429 Too Many Request

[zmlee0514]

Generally, retrieving more than 60 pages would result in a status code 429 error in "loadPage" of EhRetriever.retrieve(). Maybe we should add some sleeping mechanism.

A naive version:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

let fetchPage;
try {
    const url = `${this.ehentaiHost}/api.php`;
    const config = {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        // assign e = {'imgkey': ..., 'page': ...} to object literal {'method': ..., 'gid': ..., 'showkey': ...}
        // does not modify e
        body: JSON.stringify(Object.assign({
            method: 'showpage',
            gid: this.gallery.gid,
            showkey: this.showkey
        }, e))
    };
    let response = await this.fetch(url, config);
    while (response.status == 429) {
        await sleep(30000);
        response = await this.fetch(url, config);
    }
  
    if (!response.ok) {
       throw new Error(response.statusText);
    }
    fetchPage = await response.json();
} catch (error) {
    console.warn(error);
    throw error;
}