Code Nextflow extension stuck on “Initializing Nextflow language server…” — fixed by disabling fetchAdditionalSupport/systemCertificates

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Hi all,

I ran into an issue with the VS Code Nextflow extension where it would get stuck indefinitely on:

“Initializing Nextflow language server…”

Environment

  • macOS

  • VS Code (recent version)

  • Nextflow VS Code extension nextflow.nextflow v1.6.1

  • Nextflow CLI installed separately (works fine)

  • Java 17 installed via Homebrew (openjdk@17)

Symptoms

  • The status bar shows Initializing Nextflow language server… and never completes

  • No “Nextflow Language Server” output channel appears

  • Developer Tools console shows repeated errors like:

    TypeError: fetch failed
  at node:internal/deps/undici/undici:14900:13
  at async globalThis.fetch (...)
  at async JC (.../nextflow.nextflow-1.6.1/extension.js)

This happens even when:

  • nextflow.java.home is explicitly set

  • The language server JAR is pre-downloaded and nextflow.languageVersion is pinned

Root cause (likely)

This appears to be a VS Code extension host networking issue related to Node’s fetch + certificate handling on macOS. The failure occurs before the language server actually starts.

Fix / Workaround

Adding the following settings resolved the issue immediately:

{
  "http.fetchAdditionalSupport": false,
  "http.systemCertificates": false
}

After setting these:

  • Reload the window (Developer: Reload Window)

  • The Nextflow language server starts normally

  • Syntax highlighting, validation, etc. work as expected

Notes

  • This is not related to the Nextflow CLI or Java installation

  • curl access to GitHub works fine from the terminal

  • The issue seems specific to VS Code’s internal fetch behavior for extensions

Hopefully this helps other users who hit the same silent failure, and gives maintainers a concrete repro + workaround.

Happy to provide more details if useful.