Added example for CPP Dll useage (#3157)

examples/tauri-dynamic-lib/Readme.md

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+# Readme
+
+This is an example of compiling tauri as a dynamic shared library and running it from another app.
+
+  * src-tauri is an example of a library containing code to launch a tauri webview window.
+  * src-app1 is a small example of calling tauri from a dynamic shared library through FFI.
+
+Note that bundling of resources via tauri.conf.json may not work in some cases due to the nature of the build.
+So you have to be aware of copying any files needed to the correct paths for html / js etc.
+
+## Rust libraries
+
+Typically there are 3 types of libraries rust can generate
+
+  * rlib - rust static libraries
+  * dylib - rust shared libraries
+  * cdylib - dynamic shared libraries that can be used to interop with other languages.
+
+Typically cdylib libraries are used for interop with C / C++ Projects but this can also include other languages.
+The src-tauri example uses the cdylib crate type
+
+## Building / Running
+
+``` bash
+# First build the library
+cd src-tauri
+cargo build
+cd ..
+
+# Next build the app
+cd src-app1
+cargo build
+
+# Next run the app
+cargo run
+```

examples/tauri-dynamic-lib/src-app1/.gitignore

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+# Generated by Cargo
+# will have compiled files and executables
+/target/
+WixTools
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+config.json
+bundle.json

examples/tauri-dynamic-lib/src-app1/.license_template

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+// Copyright {20\d{2}(-20\d{2})?} Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT

examples/tauri-dynamic-lib/src-app1/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "app1"
+version = "0.1.0"
+dependencies = [
+ "libloading",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "libloading"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "afe203d669ec979b7128619bae5a63b7b42e9203c1b29146079ee05e2f604b52"
+dependencies = [
+ "cfg-if",
+ "winapi",
+]
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"

examples/tauri-dynamic-lib/src-app1/Cargo.toml

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+[package]
+name = "app1"
+version = "0.1.0"
+description = "A simple app that makes a dll call"
+edition = "2021"
+rust-version = "1.56"
+
+[workspace]
+
+[dependencies]
+libloading = "0.7.2"

examples/tauri-dynamic-lib/src-app1/src/main.rs

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+// Copyright 2019-2021 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+// This is an example of an application that loads and runs a dll
+// Typically this could be c++, we use rust here just for convenience
+// See https://michael-f-bryan.github.io/rust-ffi-guide/dynamic_loading.html
+
+use libloading::{Library, library_filename, Symbol};
+type LibFunctionType1 = fn();
+
+fn main() {
+  let library_path = library_filename("../src-tauri/target/debug/tauri_app");
+  println!("Loading run_tauri() from {:?}", library_path);
+
+  unsafe {
+    let lib = Library::new(library_path).unwrap();
+    let run_tauri: Symbol<LibFunctionType1> = lib.get(b"run_tauri").unwrap();
+    println!("Launching webview");
+    run_tauri()
+  }
+}

examples/tauri-dynamic-lib/src-tauri/.gitignore

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+# Generated by Cargo
+# will have compiled files and executables
+/target/
+WixTools
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+config.json
+bundle.json

examples/tauri-dynamic-lib/src-tauri/.license_template

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+// Copyright {20\d{2}(-20\d{2})?} Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT

examples/tauri-dynamic-lib/src-tauri/Cargo.toml

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+[package]
+name = "tauri_app"
+version = "0.1.0"
+description = "A very simple Dll Library that runs tauri and launches a webview window"
+edition = "2021"
+rust-version = "1.56"
+
+[workspace]
+
+[lib]
+crate-type = ["cdylib"]
+
+[build-dependencies]
+tauri-build = { path = "../../../core/tauri-build", features = [ "codegen" ] }
+
+[dependencies]
+serde_json = "1.0"
+serde = { version = "1.0", features = [ "derive" ] }
+tauri = { path = "../../../core/tauri", features = [] }
+
+[features]
+default = [ "custom-protocol" ]
+custom-protocol = [ "tauri/custom-protocol" ]

examples/tauri-dynamic-lib/src-tauri/build.rs

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+// Copyright 2019-2021 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+use tauri_build::{try_build, Attributes, WindowsAttributes};
+
+fn main() {
+  if let Err(error) = try_build(
+    Attributes::new()
+      .windows_attributes(WindowsAttributes::new().window_icon_path("../../.icons/icon.ico")),
+  ) {
+    panic!("error found during tauri-build: {}", error);
+  }
+}

examples/tauri-dynamic-lib/src-tauri/src/index.html

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+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Welcome to Tauri!</title>
+  </head>
+  <body>
+    <h1>Welcome to Tauri!</h1>
+  </body>
+</html>

examples/tauri-dynamic-lib/src-tauri/src/lib.rs

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+// Copyright 2019-2021 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+// This is an example of a taui app built into a dll
+// Calling lib_test1 within the dll will launch the webview
+
+#![cfg_attr(
+  all(not(debug_assertions), target_os = "windows"),
+  windows_subsystem = "windows"
+)]
+
+#[no_mangle]
+pub extern fn run_tauri() {
+  tauri::Builder::default()
+    .run(tauri::generate_context!(
+      "./tauri.conf.json"
+    ))
+    .expect("error while running tauri application");
+}

examples/tauri-dynamic-lib/src-tauri/tauri.conf.json

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+{
+  "build": {
+    "distDir": ["src/index.html"],
+    "devPath": ["src/index.html"],
+    "beforeDevCommand": "",
+    "beforeBuildCommand": ""
+  },
+  "tauri": {
+    "bundle": {
+      "active": true,
+      "targets": "all",
+      "identifier": "com.tauri.dev",
+      "icon": [
+        "../../.icons/32x32.png",
+        "../../.icons/128x128.png",
+        "../../.icons/128x128@2x.png",
+        "../../.icons/icon.icns",
+        "../../.icons/icon.ico"
+      ],
+      "resources": [],
+      "externalBin": [],
+      "copyright": "",
+      "category": "DeveloperTool",
+      "shortDescription": "",
+      "longDescription": "",
+      "deb": {
+        "depends": [],
+        "useBootstrapper": false
+      },
+      "macOS": {
+        "frameworks": [],
+        "minimumSystemVersion": "",
+        "useBootstrapper": false,
+        "exceptionDomain": ""
+      }
+    },
+    "allowlist": {
+      "all": false
+    },
+    "windows": [
+      {
+        "title": "Welcome to Tauri!",
+        "width": 800,
+        "height": 600,
+        "resizable": true,
+        "fullscreen": false
+      }
+    ],
+    "security": {
+      "csp": "default-src blob: data: filesystem: ws: wss: http: https: tauri: 'unsafe-eval' 'unsafe-inline' 'self'"
+    },
+    "updater": {
+      "active": false
+    }
+  }
+}