Add multiple root schain processing

```
ext.prebid.schains: [
   { bidders: ["shinyClicks"], schain: { SCHAIN OBJECT }},
   { bidders: ["*"], schain: { SCHAIN OBJECT }}
]
```
 * pass the correct source.ext.schain to each bidder
 * remove ext.prebid.schains before sending to the adapter

 For more information prebid/prebid-server#1091

src/main/java/org/prebid/server/auction/ExchangeService.java

@@ -7,6 +7,7 @@
 import com.iab.openrtb.request.BidRequest;
 import com.iab.openrtb.request.Imp;
 import com.iab.openrtb.request.Site;
+import com.iab.openrtb.request.Source;
 import com.iab.openrtb.request.User;
 import com.iab.openrtb.response.Bid;
 import com.iab.openrtb.response.BidResponse;
@@ -44,8 +45,10 @@
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebid;
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidCache;
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidData;
+import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidSchains;
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestTargeting;
 import org.prebid.server.proto.openrtb.ext.request.ExtSite;
+import org.prebid.server.proto.openrtb.ext.request.ExtSource;
 import org.prebid.server.proto.openrtb.ext.request.ExtUser;
 import org.prebid.server.settings.model.Account;
 import org.prebid.server.validation.ResponseBidValidator;
@@ -72,8 +75,8 @@ public class ExchangeService {
     private static final String PREBID_EXT = "prebid";
     private static final String CONTEXT_EXT = "context";
 
-    private static final String DEFAULT_CURRENCY = "USD";
     private static final BigDecimal THOUSAND = BigDecimal.valueOf(1000);
+    private static final String GENERIC_SCHAIN_KEY = "*";
 
     private final BidderCatalog bidderCatalog;
     private final StoredResponseProcessor storedResponseProcessor;
@@ -447,12 +450,13 @@ private static List<BidderRequest> getBidderRequests(
             ExtBidRequest requestExt, List<Imp> imps, List<String> firstPartyDataBidders) {
 
         final Map<String, JsonNode> bidderToPrebidBidders = bidderToPrebidBidders(requestExt);
+        final Map<String, ObjectNode> bidderToPrebidSchains = bidderToPrebidSchains(requestExt);
         final List<BidderRequest> bidderRequests = bidderToPrivacyEnforcementResult.entrySet().stream()
                 // for each bidder create a new request that is a copy of original request except buyerid, imp
                 // extensions, ext.prebid.data.bidders and ext.prebid.bidders.
                 // Also, check whether to pass user.ext.data, app.ext.data and site.ext.data or not.
                 .map(entry -> createBidderRequest(entry.getKey(), bidRequest, requestExt, imps, entry.getValue(),
-                        firstPartyDataBidders, bidderToPrebidBidders))
+                        firstPartyDataBidders, bidderToPrebidBidders, bidderToPrebidSchains))
                 .collect(Collectors.toList());
         Collections.shuffle(bidderRequests);
         return bidderRequests;
@@ -478,13 +482,36 @@ private static Map<String, JsonNode> bidderToPrebidBidders(ExtBidRequest request
         return bidderToPrebidParameters;
     }
 
