# Zen Storage Service (zenserver)

This is the implementation of the local storage service for UE5. It is intended to be deployed on
user machines either as a daemon or launched ad hoc as required during  of editor/cooker/game startup

Zen is currently EXPERIMENTAL and not intended to be used in production. We will make breaking changes to storage and application interfaces as well as significant performance improvements in the upcoming months to make it ready for general adoption.

Zen can also be deployed as a shared instance for use as a shared cache. It also supports upstream 
connectivity to cloud storage services as well as other Zen server instances.

All platforms require [xmake](xmake.io)

Download the latest release [here](https://github.com/xmake-io/xmake/releases)

## Building on Windows

### Windows Setup

To build the code you will need Visual Studio 2019 (we use c++20 features), git and vcpkg.

* Install Visual Studio 2019 Version 16.10 or later
* Install [git](https://git-scm.com/download/win)

We use vcpkg to manage some libraries. Right now it's not set up on a project local
basis and requires manual bootstrap so you will need to do the following at least once:

* open up a command line window
  * create a `git`/`github` directory somewhere for you to clone repos into
  * issue `git clone https://github.com/microsoft/vcpkg.git` and build it using the `bootstrap-vcpkg.bat` script
* optional: add the `vcpkg` directory you cloned to your PATH to allow invoking vcpkg on the command line
* issue `vcpkg integrate install` to make sure you can build from Visual Studio using package manifests

Now you are ready to start building!

### Building with Visual Studio

We currently require Visual Studio 2019 Version 16.10 or later. Visual Studio 2022 can also be used, but
currently building with the VS2022 toolchain has not been tested (please leave the sln/vcxproj un-upgraded).

* clone the `zen` repository if you haven't already
  * run `git clone https://github.com/EpicGames/zen.git`
* run `xmake project -k vsxmake2019 -a x64 -y`
* open the `vsxmake2019\zen.sln` VS solution
  * Note: if you want full connectivity with the http.sys server implementation you currently need to run 
    Visual Studio in ADMIN mode since http.sys requires elevation to be able to listen on a non-local network socket.
    You can start Visual Studio in admin mode by holding CTRL-SHIFT when launching Visual Studio. Alternatively
    you can add an URL reservation (see below) 
  * you can now build and run `zenserver` as usual from Visual Studio
  * third-party dependencies will be built the first time via the `vcpkg` integration. This is not as
    fast as it could be (it does not go wide) but should only happen on the first build and will leverage
    a local build cache.

### Building with xmake

* configure xmake `xmake config -m debug|release -a x64`
* build zenserver `xmake build zenserver`

Binaries are located in the `build` directory

## Building on Linux

The following instructions have been collated using Ubuntu 20.04.

Zen makes heavy use of C++20 features which at the time of writing has limited
toolchain and C++ library support. A minimum compiler version of GCC-11 or
Clang-12 is required, along with GNU's libstdc+++-11 or newer. Note that it is
not currently possible to use anything other than the system's default C++
library (e.g. LLVM's libc++) due to the way that Zen's third party dependencies
are managed via `vcpkg`.

The first step is to acquire a suitable compiler and C++ library. On Ubuntu 20.04
GCC-11 is not available in the standard package repositories so Ubuntu's tool-
chain test respository needs to be added to Apt (note that this is _not required_
for Ubuntu 21.04 onwards);

```
sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
```

Now GCC-11 can be install via Apt. This will also install a suitable version of
the C++ library too;

```
sudo apt install -y --no-install-recommends g++-11
g++-11 --version
```

The easiest way to tell `xmake` to use the correct compiler version is to set
the `CXX` environment variable;

```
export CXX=g++-11
```

Next we need the `xmake` build system. For this we will download and install
`xmake` as a `.deb` package. Check the project's release page for more up to
date `.deb` files;

```
wget https://github.com/xmake-io/xmake/releases/download/v2.6.4/xmake-v2.6.4.amd64.deb
sudo dpkg -i xmake-v2.6.4.amd64.deb
xmake --version
```

For some of Zen's third party dependencies are provided by Microsoft's `vcpkg`
C++ library manager. After cloning the project there is an initialisation step;

```
git clone https://github.com/microsoft/vcpkg.git ~/zen/vcpkg
~/zen/vcpkg/bootstrap-vcpkg.sh
~/zen/vcpkg/vcpkg --version
```

`xmake` uses an environment variable to find `vcpkg`. Alternatively this can be
done by including `VCPKG_ROOT=...` on the command line when invoking `xmake`;

```
export VCPKG_ROOT=~/zen/vcpkg
```

Clone the Zen project and tell `xmake` to use the correct GCC version;

```
git clone https://github.com/EpicGames/zen.git ~/zen/main
cd ~/zen/main
```

Now we are ready to build Zen.  The `-y` skips `xmake` from prompting about
updating `vcpkg` packages;

```
xmake config -y --mode=debug
xmake build
```

Note that the command above to set the build variant to debug is optional. Tests
are only built in debug.The `xmake` flags `-vD` can be useful to diagnose
`xmake` issues.

