tsweb: remove JSONHandlerFunc

It's unused and we've decided it's not what we want.

Change-Id: I425a0104e8869630b498a0adfd0f455876d6f92b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tsweb/tsweb.go

@@ -24,6 +24,7 @@ import (
 	"strings"
 	"time"
 
+	"go4.org/mem"
 	"inet.af/netaddr"
 	"tailscale.com/envknob"
 	"tailscale.com/metrics"
@@ -87,6 +88,30 @@ func AllowDebugAccess(r *http.Request) bool {
 	return false
 }
 
+
+// AcceptsEncoding reports whether r accepts the named encoding
+// ("gzip", "br", etc).
+func AcceptsEncoding(r *http.Request, enc string) bool {
+	h := r.Header.Get("Accept-Encoding")
+	if h == "" {
+		return false
+	}
+	if !strings.Contains(h, enc) && !mem.ContainsFold(mem.S(h), mem.S(enc)) {
+		return false
+	}
+	remain := h
+	for len(remain) > 0 {
+		var part string
+		part, remain, _ = strings.Cut(remain, ",")
+		part = strings.TrimSpace(part)
+		part, _, _ = strings.Cut(part, ";")
+		if part == enc {
+			return true
+		}
+	}
+	return false
+}
+
 // Protected wraps a provided debug handler, h, returning a Handler
 // that enforces AllowDebugAccess and returns forbidden replies for
 // unauthorized requests.