dotnet 10 build cleanup (#305)

## Why

The sources already use C# 14 (the `field` keyword in `SmtpAppender`'s property accessors), which
requires the .NET 10 SDK. Nothing in the repo declared that: the test projects targeted `net8.0`,
CI installed .NET 8 and the Dockerfile fetched the 8.0 channel, so a clean checkout could not
compile - it failed with `CS0501: 'SmtpAppender.To.get' must declare a body`.

This PR makes the required toolchain explicit and cleans up the surrounding build, which turned up
several unrelated defects along the way.

**The shipped surface is unchanged.** `log4net` still targets `net462;netstandard2.0` and
`log4net.Ext.Mail` still targets `netstandard2.0`. Nothing here affects consumers.

## Changes

| Commit | What |
|---|---|
| Target .NET 10 / C# 14 | test and integration-test projects `net8.0` → `net10.0`; CI `dotnet-version: 10` |
| Build net4x without Mono | delete `MonoForFramework.targets` and its two imports |
| Container image from the .NET 10 SDK image | `ubuntu:20.04` + `dotnet-install.sh` →
`mcr.microsoft.com/dotnet/sdk:10.0-noble` |
| Stop the release scripts on failed steps | `$PSNativeCommandUseErrorActionPreference` in both scripts, plus a path
fix |
| Fix the log4net.Ext.Mail package readme | `NU5039` |
| Quieten the TelnetAppender test | graceful socket shutdown |
| Update BUILDING.md | document what the build actually is |

### Mono is no longer needed to build net4x

`MonoForFramework.targets` set `FrameworkPathOverride` to Mono's `4.6.2-api` directory on Unix. That
is obsolete: the .NET SDK already adds an implicit `PackageReference` to
`Microsoft.NETFramework.ReferenceAssemblies.<tfm>` for net4x targets, and those packages were
already in the restore graph.

### net462 tests are now Windows-only

VSTest hosts net4x tests through `TestHostNetFramework/testhost.exe`, a .NET Framework executable,
so `dotnet test` aborts with `TESTRUNABORT` on Linux and macOS. `log4net.Tests` now conditions its
`TargetFrameworks` on `'$(OS)' != 'Windows_NT'`, so no unrunnable test assembly is produced. The
`net462` **library** is still built on every platform; only the test target is gated.

This also fixes the `ubuntu-22.04` and `macos-14` CI jobs, which ran a bare `dotnet test` against a
`net462` target they could not host.

###  Run CI on the latest runner images

macos-14 and ubuntu-22.04 are superseded by macos-latest (macOS 26) and ubuntu-latest (Ubuntu 24.04).
Neither new image ships Mono, so net4x tests cannot run there - which is why log4net.Tests restricts net462 to Windows.

### Release scripts continued after failed steps

`$ErrorActionPreference = 'Stop'` does not apply to native commands — they only set
`$LASTEXITCODE`. A failing `dotnet`, `git`, `zip`, `gpg` or `mvnw` was therefore ignored, and
artifacts were packaged, signed and tagged anyway. Both scripts now set
`$PSNativeCommandUseErrorActionPreference` (PowerShell 7.3+).

This was not theoretical: `NU5039` made the `log4net.Ext.Mail` pack fail, no `.nupkg` was produced,
and `build-preview.ps1` went on to gpg-sign files that did not exist. `build-preview.ps1` also built
its artifact paths with backslashes, which are not path separators outside Windows.

### TelnetAppender test noise

`SimpleTelnetClient.Dispose()` disposed the `TcpClient` while the reader was blocked in
`stream.Read`, so teardown aborted the socket and dumped an `IOException` with a stack trace on
every passing run. The cancellation token never actually broke the loop — it was only checked after
a successful read. Now the socket is shut down first, the read returns 0, and the loop exits
normally. Exceptions arriving after disposal starts are not reported; genuine failures still are.

## Verification

On Linux (Ubuntu-based, .NET SDK 10.0.110, self-built Mono present but unused by the build):

- `dotnet build ./src/log4net.sln` - succeeds, 0 warnings
- `dotnet test ./src/log4net.sln` - **292 total, 0 failed, 281 succeeded**, 11 skipped (Windows-only)
- `net462` and `net472` compile with `MonoForFramework.targets` deleted
- `log4net.Tests.Signing.AssemblyShouldBeSigned` passes - strong naming survives the
  reference-assembly switch
- `./mvnw site` works
- both scripts parse under pwsh 7.6.4; the native-error behaviour was verified directly

## For reviewers to weigh

**Nothing tests on the .NET 8 runtime any more.** `netstandard2.0` consumers on .NET 8 (LTS until
November 2026) are still supported but no longer exercised.

