[core] add support for stale responses

We're now returning stale responses from cache. Those responses will have the `stale` flag set to true. Currently, all requesters in the core code discard stale responses, and cancel the request immediately after they got a non-stale response.

23 files changed, 367 insertions, 47 deletions

diff --git a/include/mbgl/storage/response.hpp b/include/mbgl/storage/response.hpp
index e665f177fc..b232cd06f4 100644
--- a/include/mbgl/storage/response.hpp
+++ b/include/mbgl/storage/response.hpp
@@ -7,9 +7,13 @@ namespace mbgl {
 
 class Response {
 public:
+    bool isExpired() const;
+
+public:
     enum Status { Error, Successful, NotFound };
 
     Status status = Error;
+    bool stale = false;
     std::string message;
     int64_t modified = 0;
     int64_t expires = 0;
diff --git a/src/mbgl/map/map_context.cpp b/src/mbgl/map/map_context.cpp
index 0888ef2846..b197ea12f3 100644
--- a/src/mbgl/map/map_context.cpp
+++ b/src/mbgl/map/map_context.cpp
@@ -106,6 +106,10 @@ void MapContext::setStyleURL(const std::string& url) {
 
     FileSource* fs = util::ThreadContext::getFileSource();
     styleRequest = fs->request({ Resource::Kind::Style, styleURL }, util::RunLoop::getLoop(), [this, base](const Response &res) {
+        if (res.stale) {
+            // Only handle fresh responses.
+            return;
+        }
         styleRequest = nullptr;
 
         if (res.status == Response::Successful) {
diff --git a/src/mbgl/map/raster_tile_data.cpp b/src/mbgl/map/raster_tile_data.cpp
index 4ae9189a0b..cc7b6b548f 100644
--- a/src/mbgl/map/raster_tile_data.cpp
+++ b/src/mbgl/map/raster_tile_data.cpp
@@ -31,6 +31,10 @@ void RasterTileData::request(float pixelRatio,
 
     FileSource* fs = util::ThreadContext::getFileSource();
     req = fs->request({ Resource::Kind::Tile, url }, util::RunLoop::getLoop(), [url, callback, this](const Response &res) {
+        if (res.stale) {
+            // Only handle fresh responses.
+            return;
+        }
         req = nullptr;
 
         if (res.status == Response::NotFound) {
diff --git a/src/mbgl/map/source.cpp b/src/mbgl/map/source.cpp
index d723e308b1..7e30682895 100644
--- a/src/mbgl/map/source.cpp
+++ b/src/mbgl/map/source.cpp
@@ -149,6 +149,10 @@ void Source::load() {
 
     FileSource* fs = util::ThreadContext::getFileSource();
     req = fs->request({ Resource::Kind::Source, info.url }, util::RunLoop::getLoop(), [this](const Response &res) {
+        if (res.stale) {
+            // Only handle fresh responses.
+            return;
+        }
         req = nullptr;
 
         if (res.status != Response::Successful) {
diff --git a/src/mbgl/map/sprite.cpp b/src/mbgl/map/sprite.cpp
index 9c099b4aa2..a54d96f005 100644
--- a/src/mbgl/map/sprite.cpp
+++ b/src/mbgl/map/sprite.cpp
@@ -44,6 +44,10 @@ Sprite::Sprite(const std::string& baseUrl, float pixelRatio_)
     FileSource* fs = util::ThreadContext::getFileSource();
     loader->jsonRequest = fs->request({ Resource::Kind::SpriteJSON, jsonURL }, util::RunLoop::getLoop(),
                                       [this, jsonURL](const Response& res) {
+        if (res.stale) {
+            // Only handle fresh responses.
+            return;
+        }
         loader->jsonRequest = nullptr;
         if (res.status == Response::Successful) {
             loader->data->json = res.data;
@@ -60,6 +64,10 @@ Sprite::Sprite(const std::string& baseUrl, float pixelRatio_)
     loader->spriteRequest =
         fs->request({ Resource::Kind::SpriteImage, spriteURL }, util::RunLoop::getLoop(),
                     [this, spriteURL](const Response& res) {
+            if (res.stale) {
+                // Only handle fresh responses.
+                return;
+            }
             loader->spriteRequest = nullptr;
             if (res.status == Response::Successful) {
                 loader->data->image = res.data;
diff --git a/src/mbgl/map/vector_tile_data.cpp b/src/mbgl/map/vector_tile_data.cpp
index 6aa643b16f..2e683daaff 100644
--- a/src/mbgl/map/vector_tile_data.cpp
+++ b/src/mbgl/map/vector_tile_data.cpp
@@ -43,6 +43,10 @@ void VectorTileData::request(float pixelRatio, const std::function<void()>& call
 
