XHR: set lengthComputable event property to false if computing length failed

[kettanaito]

With #613 and #616, we've improved how the XHR interceptor calculates the total length of the request/response bodies. There are, however, cases when that length won't be calculated. For example, if getBodyByteLength() function fails (e.g. in Node.js v18.19 structuredClone() throws on cloning Undici Response instances; this has been fixed in later versions).

Per specification, there are also cases when calculating the total length is impossible. I suspect that's a streaming scenario, when the server itself doesn't know the total length of the streamed response body.

In either of those cases, we should set the lengthComputable property on request/response events to false. If the length is computable (default behavior right now), the property must be set to true (we may not be doing that right now).

Materials

• https://developer.mozilla.org/en-US/docs/Web/API/ProgressEvent/lengthComputable

[cu8code]

Hey, is this issue available! Would love to help!

[cu8code]

@kettanaito I am planning to add two checks
at

interceptors/src/interceptors/XMLHttpRequest/XMLHttpRequestController.ts

Line 298 in 2067cb0

const totalRequestBodyLength = await getBodyByteLength(

like this

const totalRequestBodyLength = await getBodyByteLength(this[kFetchRequest]);
    const isRequestLengthComputable = totalRequestBodyLength !== null;

    this.trigger('loadstart', this.request.upload, {
        loaded: 0,
        total: isRequestLengthComputable ? totalRequestBodyLength : 0,
        lengthComputable: isRequestLengthComputable,
    });

and

interceptors/src/interceptors/XMLHttpRequest/XMLHttpRequestController.ts

Line 398 in 2067cb0

const totalResponseBodyLength = await getBodyByteLength(response.clone())

const totalResponseBodyLength = await getBodyByteLength(response.clone());
    const isResponseLengthComputable = totalResponseBodyLength !== null;

    this.trigger('loadstart', this.request, {
        loaded: 0,
        total: isResponseLengthComputable ? totalResponseBodyLength : 0,
        lengthComputable: isResponseLengthComputable,
    });

Would like if you can review my approach!

Also, I wanted to add some test case, but I am a bit confused about how to set up a test for this! There are different runtimes, do I need to write test for individual runtimes! Ex node-browser, also how to structure it?