Tag-only protocols in multiaddr (such as /webrtc, /webrtc-direct, /noise, /quic, /http, etc) are protocols that should not be followed by any argument or value. For example, /webrtc is valid, but /webrtc/value or /webrtc=foo should be rejected.

Currently, there are two bugs affecting tag-only protocol parsing:

1. Incorrect Error Message for /tag/value Form

When parsing an address like /webrtc/value or /webrtc-direct/value, the result is rejected, but the error message is misleading:

Error: Invalid MultiAddr '/webrtc-direct/value': unknown protocol: value (string: /webrtc-direct/value)

Expected error:

Protocol 'webrtc-direct' does not take an argument

This results in confusion for users: it makes it look like "value" is an unknown protocol, rather than clearly saying that a value was wrongly given.

2. = Syntax Validation Bypass (Potential Validation Bug)

There is currently no coverage or test for what happens with /webrtc=value or /webrtc-direct=value. There are strong indications from code review (see WEBRTC_TEST_REPORT.md) that these are silently accepted as valid, which is a true validation bug. These addresses should not be accepted for tag-only protocols.

Example of problematic cases:

Multiaddr("/webrtc=value")            # Should fail, may incorrectly succeed
Multiaddr("/webrtc-direct=foo123")    # Should fail, may incorrectly succeed

Steps to Reproduce

1. Try parsing: /webrtc/value and /webrtc-direct/value
   • Observe error message is unhelpful ("unknown protocol: value") instead of "does not take an argument".
2. Try parsing: /webrtc=value and /webrtc-direct=foo
   • Check whether these are accepted or rejected. If accepted, it's a serious bug.

Expected Behavior

• An address like /tag (for tag-only protocols) should be accepted.
• An address like /tag/value or /tag=value should fail with an error message:

  Protocol 'tag' does not take an argument
  

• No silent acceptance of /tag=anything should occur.

Actual Behavior

• /tag/value is rejected, but with a bad error message ("unknown protocol: value").
• /tag=foo is either accepted (validation bug) or produces unclear output—needs confirmed/covered by tests.

What Should Be Fixed

• Improve validation and error reporting for tag-only protocols:
  • If given a value via /tag/value or /tag=value, raise a clear error: "Protocol '' does not take an argument"
• Add/extend tests:
  • Reject /webrtc=value, /webrtc-direct=value, /quic=abc, etc with correct error.
  • Ensure /protocol/value gets correct error.
• (Stretch) Audit all tag-only protocols in protocol table for this behavior.

@seetadev @lla-dane I would like to work in this issue, I discovered it after testing the webrtc_examples.py
with @Nkovaturient