+    /**
+     * Extracts a map of bidders to their arguments from {@link ObjectNode} prebid.schains.
+     */
+    private static Map<String, ObjectNode> bidderToPrebidSchains(ExtBidRequest requestExt) {
+        final ExtRequestPrebid prebid = requestExt == null ? null : requestExt.getPrebid();
+        final List<ExtRequestPrebidSchains> schains = prebid == null ? null : prebid.getSchains();
+
+        if (CollectionUtils.isEmpty(schains)) {
+            return Collections.emptyMap();
+        }
+
+        final Map<String, ObjectNode> bidderToPrebidSchains = new HashMap<>();
+        for (ExtRequestPrebidSchains schain : schains) {
+            final List<String> schainBidders = schain.getBidders();
+            if (CollectionUtils.isNotEmpty(schainBidders)) {
+                schainBidders.forEach(bidder -> bidderToPrebidSchains.put(bidder, schain.getSchain()));
+            }
+        }
+        return bidderToPrebidSchains;
+    }
+
+
     /**
      * Returns created {@link BidderRequest}
      */
     private static BidderRequest createBidderRequest(String bidder, BidRequest bidRequest, ExtBidRequest requestExt,
                                                      List<Imp> imps, PrivacyEnforcementResult privacyEnforcementResult,
                                                      List<String> firstPartyDataBidders,
-                                                     Map<String, JsonNode> bidderToPrebidBidders) {
+                                                     Map<String, JsonNode> bidderToPrebidBidders,
+                                                     Map<String, ObjectNode> bidderToPrebidSchains) {
         final App app = bidRequest.getApp();
         final ExtApp extApp = extApp(app);
         final Site site = bidRequest.getSite();
@@ -496,6 +523,7 @@ private static BidderRequest createBidderRequest(String bidder, BidRequest bidRe
                 .imp(prepareImps(bidder, imps, firstPartyDataBidders.contains(bidder)))
                 .app(prepareApp(app, extApp, firstPartyDataBidders.contains(bidder)))
                 .site(prepareSite(site, extSite, firstPartyDataBidders.contains(bidder)))
+                .source(prepareSource(bidder, bidderToPrebidSchains, bidRequest.getSource()))
                 .ext(prepareExt(bidder, firstPartyDataBidders, bidderToPrebidBidders, requestExt, bidRequest.getExt()))
                 .build());
     }
@@ -585,14 +613,45 @@ private static Site prepareSite(Site site, ExtSite extSite, boolean useFirstPart
                 : site;
     }
 
+    /**
+     * Checks whether to pass the site.ext.data depending on request having a first party data
+     * allowed for given bidder or not.
+     */
+    private static Source prepareSource(String bidder, Map<String, ObjectNode> bidderToSchain, Source receivedSource) {
+        final ObjectNode defaultSchain = bidderToSchain.get(GENERIC_SCHAIN_KEY);
+        final ObjectNode bidderSchain = bidderToSchain.getOrDefault(bidder, defaultSchain);
+
+        if (bidderSchain == null || bidderSchain.isNull()) {
+            return receivedSource;
+        }
+
+        final ObjectNode jsonExtSource = Json.mapper.valueToTree(ExtSource.of(bidderSchain));
+
+        if (receivedSource == null) {
+            return Source.builder().ext(jsonExtSource).build();
+        } else {
+            return receivedSource.toBuilder().ext(jsonExtSource).build();
+        }
+    }
+
     /**
      * Removes all bidders except the given bidder from bidrequest.ext.prebid.data.bidders and
      * bidrequest.ext.prebid.bidders to hide list of allowed bidders from initial request.
+     * Also mask bidrequest.source.ext.schain.
      */
     private static ObjectNode prepareExt(String bidder, List<String> firstPartyDataBidders,
                                          Map<String, JsonNode> bidderToPrebidBidders, ExtBidRequest requestExt,
                                          ObjectNode requestExtNode) {
+        final ExtRequestPrebid extPrebid = requestExt != null ? requestExt.getPrebid() : null;
+        if (extPrebid == null) {
+            return requestExtNode;
+        }
+
         if (firstPartyDataBidders.isEmpty() && bidderToPrebidBidders.isEmpty()) {
+            if (extPrebid.getSchains() != null) {
+                return Json.mapper.valueToTree(ExtBidRequest.of(extPrebid.toBuilder().schains(null).build()));
+            }
+
             return requestExtNode;
         }
 
@@ -608,6 +667,7 @@ private static ObjectNode prepareExt(String bidder, List<String> firstPartyDataB
         return Json.mapper.valueToTree(ExtBidRequest.of(requestExt.getPrebid().toBuilder()
                 .data(prebidData)
                 .bidders(bidders)
+                .schains(null)
                 .build()));
     }
 

src/main/java/org/prebid/server/proto/openrtb/ext/request/ExtRequestPrebid.java

@@ -5,6 +5,7 @@
 import lombok.Value;
 
 import java.math.BigDecimal;
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -49,6 +50,11 @@ public class ExtRequestPrebid {
      */
     ExtRequestPrebidData data;
 
