build: Add GitHub actions build for Windows

This is sort of a proof of concept, but since our current Windows
builder is down this might solve the problem. It includes a change for
easier code signing (taking the certificate in a secret/env var rather
than existing already on disk), but otherwise mirrors precisely what we
already do in the build server.

.github/workflows/build-syncthing.yaml

@@ -0,0 +1,94 @@
+name: Build Syncthing
+
+on:
+  pull_request:
+  push:
+
+env:
+  GO_VERSION: "1.19.3"
+  GO386: softfloat
+  GOARM: "5"
+  GOMIPS: softfloat
+
+jobs:
+
+  build-windows:
+    runs-on: windows-latest
+    name: Build and test on Windows
+    steps:
+      - name: Set git to use LF
+        # Without this, the checkout will happen with CRLF line endings,
+        # which is fine for the source code but messes up tests that depend
+        # on data on disk being as expected. Ideally, those tests should be
+        # fixed, but not today.
+        run: |
+          git config --global core.autocrlf false
+          git config --global core.eol lf
+
+      - uses: actions/checkout@v3
+
+      - uses: actions/setup-go@v3
+        # `cache: true` gives us automatic caching of modules and build
+        # cache, speeding up builds. The cache key is dependent on the Go
+        # version and our go.sum contents.
+        with:
+          go-version: ${{ env.GO_VERSION }}
+          cache: true
+
+      - name: Build and test
+        run: |
+          go run build.go
+          go run build.go test
+
+  package-windows:
+    runs-on: windows-latest
+    name: Create packages for Windows
+    environment: signing
+    needs:
+      - build-windows
+    steps:
+      - name: Set git to use LF
+        run: |
+          git config --global core.autocrlf false
+          git config --global core.eol lf
+
+      - uses: actions/checkout@v3
+        # `fetch-depth: 0` because we want to check out the entire repo
+        # including tags and branches, not just the latest commit which
+        # lacks version info.
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-go@v3
+        with:
+          go-version: ${{ env.GO_VERSION }}
+          cache: true
+
+      - uses: actions/cache@v3
+        with:
+          path: |
+            ~\AppData\Local\go-build
+            ~\go\pkg\mod
+          key: ${{ runner.os }}-go-${{ env.GOVERSION }}-package-${{ hashFiles('**/go.sum') }}
+
+      - name: Install dependencies
+        run: |
+          go install github.com/josephspurrier/goversioninfo/cmd/goversioninfo@v1.4.0
+
+      - name: Create packages
+        run: |
+          go run build.go -goarch amd64 zip
+          go run build.go -goarch arm zip
+          go run build.go -goarch arm64 zip
+          go run build.go -goarch 386 zip
+        env:
+          CODESIGN_SIGNTOOL: ${{ secrets.CODESIGN_SIGNTOOL }}
+          CODESIGN_CERTIFICATE_BASE64: ${{ secrets.CODESIGN_CERTIFICATE_BASE64 }}
+          CODESIGN_CERTIFICATE_PASSWORD: ${{ secrets.CODESIGN_CERTIFICATE_PASSWORD }}
+          CODESIGN_TIMESTAMP_SERVER: ${{ secrets.CODESIGN_TIMESTAMP_SERVER }}
+
+      - name: Archive artifacts
+        uses: actions/upload-artifact@v3
+        with:
+          name: packages
+          path: syncthing-windows-*.zip

build.go

@@ -15,6 +15,7 @@ import (
 	"bytes"
 	"compress/flate"
 	"compress/gzip"
+	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"flag"
@@ -1383,6 +1384,33 @@ func windowsCodesign(file string) {
 		args := []string{"sign", "/fd", algo}
 		if f := os.Getenv("CODESIGN_CERTIFICATE_FILE"); f != "" {
 			args = append(args, "/f", f)
+		} else if b := os.Getenv("CODESIGN_CERTIFICATE_BASE64"); b != "" {
+			// Decode the PFX certificate from base64.
+			bs, err := base64.RawStdEncoding.DecodeString(b)
+			if err != nil {
+				log.Println("Codesign: signing failed: decoding base64:", err)
+				return
+			}
+
+			// Write it to a temporary file
+			f, err := os.CreateTemp("", "codesign-*.pfx")
+			if err != nil {
+				log.Println("Codesign: signing failed: creating temp file:", err)
+				return
+			}
+			_ = f.Chmod(0600) // best effort remove other users' access
+			defer os.Remove(f.Name())
+			if _, err := f.Write(bs); err != nil {
+				log.Println("Codesign: signing failed: writing temp file:", err)
+				return
+			}
+			if err := f.Close(); err != nil {
+				log.Println("Codesign: signing failed: closing temp file:", err)
+				return
+			}
+
+			// Use that when signing
+			args = append(args, "/f", f.Name())
 		}
 		if p := os.Getenv("CODESIGN_CERTIFICATE_PASSWORD"); p != "" {
 			args = append(args, "/p", p)
@@ -1402,7 +1430,7 @@ func windowsCodesign(file string) {
 
 		bs, err := runError(st, args...)
 		if err != nil {
-			log.Println("Codesign: signing failed:", string(bs))
+			log.Printf("Codesign: signing failed: %v: %s", err, string(bs))
 			return
 		}
 		log.Println("Codesign: successfully signed", file, "using", algo)