     FileSource* fs = util::ThreadContext::getFileSource();
     req = fs->request({ Resource::Kind::Tile, url }, util::RunLoop::getLoop(), [url, callback, this](const Response &res) {
+        if (res.stale) {
+            // Only handle fresh responses.
+            return;
+        }
         req = nullptr;
 
         if (res.status == Response::NotFound) {
diff --git a/src/mbgl/storage/default_file_source.cpp b/src/mbgl/storage/default_file_source.cpp
index 7b3cff8253..71c42f6220 100644
--- a/src/mbgl/storage/default_file_source.cpp
+++ b/src/mbgl/storage/default_file_source.cpp
@@ -8,7 +8,6 @@
 #include <mbgl/platform/log.hpp>
 
 #include <mbgl/util/uv_detail.hpp>
-#include <mbgl/util/chrono.hpp>
 #include <mbgl/util/thread.hpp>
 #include <mbgl/util/mapbox.hpp>
 #include <mbgl/util/exception.hpp>
@@ -102,43 +101,79 @@ void DefaultFileSource::Impl::add(Request* req) {
     const Resource& resource = req->resource;
     DefaultFileRequest* request = find(resource);
 
-    if (request) {
-        request->observers.insert(req);
-        return;
+    if (!request) {
+        request = &pending.emplace(resource, resource).first->second;
     }
 
-    request = &pending.emplace(resource, resource).first->second;
+    // Add this request as an observer so that it'll get notified when something about this
+    // request changes.
     request->observers.insert(req);
 
-    if (cache) {
-        startCacheRequest(request);
+    update(request);
+
+    if (request->response) {
+        // We've got a response, so send the (potentially stale) response to the requester.
+        req->notify(request->response);
+    }
+}
+
+void DefaultFileSource::Impl::update(DefaultFileRequest* request) {
+    if (request->response) {
+        // We've at least obtained a cache value, potentially we also got a final response.
+        // The observers have been notified already; send what we have to the new one as well.
+
+        // Before returning the existing response, make sure that it is still fresh.
+        if (!request->response->stale && request->response->isExpired()) {
+            // Create a new Response object with `stale = true`, but the same data, and
+            // replace the current request object we have.
+            // TODO: Make content shared_ptrs so we won't make copies of the content.
+            auto response = std::make_shared<Response>(*request->response);
+            response->stale = true;
+            request->response = response;
+        }
+
+        if (request->response->stale && !request->realRequest) {
+            // We've returned a stale response; now make sure the requester also gets a fresh
+            // response eventually. It's possible that there's already a request in progress.
+            // Note that this will also trigger updates to all other existing listeners.
+            // Since we already have data, we're going to verify
+            startRealRequest(request, request->response);
+        }
+    } else if (!request->cacheRequest && !request->realRequest) {
+        // There is no request in progress, and we don't have a response yet. This means we'll have
+        // to start the request ourselves.
+        if (cache) {
+            startCacheRequest(request);
+        } else {
+            startRealRequest(request);
+        }
     } else {
-        startRealRequest(request);
+        // There is a request in progress. We just have to wait.
     }
 }
 