+    /**
+     * Defines the contract for bidrequest.ext.prebid.schains
+     */
+    List<ExtRequestPrebidSchains> schains;
+
     /**
      * Defines the contract for bidrequest.ext.prebid.bidders
      */

src/main/java/org/prebid/server/proto/openrtb/ext/request/ExtRequestPrebidSchains.java

@@ -0,0 +1,26 @@
+package org.prebid.server.proto.openrtb.ext.request;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import lombok.AllArgsConstructor;
+import lombok.Value;
+
+import java.util.List;
+
+/**
+ * Defines the contract for bidrequest.ext.prebid.schains
+ */
+@AllArgsConstructor(staticName = "of")
+@Value
+public class ExtRequestPrebidSchains {
+
+    /**
+     * Defines the contract for bidrequest.ext.prebid.schains[i].bidders
+     */
+    List<String> bidders;
+
+    /**
+     * Defines the contract for bidrequest.ext.prebid.schains[i].schain
+     */
+    ObjectNode schain;
+}
+

src/main/java/org/prebid/server/proto/openrtb/ext/request/ExtSource.java

@@ -0,0 +1,19 @@
+package org.prebid.server.proto.openrtb.ext.request;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import lombok.AllArgsConstructor;
+import lombok.Value;
+
+/**
+ * Defines the contract for bidrequest.source.ext
+ */
+@AllArgsConstructor(staticName = "of")
+@Value
+public class ExtSource {
+
+    /**
+     * Defines the contract for bidrequest.source.ext.schain
+     */
+    ObjectNode schain;
+}
+

src/test/java/org/prebid/server/auction/ExchangeServiceTest.java

@@ -62,6 +62,7 @@
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidCacheBids;
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidCacheVastxml;
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidData;
+import org.prebid.server.proto.openrtb.ext.request.ExtRequestPrebidSchains;
 import org.prebid.server.proto.openrtb.ext.request.ExtRequestTargeting;
 import org.prebid.server.proto.openrtb.ext.request.ExtSite;
 import org.prebid.server.proto.openrtb.ext.request.ExtUser;
@@ -354,6 +355,63 @@ public void shouldPassRequestWithExtPrebidToDefinedBidder() {
                 .containsOnly(entry("bidder", mapper.createObjectNode().put("test2", "test2")));
     }
 
