From 19c12c36cde6b2bf1d266932e6e5988be3243f22 Mon Sep 17 00:00:00 2001
From: Demetrio Girardi <dgirardi@prebid.org>
Date: Wed, 8 May 2024 11:14:58 -0700
Subject: [PATCH] PBS adapter: do not set bidder schain in source.ext.schain

---
 .../prebidServerBidAdapter/ortbConverter.js   | 11 +-----
 .../modules/prebidServerBidAdapter_spec.js    | 35 +++++++++++--------
 2 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/modules/prebidServerBidAdapter/ortbConverter.js b/modules/prebidServerBidAdapter/ortbConverter.js
index e0f038767c2..7f4ffc84070 100644
--- a/modules/prebidServerBidAdapter/ortbConverter.js
+++ b/modules/prebidServerBidAdapter/ortbConverter.js
@@ -197,9 +197,7 @@ const PBS_CONVERTER = ortbConverter({
         context.actualBidderRequests.forEach(req => orig(ortbRequest, req, context));
       },
       sourceExtSchain(orig, ortbRequest, proxyBidderRequest, context) {
-        // pass schains in ext.prebid.schains, with the most commonly used one in source.ext.schain
-        let mainChain;
-
+        // pass schains in ext.prebid.schains
         let chains = (deepAccess(ortbRequest, 'ext.prebid.schains') || []);
         const chainBidders = new Set(chains.flatMap((item) => item.bidders));
 
@@ -218,17 +216,10 @@ const PBS_CONVERTER = ortbConverter({
                 chains[key] = {bidders: new Set(), schain};
               }
               bidders.forEach((bidder) => chains[key].bidders.add(bidder));
-              if (mainChain == null || chains[key].bidders.size > mainChain.bidders.size) {
-                mainChain = chains[key]
-              }
               return chains;
             }, {})
         ).map(({bidders, schain}) => ({bidders: Array.from(bidders), schain}));
 
-        if (mainChain != null) {
-          deepSetValue(ortbRequest, 'source.ext.schain', mainChain.schain);
-        }
-
         if (chains.length) {
           deepSetValue(ortbRequest, 'ext.prebid.schains', chains);
         }
diff --git a/test/spec/modules/prebidServerBidAdapter_spec.js b/test/spec/modules/prebidServerBidAdapter_spec.js
index 9c2ac8a23a9..8e92cecd36b 100644
--- a/test/spec/modules/prebidServerBidAdapter_spec.js
+++ b/test/spec/modules/prebidServerBidAdapter_spec.js
@@ -2377,23 +2377,28 @@ describe('S2S Adapter', function () {
       ]);
     });
 
-    it('should "promote" the most reused bidder schain to source.ext.schain', () => {
-      const bidderReqs = [
-        {...deepClone(BID_REQUESTS[0]), bidderCode: 'A'},
-        {...deepClone(BID_REQUESTS[0]), bidderCode: 'B'},
-        {...deepClone(BID_REQUESTS[0]), bidderCode: 'C'}
-      ];
-      const chain1 = {chain: 1};
-      const chain2 = {chain: 2};
+    Object.entries({
+      'set': {},
+      'override': {source: {ext: {schain: 'pub-provided'}}}
+    }).forEach(([t, fpd]) => {
+      it(`should not ${t} source.ext.schain`, () => {
+        const bidderReqs = [
+          {...deepClone(BID_REQUESTS[0]), bidderCode: 'A'},
+          {...deepClone(BID_REQUESTS[0]), bidderCode: 'B'},
+          {...deepClone(BID_REQUESTS[0]), bidderCode: 'C'}
+        ];
+        const chain1 = {chain: 1};
+        const chain2 = {chain: 2};
 
-      bidderReqs[0].bids[0].schain = chain1;
-      bidderReqs[1].bids[0].schain = chain2;
-      bidderReqs[2].bids[0].schain = chain2;
+        bidderReqs[0].bids[0].schain = chain1;
+        bidderReqs[1].bids[0].schain = chain2;
+        bidderReqs[2].bids[0].schain = chain2;
 
-      adapter.callBids(REQUEST, bidderReqs, addBidResponse, done, ajax);
-      const req = JSON.parse(server.requests[0].requestBody);
-      expect(req.source.ext.schain).to.eql(chain2);
-    });
+        adapter.callBids({...REQUEST, ortb2Fragments: {global: fpd}}, bidderReqs, addBidResponse, done, ajax);
+        const req = JSON.parse(server.requests[0].requestBody);
+        expect(req.source?.ext?.schain).to.eql(fpd?.source?.ext?.schain);
+      })
+    })
 
     it('passes multibid array in request', function () {
       const bidRequests = utils.deepClone(BID_REQUESTS);