**The MCR image reference is fully qualified**, so it needs no registry configuration and no login.

Author: FreeAndNil

.github/workflows/build.yaml

@@ -33,7 +33,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ macos-14, ubuntu-22.04, windows-latest ]
+        os: [ macos-latest, ubuntu-latest, windows-latest ]
 
     env:
       DOTNET_SKIP_FIRST_TIME_EXPERIENCE: 1
@@ -47,7 +47,7 @@ jobs:
       - name: Set up dotnet
         uses: actions/setup-dotnet@6bd8b7f7774af54e05809fcc5431931b3eb1ddee   # 4.0.1
         with:
-          dotnet-version: 8
+          dotnet-version: 10
           dotnet-quality: ga
 
       - name: Build

Dockerfile

@@ -16,34 +16,19 @@
 
 # MAINTAINER Jan Friedrich
 
-FROM ubuntu:20.04
-ENV DEBIAN_FRONTEND=noninteractive \
-    TZ=Etc/UTC
+# Ubuntu 24.04 (noble) with the .NET 10 SDK already installed - noble is the only Ubuntu
+# variant published for .NET 10. The reference is fully qualified, so it needs no registry
+# configuration and no login, unlike the short name it replaces.
+FROM mcr.microsoft.com/dotnet/sdk:10.0-noble
+ENV TZ=Etc/UTC
 
-# Install Mono SDK (compiler, msbuild, runtime, etc.)
-RUN apt-get update && \
-    apt-get install -y gnupg ca-certificates && \
-    apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF && \
-    echo "deb https://download.mono-project.com/repo/ubuntu stable-focal main" | tee /etc/apt/sources.list.d/mono-official-stable.list && \
-    apt-get update && \
-    apt-get install -y mono-complete && \
-    rm -rf /var/lib/apt/lists/*
+# Mono is not required: the net4x targets are compiled against the
+# Microsoft.NETFramework.ReferenceAssemblies packages that the .NET SDK references implicitly.
+# Mono would only be needed to *execute* net4x assemblies, which this image does not do.
 
-# Check Mono version
-RUN mono --version
-
-RUN apt-get update \
-  && apt-get upgrade -y \
-  && apt-get install -y wget \
-  && apt-get install -y tree \
-  && wget https://dot.net/v1/dotnet-install.sh -O dotnet-install.sh \
-  && chmod +x ./dotnet-install.sh \
-  && ./dotnet-install.sh --channel 8.0
 ENV DOTNET_NOLOGO=true
 ENV DOTNET_SKIP_FIRST_TIME_EXPERIENCE=true
-ENV DOTNET_ROOT=/root/.dotnet
-ENV PATH="$PATH:$DOTNET_ROOT:$DOTNET_ROOT/tools"
-  
+
 ADD . /logging-log4net
 RUN dotnet restore /logging-log4net/src/log4net.sln
 RUN dotnet build -c Release /logging-log4net/src/log4net.sln

doc/BUILDING.md

@@ -6,11 +6,10 @@ Log4net provides support for the following targets
 
 TL;DR (Windows):
 - install Visual Studio Build Tools (at least VS2019)
-- install nodejs (at least v16)
-- install dotnet (v8+) and the .NET SDK (current latest)
+- install the .NET SDK (v10 or better - the sources use C# 14 language features)
 - in the project folder:
-  - `npm i`
-  - `npm run build`
+  - `dotnet build src/log4net.sln`
+  - `dotnet test src/log4net.sln`
 
 TL;DR (Docker):
 - install docker (if you haven't already)
@@ -25,49 +24,43 @@ TL;DR (Docker):
     - `dotnet test /logging-log4net/src/log4net.sln`
 
