ci: add Windows build (MSYS2/mingw-w64) (#20)

* ci: add Windows build via MSYS2/mingw-w64

Build the netsnmp C extension on Windows using the MSYS2 mingw-w64
toolchain, which provides net-snmp (with net-snmp-config), gcc and a
matching Python so setup.py works unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KG1c9XtKawkvig5PnZjC8

* ci: build net-snmp from source under MSYS2

net-snmp is not packaged for Windows in MSYS2, vcpkg or conda-forge, so
build the client library from source into the mingw64 prefix. This puts
net-snmp-config on PATH so setup.py works unchanged. Result is cached.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KG1c9XtKawkvig5PnZjC8

* windows: make setup.py and client_intf.c build under mingw

- setup.py: invoke net-snmp-config via sh on Windows (cmd.exe cannot exec
  the shell script) and link ws2_32 for the winsock symbols.
- client_intf.c: use winsock2.h/ws2tcpip.h instead of arpa/inet.h and
  netdb.h on _WIN32.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KG1c9XtKawkvig5PnZjC8

* ci: fix net-snmp cache path to runner.temp msys64 location

setup-msys2 installs to $RUNNER_TEMP\msys64, not C:\msys64, so the
cache never matched and net-snmp was rebuilt every run.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KG1c9XtKawkvig5PnZjC8

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: bluecmd

.github/workflows/windows.yml

@@ -0,0 +1,82 @@
+name: Windows build
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+  workflow_dispatch:
+
+env:
+  NETSNMP_VERSION: "5.9.4"
+
+jobs:
+  build:
+    name: Build (MSYS2 / mingw-w64)
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up MSYS2
+        uses: msys2/setup-msys2@v2
+        with:
+          msystem: MINGW64
+          update: true
+          install: >-
+            base-devel
+            mingw-w64-x86_64-gcc
+            mingw-w64-x86_64-openssl
+            mingw-w64-x86_64-python
+            mingw-w64-x86_64-python-setuptools
+            perl
+            make
+            tar
+            wget
+
+      # net-snmp is not packaged in MSYS2/vcpkg/conda-forge for Windows, so
+      # build the client library from source into the mingw64 prefix. This
+      # gives us net-snmp-config on PATH, which setup.py relies on.
+      - name: Cache net-snmp install
+        id: cache-netsnmp
+        uses: actions/cache@v4
+        with:
+          path: |
+            ${{ runner.temp }}\msys64\mingw64\bin\net-snmp-config
+            ${{ runner.temp }}\msys64\mingw64\bin\libnetsnmp-*.dll
+            ${{ runner.temp }}\msys64\mingw64\lib\libnetsnmp*
+            ${{ runner.temp }}\msys64\mingw64\include\net-snmp
+          key: netsnmp-${{ env.NETSNMP_VERSION }}-mingw64
+
+      - name: Build and install net-snmp
+        if: steps.cache-netsnmp.outputs.cache-hit != 'true'
+        run: |
+          set -euxo pipefail
+          cd "$RUNNER_TEMP"
+          wget -q "https://downloads.sourceforge.net/project/net-snmp/net-snmp/${NETSNMP_VERSION}/net-snmp-${NETSNMP_VERSION}.tar.gz"
+          tar xf "net-snmp-${NETSNMP_VERSION}.tar.gz"
+          cd "net-snmp-${NETSNMP_VERSION}"
+          ./configure \
+            --prefix=/mingw64 \
+            --with-defaults \
+            --disable-agent \
+            --disable-applications \
+            --disable-manuals \
+            --disable-scripts \
+            --disable-mibs \
+            --without-perl-modules \
+            --disable-embedded-perl \
+            --with-openssl=/mingw64
+          make -j$(nproc)
+          make install
+
+      - name: Show toolchain versions
+        run: |
+          gcc --version
+          python --version
+          net-snmp-config --version
+          net-snmp-config --libs
+
+      - name: Build extension
+        run: python setup.py build

netsnmp/client_intf.c

@@ -4,14 +4,22 @@
 #include <net-snmp/net-snmp-config.h>
 #include <net-snmp/net-snmp-includes.h>
 #include <sys/types.h>
+#ifdef _WIN32
+/* On Windows the socket API (inet_addr, etc.) lives in winsock, not the
+   POSIX arpa/inet.h and netdb.h headers. net-snmp-includes.h already pulls
+   in winsock2.h; ws2tcpip.h provides the address helpers we use. */
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#else
 #include <arpa/inet.h>
+#include <netdb.h>
+#endif
 #include <errno.h>
 #include <stdio.h>
 #include <ctype.h>
 #ifdef I_SYS_TIME
 #include <sys/time.h>
 #endif
-#include <netdb.h>
 #include <stdlib.h>
 
 #ifdef HAVE_REGEX_H

setup.py

@@ -11,10 +11,22 @@
         basedir = string.split(arg,'=')[1]
         sys.argv.remove(arg)
 
-netsnmp_libs = os.popen('net-snmp-config --libs').read()
+def netsnmp_config(flag):
+    cmd = 'net-snmp-config ' + flag
+    if sys.platform == 'win32':
+        # net-snmp-config is a POSIX shell script; on Windows os.popen goes
+        # through cmd.exe which can't execute it, so run it via sh (available
+        # in the MSYS2/mingw environment used to build the extension).
+        cmd = 'sh -c "net-snmp-config %s"' % flag
+    return os.popen(cmd).read()
+
+netsnmp_libs = netsnmp_config('--libs')
 libdirs = re.findall(r" -L(\S+)", netsnmp_libs)
 incdirs = []
 libs = re.findall(r" -l(\S+)", netsnmp_libs)
+if sys.platform == 'win32':
+    # inet_addr() and the winsock symbols net-snmp relies on come from ws2_32.
+    libs.append('ws2_32')
 
 setup(
     name="python3-netsnmp", version="1.1a2",