{"record":{"id":"d0ec57169241b2c3","repo":"rohitg00/ai-engineering-from-scratch","slug":"32020","errorCode":"-32020","errorMessage":"Malformed Base64 MCP header value","messagePattern":"Malformed Base64 MCP header value","errorType":"validation","errorClass":"RpcFault","httpStatus":null,"severity":"error","filePath":"phases/13-tools-and-protocols/09-mcp-transports/code/main.py","lineNumber":130,"sourceCode":"    return origin is None or origin in ORIGIN_ALLOWLIST\n\n\ndef encode_header_value(value: str) -> str:\n    safe = all(0x20 <= ord(character) <= 0x7E for character in value)\n    sentinel = value.startswith(\"=?base64?\") and value.endswith(\"?=\")\n    if safe and value == value.strip() and not sentinel:\n        return value\n    encoded = base64.b64encode(value.encode(\"utf-8\")).decode(\"ascii\")\n    return f\"=?base64?{encoded}?=\"\n\n\ndef decode_header_value(value: str) -> str:\n    if value.startswith(\"=?base64?\") and value.endswith(\"?=\"):\n        encoded = value[len(\"=?base64?\") : -2]\n        try:\n            return base64.b64decode(encoded, validate=True).decode(\"utf-8\")\n        except (ValueError, UnicodeDecodeError) as exc:\n            raise RpcFault(-32020, \"Malformed Base64 MCP header value\") from exc\n    if any(ord(character) < 0x20 or ord(character) > 0x7E for character in value):\n        raise RpcFault(-32020, \"Malformed MCP header value\")\n    return value\n\n\ndef body_name(message: dict[str, Any]) -> str | None:\n    params = message.get(\"params\", {})\n    if message.get(\"method\") == \"resources/read\":\n        value = params.get(\"uri\")\n    elif message.get(\"method\") in {\"tools/call\", \"prompts/get\"}:\n        value = params.get(\"name\")\n    else:\n        return None\n    return value if isinstance(value, str) else None\n\n\ndef http_headers_for(\n    message: dict[str, Any],","sourceCodeStart":112,"sourceCodeEnd":148,"githubUrl":"https://github.com/rohitg00/ai-engineering-from-scratch/blob/39ea8a1c6d0b61f071226eff7ede4d4105fed820/phases/13-tools-and-protocols/09-mcp-transports/code/main.py#L112-L148","documentation":"Error \"Malformed Base64 MCP header value\" thrown in rohitg00/ai-engineering-from-scratch.","triggerScenarios":"Thrown at phases/13-tools-and-protocols/09-mcp-transports/code/main.py:130 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"39ea8a1c6d0b61f071226eff7ede4d4105fed820","analyzedAt":"2026-08-26T03:13:46.626Z","schemaVersion":2},"datasetVersion":"2026-08-26T07:17:17.940Z"}