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import type {
default as BareClient,
BareHeaders,
} from "@mercuryworkshop/bare-mux";
import { rewriteUrl, type URLMeta } from "./url";
import { getSiteDirective } from "../security/siteTests";
interface StoredReferrerPolicies {
get(url: string): Promise<{ policy: string; referrer: string } | null>;
set(url: string, policy: string, referrer: string): Promise<void>;
}
/**
* Headers for security policy features that haven't been emulated yet
*/
const SEC_HEADERS = new Set([
"cross-origin-embedder-policy",
"cross-origin-opener-policy",
"cross-origin-resource-policy",
"content-security-policy",
"content-security-policy-report-only",
"expect-ct",
"feature-policy",
"origin-isolation",
"strict-transport-security",
"upgrade-insecure-requests",
"x-content-type-options",
"x-download-options",
"x-frame-options",
"x-permitted-cross-domain-policies",
"x-powered-by",
"x-xss-protection",
// This needs to be emulated, but for right now it isn't that important of a feature to be worried about
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Clear-Site-Data
"clear-site-data",
]);
/**
* Headers that are actually URLs that need to be rewritten
*/
const URL_HEADERS = new Set(["location", "content-location", "referer"]);
function rewriteLinkHeader(link: string, meta: URLMeta) {
return link.replace(/<(.*)>/gi, (match) => rewriteUrl(match, meta));
}
/**
* Rewrites response headers
* @param rawHeaders Headers before they were rewritten
* @param meta Parsed Proxy URL
* @param client `BareClient` instance used for fetching
* @param isNavigationRequest Whether the request is a navigation request
*/
export async function rewriteHeaders(
rawHeaders: BareHeaders,
meta: URLMeta,
client: BareClient,
storedReferrerPolicies: StoredReferrerPolicies
) {
const headers = {};
for (const key in rawHeaders) {
headers[key.toLowerCase()] = rawHeaders[key];
}
for (const cspHeader of SEC_HEADERS) {
delete headers[cspHeader];
}
for (const urlHeader of URL_HEADERS) {
if (headers[urlHeader])
headers[urlHeader] = rewriteUrl(
headers[urlHeader]?.toString() as string,
meta
);
}
if (typeof headers["link"] === "string") {
headers["link"] = rewriteLinkHeader(headers["link"], meta);
} else if (Array.isArray(headers["link"])) {
headers["link"] = headers["link"].map((link) =>
rewriteLinkHeader(link, meta)
);
}
// Emulate the referrer policy to set it back to what it should've been without Force Referrer in place
if (typeof headers["referer"] === "string") {
const referrerUrl = new URL(headers["referer"]);
const storedPolicyData = await storedReferrerPolicies.get(referrerUrl.href);
if (storedPolicyData) {
const storedReferrerPolicy = storedPolicyData.policy
.toLowerCase()
.split(",")
.map((rawDir) => rawDir.trim());
if (
storedReferrerPolicy.includes("no-referrer") ||
(storedReferrerPolicy.includes("no-referrer-when-downgrade") &&
meta.origin.protocol === "http:" &&
referrerUrl.protocol === "https:")
) {
delete headers["referer"];
} else if (storedReferrerPolicy.includes("origin")) {
headers["referer"] = referrerUrl.origin;
} else if (storedReferrerPolicy.includes("origin-when-cross-origin")) {
if (referrerUrl.origin !== meta.origin.origin) {
headers["referer"] = referrerUrl.origin;
} else {
headers["referer"] = referrerUrl.href;
}
} else if (storedReferrerPolicy.includes("same-origin")) {
if (referrerUrl.origin === meta.origin.origin) {
headers["referer"] = referrerUrl.href;
} else {
delete headers["referer"];
}
} else if (storedReferrerPolicy.includes("strict-origin")) {
if (
meta.origin.protocol === "http:" &&
referrerUrl.protocol === "https:"
) {
delete headers["referer"];
} else {
headers["referer"] = referrerUrl.origin;
}
}
// `strict-origin-when-cross-origin` is the default behavior anyway
else {
if (referrerUrl.origin === meta.origin.origin) {
headers["referer"] = referrerUrl.href;
} else if (
meta.origin.protocol === "http:" &&
referrerUrl.protocol === "https:"
) {
delete headers["referer"];
} else {
headers["referer"] = referrerUrl.origin;
}
}
}
}
if (
typeof headers["sec-fetch-dest"] === "string" &&
headers["sec-fetch-dest"] === ""
) {
headers["sec-fetch-dest"] = "empty";
}
if (
typeof headers["sec-fetch-site"] === "string" &&
headers["sec-fetch-site"] !== "none"
) {
if (typeof headers["referer"] === "string") {
headers["sec-fetch-site"] = await getSiteDirective(
meta,
new URL(headers["referer"]),
client
);
} else {
console.warn(
"Missing referrer header; can't rewrite sec-fetch-site properly. Falling back to unsafe deletion."
);
delete headers["sec-fetch-site"];
}
}
return headers;
}
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