chore: import upstream snapshot with attribution

tests/issues/test_342_base64_encoding.py

@@ -0,0 +1,52 @@
+"""Test for base64 encoding issue in MCP server.
+
+This test verifies that binary resource data is encoded with standard base64
+(not urlsafe_b64encode), so BlobResourceContents validation succeeds.
+"""
+
+import base64
+
+import pytest
+from mcp_types import BlobResourceContents
+
+from mcp import Client
+from mcp.server.mcpserver import MCPServer
+
+pytestmark = pytest.mark.anyio
+
+
+async def test_server_base64_encoding():
+    """Tests that binary resource data round-trips correctly through base64 encoding.
+
+    The test uses binary data that produces different results with urlsafe vs standard
+    base64, ensuring the server uses standard encoding.
+    """
+    mcp = MCPServer("test")
+
+    # Create binary data that will definitely result in + and / characters
+    # when encoded with standard base64
+    binary_data = bytes(list(range(255)) * 4)
+
+    # Sanity check: our test data 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"
+
+    @mcp.resource("test://binary", mime_type="application/octet-stream")
+    def get_binary() -> bytes:
+        """Return binary test data."""
+        return binary_data
+
+    async with Client(mcp) as client:
+        result = await client.read_resource("test://binary")
+        assert len(result.contents) == 1
+
+        blob_content = result.contents[0]
+        assert isinstance(blob_content, BlobResourceContents)
+
+        # Verify standard base64 was used (not urlsafe)
+        assert blob_content.blob == standard_b64
+
+        # Verify we can decode the data back correctly
+        decoded = base64.b64decode(blob_content.blob)
+        assert decoded == binary_data