Change size prediction logic

src/main/java/org/prebid/server/cookie/UidsCookieService.java

@@ -42,12 +42,6 @@ public class UidsCookieService {
     private static final int MIN_NUMBER_OF_UID_COOKIES = 1;
     private static final int MAX_NUMBER_OF_UID_COOKIES = 30;
 
-    // {"tempUIDs":{},"optout":false}
-    private static final int TEMP_UIDS_BASE64_BYTES = "eyJ0ZW1wVUlEcyI6e30sIm9wdG91dCI6ZmFsc2V9".length();
-    // "":{"uid":"","expires":"1970-01-01T00:00:00.000000000Z"},
-    private static final int UID_BASE64_BYTES = ("IiI6eyJ1aWQiOiIiLCJleHBpcmVzI"
-            + "joiMTk3MC0wMS0wMVQwMDowMDowMC4wMDAwMDAwMDBaIn0s").length();
-
     private final String optOutCookieName;
     private final String optOutCookieValue;
     private final String hostCookieFamily;
@@ -287,30 +281,27 @@ public List<Cookie> splitUidsIntoCookies(UidsCookie uidsCookie) {
         final Iterator<String> cookieFamilies = cookieFamilyNamesByDescPriorityAndExpiration(uidsCookie);
         final List<Cookie> splitCookies = new ArrayList<>();
 
-        final int staticCookieDataBytes = makeCookie(COOKIE_NAME, StringUtils.EMPTY, ttlSeconds).encode().length();
-
+        final int cookieSchemaSize = UidsCookieSize.schemaSize(makeCookie(COOKIE_NAME, StringUtils.EMPTY, ttlSeconds));
         String nextCookieFamily = null;
+        for (int i = 0; i < numberOfUidCookies; i++) {
+            final int digits = i < 10 ? Integer.signum(i) : 2;
+            final UidsCookieSize uidsCookieSize = new UidsCookieSize(cookieSchemaSize + digits, maxCookieSizeBytes);
 
-        for (int uidsIndex = 0; uidsIndex < numberOfUidCookies; uidsIndex++) {
-            int actualCookieSize = staticCookieDataBytes + TEMP_UIDS_BASE64_BYTES;
             final Map<String, UidWithExpiry> tempUids = new HashMap<>();
-
             while (nextCookieFamily != null || cookieFamilies.hasNext()) {
                 nextCookieFamily = nextCookieFamily == null ? cookieFamilies.next() : nextCookieFamily;
-
                 final UidWithExpiry uidWithExpiry = uids.get(nextCookieFamily);
-                actualCookieSize += UID_BASE64_BYTES
-                        + calculateCookieSize(uidsIndex, nextCookieFamily, uidWithExpiry.getUid());
 
-                if (maxCookieSizeBytes > 0 && actualCookieSize > maxCookieSizeBytes) {
+                uidsCookieSize.addUid(nextCookieFamily, uidWithExpiry.getUid());
+                if (!uidsCookieSize.isValid()) {
                     break;
                 }
 
                 tempUids.put(nextCookieFamily, uidWithExpiry);
                 nextCookieFamily = null;
             }
 
-            final String uidsName = uidsIndex == 0 ? COOKIE_NAME : COOKIE_NAME_FORMAT.formatted(uidsIndex + 1);
+            final String uidsName = i == 0 ? COOKIE_NAME : COOKIE_NAME_FORMAT.formatted(i + 1);
 
             if (tempUids.isEmpty()) {
                 splitCookies.add(expiredCookie(uidsName));
@@ -330,14 +321,6 @@ public List<Cookie> splitUidsIntoCookies(UidsCookie uidsCookie) {
         return splitCookies;
     }
 
-    private static int calculateCookieSize(int uidsIndex, String cookieFamily, String uid) {
-        final int approximateBase64CookieFamilySize = (int) Math.ceil(cookieFamily.length() * 1.33);
-        final int approximateBase64UidSize = (int) Math.ceil(uid.length() * 1.33);
-        final int uidsIndexSize = uidsIndex == 0 ? 0 : 2;
-
-        return uidsIndexSize + approximateBase64CookieFamilySize + approximateBase64UidSize;
-    }
-
     private Iterator<String> cookieFamilyNamesByDescPriorityAndExpiration(UidsCookie uidsCookie) {
         return uidsCookie.getCookieUids().getUids().entrySet().stream()
                 .sorted(this::compareCookieFamilyNames)

src/main/java/org/prebid/server/cookie/UidsCookieSize.java

@@ -0,0 +1,73 @@
+package org.prebid.server.cookie;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import io.vertx.core.http.Cookie;
+import org.apache.commons.lang3.StringUtils;
+import org.prebid.server.json.ObjectMapperProvider;
+
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+
+public class UidsCookieSize {
+
+    // {"tempUIDs":{},"optout":false}
+    private static final int TEMP_UIDS_BASE64_BYTES = "eyJ0ZW1wVUlEcyI6e30sIm9wdG91dCI6ZmFsc2V9".length();
+    private static final int UID_TEMPLATE_BYTES;
+
+    static {
+        try {
+            UID_TEMPLATE_BYTES = "\"\":{\"uid\":\"\",\"expires\":\"%s\"},"
+                    .formatted(ObjectMapperProvider.mapper().writeValueAsString(
+                            ZonedDateTime.ofInstant(Instant.ofEpochSecond(0, 1), ZoneId.of("UTC"))))
+                    .length();
+        } catch (JsonProcessingException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private final int cookieSchemaSize;
+    private final int maxSize;
+    private int encodedUidsSize;
+
+    public UidsCookieSize(int cookieSchemaSize, int maxSize) {
+        this.cookieSchemaSize = cookieSchemaSize;
+        this.maxSize = maxSize;
+
+        encodedUidsSize = 0;
+    }
+
+    public static int schemaSize(Cookie cookieSchema) {
+        return cookieSchema.setValue(StringUtils.EMPTY).encode().length();
+    }
+
+    public boolean isValid() {
+        return maxSize <= 0 || totalSize() <= maxSize;
+    }
+
+    public int totalSize() {
+        return cookieSchemaSize
+                + TEMP_UIDS_BASE64_BYTES
+                + Base64Size.base64Size(encodedUidsSize);
+    }
+
+    public void addUid(String cookieFamily, String uid) {
+        final int uidSize = UID_TEMPLATE_BYTES + cookieFamily.length() + uid.length();
+        encodedUidsSize = Base64Size.encodeSize(Base64Size.decodeSize(encodedUidsSize) + uidSize);
+    }
+
+    private static class Base64Size {
+
+        public static int encodeSize(int size) {
+            return size / 3 * 4 + size % 3;
+        }
+
+        public static int decodeSize(int encodedSize) {
+            return encodedSize / 4 * 3 + encodedSize % 4;
+        }
+
+        private static int base64Size(int encodedSize) {
+            return (encodedSize & -4) + 4 * Integer.signum(encodedSize % 4);
+        }
+    }
+}