1NmsxoQPKY0yuDUmstAHYpMa2_oxVtw0RW_QAdpzBQA8yWM0xOIN1ZHCCdl8

should produce

...
  "secp256k1" 03ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd3138
...

Actual behaviour

...
  "secp256k1" a103ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd3138
...

Notice the extra a1 at the beginning.
The produced secp256k1 is 34 bytes long, whereas 33 bytes are expected - Source

It seems all hex data are displayed with 1 extra prefix byte.

Example with:

./devp2p enrdump "enr:-Ku4QImhMc1z8yCiNJ1TyUxdcfNucje3BGwEHzodEZUan8PherEo4sF7pPHPSIB1NNuSg5fZy7qFsjmUKs2ea1Whi0EBh2F0dG5ldHOIAAAAAAAAAACEZXRoMpD1pf1CAAAAAP__________gmlkgnY0gmlwhBLf22SJc2VjcDI1NmsxoQOVphkDqal4QzPMksc5wnpuC3gvSC8AfbFOnZY_On34wIN1ZHCCIyg"
Node ID: 191bbf49632da5393590a33d54421e79e8e5c96ade72f0ba69e1803095de6b04
URLv4:   enode://95a61903a9a9784333cc92c739c27a6e0b782f482f007db14e9d963f3a7df8c01ad6a387e8021f13e684e576ca9e5d8759b3116df521b280a887a0bdc72e457f@18.223.219.100:0?discport=9000
Record has sequence number 1 and 6 key/value pairs.
  "attnets"   880000000000000000
  "eth2"      90f5a5fd4200000000ffffffffffffffff
  "id"        "v4"
  "ip"        18.223.219.100
  "secp256k1" a10395a61903a9a9784333cc92c739c27a6e0b782f482f007db14e9d963f3a7df8c0
  "udp"       9000

• secp256k1 has 1 extra bytes (expected: 33 - actual 34) - Source
• eth2 has 1 extra bytes (expected: 16 - actual 17) - Source
• attnets seems to have extra prefix 88

[weiihann]

I think the prefix each means the length of the data followed by it, that is:

• secp256k1 with a prefix of a1, which is 161 in decimal, then 161 - 128 based on the RLP specs, is 33, which represents the length of the actual secp256k1 value in bytes
• eth2 with a prefix of 90, which is 144 in decimal, then 144 - 128 = 16, which represents the length of the actual eth2 value in bytes
• attnets with a prefix of 88, which is 136 in decimal, 136 - 128 = 8, which represents the length of the actual attnets value in bytes

Will work on this issue