fix: prevent stdio_server from closing real stdin/stdout - #2627
Closed
EvanYao826 wants to merge 1 commit into
Closed
fix: prevent stdio_server from closing real stdin/stdout#2627EvanYao826 wants to merge 1 commit into
EvanYao826 wants to merge 1 commit into
Conversation
Copy link
Copy Markdown
Sorry, something went wrong.
Duplicate stdin/stdout file descriptors with os.dup() before wrapping in TextIOWrapper. Without this, closing the wrapper also closes sys.stdin.buffer / sys.stdout.buffer, breaking any subsequent stdio operations in the caller process. Fixes modelcontextprotocol#1933
Copy link
Copy Markdown
Contributor
|
Closing as a duplicate of #2040, which uses the closefd=False approach discussed in review there. Thanks for the contribution. |
Sorry, something went wrong.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
Fixes #1933
stdio_server() wraps sys.stdin.buffer / sys.stdout.buffer in TextIOWrapper. When the server exits, these wrappers close the underlying binary streams, which also closes the real process stdin/stdout. Any subsequent print() or input() in the caller raises ValueError: I/O operation on closed file.
Root cause
TextIOWrapper.__exit__ closes the wrapped buffer. When that buffer is sys.stdin.buffer, the close propagates to the real file descriptor.
Fix
Use os.dup() to duplicate the file descriptors before wrapping. Closing the wrapper now only closes the duplicate, leaving the original process handles intact.
When stdin/stdout lack real file descriptors (e.g. io.BytesIO in tests), fall back to the original behavior.
Changes