 TL;DR (!Windows):
-- install the dotnet SDK - v8 or better
-- install Mono (you're going to need it to target certain versions of .NET)
-- install nodejs 16+
-  - in the project folder:
-  - `npm i`
-  - `export DOTNET_CORE=1 npm run build`
-    - we force using `dotnet` on non-windows targets for now. At some point,
-      this should become automatic
+- install the dotnet SDK - v10 or better (the sources use C# 14 language features)
+- in the project folder:
+  - `dotnet build src/log4net.sln`
+  - `dotnet test src/log4net.sln`
+- Mono is *not* required. The `net462` / `net472` targets are compiled against the
+  `Microsoft.NETFramework.ReferenceAssemblies` packages that the .NET SDK references
+  implicitly. Mono would only be needed to *execute* net4x assemblies.
+- the `log4net.Tests` project skips `net462` on non-Windows platforms: VSTest hosts net4x tests
+  through `TestHostNetFramework/testhost.exe`, which needs a .NET Framework runtime - Mono, off
+  Windows. The Ubuntu 24.04 and macOS 26 runner images no longer ship Mono, so the run would
+  abort with `TESTRUNABORT`. The `net462` tests run only on the Windows job in CI.
 
 ## The full story
 
 Options:
 - build locally. Suggested environment:
     - Pre-requisites:
-        - Visual Studio 2019 Build Tools
-            - include desktop targets at least
-            - include dotnet core targets or download and install
-                the latest dotnet sdk (you will need at least v8)
+        - the .NET SDK, at least v10 (the sources use C# 14 language features)
+        - on Windows: Visual Studio 2019 Build Tools or later, including desktop targets
+          - only Windows can *run* the `net462` tests; elsewhere that target is skipped
     - Binaries can be built with a Visual Studio or Rider installation
     - Binaries, packages and a release zip can be built via commandline
-        - Ensure that you have a reasonably modern NodeJS installed (at least version 8+)
-            - `npm ci`
-            - `npm run build`
-            - optionally `npm test` to run all tests
-            - optionally `npm run release` to generate release artifacts
-- build locally (CLI edition)
-  - install nodejs (at least v16)
-  - `npm i`
-  - `npm run build`
-- build via docker for windows, using the `build-with-docker-for-windows.bat` script
-- build via the vs2019 Windows AppVeyor image. There is an appveyor.yml file
-    included which (should) build if you set up AppVeyer to track
-    your fork. AppVeyer is free for open-source projects.
-    (TODO: should have a link to the official AppVeyor build)
+        - `dotnet build src/log4net.sln`
+        - optionally `dotnet test src/log4net.sln` to run all tests
+        - release artifacts are generated by the scripts under `scripts/`:
+            - `scripts/build-preview.ps1` for a preview package
+            - `scripts/build-release.ps1` for a full release
+- build via docker, see the Docker section above
 
 ## Updating the site
 
 Log4Net uses Maven to build the site. Source artifacts can be found under `src/site`.
-Building the site can be accomplished with `npm run build-site`. You should have maven
-installed:
-- Windows: get it from Scoop
-- OSX: get it from Homebrew
-- Linux: use your package manager
+Building the site can be accomplished with `./mvnw site` (`.\mvnw.cmd site` on Windows) - the
+committed Maven wrapper fetches the pinned Maven version, so only a JDK is required. This is
+also what `scripts/build-release.ps1` uses. The `antora` profile inherited from `logging-parent`
+activates automatically because `src/site/antora` exists; it installs Antora and runs it against
+`antora-playbook.yaml`, so no separate npm step is needed.
 
 The site will be generated in `target/site`, and can be viewed locally. Updates should
 be pushed to the `asf-staging` branch of [https://github.com/apache/logging-log4net-site](https://github.com/apache/logging-log4net-site])

