DGS-11414: add pagination for get all subjects

client/src/main/java/io/confluent/kafka/schemaregistry/client/rest/RestService.java

@@ -1287,6 +1287,19 @@ public List<String> getAllSubjects(Map<String, String> requestProperties,
     return response;
   }
 
+  public List<String> getAllSubjectsWithPagination(int limit)
+          throws IOException, RestClientException {
+    return getAllSubjectsWithPagination(DEFAULT_REQUEST_PROPERTIES, limit);
+  }
+
+  public List<String> getAllSubjectsWithPagination(Map<String, String> requestProperties, int limit)
+          throws IOException, RestClientException {
+    String url = "/subjects?limit=" + limit;
+    List<String> response = httpRequest(url, "GET", null, requestProperties,
+            ALL_TOPICS_RESPONSE_TYPE);
+    return response;
+  }
+
   public List<String> getDeletedOnlySubjects(String subjectPrefix)
       throws IOException, RestClientException {
     return getAllSubjects(DEFAULT_REQUEST_PROPERTIES, subjectPrefix, false, true);

core/src/main/java/io/confluent/kafka/schemaregistry/rest/SchemaRegistryConfig.java

@@ -219,6 +219,17 @@ public class SchemaRegistryConfig extends RestConfig {
   public static final String SCHEMA_SEARCH_MAX_LIMIT_CONFIG = "schema.search.max.limit";
   public static final int SCHEMA_SEARCH_MAX_LIMIT_DEFAULT = 1000;
 
+  /**
+   * <code>subject.search.default.limit</code>
+   */
+  public static final String SUBJECT_SEARCH_DEFAULT_LIMIT_CONFIG = "subject.search.default.limit";
+  public static final int SUBJECT_SEARCH_DEFAULT_LIMIT_DEFAULT = 20000;
+  /**
+   * <code>subject.search.max.limit</code>
+   */
+  public static final String SUBJECT_SEARCH_MAX_LIMIT_CONFIG = "subject.search.max.limit";
+  public static final int SUBJECT_SEARCH_MAX_LIMIT_DEFAULT = 20000;
+
   public static final String METADATA_ENCODER_SECRET_CONFIG = "metadata.encoder.secret";
   public static final String METADATA_ENCODER_OLD_SECRET_CONFIG = "metadata.encoder.old.secret";
 
@@ -378,6 +389,10 @@ public class SchemaRegistryConfig extends RestConfig {
       "The default limit for schema searches.";
   protected static final String SCHEMA_SEARCH_MAX_LIMIT_DOC =
       "The max limit for schema searches.";
+  protected static final String SUBJECT_SEARCH_DEFAULT_LIMIT_DOC =
+          "The default limit for subject searches.";
+  protected static final String SUBJECT_SEARCH_MAX_LIMIT_DOC =
+          "The max limit for subject searches.";
   protected static final String METADATA_ENCODER_SECRET_DOC =
       "The secret used to encrypt and decrypt encoder keysets. "
       + "Use a random string with high entropy.";
@@ -599,6 +614,14 @@ DEFAULT_KAFKASTORE_WRITE_MAX_RETRIES, atLeast(0),
         SCHEMA_SEARCH_MAX_LIMIT_DEFAULT,
         ConfigDef.Importance.LOW, SCHEMA_SEARCH_MAX_LIMIT_DOC
     )
+    .define(SUBJECT_SEARCH_DEFAULT_LIMIT_CONFIG, ConfigDef.Type.INT,
+            SUBJECT_SEARCH_DEFAULT_LIMIT_DEFAULT,
+            ConfigDef.Importance.LOW, SUBJECT_SEARCH_DEFAULT_LIMIT_DOC
+    )
+    .define(SUBJECT_SEARCH_MAX_LIMIT_CONFIG, ConfigDef.Type.INT,
+            SUBJECT_SEARCH_MAX_LIMIT_DEFAULT,
+            ConfigDef.Importance.LOW, SUBJECT_SEARCH_MAX_LIMIT_DOC
+    )
     .define(METADATA_ENCODER_SECRET_CONFIG, ConfigDef.Type.PASSWORD, null,
         ConfigDef.Importance.HIGH, METADATA_ENCODER_SECRET_DOC
     )

core/src/main/java/io/confluent/kafka/schemaregistry/rest/client/LocalSchemaRegistryClient.java

