# TODO: We don't need "/p2p/{peer_id}" postfix actually

[acul71]

TODO Analysis: BasicHost.get_addrs() p2p Postfix Issue

Issue Location

File: libp2p/host/basic_host.py:140
Method: get_addrs()
TODO Comment: # TODO: We don't need "/p2p/{peer_id}" postfix actually.

Current Status Analysis

Current Implementation

The get_addrs() method in BasicHost currently:

1. Gets the peer ID from self.get_id()
2. Creates a p2p multiaddr part: f"/p2p/{self.get_id()!s}"
3. Iterates through all transport listeners in self._network.listeners.values()
4. For each listener, gets its addresses via transport.get_addrs()
5. Encapsulates each address with the p2p part using addr.encapsulate(p2p_part)

def get_addrs(self) -> list[multiaddr.Multiaddr]:
    """
    :return: all the multiaddr addresses this host is listening to
    """
    # TODO: We don't need "/p2p/{peer_id}" postfix actually.
    p2p_part = multiaddr.Multiaddr(f"/p2p/{self.get_id()!s}")

    addrs: list[multiaddr.Multiaddr] = []
    for transport in self._network.listeners.values():
        for addr in transport.get_addrs():
            addrs.append(addr.encapsulate(p2p_part))
    return addrs

What the TODO Suggests

The TODO suggests that the /p2p/{peer_id} postfix should not be added to the addresses returned by get_addrs().

What Must Be Done to Fix This Issue

1. Remove the p2p encapsulation

The fix would be to simply return the raw transport addresses without adding the /p2p/{peer_id} postfix:

def get_addrs(self) -> list[multiaddr.Multiaddr]:
    """
    :return: all the multiaddr addresses this host is listening to
    """
    addrs: list[multiaddr.Multiaddr] = []
    for transport in self._network.listeners.values():
        for addr in transport.get_addrs():
            addrs.append(addr)  # Remove the .encapsulate(p2p_part)
    return addrs

2. Impact Analysis Required

a) Interface Compliance

• The IHost interface in abc.py defines get_addrs() to return list[Multiaddr]
• The interface doesn't specify whether addresses should include the p2p postfix
• Other implementations like PeerData.get_addrs() return raw addresses without p2p postfix

b) Usage Patterns

• Many tests and examples expect addresses with p2p postfix for peer identification
• The identify protocol uses host.get_addrs() to share listening addresses
• Some code explicitly decapsulates the p2p part (see tests/utils/interop/utils.py:32)

c) Transport Layer Behavior

• Transport listeners (like TCPListener) return raw addresses like /ip4/127.0.0.1/tcp/8000
• The network layer manages the relationship between addresses and peer IDs

3. Recommended Approach

Option A: Remove p2p postfix (as TODO suggests)

Pros:

• Cleaner separation of concerns
• Transport addresses are pure
• Aligns with transport layer behavior

Cons:

• Breaking change
• Requires updating all code that expects p2p addresses

Option B: Keep current behavior but add a new method

Pros:

• Backward compatibility
• Clear separation of concerns

Cons:

• API bloat
• Potential confusion about which method to use

Implementation:

def get_transport_addrs(self) -> list[multiaddr.Multiaddr]:
    """Return raw transport addresses without p2p postfix."""
    addrs: list[multiaddr.Multiaddr] = []
    for transport in self._network.listeners.values():
        for addr in transport.get_addrs():
            addrs.append(addr)
    return addrs

def get_addrs(self) -> list[multiaddr.Multiaddr]:
    """Return addresses with p2p postfix (for backward compatibility)."""
    # Current implementation

Option C: Make it configurable

Pros:

• Flexible
• Backward compatibility with default

Cons:

• More complex API
• Potential for inconsistent usage

Implementation:

def get_addrs(self, include_p2p: bool = True) -> list[multiaddr.Multiaddr]:
    """
    :param include_p2p: Whether to include p2p postfix
    :return: all the multiaddr addresses this host is listening to
    """
    addrs: list[multiaddr.Multiaddr] = []
    for transport in self._network.listeners.values():
        for addr in transport.get_addrs():
            if include_p2p:
                p2p_part = multiaddr.Multiaddr(f"/p2p/{self.get_id()!s}")
                addrs.append(addr.encapsulate(p2p_part))
            else:
                addrs.append(addr)
    return addrs

4. Required Changes if Implementing Option A

1. Update the method implementation (remove encapsulation)
2. Update all tests that expect p2p addresses
3. Update examples that use get_addrs()
4. Update documentation to clarify the new behavior
5. Consider adding a new method like get_p2p_addrs() if p2p addresses are still needed

5. Testing Strategy

You would need to:

1. Run the full test suite to identify breaking changes
2. Update tests that expect p2p addresses
3. Verify that peer discovery and identification still work correctly
4. Test interoperability with other libp2p implementations

6. Files That Would Need Updates

Core Implementation

• libp2p/host/basic_host.py - Main implementation

Tests (if breaking change)

• tests/core/host/test_*.py - Host-related tests
• tests/core/identity/identify/test_*.py - Identify protocol tests
• tests/core/examples/test_examples.py - Example tests
• tests/utils/interop/utils.py - Interop utilities

Examples

• examples/*/ - All example files that use get_addrs()

Documentation

• docs/ - Update any documentation referencing the behavior

Conclusion

The TODO suggests this is a known issue that needs addressing, but it requires careful consideration of the impact on the entire codebase and ecosystem. The choice between the three options depends on:

• Timeline: How quickly the change needs to be made
• Compatibility requirements: Whether backward compatibility is required
• Codebase maturity: How many external users depend on the current behavior

Recommendation: Start with Option B (add new method) to maintain backward compatibility while providing the cleaner API, then consider deprecating the old behavior in a future major version.

[pacrob]

This is a great breakdown, @acul71, thanks! I agree with your recommendation.