[GitHub] [trafficcontrol] ocket8888 commented on a change in pull request #3862: Add Traffic Ops /deliveryservices, /servers If-Modified-Since support

[GitBox <gi...@apache.org>]

ocket8888 commented on a change in pull request #3862: Add Traffic Ops /deliveryservices, /servers If-Modified-Since support
URL: https://github.com/apache/trafficcontrol/pull/3862#discussion_r364910851
 
 

 ##########
 File path: lib/go-rfc/cachecontrol.go
 ##########
 @@ -0,0 +1,110 @@
+package rfc
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import (
+	"errors"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const HdrETag = "ETag"
+const HdrIfNoneMatch = "If-None-Match"
+const HdrIfModifiedSince = "If-Modified-Since"
+const HdrLastModified = "Last-Modified"
+const HdrCacheControl = "Cache-Control"
+
+const ETagVersion = 0
+
+// NotModified is a helper type for users of this library.
+// It allows users to return a NotModified instead of a bool, to make it obvious what the value is.
+type NotModified bool
+
+const IsModified = NotModified(false)
+const IsNotModified = NotModified(true)
+
+// AddModifiedHdrs adds the ETag and Last-Modified headers to the response of w.
+// This must be called before any body is written, of course, or the headers won't be.
+// The lastModified should be the last time this resource was modified.
+func AddModifiedHdrs(w http.ResponseWriter, lastModified time.Time) {
+	w.Header().Set(HdrCacheControl, `max-age=0, must-revalidate`)
+	w.Header().Set(HdrLastModified, FormatHTTPDate(lastModified))
+	w.Header().Set(HdrETag, ETag(lastModified))
+}
+
+// GetModifiedHdr gets the modified time from the ETag or Last-Modified.
+// Returns the modified time, and whether a time was found.
+func GetModifiedHdr(r *http.Request) (time.Time, bool) {
+	// Note we intentionally ignore errors. Logging client errs would be spammy and a potential attack vector, and we want to just return the real object to the client, not an error, if their headers were malformed.
+	if eTag := r.Header.Get(HdrIfNoneMatch); eTag != "" {
+		if t, err := ParseETag(eTag); err == nil {
+			return t, true
+		}
+	}
+	if lastModified := r.Header.Get(HdrIfModifiedSince); lastModified != "" {
+		if t, ok := ParseHTTPDate(lastModified); ok {
+			return t, true
+		}
+	}
+	return time.Time{}, false
+}
+
+// FormatHTTPDate formats t as an RFC7231§7.1.1 HTTP-date.
+func FormatHTTPDate(t time.Time) string {
+	return t.Format(time.RFC1123)
+}
+
+// ETag takes the last time the object was modified, and returns an ETag string. Note the string is the complete header value, including quotes. ETags must be quoted strings.
+func ETag(t time.Time) string {
+	return `"v` + strconv.Itoa(ETagVersion) + `-` + strconv.FormatInt(t.UnixNano(), 36) + `"`
 
 Review comment:
   Is it okay to just use the timestamp for an entity tag? Requests are handled in parallel, so it's possible (though extremely unlikely with nanosecond precision) that two different entities would wind up with the same tag.

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
users@infra.apache.org


With regards,
Apache Git Services