fix(download): await temp-file unlink + cp() to stop ENOENT race + un…

[NadeemIqbal]

Fixes #1018.

Summary

_downloadFile had two latent bugs that surface together on Android 14 + New Architecture. Rewriting the function with proper async/await throughout closes both — no public API change.

Root cause

1. ENOENT race on .pdf.tmp

The pre-fetch cleanup was fire-and-forget:

const tempCacheFile = cacheFile + '.tmp';
this._unlinkFile(tempCacheFile);   // returns a Promise, not awaited

this.lastRNBFTask = ReactNativeBlobUtil.config({ path: tempCacheFile, ... }).fetch(...)

_unlinkFile is async, so the deletion of tempCacheFile runs concurrently with the native open(path) inside ReactNativeBlobUtil.fetch. On Android 14 + New Architecture the timing flips and open lands while the file is mid-delete, surfacing as:

Error: /data/user/0/<pkg>/cache/<sha1>.pdf.tmp: open failed: ENOENT (No such file or directory)

2. Uncaught rejection bypassing onError

The success path was structured as:

this.lastRNBFTask = config().fetch().progress().catch(handler);
this.lastRNBFTask
    .then(async (res) => {
        ...
        ReactNativeBlobUtil.fs.cp(tempCacheFile, cacheFile)   // not awaited
            .then(() => { ... })
            .catch(async (error) => { throw error });          // re-throw escapes
    })
    .catch(...);

The inner cp(...).then(...).catch(err => { throw err }) is never awaited from the outer .then. Any cp rejection re-thrown from the inner .catch becomes an unhandled promise rejection instead of propagating to the outer .catch → _onError is never called → the onError prop never fires.

Fix

Rewrite _downloadFile with async/await throughout — single try/catch covering the whole flow:

• await the temp-file unlink before starting the fetch (closes the ENOENT race)
• await the fetch, stat check, cacheFile unlink, and cp into the final location, all inside one try
• Single catch cleans up both temp + final files and calls _onError exactly once

this.lastRNBFTask is still assigned to the in-flight fetch task before await, so the cancellation paths in setNativeProps / componentWillUnmount still find a cancellable task.

API impact

None. Public component API unchanged. No new dependencies.

Test plan

• Android 14 (API 34) with newArchEnabled=true — <Pdf source={{ uri: '<remote-url>', cache: true }} /> on fresh install no longer crashes with ENOENT
• Forced network failure (airplane mode / 404 URL) → error flows through the onError prop (was: escaped as Uncaught (in promise))
• Android 13 + old architecture — no regression
• iOS — no regression (this path is shared, but the bug only manifested on Android)
• Repeated unmount/remount mid-download — cancel() still aborts the fetch correctly

Syntax verified locally via node --check index.js.