scripts/build-preview.ps1

@@ -2,11 +2,19 @@ param(
   $Version = '3.4.0',
   $Preview = '1'
 )
+
+Set-StrictMode -Version Latest
+$ErrorActionPreference = 'Stop'
+# $ErrorActionPreference alone does not apply to native commands: dotnet, gpg and git only set
+# $LASTEXITCODE, so without this a failing build would still be signed and tagged.
+# Requires PowerShell 7.3+.
+$PSNativeCommandUseErrorActionPreference = $true
+
 'building ...'
 dotnet build -c Release "-p:GeneratePackages=true;PackageVersion=$Version-preview.$Preview" $PSScriptRoot/../src/log4net.sln
 'signing ...'
-gpg --armor --output $PSScriptRoot\..\build\artifacts\log4net.$Version-preview.$Preview.nupkg.asc --detach-sig $PSScriptRoot\..\build\artifacts\log4net.$Version-preview.$Preview.nupkg
-gpg --armor --output $PSScriptRoot\..\build\artifacts\log4net.Ext.Mail.$Version-preview.$Preview.nupkg.asc --detach-sig $PSScriptRoot\..\build\artifacts\log4net.Ext.Mail.$Version-preview.$Preview.nupkg
+gpg --armor --output $PSScriptRoot/../build/artifacts/log4net.$Version-preview.$Preview.nupkg.asc --detach-sig $PSScriptRoot/../build/artifacts/log4net.$Version-preview.$Preview.nupkg
+gpg --armor --output $PSScriptRoot/../build/artifacts/log4net.Ext.Mail.$Version-preview.$Preview.nupkg.asc --detach-sig $PSScriptRoot/../build/artifacts/log4net.Ext.Mail.$Version-preview.$Preview.nupkg
 'create tag?'
 pause
 'creating tag ...'

scripts/build-release.ps1

@@ -4,6 +4,10 @@ param(
 
 Set-StrictMode -Version Latest
 $ErrorActionPreference = 'Stop'
+# $ErrorActionPreference alone does not apply to native commands: dotnet, git, zip, gpg and mvnw
+# only set $LASTEXITCODE, so without this a failing build would still be packaged and signed.
+# Requires PowerShell 7.3+.
+$PSNativeCommandUseErrorActionPreference = $true
 
 function Write-HashAndSignature
 {

src/MonoForFramework.targets

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="changed">
+  <issue id="305" link="https://github.com/apache/logging-log4net/pull/305"/>
+  <description format="asciidoc">
+    Mono is no longer required to build the `net462` and `net472` targets on Linux and macOS.
+    `MonoForFramework.targets` and its `FrameworkPathOverride` handling were removed in favour of
+    the `Microsoft.NETFramework.ReferenceAssemblies` packages that the .NET SDK already references
+    implicitly. Mono is still needed to *run* .NET Framework assemblies: CI moved to
+    `ubuntu-latest` (Ubuntu 24.04) and `macos-latest` (macOS 26), which no longer ship Mono, so
+    the `net462` tests now run only on the Windows job and the Mono guards in the test suite were
+    dropped. Support for *running* log4net under Mono is unaffected - the runtime check in
+    `log4net.Util.SystemInfo` is unchanged
+  </description>
+</entry>

src/changelog/3.4.0/305-build-net4x-without-mono.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="changed">
+  <issue id="305" link="https://github.com/apache/logging-log4net/pull/305"/>
+  <description format="asciidoc">
+    build the container image from `mcr.microsoft.com/dotnet/sdk:10.0-noble` instead of installing
+    a SDK into `ubuntu:20.04` with `dotnet-install.sh`. This moves off an Ubuntu release that left
+    standard support in April 2025 and drops the download step, the Mono packages and the
+    `DOTNET_ROOT` and `PATH` handling
+  </description>
+</entry>

src/changelog/3.4.0/305-docker-sdk-image.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="305" link="https://github.com/apache/logging-log4net/pull/305"/>
+  <description format="asciidoc">
+    fix the `log4net.Ext.Mail` package failing to pack with `NU5039` (`The readme file 'README.md'
+    does not exist in the package`), because the `README.md` item was packed without a
+    `PackagePath`
+  </description>
+</entry>

src/changelog/3.4.0/305-fix-ext-mail-package-readme.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="305" link="https://github.com/apache/logging-log4net/pull/305"/>
+  <description format="asciidoc">
+    fix the release scripts continuing after a failed step: `$ErrorActionPreference` does not apply
+    to native commands, so a failing `dotnet`, `git`, `zip`, `gpg` or `mvnw` went unnoticed and the
+    artifacts were packaged, signed and tagged anyway. Both `scripts/build-preview.ps1` and
+    `scripts/build-release.ps1` now set `$PSNativeCommandUseErrorActionPreference`. Also fix
+    `scripts/build-preview.ps1` outside Windows, where the artifact paths handed to `gpg` were
+    built with backslashes, which are not path separators on Linux or macOS
+  </description>
+</entry>