From a76682466062ef2c972d19f259feeef1c46a44a3 Mon Sep 17 00:00:00 2001
From: Matthew Bauer <mjbauer95@gmail.com>
Date: Fri, 22 Jan 2021 14:46:40 -0600
Subject: [PATCH 1/2] Handle missing etag in 304 Not Modified response

GitHub now omits the etag, but 304 implies it matches the one we
provided. Just use that one to avoid having an etag-less resource.

Fixes #4469
---
 src/libstore/filetransfer.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 31b4215a9..1b7eae3ec 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -375,6 +375,13 @@ struct curlFileTransfer : public FileTransfer
             else if (code == CURLE_OK && successfulStatuses.count(httpStatus))
             {
                 result.cached = httpStatus == 304;
+
+                // In 2021, GitHub responds to If-None-Match with 304,
+                // but omits ETag. We just use the If-None-Match etag
+                // since 304 implies they are the same.
+                if (httpStatus == 304 && result.etag == "")
+                    result.etag = request.expectedETag;
+
                 act.progress(result.bodySize, result.bodySize);
                 done = true;
                 callback(std::move(result));

From 1ea5f0b66ca43eb1f6c552b59de170d61bcf540c Mon Sep 17 00:00:00 2001
From: Matthew Bauer <mjbauer95@gmail.com>
Date: Fri, 22 Jan 2021 23:19:52 -0600
Subject: [PATCH 2/2] Remove expectedETag assert in tarball.cc

---
 src/libfetchers/tarball.cc | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index 56c014a8c..b8d7d2c70 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -64,7 +64,6 @@ DownloadFileResult downloadFile(
 
     if (res.cached) {
         assert(cached);
-        assert(request.expectedETag == res.etag);
         storePath = std::move(cached->storePath);
     } else {
         StringSink sink;