 void DefaultFileSource::Impl::startCacheRequest(DefaultFileRequest* request) {
     // Check the cache for existing data so that we can potentially
     // revalidate the information without having to redownload everything.
-    request->cacheRequest = cache->get(request->resource, [this, request](std::unique_ptr<Response> response) {
-        auto expired = [&response] {
-            const int64_t now = std::chrono::duration_cast<std::chrono::seconds>(
-                                    SystemClock::now().time_since_epoch()).count();
-            return response->expires <= now;
-        };
-
-        if (!response || expired()) {
+    request->cacheRequest = cache->get(request->resource, [this, request](std::shared_ptr<Response> response) {
+        request->cacheRequest = nullptr;
+        if (response) {
+            response->stale = response->isExpired();
+
+            // Notify in all cases; requestors can decide whether they want to use stale responses.
+            notify(request, response, FileCache::Hint::No);
+        }
+
+        if (!response || response->stale) {
             // No response or stale cache. Run the real request.
-            startRealRequest(request, std::move(response));
-        } else {
-            // The response is fresh. We're good to notify the caller.
-            notify(request, std::move(response), FileCache::Hint::No);
+            startRealRequest(request, response);
         }
     });
 }
 
 void DefaultFileSource::Impl::startRealRequest(DefaultFileRequest* request, std::shared_ptr<const Response> response) {
     auto callback = [request, this] (std::shared_ptr<const Response> res, FileCache::Hint hint) {
+        request->realRequest = nullptr;
         notify(request, res, hint);
     };
 
@@ -181,6 +216,7 @@ void DefaultFileSource::Impl::notify(DefaultFileRequest* request, std::shared_pt
     assert(response);
 
     // Notify all observers.
+    request->response = response;
     for (auto req : request->observers) {
         req->notify(response);
     }
@@ -189,8 +225,6 @@ void DefaultFileSource::Impl::notify(DefaultFileRequest* request, std::shared_pt
         // Store response in database
         cache->put(request->resource, response, hint);
     }
-
-    pending.erase(request->resource);
 }
 
 }
diff --git a/src/mbgl/storage/default_file_source_impl.hpp b/src/mbgl/storage/default_file_source_impl.hpp
index bb28933798..980eedc118 100644
--- a/src/mbgl/storage/default_file_source_impl.hpp
+++ b/src/mbgl/storage/default_file_source_impl.hpp
@@ -15,6 +15,7 @@ class RequestBase;
 struct DefaultFileRequest {
     const Resource resource;
     std::set<Request*> observers;
+    std::shared_ptr<const Response> response;
 
     std::unique_ptr<WorkRequest> cacheRequest;
     RequestBase* realRequest = nullptr;
@@ -39,6 +40,7 @@ public:
 private:
     DefaultFileRequest* find(const Resource&);
 
+    void update(DefaultFileRequest*);
     void startCacheRequest(DefaultFileRequest*);
     void startRealRequest(DefaultFileRequest*, std::shared_ptr<const Response> = nullptr);
     void notify(DefaultFileRequest*, std::shared_ptr<const Response>, FileCache::Hint);
diff --git a/src/mbgl/storage/request.cpp b/src/mbgl/storage/request.cpp
index f8ad555379..55913846cf 100644
--- a/src/mbgl/storage/request.cpp
+++ b/src/mbgl/storage/request.cpp
@@ -49,7 +49,6 @@ Request::~Request() = default;
 
 // Called in the FileSource thread.
 void Request::notify(const std::shared_ptr<const Response> &response_) {
-    assert(!std::atomic_load(&response));
     assert(response_);
     std::atomic_store(&response, response_);
     async->send();
diff --git a/src/mbgl/storage/response.cpp b/src/mbgl/storage/response.cpp
new file mode 100644
index 0000000000..628a2a3b99
--- /dev/null
+++ b/src/mbgl/storage/response.cpp
@@ -0,0 +1,12 @@
+#include <mbgl/storage/response.hpp>
+#include <mbgl/util/chrono.hpp>
+
+namespace mbgl {
+
+bool Response::isExpired() const {
+    const int64_t now = std::chrono::duration_cast<std::chrono::seconds>(
+                                    SystemClock::now().time_since_epoch()).count();
+    return expires <= now;
+}
+
+} // namespace mbgl
diff --git a/src/mbgl/text/glyph_pbf.cpp b/src/mbgl/text/glyph_pbf.cpp
index e37e656d91..f351e66c2a 100644
--- a/src/mbgl/text/glyph_pbf.cpp
+++ b/src/mbgl/text/glyph_pbf.cpp
@@ -75,6 +75,10 @@ GlyphPBF::GlyphPBF(GlyphStore* store,
     });
 
