Make assets generation deterministic

By passing "-modtime 1" flag into go-bindata command it uses the same
unix timestamp (1) for every file in the fake filesystem. Thereby every
execution of "make assets" results in the same asset outputs if the
inputs were the same. This forces us to set the "Cache-Control"
attribute to "no-cache".

Makefile

@@ -58,8 +58,9 @@ docker:
 assets:
 	@echo ">> writing assets"
 	-@$(GO) get -u github.com/jteeuwen/go-bindata/...
-	@go-bindata $(bindata_flags) -pkg ui -o ui/bindata.go ui/app/index.html ui/app/script.js
-	@go-bindata $(bindata_flags) -pkg deftmpl -o template/internal/deftmpl/bindata.go template/default.tmpl
+# Using "-modtime 1" to make assets target deterministic. It sets all file time stamps to unix timestamp 1
+	@go-bindata $(bindata_flags) -modtime 1 -pkg ui -o ui/bindata.go ui/app/index.html ui/app/script.js
+	@go-bindata $(bindata_flags) -modtime 1 -pkg deftmpl -o template/internal/deftmpl/bindata.go template/default.tmpl
 
 promu:
 	@GOOS=$(shell uname -s | tr A-Z a-z) \

ui/web.go

@@ -40,6 +40,7 @@ func serveAsset(w http.ResponseWriter, req *http.Request, fp string) {
 		return
 	}
 
+	w.Header().Set("Cache-Control", "no-cache")
 	http.ServeContent(w, req, info.Name(), info.ModTime(), bytes.NewReader(file))
 }