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/**
* WebBlob is a Blob implementation for web resources that supports range requests.
*/
interface WebBlobCreateOptions {
/**
* @default 1_000_000
*
* Objects below that size will immediately be fetched and put in RAM, rather
* than streamed ad-hoc
*/
cacheBelow?: number;
/**
* Custom fetch function to use instead of the default one, for example to use a proxy or edit headers.
*/
fetch?: typeof fetch;
}
export class WebBlob extends Blob {
static async create(url: URL, opts?: WebBlobCreateOptions): Promise<Blob> {
const customFetch = opts?.fetch ?? fetch;
const response = await customFetch(url, { method: "HEAD" });
const size = Number(response.headers.get("content-length"));
const contentType = response.headers.get("content-type") || "";
const supportRange = response.headers.get("accept-ranges") === "bytes";
if (!supportRange || size < (opts?.cacheBelow ?? 1_000_000)) {
return await (await customFetch(url)).blob();
}
return new WebBlob(url, 0, size, contentType, true, customFetch);
}
private url: URL;
private start: number;
private end: number;
private contentType: string;
private full: boolean;
private fetch: typeof fetch;
constructor(url: URL, start: number, end: number, contentType: string, full: boolean, customFetch: typeof fetch) {
super([]);
this.url = url;
this.start = start;
this.end = end;
this.contentType = contentType;
this.full = full;
this.fetch = customFetch;
}
override get size(): number {
return this.end - this.start;
}
override get type(): string {
return this.contentType;
}
override slice(start = 0, end = this.size): WebBlob {
if (start < 0 || end < 0) {
new TypeError("Unsupported negative start/end on FileBlob.slice");
}
const slice = new WebBlob(
this.url,
this.start + start,
Math.min(this.start + end, this.end),
this.contentType,
start === 0 && end === this.size ? this.full : false,
this.fetch
);
return slice;
}
override async arrayBuffer(): Promise<ArrayBuffer> {
const result = await this.fetchRange();
return result.arrayBuffer();
}
override async text(): Promise<string> {
const result = await this.fetchRange();
return result.text();
}
override stream(): ReturnType<Blob["stream"]> {
const stream = new TransformStream();
this.fetchRange()
.then((response) => response.body?.pipeThrough(stream))
.catch((error) => stream.writable.abort(error.message));
return stream.readable;
}
private fetchRange(): Promise<Response> {
const fetch = this.fetch; // to avoid this.fetch() which is bound to the instance instead of globalThis
if (this.full) {
return fetch(this.url);
}
return fetch(this.url, {
headers: {
Range: `bytes=${this.start}-${this.end - 1}`,
},
});
}
}
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