Fix git lfs for github fetcher

According to
https://github.com/git-lfs/git-lfs/blob/main/docs/api/server-discovery.md
LFS endpoints must end in `.git`.

Resolves #15285

Signed-off-by: Lisanna Dettwyler <lisanna.dettwyler@gmail.com>

Author: lisanna-dettwyler

src/libfetchers-tests/git-lfs-fetch.cc

@@ -0,0 +1,24 @@
+#include "nix/fetchers/git-lfs-fetch.hh"
+#include "nix/util/url.hh"
+
+#include <gtest/gtest.h>
+
+namespace nix::lfs {
+
+struct GitLFSTest : public ::testing::Test
+{
+    void test(std::string input, std::string expected)
+    {
+        ASSERT_EQ(getLfsApi(parseURL(input)).endpoint, expected);
+    }
+};
+
+TEST_F(GitLFSTest, get_lfs_api)
+{
+    test("https://git-server.com/foo/bar", "https://git-server.com/foo/bar.git/info/lfs");
+    test("https://git-server.com/foo/bar.git", "https://git-server.com/foo/bar.git/info/lfs");
+    test("https://git-server.com", "https://git-server.com/.git/info/lfs");
+    test("https://git-server.com/foo/bar/", "https://git-server.com/foo/bar.git//info/lfs");
+};
+
+} // namespace nix::lfs

src/libfetchers-tests/meson.build

@@ -41,6 +41,7 @@ subdir('nix-meson-build-support/common')
 sources = files(
   'access-tokens.cc',
   'attrs.cc',
+  'git-lfs-fetch.cc',
   'git-utils.cc',
   'git.cc',
   'input.cc',

src/libfetchers/git-lfs-fetch.cc

@@ -46,17 +46,7 @@ static void downloadToSink(
             "hash mismatch while fetching %s: expected sha256:%s but got sha256:%s", url, sha256Expected, sha256Actual);
 }
 
-namespace {
-
-struct LfsApiInfo
-{
-    std::string endpoint;
-    std::optional<std::string> authHeader;
-};
-
-} // namespace
-
-static LfsApiInfo getLfsApi(const ParsedURL & url)
+LfsApiInfo getLfsApi(ParsedURL url)
 {
     assert(url.authority.has_value());
     if (url.scheme == "ssh") {
@@ -96,7 +86,28 @@ static LfsApiInfo getLfsApi(const ParsedURL & url)
         return {queryResp.at("href").get<std::string>(), authIt->get<std::string>()};
     }
 
-    return {url.to_string() + "/info/lfs", std::nullopt};
+    // Try to mimic what git-lfs will do to plain remotes
+    // https://github.com/git-lfs/git-lfs/blob/main/docs/api/server-discovery.md
+    bool hasDotGit = false;
+    for (auto it = url.path.rbegin(); it != url.path.rend(); ++it) {
+        if (it->empty())
+            continue;
+        if (it->ends_with(".git")) {
+            hasDotGit = true;
+            break;
+        } else {
+            *it += ".git";
+            hasDotGit = true;
+            break;
+        }
+    }
+    if (!hasDotGit)
+        url.path.push_back(".git");
+
+    url.path.push_back("info");
+    url.path.push_back("lfs");
+
+    return {url.to_string(), std::nullopt};
 }
 
 typedef std::unique_ptr<git_config, Deleter<git_config_free>> GitConfig;

src/libfetchers/include/nix/fetchers/git-lfs-fetch.hh

@@ -43,4 +43,12 @@ struct Fetch
     std::vector<nlohmann::json> fetchUrls(const std::vector<Pointer> & pointers) const;
 };
 
+struct LfsApiInfo
+{
+    std::string endpoint;
+    std::optional<std::string> authHeader;
+};
+
+LfsApiInfo getLfsApi(ParsedURL url);
+
 } // namespace nix::lfs