get-uri
Version:
Returns a `stream.Readable` from a URI string
187 lines • 6.92 kB
JavaScript
import http_ from 'http';
import https from 'https';
import { once } from 'events';
import createDebug from 'debug';
import HTTPError from './http-error.js';
import NotFoundError from './notfound.js';
import NotModifiedError from './notmodified.js';
const debug = createDebug('get-uri:http');
/**
* Returns a Readable stream from an "http:" URI.
*/
export const http = async (url, opts = {}) => {
debug('GET %o', url.href);
const cache = getCache(url, opts.cache);
// first check the previous Expires and/or Cache-Control headers
// of a previous response if a `cache` was provided
if (cache && isFresh(cache) && typeof cache.statusCode === 'number') {
// check for a 3xx "redirect" status code on the previous cache
const type = (cache.statusCode / 100) | 0;
if (type === 3 && cache.headers.location) {
debug('cached redirect');
throw new Error('TODO: implement cached redirects!');
}
// otherwise we assume that it's the destination endpoint,
// since there's nowhere else to redirect to
throw new NotModifiedError();
}
// 5 redirects allowed by default
const maxRedirects = typeof opts.maxRedirects === 'number' ? opts.maxRedirects : 5;
debug('allowing %o max redirects', maxRedirects);
let mod;
if (opts.http) {
// the `https` module passed in from the "http.js" file
mod = opts.http;
debug('using secure `https` core module');
}
else {
mod = http_;
debug('using `http` core module');
}
const options = { ...opts };
// add "cache validation" headers if a `cache` was provided
if (cache) {
const prevHeaders = options.headers;
const headers = {};
if (prevHeaders && !Array.isArray(prevHeaders)) {
Object.assign(headers, prevHeaders);
}
options.headers = headers;
const lastModified = cache.headers['last-modified'];
if (lastModified) {
headers['If-Modified-Since'] = lastModified;
debug('added "If-Modified-Since" request header: %o', lastModified);
}
const etag = cache.headers.etag;
if (etag) {
headers['If-None-Match'] = etag;
debug('added "If-None-Match" request header: %o', etag);
}
}
const req = mod.get(url, options);
const [res] = await once(req, 'response');
const code = res.statusCode || 0;
// assign a Date to this response for the "Cache-Control" delta calculation
res.date = Date.now();
res.parsed = url;
debug('got %o response status code', code);
// any 2xx response is a "success" code
const type = (code / 100) | 0;
// check for a 3xx "redirect" status code
const location = res.headers.location;
if (type === 3 && location) {
if (!opts.redirects)
opts.redirects = [];
const redirects = opts.redirects;
if (redirects.length < maxRedirects) {
debug('got a "redirect" status code with Location: %o', location);
// flush this response - we're not going to use it
res.resume();
// hang on to this Response object for the "redirects" Array
redirects.push(res);
const newUri = new URL(location, url.href);
debug('resolved redirect URL: %o', newUri.href);
const left = maxRedirects - redirects.length;
debug('%o more redirects allowed after this one', left);
// check if redirecting to a different protocol
if (newUri.protocol !== url.protocol) {
opts.http = newUri.protocol === 'https:' ? https : undefined;
}
return http(newUri, opts);
}
}
// if we didn't get a 2xx "success" status code, then create an Error object
if (type !== 2) {
res.resume();
if (code === 304) {
throw new NotModifiedError();
}
else if (code === 404) {
throw new NotFoundError();
}
// other HTTP-level error
throw new HTTPError(code);
}
if (opts.redirects) {
// store a reference to the "redirects" Array on the Response object so that
// they can be inspected during a subsequent call to GET the same URI
res.redirects = opts.redirects;
}
return res;
};
/**
* Returns `true` if the provided cache's "freshness" is valid. That is, either
* the Cache-Control header or Expires header values are still within the allowed
* time period.
*
* @return {Boolean}
* @api private
*/
function isFresh(cache) {
let fresh = false;
let expires = parseInt(cache.headers.expires || '', 10);
const cacheControl = cache.headers['cache-control'];
if (cacheControl) {
// for Cache-Control rules, see: http://www.mnot.net/cache_docs/#CACHE-CONTROL
debug('Cache-Control: %o', cacheControl);
const parts = cacheControl.split(/,\s*?\b/);
for (let i = 0; i < parts.length; i++) {
const part = parts[i];
const subparts = part.split('=');
const name = subparts[0];
switch (name) {
case 'max-age':
expires =
(cache.date || 0) + parseInt(subparts[1], 10) * 1000;
fresh = Date.now() < expires;
if (fresh) {
debug('cache is "fresh" due to previous %o Cache-Control param', part);
}
return fresh;
case 'must-revalidate':
// XXX: what we supposed to do here?
break;
case 'no-cache':
case 'no-store':
debug('cache is "stale" due to explicit %o Cache-Control param', name);
return false;
default:
// ignore unknown cache value
break;
}
}
}
else if (expires) {
// for Expires rules, see: http://www.mnot.net/cache_docs/#EXPIRES
debug('Expires: %o', expires);
fresh = Date.now() < expires;
if (fresh) {
debug('cache is "fresh" due to previous Expires response header');
}
return fresh;
}
return false;
}
/**
* Attempts to return a previous Response object from a previous GET call to the
* same URI.
*
* @api private
*/
function getCache(url, cache) {
if (cache) {
if (cache.parsed && cache.parsed.href === url.href) {
return cache;
}
if (cache.redirects) {
for (let i = 0; i < cache.redirects.length; i++) {
const c = getCache(url, cache.redirects[i]);
if (c) {
return c;
}
}
}
}
return null;
}
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