Set correct content type and send once (#1965)

Set correct Content-Type headers on each endpoint rather than on the router. The router would, at times, send two Content-Type headers and other times just send the wrong one.

pkg/download/latest.go

@@ -17,6 +17,7 @@ const PathLatest = "/{module:.+}/@latest"
 func LatestHandler(dp Protocol, lggr log.Entry, df *mode.DownloadFile) http.Handler {
 	const op errors.Op = "download.LatestHandler"
 	f := func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 		mod, err := paths.GetModule(r)
 		if err != nil {
 			lggr.SystemErr(errors.E(op, err))

pkg/download/list.go

@@ -18,6 +18,7 @@ const PathList = "/{module:.+}/@v/list"
 func ListHandler(dp Protocol, lggr log.Entry, df *mode.DownloadFile) http.Handler {
 	const op errors.Op = "download.ListHandler"
 	f := func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
 		mod, err := paths.GetModule(r)
 		if err != nil {
 			lggr.SystemErr(errors.E(op, err))

pkg/download/version_info.go

@@ -15,6 +15,7 @@ const PathVersionInfo = "/{module:.+}/@v/{version}.info"
 func InfoHandler(dp Protocol, lggr log.Entry, df *mode.DownloadFile) http.Handler {
 	const op errors.Op = "download.InfoHandler"
 	f := func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
 		mod, ver, err := getModuleParams(r, op)
 		if err != nil {
 			lggr.SystemErr(err)

pkg/download/version_module.go

@@ -15,6 +15,7 @@ const PathVersionModule = "/{module:.+}/@v/{version}.mod"
 func ModuleHandler(dp Protocol, lggr log.Entry, df *mode.DownloadFile) http.Handler {
 	const op errors.Op = "download.VersionModuleHandler"
 	f := func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 		mod, ver, err := getModuleParams(r, op)
 		if err != nil {
 			err = errors.E(op, errors.M(mod), errors.V(ver), err)