@@ -259,8 +259,7 @@ public synchronized List<ParsedSchema> getSchemas(
     if (!DEFAULT_TENANT.equals(schemaRegistry.tenant())) {
       subjectPrefix = schemaRegistry.tenant() + TENANT_DELIMITER + subjectPrefix;
     }
-    Iterator<ExtendedSchema> schemas = null;
-    List<ParsedSchema> result = new ArrayList<>();
+    List<ExtendedSchema> schemas;
     String errorMessage = "Error while getting schemas for prefix " + subjectPrefix;
     try {
       schemas = schemaRegistry.getVersionsWithSubjectPrefix(
@@ -274,11 +273,9 @@ public synchronized List<ParsedSchema> getSchemas(
     } catch (SchemaRegistryException e) {
       throw Errors.schemaRegistryException(errorMessage, e);
     }
-    while (schemas.hasNext()) {
-      Schema s = schemas.next();
-      result.add(parseSchema(s).get());
-    }
-    return result;
+    return schemas.stream()
+      .map(schema -> parseSchema(schema).get())
+      .collect(Collectors.toList());
   }
 
   @Override

core/src/main/java/io/confluent/kafka/schemaregistry/rest/resources/SchemasResource.java

@@ -46,10 +46,9 @@
 import javax.ws.rs.DefaultValue;
 import javax.ws.rs.QueryParam;
 import javax.ws.rs.PathParam;
-import java.util.ArrayList;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 @Path("/schemas")
 @Produces({Versions.SCHEMA_REGISTRY_V1_JSON_WEIGHTED,
@@ -100,8 +99,7 @@ public List<ExtendedSchema> getSchemas(
       @DefaultValue("0") @QueryParam("offset") int offset,
       @Parameter(description = "Pagination size for results. Ignored if negative")
       @DefaultValue("-1") @QueryParam("limit") int limit) {
-    Iterator<ExtendedSchema> schemas;
-    List<ExtendedSchema> filteredSchemas = new ArrayList<>();
+    List<ExtendedSchema> schemas;
     String errorMessage = "Error while getting schemas for prefix " + subjectPrefix;
     LookupFilter filter = lookupDeletedSchema ? LookupFilter.INCLUDE_DELETED : LookupFilter.DEFAULT;
     try {
@@ -117,17 +115,11 @@ public List<ExtendedSchema> getSchemas(
     } catch (SchemaRegistryException e) {
       throw Errors.schemaRegistryException(errorMessage, e);
     }
-    limit = schemaRegistry.normalizeLimit(limit);
-    int toIndex = offset + limit;
-    int index = 0;
-    while (schemas.hasNext() && index < toIndex) {
-      ExtendedSchema schema = schemas.next();
-      if (index >= offset) {
-        filteredSchemas.add(schema);
-      }
-      index++;
-    }
-    return filteredSchemas;
+    limit = schemaRegistry.normalizeSchemaLimit(limit);
+    return schemas.stream()
+      .skip(offset)
+      .limit(limit)
+      .collect(Collectors.toList());
   }
 
   @GET

core/src/main/java/io/confluent/kafka/schemaregistry/rest/resources/SubjectsResource.java

