Return buffer instead of file_path if cache unavailable for model loading

[PrafulB]

This PR resolves #1249 and #1279 . When running in a Node.js environment, there's an edge case where the unavailability of a caching system causes an error when loading model files. The problematic code is here.. Can be verified by simply setting both env.useFSCache and env.useCustomCache to false.

Specifically, in a Node.js environment, getModelFile() attempts to download the respective model.onnx (or equivalent) file, store it in a cache and return the path to it. In cases where caching is disabled or unavailable and a remote model is to be loaded, cache stays undefined and the cache.match() call throws an error. Can be verified by simply setting both env.useFSCache and env.useCustomCache to false.

This PR makes it so that the file_path is only requested if the environment is Node.js AND either of the two caching options are available. Otherwise, the buffer containing the model file is returned as is.

[xenova]

@PrafulB I made some minor modifications to also allow for custom cache mechanisms to work with Response or string return values. i.e., the following cases now all work:

import * as transformers from '@huggingface/transformers';

async function run() {
    const pipe = await transformers.pipeline(
        "sentiment-analysis",
        "Xenova/distilbert-base-uncased-finetuned-sst-2-english",
        { dtype: "fp32" }
    );
    const result = await pipe("I love transformers.js!");
    console.log(result);
}

// Default
await run();

// No file cache
transformers.env.useFSCache = false;
await run();
transformers.env.useFSCache = true;

// Custom cache that does nothing
class CustomCache {
    async put(key, value) {
        /* Simulate adding nothing to the cache (e.g., no more storage available) */
    }
    async match(key) {
        /* Simulate a cache miss */
    }
}

transformers.env.useCustomCache = true;
transformers.env.customCache = new CustomCache();
await run();

I'm hoping to include this fix in the next version (v3.5), so if possible, can you confirm these changes meet your requirements still? Thanks!

[HuggingFaceDocBuilderDev]

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[PrafulB]

The changes look good to me. If I could make one final suggestion though? In the case where both useFSCache and useCustomCache are set to true (perhaps because useFSCache is true by default and the user forgot to unset it), the code defaults to the FileCache instead of the user-defined custom cache (see utils/hub.js L437). It should be the other way around, no?
Perhaps I should have raised another issue, but the fix seems simple enough, just inverting the order of the two if blocks should do the trick.
To that point, the test code you posted does not actually use the CustomCache implementation because you reset useFSCache to true after the second run() 😛.

[PrafulB]

Created PR #1285 to track this and keep it separate from this one.

[xenova]

Great point! 🧠 Thanks!