     auto requestCallback = [this, store, fontStack, url](const Response &res) {
+        if (res.stale) {
+            // Only handle fresh responses.
+            return;
+        }
         req = nullptr;
 
         if (res.status != Response::Successful) {
diff --git a/test/storage/cache_response.cpp b/test/storage/cache_response.cpp
index 0fba2ba5e7..1294513858 100644
--- a/test/storage/cache_response.cpp
+++ b/test/storage/cache_response.cpp
@@ -14,27 +14,35 @@ TEST_F(Storage, CacheResponse) {
     DefaultFileSource fs(&cache);
 
     const Resource resource { Resource::Unknown, "http://127.0.0.1:3000/cache" };
+    Response response;
 
     Request* req = fs.request(resource, uv_default_loop(), [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Response 1", res.data);
         EXPECT_LT(0, res.expires);
         EXPECT_EQ(0, res.modified);
         EXPECT_EQ("", res.etag);
         EXPECT_EQ("", res.message);
+        response = res;
+    });
+
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
 
-        req = fs.request(resource, uv_default_loop(), [&, res](const Response &res2) {
-            fs.cancel(req);
-            EXPECT_EQ(res.status, res2.status);
-            EXPECT_EQ(res.data, res2.data);
-            EXPECT_EQ(res.expires, res2.expires);
-            EXPECT_EQ(res.modified, res2.modified);
-            EXPECT_EQ(res.etag, res2.etag);
-            EXPECT_EQ(res.message, res2.message);
-
-            CacheResponse.finish();
-        });
+    // Now test that we get the same values as in the previous request. If we'd go to the server
+    // again, we'd get different values.
+    req = fs.request(resource, uv_default_loop(), [&](const Response &res) {
+        fs.cancel(req);
+        EXPECT_EQ(response.status, res.status);
+        EXPECT_EQ(response.stale, res.stale);
+        EXPECT_EQ(response.data, res.data);
+        EXPECT_EQ(response.expires, res.expires);
+        EXPECT_EQ(response.modified, res.modified);
+        EXPECT_EQ(response.etag, res.etag);
+        EXPECT_EQ(response.message, res.message);
+
+        CacheResponse.finish();
     });
 
     uv_run(uv_default_loop(), UV_RUN_DEFAULT);
diff --git a/test/storage/cache_revalidate.cpp b/test/storage/cache_revalidate.cpp
index 8ebedef01b..90633b83ac 100644
--- a/test/storage/cache_revalidate.cpp
+++ b/test/storage/cache_revalidate.cpp
@@ -5,29 +5,58 @@
 #include <mbgl/storage/default_file_source.hpp>
 #include <mbgl/storage/sqlite_cache.hpp>
 
-TEST_F(Storage, CacheRevalidate) {
+TEST_F(Storage, CacheRevalidateSame) {
     SCOPED_TEST(CacheRevalidateSame)
-    SCOPED_TEST(CacheRevalidateModified)
-    SCOPED_TEST(CacheRevalidateEtag)
 
     using namespace mbgl;
 
     SQLiteCache cache(":memory:");
     DefaultFileSource fs(&cache);
 
