Add companion application

companion.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"embed"
+	"io"
+	"net/http"
+	"strconv"
+)
+
+// Cross-compiled companion binaries served as downloads from the wiki footer
+// flyout when no local companion is detected. The Makefile produces these
+// before invoking `go build .`; missing files will fail the build at compile
+// time via the embed directive below.
+//
+//go:embed companion/datascape-companion-windows-amd64.exe
+//go:embed companion/datascape-companion-linux-amd64
+var companionBinaries embed.FS
+
+func init() {
+	http.HandleFunc("/companion/download/windows", serveCompanionBinary(
+		"companion/datascape-companion-windows-amd64.exe",
+		"datascape-companion.exe",
+	))
+	http.HandleFunc("/companion/download/linux", serveCompanionBinary(
+		"companion/datascape-companion-linux-amd64",
+		"datascape-companion",
+	))
+}
+
+func serveCompanionBinary(embedPath, downloadName string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			w.Header().Set("Allow", http.MethodGet)
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		f, err := companionBinaries.Open(embedPath)
+		if err != nil {
+			http.Error(w, "companion binary not available", http.StatusNotFound)
+			return
+		}
+		defer f.Close()
+		info, err := f.Stat()
+		if err != nil {
+			http.Error(w, "companion binary not available", http.StatusInternalServerError)
+			return
+		}
+		w.Header().Set("Content-Type", "application/octet-stream")
+		w.Header().Set("Content-Disposition", `attachment; filename="`+downloadName+`"`)
+		w.Header().Set("Content-Length", strconv.FormatInt(info.Size(), 10))
+		_, _ = io.Copy(w, f)
+	}
+}