### Distribution compatibility

Builds for Linux have a dependency on a modern version of the C++ library that
supports Zen's use of C++20 and the GCC-11 toolchain used (assuming the above
build instructions are adhered to). However there is no guarantee that the this
dependency is met when building on one Linux install and running on another. For
example, at the time of writing the LTS version of Ubuntu and Debian do not have
GCC-11's version of libstdc++.so.6 available in their package repositories.

To solve this, `xmake bundle` will bundle the required C++ .so and zenserver
binary together using AppImage. This can briefly be summarised as create a
squashfs file system containing zenserver and any C++ shared objects list with
`lld`. This file system is then concatenated with AppImage's runtime. This is
implemented in `scripts/bundle_linux.sh`. More details can be found here;

https://github.com/AppImage/AppImageKit

## Building on Mac

Building on Mac is very similar to Linux; install xmake, clone vcpkg and Zen and
then build the project. Here is a short summary;

```
## vcpkg
git clone https://github.com/microsoft/vcpkg.git ~/zen/vcpkg
~/zen/vcpkg/bootstrap-vcpkg.sh
~/zen/vcpkg/vcpkg --version

## xmake
curl -L https://github.com/xmake-io/xmake/releases/download/v2.6.2/xmake-v2.6.2.macosx.pkg > xmake-v2.6.2.macosx.pkg
sudo installer -pkg xmake-v2.6.2.macosx.pkg -target /

## Zen
git clone https://github.com/EpicGames/zen.git ~/zen/main
cd ~/zen/main

## Build
export VCPKG_ROOT=~/zen/vcpkg
xmake config -y --mode=debug --arch=x86_64
xmake build
```

# Implementation Notes

* The implementation currently depends only on a few libraries including the C++ standard library
* It uses exceptions for errors
* It is currently not portable as it uses Windows APIs directly. But as we all know, there is no 
  portable code, just code that has been ported many times. The plan is to implement support for 
  MacOS and Linux soon, and some research to enable it has been done
* `zenservice.exe` currently requires elevated access to enable `http.sys` access. This will be relaxed 
  in the future by offering to use a portable server interface without elevation
* The service endpoints are currently open on all NICs and will respond to requests from any host. This
  will be tightened up in the future to require some degree of authentication to satisfy security 
  requirements

# Contributing Code

To run the pre-commit scripts you'll need a few things:

* We rely on clang-format for consistent code formatting. You can install version 12 or later from https://llvm.org/builds/
* The helper scripts also depend on Python 3.x, which you may install from https://www.python.org/downloads/windows/ (I am presently using 3.9.5 which works). NOTE: *do* check the option to add Python to your PATH!

Once you have those dependencies, you can simply run `prepare_commit.bat` to ensure the code is properly formatted and has the Epic copyright header comment. I'm sure there's a better way to integrate this into the git submit flow but my git-fu is not strong enough yet to know how to do that best.

# Debugging

When debugging multi-process scenarios such as when running `zenserver-test`, the [Microsoft Child Process Debugging Power Tool](https://marketplace.visualstudio.com/items?itemName=vsdbgplat.MicrosoftChildProcessDebuggingPowerTool) 
is incredibly handy. When that is installed you may enable auto-attach to child processes via the Debug -> Other Debug Targets menu in Visual Studio.

# Testing

* There are some test projects
  * `zencore-test` exercises unit tests in the zencore project
  * `zenserver-test` exercises the zen server itself (functional tests)

The tests are implemented using [doctest](https://github.com/onqtam/doctest), which is similar to Catch in usage.

# Adding a http.sys URL reservation (Windows only)

Registering a handler for an HTTP endpoint requires either process elevation (i.e running Zen as admin) or a one-time URL reservation. An URL reservation can be added by issuing a command like

`netsh http add urlacl url=http://*:1337/ user=stefan.boberg` (enable for a specific user)

or 

`netsh http add urlacl url=http://*:1337/ sddl=D:(A;;GX;;;S-1-1-0)` (enable for any authenticated user)

# Coding Standards

See [CODING.md](CODING.md)

Run `prepare_commit.bat` before committing code. It ensures all source files are formatted with
clang-format which you will need to install.

(More helpful instructions needed here :)