+    const Response *reference = nullptr;
+
     const Resource revalidateSame { Resource::Unknown, "http://127.0.0.1:3000/revalidate-same" };
-    Request* req = fs.request(revalidateSame, uv_default_loop(), [&](const Response &res) {
-        fs.cancel(req);
+    Request* req1 = nullptr;
+    Request* req2 = nullptr;
+    req1 = fs.request(revalidateSame, uv_default_loop(), [&](const Response &res) {
+        // This callback can get triggered multiple times. We only care about the first invocation.
+        // It will get triggered again when refreshing the req2 (see below).
+        static bool first = true;
+        if (!first) {
+            return;
+        }
+        first = false;
+
+        EXPECT_EQ(nullptr, reference);
+        reference = &res;
+
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Response", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
         EXPECT_EQ("snowfall", res.etag);
         EXPECT_EQ("", res.message);
 
-        req = fs.request(revalidateSame, uv_default_loop(), [&, res](const Response &res2) {
-            fs.cancel(req);
+        req2 = fs.request(revalidateSame, uv_default_loop(), [&, res](const Response &res2) {
+            // Make sure we get a different object than before, since this request should've been revalidated.
+            EXPECT_TRUE(reference != &res2);
+
+            if (res2.stale) {
+                // Discard stale responses, if any.
+                return;
+            }
+
+            ASSERT_TRUE(req1);
+            fs.cancel(req1);
+            req1 = nullptr;
+
+            ASSERT_TRUE(req2);
+            fs.cancel(req2);
+            req2 = nullptr;
+
             EXPECT_EQ(Response::Successful, res2.status);
+            EXPECT_EQ(false, res.stale);
             EXPECT_EQ("Response", res2.data);
             // We use this to indicate that a 304 reply came back.
             EXPECT_LT(0, res2.expires);
@@ -40,11 +69,37 @@ TEST_F(Storage, CacheRevalidate) {
         });
     });
 
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+}
+
+TEST_F(Storage, CacheRevalidateModified) {
+    SCOPED_TEST(CacheRevalidateModified)
+
+    using namespace mbgl;
+
+    SQLiteCache cache(":memory:");
+    DefaultFileSource fs(&cache);
+
+    const Response *reference = nullptr;
+
     const Resource revalidateModified{ Resource::Unknown,
                                        "http://127.0.0.1:3000/revalidate-modified" };
-    Request* req2 = fs.request(revalidateModified, uv_default_loop(), [&](const Response &res) {
-        fs.cancel(req2);
+    Request* req1 = nullptr;
+    Request* req2 = nullptr;
+    req1 = fs.request(revalidateModified, uv_default_loop(), [&](const Response& res) {
+        // This callback can get triggered multiple times. We only care about the first invocation.
+        // It will get triggered again when refreshing the req2 (see below).
+        static bool first = true;
+        if (!first) {
+            return;
+        }
+        first = false;
+
+        EXPECT_EQ(nullptr, reference);
+        reference = &res;
+
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Response", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(1420070400, res.modified);
@@ -52,8 +107,24 @@ TEST_F(Storage, CacheRevalidate) {
         EXPECT_EQ("", res.message);
 
         req2 = fs.request(revalidateModified, uv_default_loop(), [&, res](const Response &res2) {
+            // Make sure we get a different object than before, since this request should've been revalidated.
+            EXPECT_TRUE(reference != &res2);
+
+            if (res2.stale) {
+                // Discard stale responses, if any.
+                return;
+            }
+
+            ASSERT_TRUE(req1);
+            fs.cancel(req1);
+            req1 = nullptr;
+
+            ASSERT_TRUE(req2);
             fs.cancel(req2);
+            req2 = nullptr;
+
             EXPECT_EQ(Response::Successful, res2.status);
+            EXPECT_EQ(false, res.stale);
             EXPECT_EQ("Response", res2.data);
             // We use this to indicate that a 304 reply came back.
             EXPECT_LT(0, res2.expires);
@@ -65,19 +136,61 @@ TEST_F(Storage, CacheRevalidate) {
         });
     });
 
