Add util.NeedsUpdate to check for updates

util/update.go

@@ -0,0 +1,25 @@
+package util
+
+import (
+	"log"
+
+	"github.com/rwxrob/json"
+)
+
+// NeedsUpdate compares the current isosec integer (second at GMT) to
+// that retrieved from the URL (usually pointing to a file called
+// UPDATED) which must return nothing but a single isosec integer (which
+// is unmarshaled as a JSON number). Returns 1 if needed, 0 if not
+// needed, and -1 if unable to determine (and will log any error
+// encountered).
+func NeedsUpdate(current int, url string) int {
+	var remote int
+	if err := json.Req(`GET`, url, nil, nil, &remote); err != nil {
+		log.Print(err)
+		return -1
+	}
+	if remote > current {
+		return 1
+	}
+	return 0
+}

util/update_test.go

@@ -0,0 +1,44 @@
+package util_test
+
+import (
+	"fmt"
+	"net/http"
+	ht "net/http/httptest"
+
+	"github.com/rwxrob/bonzai/util"
+)
+
+func ExampleCheckUpdated() {
+
+	handler := http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			fmt.Fprintf(w, `20220322080540`)
+		})
+	older := ht.NewServer(handler)
+	defer older.Close()
+
+	handler = http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			fmt.Fprintf(w, `20220322080546`)
+		})
+	newer := ht.NewServer(handler)
+	defer newer.Close()
+
+	handler = http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			fmt.Fprintf(w, `20220322080542`)
+		})
+	same := ht.NewServer(handler)
+	defer same.Close()
+
+	fmt.Println(util.NeedsUpdate(20220322080542, older.URL))
+	fmt.Println(util.NeedsUpdate(20220322080542, newer.URL))
+	fmt.Println(util.NeedsUpdate(20220322080542, same.URL))
+	fmt.Println(util.NeedsUpdate(20220322080542, "foobar"))
+
+	// Output:
+	// 0
+	// 1
+	// 0
+	// -1
+}