@@ -40,6 +40,7 @@
 import io.swagger.v3.oas.annotations.tags.Tag;
 import io.swagger.v3.oas.annotations.tags.Tags;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -61,6 +62,8 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 @Path("/subjects")
 @Produces({Versions.SCHEMA_REGISTRY_V1_JSON_WEIGHTED,
@@ -229,6 +232,10 @@ public Set<String> list(
       @DefaultValue(QualifiedSubject.CONTEXT_WILDCARD)
       @Parameter(description = "Subject name prefix")
       @QueryParam("subjectPrefix") String subjectPrefix,
+      @Parameter(description = "Pagination offset for results")
+      @DefaultValue("0") @QueryParam("offset") int offset,
+      @Parameter(description = "Pagination size for results. Ignored if negative")
+      @DefaultValue("-1") @QueryParam("limit") int limit,
       @Parameter(description = "Whether to look up deleted subjects")
       @QueryParam("deleted") boolean lookupDeletedSubjects,
       @Parameter(description = "Whether to return deleted subjects only")
@@ -242,8 +249,15 @@ public Set<String> list(
       filter = LookupFilter.INCLUDE_DELETED;
     }
     try {
-      return schemaRegistry.listSubjectsWithPrefix(
-          subjectPrefix != null ? subjectPrefix : QualifiedSubject.CONTEXT_WILDCARD, filter);
+      Set<String> subjects = schemaRegistry.listSubjectsWithPrefix(
+              subjectPrefix != null ? subjectPrefix : QualifiedSubject.CONTEXT_WILDCARD, filter);
+      Stream<String> stream = subjects.stream();
+
+      limit = schemaRegistry.normalizeSubjectLimit(limit);
+      return stream
+        .skip(offset)
+        .limit(limit)
+        .collect(Collectors.toCollection(LinkedHashSet::new)); // preserve order
     } catch (SchemaRegistryStoreException e) {
       throw Errors.storeException("Error while listing subjects", e);
     } catch (SchemaRegistryException e) {

core/src/main/java/io/confluent/kafka/schemaregistry/storage/KafkaSchemaRegistry.java

@@ -151,8 +151,10 @@ public class KafkaSchemaRegistry implements SchemaRegistry, LeaderAwareSchemaReg
   private final int initTimeout;
   private final boolean initWaitForReader;
   private final int kafkaStoreMaxRetries;
-  private final int searchDefaultLimit;
-  private final int searchMaxLimit;
+  private final int schemaSearchDefaultLimit;
+  private final int schemaSearchMaxLimit;
+  private final int subjectSearchDefaultLimit;
+  private final int subjectSearchMaxLimit;
   private final boolean delayLeaderElection;
   private final boolean allowModeChanges;
   private final boolean enableStoreHealthCheck;
@@ -225,9 +227,13 @@ public KafkaSchemaRegistry(SchemaRegistryConfig config,
         .expireAfterAccess(config.getInt(SchemaRegistryConfig.SCHEMA_CACHE_EXPIRY_SECS_CONFIG),
                 TimeUnit.SECONDS)
         .build(s -> loadSchema(s.getSchema(), s.isNew(), s.isNormalize()));
-    this.searchDefaultLimit =
-        config.getInt(SchemaRegistryConfig.SCHEMA_SEARCH_DEFAULT_LIMIT_CONFIG);
-    this.searchMaxLimit = config.getInt(SchemaRegistryConfig.SCHEMA_SEARCH_MAX_LIMIT_CONFIG);
+    this.schemaSearchDefaultLimit =
+            config.getInt(SchemaRegistryConfig.SCHEMA_SEARCH_DEFAULT_LIMIT_CONFIG);
+    this.schemaSearchMaxLimit = config.getInt(SchemaRegistryConfig.SCHEMA_SEARCH_MAX_LIMIT_CONFIG);
+    this.subjectSearchDefaultLimit =
+            config.getInt(SchemaRegistryConfig.SUBJECT_SEARCH_DEFAULT_LIMIT_CONFIG);
+    this.subjectSearchMaxLimit =
+            config.getInt(SchemaRegistryConfig.SUBJECT_SEARCH_MAX_LIMIT_CONFIG);
     this.lookupCache = lookupCache();
     this.idGenerator = identityGenerator(config);
     this.kafkaStore = kafkaStore(config);
@@ -599,14 +605,22 @@ public SchemaProvider schemaProvider(String schemaType) {
     return providers.get(schemaType);
   }
 
