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‎.gitignore

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.DS_Store
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package-lock.json

‎LICENSE

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MIT License
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Copyright (c) 2024 DistroAV
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.

‎README.md

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# firebase-functions-future-async-nested
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This repo is an example/test app to repro a problem I am seeing using https://github.com/firebase/firebase-cpp-sdk where `firebase::Future<firebase::functions::HttpsCallableResult>`
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appears to deadlock when nested inside a `Future::OnCompletion`.
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The problem happens on both the Emulator and the live project.
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Opened firebase-cpp-sdk Issue: https://github.com/firebase/firebase-cpp-sdk/issues/1621
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Example...
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Works:
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```C++
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auto value = Foo();
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cout << "tid=" << pthread_self() << " Foo #1: value=" << value << endl;
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value = Foo();
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cout << "tid=" << pthread_self() << " Foo #2: value=" << value << endl;
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auto future = FooAsync([](int value) {
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cout << "tid=" << pthread_self() << " FooAsync #1: value=" << value << endl;
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});
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future = FooAsync([](int value) {
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cout << "tid=" << pthread_self() << " FooAsync #2: value=" << value << endl;
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});
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```
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Deadlocks:
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```C++
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future = FooAsync([](int value) {
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cout << "tid=" << pthread_self() << " FooAsync #3: value=" << value << endl;
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FooAsync([](int value) { // <- deadlocks a few levels into this call and firebase never logs it called the firebase function
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cout << "tid=" << pthread_self() << " FooAsync #4: value=" << value << endl;
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});
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});
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```
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Log of the above 6 calls:
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```bash
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% ./FirebaseExample
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WARNING: Database URL not set in the Firebase config.
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DEBUG: Creating Firebase App __FIRAPP_DEFAULT for Firebase C++ 12.1.0
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DEBUG: Validating semaphore creation.
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DEBUG: Added app name=__FIRAPP_DEFAULT: options, api_key=..., app_id=..., database_url=, messaging_sender_id=..., storage_bucket=..., project_id=... (0x...)
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Using Functions Emulator at 127.0.0.1:5001
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tid=0x1fefccc00 +Foo(...)
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tid=0x1fefccc00 +Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 Call: `foo` +Call(...)
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DEBUG: Calling Cloud Function with url: 127.0.0.1:5001/functions-futures-async-nested/us-central1/foo
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data: {"data":null}
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tid=0x1fefccc00 Call: `foo` -Call(...)
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tid=0x1fefccc00 ProcessEvents(100)
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DEBUG: Cloud Function response body = {"result":200}
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tid=0x1fefccc00 +OnCallCompleted(...)
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tid=0x1fefccc00 -OnCallCompleted(...)
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tid=0x1fefccc00 -Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 -Foo(...)
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tid=0x1fefccc00 Foo #1: value=200
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tid=0x1fefccc00 +Foo(...)
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tid=0x1fefccc00 +Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 Call: `foo` +Call(...)
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DEBUG: Calling Cloud Function with url: 127.0.0.1:5001/functions-futures-async-nested/us-central1/foo
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data: {"data":null}
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tid=0x1fefccc00 Call: `foo` -Call(...)
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tid=0x1fefccc00 ProcessEvents(100)
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DEBUG: Cloud Function response body = {"result":200}
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tid=0x1fefccc00 +OnCallCompleted(...)
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tid=0x1fefccc00 -OnCallCompleted(...)
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tid=0x1fefccc00 -Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 -Foo(...)
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tid=0x1fefccc00 Foo #2: value=200
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tid=0x1fefccc00 +FooAsync(...)
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tid=0x1fefccc00 +Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 Call: `foo` +Call(...)
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DEBUG: Calling Cloud Function with url: 127.0.0.1:5001/functions-futures-async-nested/us-central1/foo
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data: {"data":null}
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tid=0x1fefccc00 Call: `foo` -Call(...)
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DEBUG: Cloud Function response body = {"result":200}
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tid=0x16b7fb000 +OnCallCompleted(...)
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tid=0x16b7fb000 FooAsync #1: value=200
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tid=0x16b7fb000 -OnCallCompleted(...)
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tid=0x1fefccc00 -Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 -FooAsync(...)
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tid=0x1fefccc00 +FooAsync(...)
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tid=0x1fefccc00 +Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 Call: `foo` +Call(...)
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DEBUG: Calling Cloud Function with url: 127.0.0.1:5001/functions-futures-async-nested/us-central1/foo
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data: {"data":null}
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tid=0x1fefccc00 Call: `foo` -Call(...)
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DEBUG: Cloud Function response body = {"result":200}
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tid=0x16b7fb000 +OnCallCompleted(...)
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tid=0x16b7fb000 FooAsync #2: value=200
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tid=0x16b7fb000 -OnCallCompleted(...)
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tid=0x1fefccc00 -Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 -FooAsync(...)
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tid=0x1fefccc00 +FooAsync(...)
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tid=0x1fefccc00 +Cloud::Call(`foo`, ...)
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tid=0x1fefccc00 Call: `foo` +Call(...)
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DEBUG: Calling Cloud Function with url: 127.0.0.1:5001/functions-futures-async-nested/us-central1/foo
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data: {"data":null}
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tid=0x1fefccc00 Call: `foo` -Call(...)
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DEBUG: Cloud Function response body = {"result":200}
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tid=0x16b7fb000 +OnCallCompleted(...)
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tid=0x16b7fb000 FooAsync #3: value=200
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tid=0x16b7fb000 +FooAsync(...)
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tid=0x16b7fb000 +Cloud::Call(`foo`, ...)
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^C
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```
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Note at the end that the app hung indefinitely before the 6th `DEBUG: Calling Cloud Function` was logged and I had to Ctrl-Break.
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I suspect this has something to do with the muxtex(s)/semaphore(s) used to track pending Futures and their OnCompletion.
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One **admittedly not directly related** hint I got about this was from https://github.com/firebase/firebase-cpp-sdk/issues/51#issuecomment-654535769
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> In my case I resolved the issue by ensuring the HttpsCallableReference was not destroyed until the future had resolved. The destructor for this class releases the future and calls rest::CleanupTransportCurl() which I imagine is the cause of the problem.
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It seems like the official code could stand for a bit more verbose logging around these areas... but what do I know?
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I am not certain if these issues are [closely?] related:
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* https://github.com/firebase/firebase-cpp-sdk/issues/61
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* ...
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## To test/run/use...
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### firebase functions
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```bash
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cd firebase
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```
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To run in emulator:
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```bash
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firebase emulators:start --only functions
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```
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To deploy to firebase cloud:
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```bash
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firebase deploy --only functions
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```
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### app
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To build:
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```bash
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cd app
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# once, or whenever firebase-cpp-sdk changes
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pushd libs
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./get-firebase-cpp-sdk.sh
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popd
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mkdir -p build && cd $_
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# Define an Android app in your firebase project and download its google-services.json
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cp /path/to/your/google-services.json .
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# once, or whenever CMakeLists.txt changes
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cmake ..
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# whenever code changes
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cmake --build .
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```
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To run [and use firebase emulator by default]:
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```bash
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./FirebaseExample
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```
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To run and not use emulator [use firebase cloud]:
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```bash
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./FirebaseExample --no-emulator
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```