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+}
+
+TEST_F(Storage, CacheRevalidateEtag) {
+    SCOPED_TEST(CacheRevalidateEtag)
+
+    using namespace mbgl;
+
+    SQLiteCache cache(":memory:");
+    DefaultFileSource fs(&cache);
+
+    const Response *reference = nullptr;
+
     const Resource revalidateEtag { Resource::Unknown, "http://127.0.0.1:3000/revalidate-etag" };
-    Request* req3 = fs.request(revalidateEtag, uv_default_loop(), [&](const Response &res) {
-        fs.cancel(req3);
+    Request* req1 = nullptr;
+    Request* req2 = nullptr;
+    req1 = fs.request(revalidateEtag, uv_default_loop(), [&](const Response &res) {
+        // This callback can get triggered multiple times. We only care about the first invocation.
+        // It will get triggered again when refreshing the req2 (see below).
+        static bool first = true;
+        if (!first) {
+            return;
+        }
+        first = false;
+
+        EXPECT_EQ(nullptr, reference);
+        reference = &res;
+
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Response 1", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
         EXPECT_EQ("response-1", res.etag);
         EXPECT_EQ("", res.message);
 
-        req3 = fs.request(revalidateEtag, uv_default_loop(), [&, res](const Response &res2) {
-            fs.cancel(req3);
+        req2 = fs.request(revalidateEtag, uv_default_loop(), [&, res](const Response &res2) {
+            // Make sure we get a different object than before, since this request should've been revalidated.
+            EXPECT_TRUE(reference != &res2);
+
+            if (res2.stale) {
+                // Discard stale responses, if any.
+                return;
+            }
+
+            ASSERT_TRUE(req1);
+            fs.cancel(req1);
+            req1 = nullptr;
+
+            ASSERT_TRUE(req2);
+            fs.cancel(req2);
+            req2 = nullptr;
+
             EXPECT_EQ(Response::Successful, res2.status);
+            EXPECT_EQ(false, res.stale);
             EXPECT_EQ("Response 2", res2.data);
             EXPECT_EQ(0, res2.expires);
             EXPECT_EQ(0, res2.modified);
diff --git a/test/storage/directory_reading.cpp b/test/storage/directory_reading.cpp
index 11298dff8b..f0bc7ea6d2 100644
--- a/test/storage/directory_reading.cpp
+++ b/test/storage/directory_reading.cpp
@@ -19,6 +19,7 @@ TEST_F(Storage, AssetReadDirectory) {
                [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Error, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ(0ul, res.data.size());
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
diff --git a/test/storage/file_reading.cpp b/test/storage/file_reading.cpp
index dc0620b78b..434af703f2 100644
--- a/test/storage/file_reading.cpp
+++ b/test/storage/file_reading.cpp
@@ -20,6 +20,7 @@ TEST_F(Storage, AssetEmptyFile) {
                [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ(0ul, res.data.size());
         EXPECT_EQ(0, res.expires);
         EXPECT_LT(1420000000, res.modified);
@@ -46,6 +47,7 @@ TEST_F(Storage, AssetNonEmptyFile) {
                uv_default_loop(), [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ(16ul, res.data.size());
         EXPECT_EQ(0, res.expires);
         EXPECT_LT(1420000000, res.modified);
@@ -73,6 +75,7 @@ TEST_F(Storage, AssetNonExistentFile) {
                uv_default_loop(), [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Error, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ(0ul, res.data.size());
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
diff --git a/test/storage/http_cancel.cpp b/test/storage/http_cancel.cpp
index 2eb599eeaa..5743ccb8f7 100644
--- a/test/storage/http_cancel.cpp
+++ b/test/storage/http_cancel.cpp
@@ -39,6 +39,7 @@ TEST_F(Storage, HTTPCancelMultiple) {
     Request* req = fs.request(resource, uv_default_loop(), [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
diff --git a/test/storage/http_coalescing.cpp b/test/storage/http_coalescing.cpp
index 9dfa855501..8558362034 100644
--- a/test/storage/http_coalescing.cpp
+++ b/test/storage/http_coalescing.cpp
@@ -50,3 +50,108 @@ TEST_F(Storage, HTTPCoalescing) {
 
