feat(3p/nix): add MockBinaryCacheStore

This adds an implementation of BinaryCacheStore to be used by tests exercising both the logic inherent to BinaryCacheStore and more general Store tests.

A new library target, nixstoremock, is created to indicate that this file is intended only for use in tests and not in user-facing code.

Change-Id: Ib68f777238843a4f3a2303db8a69735fbc22d161
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1645
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

third_party/nix/src/libstore/mock-binary-cache-store.cc

@@ -0,0 +1,91 @@
+#include "libstore/mock-binary-cache-store.hh"
+
+#include <glog/logging.h>
+
+namespace nix {
+
+MockBinaryCacheStore::MockBinaryCacheStore(const Params& params)
+    : BinaryCacheStore(params), contents_(), errorInjections_() {}
+
+std::string MockBinaryCacheStore::getUri() { return "mock://1"; }
+
+bool MockBinaryCacheStore::fileExists(const std::string& path) {
+  ThrowInjectedErrors(path);
+
+  return contents_.find(path) != contents_.end();
+};
+
+void MockBinaryCacheStore::upsertFile(const std::string& path,
+                                      const std::string& data,
+                                      const std::string& mimeType) {
+  ThrowInjectedErrors(path);
+
+  contents_[path] = MemoryFile{data, mimeType};
+}
+
+void MockBinaryCacheStore::getFile(
+    const std::string& path,
+    Callback<std::shared_ptr<std::string>> callback) noexcept {
+  auto eit = errorInjections_.find(path);
+  if (eit != errorInjections_.end()) {
+    try {
+      eit->second();
+      LOG(FATAL) << "thrower failed to throw";
+    } catch (...) {
+      callback.rethrow();
+    }
+    return;
+  }
+
+  auto it = contents_.find(path);
+  if (it == contents_.end()) {
+    try {
+      throw NoSuchBinaryCacheFile(absl::StrCat(
+          "file '", path, "' was not added to the MockBinaryCache"));
+    } catch (...) {
+      callback.rethrow();
+    }
+    return;
+  }
+  callback(std::make_shared<std::string>(it->second.data));
+}
+
+PathSet MockBinaryCacheStore::queryAllValidPaths() {
+  PathSet paths;
+
+  for (auto it : contents_) {
+    paths.insert(it.first);
+  }
+
+  return paths;
+}
+
+void MockBinaryCacheStore::DeleteFile(const std::string& path) {
+  contents_.erase(path);
+}
+
+// Same as upsert, but bypasses injected errors.
+void MockBinaryCacheStore::SetFileContentsForTest(const std::string& path,
+                                                  const std::string& data,
+                                                  const std::string& mimeType) {
+  contents_[path] = MemoryFile{data, mimeType};
+}
+
+void MockBinaryCacheStore::PrepareErrorInjection(
+    const std::string& path, std::function<void()> err_factory) {
+  errorInjections_[path] = err_factory;
+}
+
+void MockBinaryCacheStore::CancelErrorInjection(const std::string& path) {
+  errorInjections_.erase(path);
+}
+
+void MockBinaryCacheStore::ThrowInjectedErrors(const std::string& path) {
+  auto it = errorInjections_.find(path);
+  if (it != errorInjections_.end()) {
+    it->second();
+    LOG(FATAL) << "thrower failed to throw";
+  }
+}
+
+}  // namespace nix