From 0d055f9fab35e5acac7c9cc32427bed161070d92 Mon Sep 17 00:00:00 2001
From: Daniel Vigovszky <daniel.vigovszky@gmail.com>
Date: Sun, 9 Apr 2023 13:11:40 +0200
Subject: [PATCH] Log a warning in case of fatal errors (#2084)

* Log a warning in case of fatal errors

* Format
---
 zio-http/src/main/scala/zio/http/Server.scala       | 13 ++++++++++++-
 .../http/netty/server/ServerInboundHandler.scala    | 10 +++++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/zio-http/src/main/scala/zio/http/Server.scala b/zio-http/src/main/scala/zio/http/Server.scala
index de050ce3a7..0dc7dd41a5 100644
--- a/zio-http/src/main/scala/zio/http/Server.scala
+++ b/zio-http/src/main/scala/zio/http/Server.scala
@@ -53,6 +53,7 @@ object Server {
     responseCompression: Option[ResponseCompressionConfig],
     requestStreaming: RequestStreaming,
     maxHeaderSize: Int,
+    logWarningOnFatalError: Boolean,
   ) {
     self =>
 
@@ -96,6 +97,12 @@ object Server {
      */
     def keepAlive(enable: Boolean): Config = self.copy(keepAlive = enable)
 
+    /**
+     * Log a warning in case of fatal errors when an error response cannot be
+     * sent back to the client
+     */
+    def logWarningOnFatalError(enable: Boolean): Config = self.copy(logWarningOnFatalError = enable)
+
     /**
      * Configure the server to use `maxHeaderSize` value when encode/decode
      * headers.
@@ -148,7 +155,8 @@ object Server {
         Decompression.config.nested("request-decompression").withDefault(Config.default.requestDecompression) ++
         ResponseCompressionConfig.config.nested("response-compression").optional ++
         RequestStreaming.config.nested("request-streaming").withDefault(Config.default.requestStreaming) ++
-        zio.Config.int("max-header-size").withDefault(Config.default.maxHeaderSize)
+        zio.Config.int("max-header-size").withDefault(Config.default.maxHeaderSize) ++
+        zio.Config.boolean("log-warning-on-fatal-error").withDefault(Config.default.logWarningOnFatalError)
     }.map {
       case (
             sslConfig,
@@ -160,6 +168,7 @@ object Server {
             responseCompression,
             requestStreaming,
             maxHeaderSize,
+            logWarningOnFatalError,
           ) =>
         Config(
           sslConfig = sslConfig,
@@ -170,6 +179,7 @@ object Server {
           responseCompression = responseCompression,
           requestStreaming = requestStreaming,
           maxHeaderSize = maxHeaderSize,
+          logWarningOnFatalError = logWarningOnFatalError,
         )
     }
 
@@ -182,6 +192,7 @@ object Server {
       responseCompression = None,
       requestStreaming = RequestStreaming.Disabled(1024 * 100),
       maxHeaderSize = 8192,
+      logWarningOnFatalError = true,
     )
 
     final case class ResponseCompressionConfig(
diff --git a/zio-http/src/main/scala/zio/http/netty/server/ServerInboundHandler.scala b/zio-http/src/main/scala/zio/http/netty/server/ServerInboundHandler.scala
index d388f89fed..b3e518b416 100644
--- a/zio-http/src/main/scala/zio/http/netty/server/ServerInboundHandler.scala
+++ b/zio-http/src/main/scala/zio/http/netty/server/ServerInboundHandler.scala
@@ -116,7 +116,15 @@ private[zio] final case class ServerInboundHandler(
           runtime.run(ctx, () => {}) {
             // We cannot return the generated response from here, but still calling the handler for its side effect
             // for example logging.
-            app.runServerErrorOrNull(Cause.die(t)).unit
+            app
+              .runServerErrorOrNull(Cause.die(t))
+              .tap { response =>
+                if (config.logWarningOnFatalError)
+                  ZIO.logWarningCause(s"Fatal exception in Netty, cannot send error response $response", Cause.die(t))
+                else
+                  ZIO.unit
+              }
+              .unit
           }
         }
         super.exceptionCaught(ctx, t)