     uv_run(uv_default_loop(), UV_RUN_DEFAULT);
 }
+
+TEST_F(Storage, HTTPMultiple) {
+    SCOPED_TEST(HTTPMultiple)
+
+    using namespace mbgl;
+
+    DefaultFileSource fs(nullptr);
+
+    const Response *reference = nullptr;
+
+    const Resource resource { Resource::Unknown, "http://127.0.0.1:3000/test?expires=2147483647" };
+    Request* req1 = nullptr;
+    Request* req2 = nullptr;
+    req1 = fs.request(resource, uv_default_loop(), [&] (const Response &res) {
+        EXPECT_EQ(nullptr, reference);
+        reference = &res;
+
+        // Do not cancel the request right away.
+        EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ("Hello World!", res.data);
+        EXPECT_EQ(2147483647, res.expires);
+        EXPECT_EQ(0, res.modified);
+        EXPECT_EQ("", res.etag);
+        EXPECT_EQ("", res.message);
+
+        // Start a second request for the same resource after the first one has been completed.
+        req2 = fs.request(resource, uv_default_loop(), [&] (const Response &res2) {
+            // Make sure we get the same object ID as before.
+            EXPECT_EQ(reference, &res2);
+
+            // Now cancel both requests after both have been notified.
+            fs.cancel(req1);
+            fs.cancel(req2);
+
+            EXPECT_EQ(Response::Successful, res2.status);
+            EXPECT_EQ("Hello World!", res2.data);
+            EXPECT_EQ(2147483647, res2.expires);
+            EXPECT_EQ(0, res2.modified);
+            EXPECT_EQ("", res2.etag);
+            EXPECT_EQ("", res2.message);
+
+            HTTPMultiple.finish();
+        });
+    });
+
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+}
+
+// Tests that we get stale responses from previous requests when requesting the same thing again.
+TEST_F(Storage, HTTPStale) {
+    SCOPED_TEST(HTTPStale)
+
+    using namespace mbgl;
+
+    DefaultFileSource fs(nullptr);
+
+    int updates = 0;
+    int stale = 0;
+
+    const Resource resource { Resource::Unknown, "http://127.0.0.1:3000/test" };
+    Request* req1 = nullptr;
+    Request* req2 = nullptr;
+    req1 = fs.request(resource, uv_default_loop(), [&] (const Response &res) {
+        // Do not cancel the request right away.
+        EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ("Hello World!", res.data);
+        EXPECT_EQ(false, res.stale);
+        EXPECT_EQ(0, res.expires);
+        EXPECT_EQ(0, res.modified);
+        EXPECT_EQ("", res.etag);
+        EXPECT_EQ("", res.message);
+
+        // Don't start the request twice in case this callback gets fired multiple times.
+        if (req2) {
+            return;
+        }
+
+        updates++;
+
+        // Start a second request for the same resource after the first one has been completed.
+        req2 = fs.request(resource, uv_default_loop(), [&] (const Response &res2) {
+            EXPECT_EQ(Response::Successful, res2.status);
+            EXPECT_EQ("Hello World!", res2.data);
+            EXPECT_EQ(0, res2.expires);
+            EXPECT_EQ(0, res2.modified);
+            EXPECT_EQ("", res2.etag);
+            EXPECT_EQ("", res2.message);
+
+            if (res2.stale) {
+                EXPECT_EQ(0, stale);
+                stale++;
+            } else {
+                // Now cancel both requests after both have been notified.
+                fs.cancel(req1);
+                fs.cancel(req2);
+                HTTPStale.finish();
+            }
+        });
+    });
+
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+
+    EXPECT_EQ(1, stale);
+    EXPECT_EQ(1, updates);
+}
diff --git a/test/storage/http_error.cpp b/test/storage/http_error.cpp
index aebc75405d..50b46a41b8 100644
--- a/test/storage/http_error.cpp
+++ b/test/storage/http_error.cpp
@@ -37,6 +37,7 @@ TEST_F(Storage, HTTPError) {
