`tools/gen_code_table.py` uses fragile name-pattern categorization instead of tag data

[sumanjeet0012]

tools/gen_code_table.py re-derives codec categories (multihash, multiaddr, ipld, etc.) from name patterns instead of using the tag data that is available in the upstream CSV. This duplicates the same fragile logic as _get_tag() and can misclassify codecs.

Problem

In tools/gen_code_table.py (lines 80–165), codecs are categorized using 8 separate pattern lists:

multihash_patterns = ["sha", "keccak", "blake", "md4", "md5", "ripemd", ...]
multiaddr_patterns = ["ip4", "tcp", "udp", "dns", "quic", ...]
ipld_patterns = ["cid", "raw", "dag-", "eth-", "bitcoin", ...]
# ... 5 more pattern lists

Each codec name is tested against these patterns using substring matching:

if any(h in name for h in multihash_patterns):
    categories["multihash"].append(...)
elif any(a in name for a in multiaddr_patterns):
    categories["multiaddr"].append(...)

Problems:

1. Duplicates _get_tag() logic — same fragile pattern matching in two places
2. Can misclassify — a codec named "sha2-transport" would match multihash_patterns before transport
3. Missing categories — codecs in categories like multisig, nonce, vlad, shelter, softhash, multikey all fall into "other" because there are no patterns for them
4. Maintenance burden — adding a new codec category requires updating pattern lists in TWO files (gen_code_table.py and code.py)

Proposed Solution

1. Once constants.py includes tag metadata (see related issue), update gen_code_table.py to read the tag directly:

   for name, info in sorted(CODECS.items(), key=lambda x: x[1]["prefix"]):
       tag = info.get("tag", "other")
       categories[tag].append((const_name, info["prefix"], name))

2. Remove all 8 pattern lists from gen_code_table.py.

3. Use the tag as the section header in the generated code_table.py:

   # Multihash
   SHA2_256: Code = Code(0x12)  # sha2-256
   ...
   # Multiaddr
   IP4: Code = Code(0x04)  # ip4
   ...

Related

• Issue: constants.py entries lack tag metadata
• Issue: Replace hardcoded _get_tag() with data-driven TAG_TABLE
• Generator: tools/gen_code_table.py