‎app/.gitignore

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build/
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google-services*.json

‎app/CMakeLists.txt

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cmake_minimum_required(VERSION 3.10)
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# Set the project name and version
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project(FirebaseExample VERSION 1.0)
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# Specify the C++ standard
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set(CMAKE_CXX_STANDARD 11)
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set(CMAKE_CXX_STANDARD_REQUIRED True)
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# Add the executable
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add_executable(${PROJECT_NAME} main.cpp)
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# "`firebase_app` is required and must always be listed last"
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set(firebase_libs firebase_app_check firebase_auth firebase_firestore firebase_functions firebase_app)
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if(APPLE)
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set(ADDITIONAL_LIBS
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gssapi_krb5
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pthread
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"-framework CoreFoundation"
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"-framework Foundation"
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"-framework GSS"
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"-framework Security"
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"-framework SystemConfiguration")
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elseif(MSVC)
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set(ADDITIONAL_LIBS advapi32 ws2_32 crypt32 iphlpapi psapi userenv)
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else()
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set(ADDITIONAL_LIBS pthread)
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endif()
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set(FIREBASE_SDK_DIR ${CMAKE_SOURCE_DIR}/libs/firebase_cpp_sdk)
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add_subdirectory(${FIREBASE_SDK_DIR} EXCLUDE_FROM_ALL)
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target_include_directories(${PROJECT_NAME} PRIVATE ${FIREBASE_SDK_DIR}/include)
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target_link_libraries(${PROJECT_NAME} PRIVATE ${firebase_libs} ${ADDITIONAL_LIBS})

‎app/libs/.gitignore

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firebase_cpp_sdk

‎app/libs/get-firebase-cpp-sdk.sh

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#!/bin/bash
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# https://api.github.com/repos/firebase/firebase-cpp-sdk/releases/latest
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# https://github.com/firebase/firebase-cpp-sdk/releases/latest
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SDK_VERSION="12.1.0"
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ZIP_FILE="firebase_cpp_sdk_${SDK_VERSION}.zip"
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URL="https://dl.google.com/firebase/sdk/cpp/${ZIP_FILE}"
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FIREBASE_CPP_SDK_DIR="./firebase_cpp_sdk"
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rm -rf ${FIREBASE_CPP_SDK_DIR}
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mkdir -p ${FIREBASE_CPP_SDK_DIR}
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pushd ${FIREBASE_CPP_SDK_DIR} >/dev/null
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echo "Downloading Firebase C++ SDK version ${SDK_VERSION}..."
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curl -L ${URL} -o ${ZIP_FILE}
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echo "Extracting ${ZIP_FILE}..."
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extraction_inclusions=(
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"include/*"
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"libs/linux/x86_64/cxx11/*"
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"libs/darwin/universal/*"
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"libs/windows/*/MD/x64/*"
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"CMakeLists.txt"
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"NOTICES"
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"readme.md"
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)
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BASE_DIR_NAME=$(basename ${FIREBASE_CPP_SDK_DIR})
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prefixed_paths=()
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for path in "${extraction_inclusions[@]}"; do
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prefixed_paths+=("${BASE_DIR_NAME}/${path}")
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done
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unzip ${ZIP_FILE} "${prefixed_paths[@]}" -d ..
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echo "Cleaning up..."
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rm ${ZIP_FILE}
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popd >/dev/null
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echo "Firebase C++ SDK setup complete."

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