don't trigger a HTTP request twice

src/mbgl/storage/default_file_source.cpp

@@ -101,9 +101,11 @@ void DefaultFileSource::Impl::startCacheRequest(const Resource& resource) {
     cache->get(resource, [this, resource](std::unique_ptr<Response> response) {
         DefaultFileRequest* request = find(resource);
 
-        if (!request) {
+        if (!request || request->request) {
             // There is no request for this URL anymore. Likely, the request was canceled
             // before we got around to process the cache result.
+            // The second possibility is that a request has already been started by another cache
+            // request. In this case, we don't have to do anything either.
             return;
         }
 

test/storage/http_issue_1369.cpp

@@ -0,0 +1,44 @@
+#include "storage.hpp"
+
+#include <uv.h>
+
+#include <mbgl/storage/default_file_source.hpp>
+#include <mbgl/storage/sqlite_cache.hpp>
+
+// Test for https://github.com/mapbox/mapbox-gl-native/issue/1369
+//
+// A request for http://example.com is made. This triggers a cache get. While the cache get is
+// pending, the request is canceled. This removes it from pending. Then, still while the cache get
+// is pending, a second request is made for the same resource. This adds an entry back to pending
+// and queues another cache request, even though the first one is still pending. Now both cache
+// requests resolve to misses, resulting in two HTTP requests for the same resource. The first one
+// will notify as expected, the second one will have bound a DefaultFileRequest* in the lambda that
+// gets invalidated by the first notify's pending.erase, and when it gets notified, the crash
+// occurs.
+
+TEST_F(Storage, HTTPIssue1369) {
+    SCOPED_TEST(HTTPIssue1369)
+
+    using namespace mbgl;
+
+    SQLiteCache cache;
+    DefaultFileSource fs(&cache);
+
+    const Resource resource { Resource::Unknown, "http://127.0.0.1:3000/test" };
+
+    auto req = fs.request(resource, uv_default_loop(), [&](const Response&) {
+        ADD_FAILURE() << "Callback should not be called";
+    });
+    fs.cancel(req);
+    fs.request(resource, uv_default_loop(), [&](const Response &res) {
+        EXPECT_EQ(Response::Successful, res.status);
+        EXPECT_EQ("Hello World!", res.data);
+        EXPECT_EQ(0, res.expires);
+        EXPECT_EQ(0, res.modified);
+        EXPECT_EQ("", res.etag);
+        EXPECT_EQ("", res.message);
+        HTTPIssue1369.finish();
+    });
+
+    uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+}

test/test.gypi

@@ -66,6 +66,7 @@
         'storage/http_coalescing.cpp',
         'storage/http_error.cpp',
         'storage/http_header_parsing.cpp',
+        'storage/http_issue_1369.cpp',
         'storage/http_load.cpp',
         'storage/http_noloop.cpp',
         'storage/http_other_loop.cpp',