cmd/golangorg: add blog to valid hosts

Also hard-code EnforceHosts behavior.
It was only optional to enable the old tip.golang.org server,
but that code is dead or at least no longer pointed to by DNS.

Hard-coding the EnforceHosts behavior makes for fewer
prod-only test failures.

Change-Id: Ib958b3f088c8175e67708efcd07426b9628b207b
Reviewed-on: https://go-review.googlesource.com/c/website/+/343311
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

cmd/golangorg/server.go

@@ -35,7 +35,6 @@ import (
 	"golang.org/x/website/internal/backport/osfs"
 	"golang.org/x/website/internal/codewalk"
 	"golang.org/x/website/internal/dl"
-	"golang.org/x/website/internal/env"
 	"golang.org/x/website/internal/gitfs"
 	"golang.org/x/website/internal/history"
 	"golang.org/x/website/internal/memcache"
@@ -211,9 +210,7 @@ func NewHandler(contentDir, goroot string) http.Handler {
 	mux.Handle("learn.go.dev/", redirectPrefix("https://go.dev/learn/"))
 
 	var h http.Handler = mux
-	if env.EnforceHosts() {
-		h = hostEnforcerHandler(h)
-	}
+	h = hostEnforcerHandler(h)
 	h = hostPathHandler(h)
 	return h
 }
@@ -362,13 +359,15 @@ func fmtHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 var validHosts = map[string]bool{
-	"go.dev":           true,
-	"learn.go.dev":     true,
 	"golang.org":       true,
 	"golang.google.cn": true,
+	"beta.golang.org":  true,
+	"blog.golang.org":  true,
 	"m.golang.org":     true,
 	"tip.golang.org":   true,
-	"beta.golang.org":  true,
+
+	"go.dev":       true,
+	"learn.go.dev": true,
 }
 
 // hostEnforcerHandler redirects http://foo.golang.org/bar to https://golang.org/bar.

internal/env/env.go

@@ -12,10 +12,7 @@ import (
 	"strconv"
 )
 
-var (
-	enforceHosts       = boolEnv("GOLANGORG_ENFORCE_HOSTS")
-	requireDLSecretKey = boolEnv("GOLANGORG_REQUIRE_DL_SECRET_KEY")
-)
+var requireDLSecretKey = boolEnv("GOLANGORG_REQUIRE_DL_SECRET_KEY")
 
 // RequireDLSecretKey reports whether the download server secret key
 // is expected to already exist, and the download server should panic
@@ -24,11 +21,6 @@ func RequireDLSecretKey() bool {
 	return requireDLSecretKey
 }
 
-// EnforceHosts reports whether host filtering should be enforced.
-func EnforceHosts() bool {
-	return enforceHosts
-}
-
 func boolEnv(key string) bool {
 	v := os.Getenv(key)
 	if v == "" {