pcs: Use if-unmodified-since to avoid unnecessary rendering

wikimedia · Jul 11, 2024 · b16dab0 · b16dab0
1 parent bb97750
commit b16dab0
Showing 1 changed file with 34 additions and 12 deletions.
diff --git a/v1/pcs/stored_endpoint.js b/v1/pcs/stored_endpoint.js
@@ -3,6 +3,27 @@
 const HyperSwitch = require('hyperswitch');
 const URI = HyperSwitch.URI;
 const mwUtils = require('../../lib/mwUtil');
+const uuidUtils = require('../../lib/uuidUtils');
+
+/**
+ * Checks whether the content has been modified since the timestamp
+ * in `if-unmodified-since` header of the request
+ * @param  {Object} req the request
+ * @param  {Object} res the response
+ * @return {boolean}    true if content has beed modified
+ */
+function isModifiedSince(req, res) {
+    try {
+        if (req.headers['if-unmodified-since']) {
+            const jobTime = Date.parse(req.headers['if-unmodified-since']);
+            const revInfo = mwUtils.parseETag(res.headers.etag);
+            return revInfo && uuidUtils.getDate(revInfo.tid) >= jobTime;
+        }
+    } catch (e) {
+        // Ignore errors from date parsing
+    }
+    return false;
+}
 
 class PCSEndpoint {
     constructor(options) {
@@ -35,22 +56,23 @@ class PCSEndpoint {
             });
         }
 
-        if (mwUtils.isNoCacheRequest(req)) {
-            return this._fetchFromPCSAndStore(hyper, req)
-            .tap((res) => {
-                this._injectCacheControl.bind(this)(res);
-                hyper.metrics.endTiming([
-                    'pcs_getContent_latency',
-                    'pcs_getContent_latency_no_cache',
-                    `pcs_getContent_latency_${rp.domain}`
-                ], startTime);
-            });
-        }
-
         return hyper.get({
             uri: new URI([rp.domain, 'sys', 'key_value', this._options.name, rp.title])
         })
         .then((res) => {
+            if (mwUtils.isNoCacheRequest(req)) {
+                if (!isModifiedSince(req, res)) {
+                    throw new HyperSwitch.HTTPError({
+                        status: 412,
+                        body: {
+                            type: 'precondition_failed',
+                            detail: 'The precondition failed'
+                        }
+                    });
+                }
+                return this._fetchFromPCS(hyper, req);
+            }
+
             if (!rp.revision ||
                 `${mwUtils.parseETag(res.headers.etag).rev}` === `${rp.revision}`) {
                 return res;