         EXPECT_LT(1, duration) << "Backoff timer didn't wait 1 second";
         EXPECT_GT(1.2, duration) << "Backoff timer fired too late";
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
@@ -54,6 +55,7 @@ TEST_F(Storage, HTTPError) {
         EXPECT_LT(1.5, duration) << "Resource wasn't retried the correct number of times";
         EXPECT_GT(1.7, duration) << "Resource wasn't retried the correct number of times";
         EXPECT_EQ(Response::Error, res.status);
+        EXPECT_EQ(false, res.stale);
 #ifdef MBGL_HTTP_NSURL
         EXPECT_TRUE(res.message ==
                         "The operation couldn’t be completed. (NSURLErrorDomain error -1004.)" ||
diff --git a/test/storage/http_header_parsing.cpp b/test/storage/http_header_parsing.cpp
index 13eab99125..93fdcb6231 100644
--- a/test/storage/http_header_parsing.cpp
+++ b/test/storage/http_header_parsing.cpp
@@ -20,6 +20,7 @@ TEST_F(Storage, HTTPHeaderParsing) {
                uv_default_loop(), [&](const Response &res) {
         fs.cancel(req1);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_EQ(1420797926, res.expires);
         EXPECT_EQ(1420794326, res.modified);
@@ -35,6 +36,7 @@ TEST_F(Storage, HTTPHeaderParsing) {
                uv_default_loop(), [&](const Response &res) {
         fs.cancel(req2);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_GT(2, std::abs(res.expires - now - 120)) << "Expiration date isn't about 120 seconds in the future";
         EXPECT_EQ(0, res.modified);
diff --git a/test/storage/http_issue_1369.cpp b/test/storage/http_issue_1369.cpp
index 954cb3b3f5..ba4e3d3885 100644
--- a/test/storage/http_issue_1369.cpp
+++ b/test/storage/http_issue_1369.cpp
@@ -33,6 +33,7 @@ TEST_F(Storage, HTTPIssue1369) {
     req = fs.request(resource, uv_default_loop(), [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
diff --git a/test/storage/http_load.cpp b/test/storage/http_load.cpp
index fa0468a848..092bf2db5a 100644
--- a/test/storage/http_load.cpp
+++ b/test/storage/http_load.cpp
@@ -25,6 +25,7 @@ TEST_F(Storage, HTTPLoad) {
             fs.cancel(reqs[i]);
             reqs[i] = nullptr;
             EXPECT_EQ(Response::Successful, res.status);
+            EXPECT_EQ(false, res.stale);
             EXPECT_EQ(std::string("Request ") +  std::to_string(current), res.data);
             EXPECT_EQ(0, res.expires);
             EXPECT_EQ(0, res.modified);
diff --git a/test/storage/http_other_loop.cpp b/test/storage/http_other_loop.cpp
index 43a655fba4..cd9fad95be 100644
--- a/test/storage/http_other_loop.cpp
+++ b/test/storage/http_other_loop.cpp
@@ -16,6 +16,7 @@ TEST_F(Storage, HTTPOtherLoop) {
                [&](const Response &res) {
         fs.cancel(req);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
diff --git a/test/storage/http_reading.cpp b/test/storage/http_reading.cpp
index 84af943025..c5e89b88e8 100644
--- a/test/storage/http_reading.cpp
+++ b/test/storage/http_reading.cpp
@@ -23,6 +23,7 @@ TEST_F(Storage, HTTPReading) {
         fs.cancel(req1);
         EXPECT_EQ(uv_thread_self(), mainThread);
         EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("Hello World!", res.data);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
@@ -36,6 +37,7 @@ TEST_F(Storage, HTTPReading) {
         fs.cancel(req2);
         EXPECT_EQ(uv_thread_self(), mainThread);
         EXPECT_EQ(Response::NotFound, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("", res.message);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);
@@ -48,6 +50,7 @@ TEST_F(Storage, HTTPReading) {
         fs.cancel(req3);
         EXPECT_EQ(uv_thread_self(), mainThread);
         EXPECT_EQ(Response::Error, res.status);
+        EXPECT_EQ(false, res.stale);
         EXPECT_EQ("HTTP status code 500", res.message);
         EXPECT_EQ(0, res.expires);
         EXPECT_EQ(0, res.modified);