-  public int normalizeLimit(int suppliedLimit) {
-    int limit = searchDefaultLimit;
-    if (suppliedLimit > 0 && suppliedLimit <= searchMaxLimit) {
+  public int normalizeLimit(int suppliedLimit, int defaultLimit, int maxLimit) {
+    int limit = defaultLimit;
+    if (suppliedLimit > 0 && suppliedLimit <= maxLimit) {
       limit = suppliedLimit;
     }
     return limit;
   }
 
+  public int normalizeSchemaLimit(int suppliedLimit) {
+    return normalizeLimit(suppliedLimit, schemaSearchDefaultLimit, schemaSearchMaxLimit);
+  }
+
+  public int normalizeSubjectLimit(int suppliedLimit) {
+    return normalizeLimit(suppliedLimit, subjectSearchDefaultLimit, subjectSearchMaxLimit);
+  }
+
   public Schema register(String subject, RegisterSchemaRequest request, boolean normalize)
       throws SchemaRegistryException {
     try {
@@ -1907,7 +1921,7 @@ public Iterator<SchemaKey> getAllVersions(String subject, LookupFilter filter)
   }
 
   @Override
-  public Iterator<ExtendedSchema> getVersionsWithSubjectPrefix(String prefix,
+  public List<ExtendedSchema> getVersionsWithSubjectPrefix(String prefix,
       boolean includeAliases,
       LookupFilter filter,
       boolean returnLatestOnly,
@@ -1921,7 +1935,7 @@ public Iterator<ExtendedSchema> getVersionsWithSubjectPrefix(String prefix,
     }
   }
 
-  private Iterator<ExtendedSchema> allVersionsWithSubjectPrefix(String prefix,
+  private List<ExtendedSchema> allVersionsWithSubjectPrefix(String prefix,
       LookupFilter filter,
       boolean returnLatestOnly,
       Predicate<Schema> postFilter)
@@ -1934,11 +1948,11 @@ private Iterator<ExtendedSchema> allVersionsWithSubjectPrefix(String prefix,
         result.addAll(schemaList);
       }
       Collections.sort(result);
-      return result.iterator();
+      return result;
     }
   }
 
-  public Iterator<ExtendedSchema> allVersionsIncludingAliasesWithSubjectPrefix(String prefix,
+  public List<ExtendedSchema> allVersionsIncludingAliasesWithSubjectPrefix(String prefix,
       LookupFilter filter,
       boolean returnLatestOnly,
       Predicate<Schema> postFilter)
@@ -1965,7 +1979,7 @@ public Iterator<ExtendedSchema> allVersionsIncludingAliasesWithSubjectPrefix(Str
         }
       }
       Collections.sort(result);
-      return result.iterator();
+      return result;
     }
   }
 

core/src/main/java/io/confluent/kafka/schemaregistry/storage/SchemaRegistry.java

@@ -77,7 +77,7 @@ Set<String> listSubjectsForId(int id, String subject, boolean returnDeleted)
   Iterator<SchemaKey> getAllVersions(String subject, LookupFilter filter)
       throws SchemaRegistryException;
 
-  Iterator<ExtendedSchema> getVersionsWithSubjectPrefix(
+  List<ExtendedSchema> getVersionsWithSubjectPrefix(
       String prefix, boolean includeAliases, LookupFilter filter,
       boolean latestOnly, Predicate<Schema> postFilter)
       throws SchemaRegistryException;

core/src/test/java/io/confluent/kafka/schemaregistry/rest/RestApiTest.java

@@ -154,6 +154,11 @@ public void testBasic() throws Exception {
                  allSubjects,
                  restApp.restClient.getAllSubjects());
 
+    // test pagination with limit of 1
+    assertEquals("Getting all subjects with pagination limit=1 should return first registered subject",
+            ImmutableList.of(allSubjects.get(0)),
+            restApp.restClient.getAllSubjectsWithPagination(1));
+
     List<Schema> latestSchemas = restApp.restClient.getSchemas(null, false, true);
     assertEquals("Getting latest schemas should return two schemas",
                  2,