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filesystem: read_text_file with head: 0 or tail: 0 returns the whole file #5184
Description
Problem
read_text_file in src/filesystem/server.ts tests head and tail for truthiness. A request for zero lines (head: 0 or tail: 0) falls through to reading the whole file, and head: 0, tail: 0 together is not rejected. The schemas accept any number, so negative or fractional counts reach headFile and tailFile in src/filesystem/lib.ts.
Expected
head and tail are checked against undefined, accept only non-negative integers, and a count of 0 returns an empty result.
Prior work
The PR(s) above targeted the pre-refactor code and are closed as part of the backlog triage in #4875; this issue is where the work continues, with the PR(s) as a prototype. Thank you to their authors.
Activity
cliffhall commentedon Oct 20, 2026
Triage: Priority Low (total 5)
buglabelFiled from the PR backlog triage (#4877). Board: Servers V2 (#43), Status
Incoming, awaiting maintainer review (no milestone yet).KissFeng commentedon Oct 26, 2026
I have prepared and verified a fix for this on a branch in my fork:
Branch:
fix/filesystem-head-tail-zeroCommit:
cc4b040Solution
src/filesystem/server.ts, explicit checkshead !== undefinedandtail !== undefinedare used instead of truthiness. When either is 0, an empty string""is returned immediately without reading the whole file.head: 0andtail: 0are supplied.src/filesystem/server.tsto enforce.int().min(0)so negative or fractional counts are rejected early.Validation
head: 0andtail: 0insrc/filesystem/__tests__/server-tools.test.ts.npm test --workspace=@modelcontextprotocol/server-filesystem..changeset/filesystem-head-tail-zero.md).Feel free to cherry-pick or pull from this branch whenever ready.
cliffhall commentedon Oct 29, 2026
Shipped in #5377, merged into
v2/main; it releases with milestone v2.3.0. Tested together with the rest of the #5269 work in the rollup #5405.fix(filesystem): return no lines for read_text_file head/tail 0