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EDIT :: emscripten_fetch_worker.js

let Status = { SUCCESS_HEADER: -1, SUCCESS_EOF: -2, ERROR_TIMEOUT: -3, ERROR_EXCEPTION: -4, }; let connections = {}; let nextConnectionID = 1; const encoder = new TextEncoder(); self.addEventListener("message", async function (event) { if (event.data.close) { let connectionID = event.data.close; delete connections[connectionID]; return; } else if (event.data.getMore) { let connectionID = event.data.getMore; let { curOffset, value, reader, intBuffer, byteBuffer } = connections[connectionID]; // if we still have some in buffer, then just send it back straight away if (!value || curOffset >= value.length) { // read another buffer if required try { let readResponse = await reader.read(); if (readResponse.done) { // read everything - clear connection and return delete connections[connectionID]; Atomics.store(intBuffer, 0, Status.SUCCESS_EOF); Atomics.notify(intBuffer, 0); // finished reading successfully // return from event handler return; } curOffset = 0; connections[connectionID].value = readResponse.value; value = readResponse.value; } catch (error) { console.log("Request exception:", error); let errorBytes = encoder.encode(error.message); let written = errorBytes.length; byteBuffer.set(errorBytes); intBuffer[1] = written; Atomics.store(intBuffer, 0, Status.ERROR_EXCEPTION); Atomics.notify(intBuffer, 0); } } // send as much buffer as we can let curLen = value.length - curOffset; if (curLen > byteBuffer.length) { curLen = byteBuffer.length; } byteBuffer.set(value.subarray(curOffset, curOffset + curLen), 0); Atomics.store(intBuffer, 0, curLen); // store current length in bytes Atomics.notify(intBuffer, 0); curOffset += curLen; connections[connectionID].curOffset = curOffset; return; } else { // start fetch let connectionID = nextConnectionID; nextConnectionID += 1; const intBuffer = new Int32Array(event.data.buffer); const byteBuffer = new Uint8Array(event.data.buffer, 8); try { const response = await fetch(event.data.url, event.data.fetchParams); // return the headers first via textencoder var headers = []; for (const pair of response.headers.entries()) { headers.push([pair[0], pair[1]]); } let headerObj = { headers: headers, status: response.status, connectionID, }; const headerText = JSON.stringify(headerObj); let headerBytes = encoder.encode(headerText); let written = headerBytes.length; byteBuffer.set(headerBytes); intBuffer[1] = written; // make a connection connections[connectionID] = { reader: response.body.getReader(), intBuffer: intBuffer, byteBuffer: byteBuffer, value: undefined, curOffset: 0, }; // set header ready Atomics.store(intBuffer, 0, Status.SUCCESS_HEADER); Atomics.notify(intBuffer, 0); // all fetching after this goes through a new postmessage call with getMore // this allows for parallel requests } catch (error) { console.log("Request exception:", error); let errorBytes = encoder.encode(error.message); let written = errorBytes.length; byteBuffer.set(errorBytes); intBuffer[1] = written; Atomics.store(intBuffer, 0, Status.ERROR_EXCEPTION); Atomics.notify(intBuffer, 0); } } }); self.postMessage({ inited: true });

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