Get Out of a TextDecoderStream() from NodeJS

Question

When I send an error message from my express nodejs app using res.status(400).send(err.stack);, I cannot seem to get out of the decoder stream I setup on the receiving end.

Here is my code in the browser (limited to the fetch portion):

fetch("/the/url", {
    method: "POST",
    body: formData,
}).then(response => {
    if (response.status === 200) {
        return response.blob().then((data) => {
            return data;
        });
    } else {
        return new Promise((resolve, reject) => {
            let err_message = "";
            let reader = response.body.pipeThrough(new TextDecoderStream()).getReader();
            reader.read().then(({done, value}) => {
                // When no more data needs to be consumed, close the stream
                if (done) {
                    reject(err_message);
                    return;
                }
                // Enqueue the next data chunk into our target stream
                err_message += value;
            });
        }).then((res) => {
            return (res)
        }).catch((err) => {
            return (err)
        });
    }
}).then((res) => {
    console.log(res)
}).catch((err) => {
    console.log(err)
});

I have put breakpoints on all subsequent then and catch but it never resolves/rejects.

Appreciate any pointers.

Chapo · Accepted Answer · 2021-03-09 03:12:26Z

In case it's helpful to someone, you need to make a recursive call to the same function to break out properly. As per the following :

fetch("/the/url", {
    method: "POST",
    body: formData,
}).then(response => {
    if (response.status === 200) {
        return response.blob().then((data) => {
            return data;
        });
    } else {
        return new Promise((resolve, reject) => {
            let err_message = "";
            let reader = response.body.pipeThrough(new TextDecoderStream()).getReader();
            reader.read().then(function processText({done, value}) {
                // When no more data needs to be consumed, close the stream
                if (done) {
                    reject(err_message);
                    return;
                }
                // Enqueue the next data chunk into our target stream
                err_message += value;
                return reader.read().then(processText);
            });
        }).then((res) => {
            return (res)
        }).catch((err) => {
            return (err)
        });
    }
}).then((res) => {
    console.log(res)
}).catch((err) => {
    console.log(err)
});

from https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream/getReader

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