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ADR-1084: Use filepath.SplitList for VMAF_MCP_ALLOW path-list parsing

  • Status: Accepted
  • Date: 2026-06-06
  • Deciders: Lusoris
  • Tags: build, windows, mcp

Context

pkg/libvmaf/paths.go parses the VMAF_MCP_ALLOW environment variable by splitting on a hardcoded ":". On Windows the OS path-list separator is ";", not ":", so a value like C:\foo;D:\bar would be incorrectly split at the drive-letter colon (C) rather than at the semicolons. The project CI matrix includes a windows-2025 runner (see .github/workflows/build.yml), confirming Windows is a supported target platform. Go's standard library provides filepath.SplitList, which splits on the correct platform separator transparently.

Decision

Replace strings.Split(extra, ":") with filepath.SplitList(extra) when parsing VMAF_MCP_ALLOW in AllowedRoots (pkg/libvmaf/paths.go).

Alternatives considered

Option Pros Cons Why not chosen
Keep ":" and document that Windows must use ";" No code change User-hostile; silently wrong on Windows; contradicts how the rest of the stdlib works The stdlib already handles this correctly
Accept ":" on Unix and ";" on Windows via build tags Explicit Duplicated logic, fragile filepath.SplitList already does exactly this

Consequences

  • Positive: VMAF_MCP_ALLOW with multiple paths works correctly on Windows (C:\foo;D:\bar) and continues to work on Unix (/a:/b).
  • Negative: None. The change is a one-line swap with identical semantics on Unix (: is the list separator on all Unix-like OSes).
  • Neutral / follow-ups: The strings import is retained because HasPrefix in ValidatePath still needs it; no import churn.

References

  • Go documentation: path/filepath.SplitList — splits a list of paths joined by the OS-specific ListSeparator.
  • .github/workflows/build.yml — os: windows-2025 matrix entry confirms Windows target.