python-sdk/tests/issues/test_342_base64_encoding.py at main · devilcoder/python-sdk · GitHub

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"""Test for base64 encoding issue in MCP server.

This test demonstrates the issue in server.py where the server uses

urlsafe_b64encode but the BlobResourceContents validator expects standard

base64 encoding.

The test should FAIL before fixing server.py to use b64encode instead of

urlsafe_b64encode.

After the fix, the test should PASS.

"""

import base64

from typing import cast

import pytest

from pydantic import AnyUrl

from mcp.server.lowlevel.helper_types import ReadResourceContents

from mcp.server.lowlevel.server import Server

from mcp.types import (

BlobResourceContents,

ReadResourceRequest,

ReadResourceRequestParams,

ReadResourceResult,

ServerResult,

)

@pytest.mark.anyio

async def test_server_base64_encoding_issue():

"""Tests that server response can be validated by BlobResourceContents.

This test will:

1. Set up a server that returns binary data

2. Extract the base64-encoded blob from the server's response

3. Verify the encoded data can be properly validated by BlobResourceContents

BEFORE FIX: The test will fail because server uses urlsafe_b64encode

AFTER FIX: The test will pass because server uses standard b64encode

"""

server = Server("test")

# Create binary data that will definitely result in + and / characters

# when encoded with standard base64

binary_data = bytes([x for x in range(255)] * 4)

# Register a resource handler that returns our test data

@server.read_resource()

async def read_resource(uri: AnyUrl) -> list[ReadResourceContents]:

return [

ReadResourceContents(

content=binary_data, mime_type="application/octet-stream"

)

]

# Get the handler directly from the server

handler = server.request_handlers[ReadResourceRequest]

# Create a request

request = ReadResourceRequest(

method="resources/read",

params=ReadResourceRequestParams(uri=AnyUrl("test://resource")),

)

# Call the handler to get the response

result: ServerResult = await handler(request)

# After (fixed code):

read_result: ReadResourceResult = cast(ReadResourceResult, result.root)

blob_content = read_result.contents[0]

# First verify our test data actually produces different encodings

urlsafe_b64 = base64.urlsafe_b64encode(binary_data).decode()

standard_b64 = base64.b64encode(binary_data).decode()

assert urlsafe_b64 != standard_b64, "Test data doesn't demonstrate"

" encoding difference"

# Now validate the server's output with BlobResourceContents.model_validate

# Before the fix: This should fail with "Invalid base64" because server

# uses urlsafe_b64encode

# After the fix: This should pass because server will use standard b64encode

model_dict = blob_content.model_dump()

# Direct validation - this will fail before fix, pass after fix

blob_model = BlobResourceContents.model_validate(model_dict)

# Verify we can decode the data back correctly

decoded = base64.b64decode(blob_model.blob)

assert decoded == binary_data

python-sdk/tests/issues/test_342_base64_encoding.py at main · devilcoder/python-sdk · GitHub

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