calling this.#grow without knowing the actual amount that needs to grow is causing troubles, went with the simpler and less error-prone code, which is calling writeSync which calls this.#grow with the size of the read buffer.

In a few minutes, I'll push an alternative reading directly to the buffer. If someone else wants to try a different approach I'm more than happy.

Posted alternative implementation in #6570

Is it really necessary to allocate 4G of memory? Does the crash occur a smaller allocations?

I can replicate the crash on master using write/writeSync when writing ~2gb, but not for readFrom, the latter allocate a maximum buffer of 4294966784, 510 bytes short of MAX_SIZE

const buf = new Deno.Buffer()
buf.writeSync(repeat("x", 2147483647));
buf.writeSync(repeat("x", 1));
// throws The buffer cannot be grown beyond the maximum size.

readFrom/Sync

const reader = new Deno.Buffer(new ArrayBuffer(4294966784 + 1));
const buf = new Deno.Buffer();
buf.readFromSync(reader);
// throws The buffer cannot be grown beyond the maximum size.

Can't replicate with a smaller amount because buf.readForm calls buf.#grow with 512 which always ends up with a max buffer of 4294966784 when trying to read any amount less than 4294966784, so not possible to replicate.