Launch with Environment Variables (#664)

Author: kblok

lib/PuppeteerSharp/Launcher.cs

@@ -108,7 +108,7 @@ public async Task<Browser> ConnectAsync(ConnectOptions options)
         /// </summary>
         /// <returns>The executable path.</returns>
         public static string GetExecutablePath()
-            => new BrowserFetcher().RevisionInfo(BrowserFetcher.DefaultRevision).ExecutablePath;
+            => ResolveExecutablePath();
 
         #endregion
 
@@ -129,8 +129,7 @@ private static string GetOrFetchChromeExecutable(LaunchOptions options)
             var chromeExecutable = options.ExecutablePath;
             if (string.IsNullOrEmpty(chromeExecutable))
             {
-                var browserFetcher = new BrowserFetcher();
-                chromeExecutable = browserFetcher.RevisionInfo(BrowserFetcher.DefaultRevision).ExecutablePath;
+                chromeExecutable = ResolveExecutablePath();
             }
 
             if (!File.Exists(chromeExecutable))
@@ -141,6 +140,38 @@ private static string GetOrFetchChromeExecutable(LaunchOptions options)
             return chromeExecutable;
         }
 
+        private static string ResolveExecutablePath()
+        {
+            var executablePath = Environment.GetEnvironmentVariable("PUPPETEER_EXECUTABLE_PATH");
+            if (!string.IsNullOrEmpty(executablePath))
+            {
+                if (!File.Exists(executablePath))
+                {
+                    throw new FileNotFoundException("Tried to use PUPPETEER_EXECUTABLE_PATH env variable to launch browser but did not find any executable", executablePath);
+                }
+                return executablePath;
+            }
+
+            var browserFetcher = new BrowserFetcher();
+            var revision = Environment.GetEnvironmentVariable("PUPPETEER_CHROMIUM_REVISION");
+            RevisionInfo revisionInfo;
+            if (!string.IsNullOrEmpty(revision) && int.TryParse(revision, out var revisionNumber))
+            {
+                revisionInfo = browserFetcher.RevisionInfo(revisionNumber);
+                if (!revisionInfo.Local)
+                {
+                    throw new FileNotFoundException("Tried to use PUPPETEER_CHROMIUM_REVISION env variable to launch browser but did not find executable", revisionInfo.ExecutablePath);
+                }
+                return revisionInfo.ExecutablePath;
+            }
+            revisionInfo = browserFetcher.RevisionInfo(BrowserFetcher.DefaultRevision);
+            if (!revisionInfo.Local)
+            {
+                throw new FileNotFoundException("Chromium revision is not downloaded. Run BrowserFetcher.DownloadAsync or download Chromium manually", revisionInfo.ExecutablePath);
+            }
+            return revisionInfo.ExecutablePath;
+        }
+
         private static Task EnsureInitialPageAsync(Browser browser)
         {
             // Wait for initial page target to be created.

lib/PuppeteerSharp/Puppeteer.cs

@@ -46,6 +46,13 @@ public static string[] GetDefaultArgs(LaunchOptions options = null)
         /// See <a href="https://www.howtogeek.com/202825/what%E2%80%99s-the-difference-between-chromium-and-chrome/">this article</a>
         /// for a description of the differences between Chromium and Chrome.
         /// <a href="https://chromium.googlesource.com/chromium/src/+/lkcr/docs/chromium_browser_vs_google_chrome.md">This article</a> describes some differences for Linux users.
+        /// 
+        /// Environment Variables
+        /// Puppeteer looks for certain <see href="https://en.wikipedia.org/wiki/Environment_variable">environment variables</see>() to aid its operations.
+        /// - <c>PUPPETEER_CHROMIUM_REVISION</c> - specify a certain version of Chromium you'd like Puppeteer to use. See <see cref="Puppeteer.LaunchAsync(LaunchOptions, ILoggerFactory)"/> on how executable path is inferred. 
+        ///   **BEWARE**: Puppeteer is only <see href="https://github.com/GoogleChrome/puppeteer/#q-why-doesnt-puppeteer-vxxx-work-with-chromium-vyyy">guaranteed to work</see> with the bundled Chromium, use at your own risk.
+        /// - <c>PUPPETEER_EXECUTABLE_PATH</c> - specify an executable path to be used in <see cref="Puppeteer.LaunchAsync(LaunchOptions, ILoggerFactory)"/>. 
+        ///   **BEWARE**: Puppeteer is only <see href="https://github.com/GoogleChrome/puppeteer/#q-why-doesnt-puppeteer-vxxx-work-with-chromium-vyyy">guaranteed to work</see> with the bundled Chromium, use at your own risk.
         /// </remarks>
         public static Task<Browser> LaunchAsync(LaunchOptions options, ILoggerFactory loggerFactory = null)
             => new Launcher(loggerFactory).LaunchAsync(options);