libstore: fix http abuses no longer working

while refactoring the curl wrapper we inadvertently broken the immutable
flake protocol, because the immutable flake protocol accumulates headers
across the entire redirect chain instead of using only the headers given
in the final response of the chain. this is a problem because Some Known
Providers Of Flake Infrastructure set rel=immutable link headers only in
the penultimate entry of the redirect chain, and curl does not regard it
as worth returning to us via its response header enumeration mechanisms.

fixes https://git.lix.systems/lix-project/lix/issues/358

Change-Id: I645c3932b465cde848bd6a3565925a1e3cbcdda0

1 files changed, 48 insertions, 5 deletions

diff --git a/tests/unit/libstore/filetransfer.cc b/tests/unit/libstore/filetransfer.cc
index 684697c69..0e5c0965e 100644
--- a/tests/unit/libstore/filetransfer.cc
+++ b/tests/unit/libstore/filetransfer.cc
@@ -23,10 +23,19 @@
 
 using namespace std::chrono_literals;
 
+namespace {
+
+struct Reply {
+    std::string status, headers;
+    std::function<std::string()> content;
+};
+
+}
+
 namespace nix {
 
 static std::tuple<uint16_t, AutoCloseFD>
-serveHTTP(std::string_view status, std::string_view headers, std::function<std::string()> content)
+serveHTTP(std::vector<Reply> replies)
 {
     AutoCloseFD listener(::socket(AF_INET6, SOCK_STREAM, 0));
     if (!listener) {
@@ -52,7 +61,7 @@ serveHTTP(std::string_view status, std::string_view headers, std::function<std::
     }
 
     std::thread(
-        [status, headers, content](AutoCloseFD socket, AutoCloseFD trigger) {
+        [replies, at{0}](AutoCloseFD socket, AutoCloseFD trigger) mutable {
             while (true) {
                 pollfd pfds[2] = {
                     {
@@ -90,12 +99,14 @@ serveHTTP(std::string_view status, std::string_view headers, std::function<std::
                     }
                 };
 
+                const auto & reply = replies[at++ % replies.size()];
+
                 send("HTTP/1.1 ");
-                send(status);
+                send(reply.status);
                 send("\r\n");
-                send(headers);
+                send(reply.headers);
                 send("\r\n");
-                send(content());
+                send(reply.content());
                 ::shutdown(conn.get(), SHUT_RDWR);
             }
         },
@@ -110,6 +121,12 @@ serveHTTP(std::string_view status, std::string_view headers, std::function<std::
     };
 }
 
+static std::tuple<uint16_t, AutoCloseFD>
+serveHTTP(std::string status, std::string headers, std::function<std::string()> content)
+{
+    return serveHTTP({{{status, headers, content}}});
+}
+
 TEST(FileTransfer, exceptionAbortsDownload)
 {
     struct Done
@@ -166,4 +183,30 @@ TEST(FileTransfer, NOT_ON_DARWIN(handlesContentEncoding))
     ft->download(FileTransferRequest(fmt("http://[::1]:%d/index", port)), sink);
     EXPECT_EQ(sink.s, original);
 }
+
+TEST(FileTransfer, usesIntermediateLinkHeaders)
+{
+    auto [port, srv] = serveHTTP({
+        {"301 ok",
+         "location: /second\r\n"
+         "content-length: 0\r\n",
+         [] { return ""; }},
+        {"307 ok",
+         "location: /third\r\n"
+         "content-length: 0\r\n",
+         [] { return ""; }},
+        {"307 ok",
+         "location: /fourth\r\n"
+         "link: <http://foo>; rel=\"immutable\"\r\n"
+         "content-length: 0\r\n",
+         [] { return ""; }},
+        {"200 ok", "content-length: 1\r\n", [] { return "a"; }},
+    });
+    auto ft = makeFileTransfer();
+    FileTransferRequest req(fmt("http://[::1]:%d/first", port));
+    req.baseRetryTimeMs = 0;
+    auto result = ft->download(req);
+    ASSERT_EQ(result.immutableUrl, "http://foo");
+}
+
 }