Improve Multiaddr Protocol Stack Handling using decapsulate_code()

Problem

Currently the code manually removes protocols using string-constructed Multiaddr objects
Location: libp2p/transport/websocket/multiaddr_utils.py

rest_multiaddr = rest_multiaddr.decapsulate(Multiaddr("/ws"))
rest_multiaddr = rest_multiaddr.decapsulate(Multiaddr(f"/sni/{sni}"))
rest_multiaddr = rest_multiaddr.decapsulate(Multiaddr("/tls"))

And circuit relay parsing performs complex protocol extraction logic instead of using protocol stack operations.

# Lines 480-521: Complex manual parsing of circuit addresses
def _parse_circuit_multiaddr(self, ma: multiaddr.Multiaddr) -> tuple[multiaddr.Multiaddr, ID]:
    # Manual protocol extraction and parsing

Drawbacks:

• String parsing overhead
• Error-prone when protocol ordering varies
• Harder to read intent
• Duplicates functionality already provided by py-multiaddr
• Fragile for edge cases (optional protocols, reordered stacks)

Proposed Solution or improvement

Use decapsulate_code(protocol_code) provided by py-multiaddr and replace some manual instance from codebase

Location: libp2p/transport/websocket/multiaddr_utils.py

# current code
rest_multiaddr = rest_multiaddr.decapsulate(Multiaddr("/ws"))
rest_multiaddr = rest_multiaddr.decapsulate(Multiaddr(f"/sni/{sni}"))
rest_multiaddr = rest_multiaddr.decapsulate(Multiaddr("/tls"))

# Replace
from multiaddr.protocols import P_WS, P_SNI, P_TLS
rest_multiaddr = maddr.decapsulate_code(P_WS)
if sni:
    rest_multiaddr = rest_multiaddr.decapsulate_code(P_SNI)
rest_multiaddr = rest_multiaddr.decapsulate_code(P_TLS)

Location: libp2p/relay/circuit_v2/transport.py

Simplify manual protocol extraction logic in _parse_circuit_multiaddr by using protocol codes

# Current code
# Lines 480-521: Complex manual parsing of circuit addresses
def _parse_circuit_multiaddr(self, ma: multiaddr.Multiaddr) -> tuple[multiaddr.Multiaddr, ID]:
    # Manual protocol extraction and parsing

# Replace
from multiaddr.protocols import P_P2P_CIRCUIT, P_P2P
# remove /p2p-circuit layer
circuit_base = ma.decapsulate_code(P_P2P_CIRCUIT)
# extract relay peer address
relay_addr = circuit_base.decapsulate_code(P_P2P)

Are you planning to do it yourself in a pull request?

Yes, the above improvements plan and suggestions are referred from discussion (py-libp2p Multiaddr Integration Status and Improvement Opportunities) #1171

@seetadev @acul71

Start in libp2p/transport/websocket/multiaddr_utils.py at the listed decapsulation code, then read _parse_circuit_multiaddr in libp2p/relay/circuit_v2/transport.py. Compare the current manual handling with py-multiaddr protocol-code operations, including optional and reordered protocols. Done means both locations use protocol codes while preserving websocket and circuit address behavior.