Create devcontainer and add .clang-format to simplify development (#509)

* Add .clang-format file

This enables format-on-save to match the style in VSCode.

Use "Google" style which matches `format.sh`.

* Add GitHub devcontainer config

This enables using things like GitHub Codespaces, which pre-configures
a container with the proper dependencies so that it can build.

I choose Ubuntu 21.04 as the base image, and needed to make one small
modification over the README instructions:

* Installed `libcurl4-openssl-dev` instead of `libcurl-dev`

The files originate from the C++ devcontainer template, with minor
modifications to install the dependency packages in `Dockerfile`.

Author: jwmcglynn

.clang-format

@@ -0,0 +1,3 @@
+---
+BasedOnStyle: Google
+---

.devcontainer/Dockerfile

@@ -0,0 +1,45 @@
+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.224.3/containers/cpp/.devcontainer/base.Dockerfile
+
+# [Choice] Debian / Ubuntu version (use Debian 11, Ubuntu 18.04/21.04 on local arm64/Apple Silicon): debian-11, debian-10, ubuntu-21.04, ubuntu-20.04, ubuntu-18.04
+ARG VARIANT="bullseye"
+FROM mcr.microsoft.com/vscode/devcontainers/cpp:0-${VARIANT}
+
+ARG USERNAME=vscode
+
+# [Optional] Install CMake version different from what base image has already installed. 
+# CMake reinstall choices: none, 3.21.5, 3.22.2, or versions from https://cmake.org/download/
+ARG REINSTALL_CMAKE_VERSION_FROM_SOURCE="3.23.1"
+
+# Use installed binaries from the system.
+# Do not download latest version of CMake and Ninja during vcpkg bootstrap!
+ENV VCPKG_FORCE_SYSTEM_BINARIES=1
+ENV VCPKG_USE_SYSTEM_BINARIES=1
+
+# Optionally install the cmake for vcpkg
+COPY ./reinstall-cmake.sh /tmp/
+RUN if [ "${REINSTALL_CMAKE_VERSION_FROM_SOURCE}" != "none" ]; then \
+    chmod +x /tmp/reinstall-cmake.sh && /tmp/reinstall-cmake.sh ${REINSTALL_CMAKE_VERSION_FROM_SOURCE}; \
+    fi \
+    && rm -f /tmp/reinstall-cmake.sh
+
+# Install dependencies.
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends \
+    libboost-dev \
+    libsodium-dev \
+    libncurses5-dev \
+    libprotobuf-dev \
+    protobuf-compiler \
+    libgflags-dev \
+    libutempter-dev \
+    build-essential \
+    ninja-build \
+    # Note that in Ubuntu 21.04, there is no libcurl-dev, use libcurl4-openssl-dev
+    libcurl4-openssl-dev
+
+#
+# Set up command history volume
+# See https://code.visualstudio.com/remote/advancedcontainers/persist-bash-history
+#
+RUN mkdir /commandhistory \
+    && chown -R $USERNAME /commandhistory

.devcontainer/devcontainer.json

@@ -0,0 +1,35 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.224.3/containers/cpp
+{
+	"name": "C++",
+	"build": {
+		"dockerfile": "Dockerfile",
+		// Update 'VARIANT' to pick an Debian / Ubuntu OS version: debian-11, debian-10, debian-9, ubuntu-21.04, ubuntu-20.04, ubuntu-18.04
+		// Use Debian 11, Debian 9, Ubuntu 18.04 or Ubuntu 21.04 on local arm64/Apple Silicon
+		"args": { "VARIANT": "ubuntu-21.04" }
+	},
+	"runArgs": ["--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined"],
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": {},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"ms-vscode.cpptools",
+		"ms-vscode.cmake-tools"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	"postCreateCommand": "git submodule update --init --recursive",
+
+	// Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "vscode",
+
+  // For sharing shell history out of the container.
+  "mounts": [
+    "source=eternalterminal-history,target=/commandhistory,type=volume"
+  ]
+}

.devcontainer/reinstall-cmake.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+#-------------------------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See https://go.microsoft.com/fwlink/?linkid=2090316 for license information.
+#-------------------------------------------------------------------------------------------------------------
+#
+set -e
+
+CMAKE_VERSION=${1:-"none"}
+
+if [ "${CMAKE_VERSION}" = "none" ]; then
+    echo "No CMake version specified, skipping CMake reinstallation"
+    exit 0
+fi
+
+# Cleanup temporary directory and associated files when exiting the script.
+cleanup() {
+    EXIT_CODE=$?
+    set +e
+    if [[ -n "${TMP_DIR}" ]]; then
+        echo "Executing cleanup of tmp files"
+        rm -Rf "${TMP_DIR}"
+    fi
+    exit $EXIT_CODE
+}
+trap cleanup EXIT
+
+
+echo "Installing CMake..."
+apt-get -y purge --auto-remove cmake
+mkdir -p /opt/cmake
+
+architecture=$(dpkg --print-architecture)
+case "${architecture}" in
+    arm64)
+        ARCH=aarch64 ;;
+    amd64)
+        ARCH=x86_64 ;;
+    *)
+        echo "Unsupported architecture ${architecture}."
+        exit 1
+        ;;
+esac
+
+CMAKE_BINARY_NAME="cmake-${CMAKE_VERSION}-linux-${ARCH}.sh"
+CMAKE_CHECKSUM_NAME="cmake-${CMAKE_VERSION}-SHA-256.txt"
+TMP_DIR=$(mktemp -d -t cmake-XXXXXXXXXX)
+
+echo "${TMP_DIR}"
+cd "${TMP_DIR}"
+
+curl -sSL "https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION}/${CMAKE_BINARY_NAME}" -O
+curl -sSL "https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION}/${CMAKE_CHECKSUM_NAME}" -O
+
+sha256sum -c --ignore-missing "${CMAKE_CHECKSUM_NAME}"
+sh "${TMP_DIR}/${CMAKE_BINARY_NAME}" --prefix=/opt/cmake --skip-license
+
+ln -s /opt/cmake/bin/cmake /usr/local/bin/cmake