module: add a read-only mode to the compile cache - #65302
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A compile cache generated ahead of time and shipped inside an application package should only ever be read: the package may be immutable or covered by an integrity check, and a cache directory that appears at run time would be a surprise. Add readOnly to module.enableCompileCache() and NODE_COMPILE_CACHE_READONLY=1: existing entries are loaded as before, nothing is serialized or persisted, flushCompileCache() is a no-op, and the cache directory is used as found rather than created, so enabling against a missing directory fails instead of making one. Signed-off-by: Shelley Vohr <shelley.vohr@gmail.com>
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A compile cache generated ahead of time and shipped inside an application package should only ever be read: the package may be immutable (an Electron
app.asar, a read-only image) or covered by an integrity check, and a cache directory that appears at run time next to shipped code is a surprise either way. Today enabling the cache always implies writing: the tag directory is created on enable, and every module without an accepted entry is serialized and persisted at exit or onflushCompileCache().This adds
readOnlytomodule.enableCompileCache()andNODE_COMPILE_CACHE_READONLY=1. With it, existing entries are looked up and loaded exactly as before; nothing is serialized into the in-memory store or written to disk,flushCompileCache()is a no-op, the write-permission check is skipped, and the cache directory is used as found rather than created, so enabling against a directory that does not exist fails (FAILED, with a message) instead of making one.EnableOptionbecomes a small flag set (PORTABLE,READ_ONLY) since the two combine. Docs cover the option, the environment variable (cli.md, node.1) and a short section in module.md;test-compile-cache-api-readonlycovers the missing-directory case, reading a previously generated cache without writing new entries, and the environment variable.Context: same application as #65293 (an Electron app shipping its main-process cache in the package); review there asked that production launches never attempt writes.