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fix(shared): strip HTTP optional whitespace before comparing Mcp-Name (#3763) #3764

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fix(shared): strip HTTP optional whitespace before comparing Mcp-Name (#3763) #3764

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5 changes: 3 additions & 2 deletions src/mcp/shared/inbound.py
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Original file line number Diff line number Diff line change
Expand Up @@ -170,9 +170,10 @@ def decode_header_value(value: str | None) -> str | None:
"""
if value is None:
return None
m = _B64_SENTINEL.fullmatch(value)
trimmed = value.strip(' \t')
m = _B64_SENTINEL.fullmatch(trimmed)
if m is None:
return value
return trimmed
payload = m.group("payload")
try:
decoded = base64.b64decode(payload, validate=True)
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8 changes: 8 additions & 0 deletions tests/shared/test_inbound.py
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Original file line number Diff line number Diff line change
Expand Up @@ -311,6 +311,14 @@ def test_header_rung_rejects_missing_or_mismatched_name_header_for_name_bearing_
assert_rejected(classify_inbound_request(body, headers=headers), HEADER_MISMATCH)


def test_header_rung_accepts_whitespace_padded_name_header() -> None:
"""Spec-mandated / RFC 9110: HTTP optional whitespace in Mcp-Name is stripped before comparison."""
body = envelope("tools/call", extra_params={"name": "echo"})
headers = matching_headers(body)
result = classify_inbound_request(body, headers=headers | {MCP_NAME_HEADER: " echo \t"})
assert isinstance(result, InboundModernRoute)


def test_header_rung_decodes_base64_sentinel_before_comparing_name() -> None:
"""Spec-mandated: servers MUST decode the `=?base64?...?=` sentinel before comparing `Mcp-Name`."""
body = envelope("tools/call", extra_params={"name": "résumé"})
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