Fix PyPI minimum-age fallback when cached metadata bypasses rewrite

packages/safe-chain/src/registryProxy/interceptors/pip/modifyPipInfo.js

@@ -6,6 +6,23 @@ export { parsePipMetadataUrl, isPipPackageInfoUrl } from "./parsePipPackageUrl.j
 import { getPipMetadataContentType, logSuppressedVersion } from "./pipMetadataResponseUtils.js";
 import { modifyPipJsonResponse } from "./modifyPipJsonResponse.js";
 
+/**
+ * Strip conditional GET headers so PyPI always returns a full 200 response
+ * with a body we can rewrite. Without this, pip sends If-None-Match /
+ * If-Modified-Since, PyPI responds 304 Not Modified (empty body), and
+ * safe-chain cannot rewrite it — leaving pip with a cached index that still
+ * lists too-young versions. Those versions are then blocked at direct-download
+ * time with a hard 403, preventing dependency resolution from completing.
+ *
+ * @param {NodeJS.Dict<string | string[]>} headers
+ * @returns {NodeJS.Dict<string | string[]>}
+ */
+export function modifyPipInfoRequestHeaders(headers) {
+  delete headers["if-none-match"];
+  delete headers["if-modified-since"];
+  return headers;
+}
+
 // Match simple-index anchor tags and capture their href so we can suppress
 // individual distribution links from PyPI HTML metadata responses.
 const HTML_ANCHOR_HREF_RE =

packages/safe-chain/src/registryProxy/interceptors/pip/pipInterceptor.js

@@ -9,6 +9,7 @@ import { openNewPackagesDatabase } from "../../../scanning/newPackagesListCache.
 import { interceptRequests } from "../interceptorBuilder.js";
 import { isExcludedFromMinimumPackageAge } from "../minimumPackageAgeExclusions.js";
 import {
+  modifyPipInfoRequestHeaders,
   modifyPipInfoResponse,
   parsePipMetadataUrl,
 } from "./modifyPipInfo.js";
@@ -61,6 +62,7 @@ function createPipRequestHandler(registry) {
       !isExcludedFromMinimumPackageAge(metadataPackageName)
     ) {
       const newPackagesDatabase = await openNewPackagesDatabase();
+      reqContext.modifyRequestHeaders(modifyPipInfoRequestHeaders);
       reqContext.modifyBody((body, headers) =>
         modifyPipInfoResponse(
           body,

packages/safe-chain/src/registryProxy/interceptors/pip/pipInterceptor.minPackageAge.spec.js

@@ -129,6 +129,28 @@ describe("pipInterceptor minimum package age", async () => {
     newlyReleasedPackageResponse = false;
   });
 
+  it("strips If-None-Match and If-Modified-Since from metadata requests to prevent 304 cache bypass", async () => {
+    const url = "https://pypi.org/simple/foo-bar/";
+    newlyReleasedPackageResponse = true;
+
+    const interceptor = pipInterceptorForUrl(url);
+    const result = await interceptor.handleRequest(url);
+
+    const headers = {
+      "if-none-match": '"some-etag"',
+      "if-modified-since": "Thu, 01 Jan 2026 00:00:00 GMT",
+      accept: "*/*",
+    };
+
+    result.modifyRequestHeaders(headers);
+
+    assert.equal(headers["if-none-match"], undefined, "If-None-Match must be stripped");
+    assert.equal(headers["if-modified-since"], undefined, "If-Modified-Since must be stripped");
+    assert.equal(headers.accept, "*/*", "unrelated headers must be preserved");
+
+    newlyReleasedPackageResponse = false;
+  });
+
   it("should not block newly released package downloads when a dot-name package matches a hyphen exclusion", async () => {
     const url =
       "https://files.pythonhosted.org/packages/xx/yy/foo.bar-2.0.0.tar.gz";