+    @Test
+    public void shouldPassRequestWithInjectedSchainInSourceExt() {
+        // given
+        final String bidder1Name = "bidder1";
+        final String bidder2Name = "bidder2";
+        final String bidder3Name = "bidder3";
+        final Bidder<?> bidder1 = mock(Bidder.class);
+        final Bidder<?> bidder2 = mock(Bidder.class);
+        final Bidder<?> bidder3 = mock(Bidder.class);
+        givenBidder(bidder1Name, bidder1, givenEmptySeatBid());
+        givenBidder(bidder2Name, bidder2, givenEmptySeatBid());
+        givenBidder(bidder3Name, bidder3, givenEmptySeatBid());
+
+        final ObjectNode schainObject = mapper.createObjectNode().put("var", "1");
+        final ObjectNode allSchainObject = mapper.createObjectNode().put("any", "any");
+        final ExtRequestPrebidSchains schain1 = ExtRequestPrebidSchains.of(Arrays.asList(bidder1Name, bidder2Name), schainObject);
+        final ExtRequestPrebidSchains allSchain = ExtRequestPrebidSchains.of(singletonList("*"), allSchainObject);
+        final ObjectNode ext = mapper.valueToTree(ExtBidRequest.of(
+                ExtRequestPrebid.builder()
+                        .schains(Arrays.asList(schain1, allSchain))
+                        .build()));
+
+        final BidRequest bidRequest = givenBidRequest(asList(
+                givenImp(singletonMap(bidder1Name, 1), identity()),
+                givenImp(singletonMap(bidder2Name, 2), identity()),
+                givenImp(singletonMap(bidder3Name, 3), identity())),
+                reqBuilder -> reqBuilder.ext(ext));
+
+        // when
+        exchangeService.holdAuction(givenRequestContext(bidRequest));
+
+        // then
+        final ArgumentCaptor<BidRequest> bidRequest1Captor = ArgumentCaptor.forClass(BidRequest.class);
+        verify(httpBidderRequester).requestBids(same(bidder1), bidRequest1Captor.capture(), any(), anyBoolean());
+        final BidRequest capturedBidRequest1 = bidRequest1Captor.getValue();
+        final JsonNode requestSchain1 = capturedBidRequest1.getSource().getExt().get("schain");
+        assertThat(requestSchain1).isNotNull();
+        assertThat(requestSchain1).isEqualTo(schainObject);
+        assertThat(capturedBidRequest1.getExt().get("prebid").get("schains")).isNull();
+
+        final ArgumentCaptor<BidRequest> bidRequest2Captor = ArgumentCaptor.forClass(BidRequest.class);
+        verify(httpBidderRequester).requestBids(same(bidder2), bidRequest2Captor.capture(), any(), anyBoolean());
+        final BidRequest capturedBidRequest2 = bidRequest2Captor.getValue();
+        final JsonNode requestSchain2 = capturedBidRequest2.getSource().getExt().get("schain");
+        assertThat(requestSchain2).isNotNull();
+        assertThat(requestSchain2).isEqualTo(schainObject);
+        assertThat(capturedBidRequest2.getExt().get("prebid").get("schains")).isNull();
+
+        final ArgumentCaptor<BidRequest> bidRequest3Captor = ArgumentCaptor.forClass(BidRequest.class);
+        verify(httpBidderRequester).requestBids(same(bidder3), bidRequest3Captor.capture(), any(), anyBoolean());
+        final BidRequest capturedBidRequest3 = bidRequest3Captor.getValue();
+        final JsonNode requestSchain3 = capturedBidRequest3.getSource().getExt().get("schain");
+        assertThat(requestSchain3).isNotNull();
+        assertThat(requestSchain3).isEqualTo(allSchainObject);
+        assertThat(capturedBidRequest3.getExt().get("prebid").get("schains")).isNull();
+    }
+
     @Test
     public void shouldReturnFailedFutureWithUnchangedMessageWhenPrivacyEnforcementServiceFails() {
         // given

src/test/resources/org/prebid/server/it/openrtb2/rubicon_appnexus/test-appnexus-bid-request-1.json

@@ -114,12 +114,17 @@
   ],
   "source": {
     "fd": 1,
-    "tid": "tid"
+    "tid": "tid",
+    "ext": {
+      "schain": {
+        "ver": "1.0"
+      }
+    }
   },
   "regs": {
     "ext": {
       "us_privacy": "1YN"
-  }
+    }
   },
   "ext": {
     "prebid": {

src/test/resources/org/prebid/server/it/openrtb2/rubicon_appnexus/test-appnexus-bid-request-2.json

@@ -102,7 +102,12 @@
   ],
   "source": {
     "fd": 1,
-    "tid": "tid"
+    "tid": "tid",
+    "ext": {
+      "schain": {
+        "ver": "1.0"
+      }
+    }
   },
   "regs": {
     "ext": {

src/test/resources/org/prebid/server/it/openrtb2/rubicon_appnexus/test-auction-rubicon-appnexus-request.json

@@ -203,6 +203,32 @@
   },
   "ext": {
     "prebid": {
+      "schains": [
+        {
+          "bidders": [
+            "rubicon"
+          ],
+          "schain": {
+            "ver": "1.0",
+            "complete": 1,
+            "nodes": [
+              {
+                "asi": "superads.com",
+                "sid": "123",
+                "hp": 1
+              }
+            ]
+          }
+        },
+        {
+          "bidders": [
+            "*"
+          ],
+          "schain": {
+            "ver": "1.0"
+          }
+        }
+      ],
       "bidders": {
         "rubicon": {
           "integration": "dmbjs"
@@ -284,4 +310,5 @@
     "ext": {
       "us_privacy": "1YN"
     }
-  }}
+  }
+}