Fix remaining count error when query edge in page

hugegraph-api/src/main/java/com/baidu/hugegraph/serializer/JsonSerializer.java

@@ -33,7 +33,7 @@
 
 import com.baidu.hugegraph.HugeException;
 import com.baidu.hugegraph.api.API;
-import com.baidu.hugegraph.backend.page.PageState;
+import com.baidu.hugegraph.backend.page.PageInfo;
 import com.baidu.hugegraph.iterator.Metadatable;
 import com.baidu.hugegraph.schema.EdgeLabel;
 import com.baidu.hugegraph.schema.IndexLabel;
@@ -101,7 +101,7 @@ private String writeIterator(String label, Iterator<?> iter,
                 if (iter instanceof GraphTraversal<?, ?>) {
                     page = TraversalUtil.page((GraphTraversal<?, ?>) iter);
                 } else if (iter instanceof Metadatable) {
-                    page = PageState.page(iter);
+                    page = PageInfo.page(iter);
                 } else {
                     throw new HugeException("Invalid paging iterator: %s",
                                             iter.getClass());

hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraEntryIterator.java

@@ -22,6 +22,7 @@
 import java.util.Iterator;
 import java.util.function.BiFunction;
 
+import com.baidu.hugegraph.backend.page.PageState;
 import com.baidu.hugegraph.backend.query.Query;
 import com.baidu.hugegraph.backend.store.BackendEntry;
 import com.baidu.hugegraph.backend.store.BackendEntryIterator;
@@ -115,6 +116,7 @@ protected String pageState() {
         if (page == null || this.results.isExhausted()) {
             return null;
         }
-        return page.toString();
+        byte[] position = page.toBytes();
+        return new PageState(position, 0, (int) this.count()).toString();
     }
 }

hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraTable.java

@@ -31,6 +31,7 @@
 
 import com.baidu.hugegraph.backend.BackendException;
 import com.baidu.hugegraph.backend.id.Id;
+import com.baidu.hugegraph.backend.page.PageState;
 import com.baidu.hugegraph.backend.query.Condition;
 import com.baidu.hugegraph.backend.query.Condition.Relation;
 import com.baidu.hugegraph.backend.query.Query;
@@ -168,8 +169,9 @@ protected void setPageState(Query query, List<Select> selects) {
                 select.setFetchSize((int) total);
                 // It's the first time if page is empty
                 if (!page.isEmpty()) {
+                    byte[] position = PageState.fromString(page).position();
                     try {
-                        select.setPagingState(PagingState.fromString(page));
+                        select.setPagingState(PagingState.fromBytes(position));
                     } catch (PagingStateException e) {
                         throw new BackendException(e);
                     }

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/PageEntryIterator.java

@@ -33,24 +33,24 @@ public class PageEntryIterator implements Iterator<BackendEntry>, Metadatable {
     private final QueryList queries;
     private final long pageSize;
     private QueryList.PageIterator results;
-    private PageState pageState;
+    private PageInfo pageInfo;
     private long remaining;
 
     public PageEntryIterator(QueryList queries, long pageSize) {
         this.queries = queries;
         this.pageSize = pageSize;
         this.results = QueryList.PageIterator.EMPTY;
-        this.pageState = this.parsePageState();
+        this.pageInfo = this.parsePageState();
         this.remaining = queries.parent().limit();
     }
 
-    private PageState parsePageState() {
+    private PageInfo parsePageState() {
         String page = this.queries.parent().pageWithoutCheck();
-        PageState pageState = PageState.fromString(page);
-        E.checkState(pageState.offset() < this.queries.total(),
+        PageInfo pageInfo = PageInfo.fromString(page);
+        E.checkState(pageInfo.offset() < this.queries.total(),
                      "Invalid page '%s' with an offset '%s' exceeds " +
-                     "the size of IdHolderList", page, pageState.offset());
-        return pageState;
+                     "the size of IdHolderList", page, pageInfo.offset());
+        return pageInfo;
     }
 
     @Override
@@ -63,26 +63,27 @@ public boolean hasNext() {
 
     private boolean fetch() {
         if ((this.remaining != Query.NO_LIMIT && this.remaining <= 0L) ||
-            this.pageState.offset() >= this.queries.total()) {
+            this.pageInfo.offset() >= this.queries.total()) {
             return false;
         }
 
         long pageSize = this.pageSize;
         if (this.remaining != Query.NO_LIMIT && this.remaining < pageSize) {
             pageSize = this.remaining;
         }
-        this.results = this.queries.fetchNext(this.pageState, pageSize);
+        this.results = this.queries.fetchNext(this.pageInfo, pageSize);
         assert this.results != null;
 
         if (this.results.iterator().hasNext()) {
             if (this.results.page() == null) {
-                this.pageState.increase();
+                this.pageInfo.increase();
             } else {
-                this.pageState.page(this.results.page());
+                this.pageInfo.page(this.results.page());
+                this.remaining -= this.results.total();
             }
             return true;
         } else {
-            this.pageState.increase();
+            this.pageInfo.increase();
             return this.fetch();
         }
     }
@@ -92,21 +93,16 @@ public BackendEntry next() {
         if (!this.hasNext()) {
             throw new NoSuchElementException();
         }
-        BackendEntry entry = this.results.iterator().next();
-        if (this.remaining != Query.NO_LIMIT) {
-            // Assume one result in each entry (just for index query)
-            this.remaining--;
-        }
-        return entry;
+        return this.results.iterator().next();
     }
 
     @Override
     public Object metadata(String meta, Object... args) {
-        if (PageState.PAGE.equals(meta)) {
-            if (this.pageState.offset() >= this.queries.total()) {
+        if (PageInfo.PAGE.equals(meta)) {
+            if (this.pageInfo.offset() >= this.queries.total()) {
                 return null;
             }
-            return this.pageState.toString();
+            return this.pageInfo.toString();
         }
         throw new NotSupportException("Invalid meta '%s'", meta);
     }

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/page/PageInfo.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2017 HugeGraph Authors
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with this
+ * work for additional information regarding copyright ownership. The ASF
+ * licenses this file to You under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package com.baidu.hugegraph.backend.page;
+
+import java.util.Base64;
+import java.util.Iterator;
+
+import com.baidu.hugegraph.HugeException;
+import com.baidu.hugegraph.backend.serializer.BytesBuffer;
+import com.baidu.hugegraph.iterator.Metadatable;
+import com.baidu.hugegraph.util.Bytes;
+import com.baidu.hugegraph.util.E;
+
+public final class PageInfo {
+
+    public static final String PAGE = "page";
+    public static final String PAGE_NONE = "";
+
+    private int offset;
+    private String page;
+
+    public PageInfo(int offset, String page) {
+        E.checkArgument(offset >= 0, "The offset must be >= 0");
+        E.checkNotNull(page, "page");
+        this.offset = offset;
+        this.page = page;
+    }
+
+    public void increase() {
+        this.offset++;
+        this.page = PAGE_NONE;
+    }
+
+    public int offset() {
+        return this.offset;
+    }
+
+    public void page(String page) {
+        this.page = page;
+    }
+
+    public String page() {
+        return this.page;
+    }
+
+    @Override
+    public String toString() {
+        return Base64.getEncoder().encodeToString(this.toBytes());
+    }
+
+    public byte[] toBytes() {
+        byte[] pageState = PageState.toBytes(this.page);
+        int length = 2 + BytesBuffer.INT_LEN + pageState.length;
+        BytesBuffer buffer = BytesBuffer.allocate(length);
+        buffer.writeInt(this.offset);
+        buffer.writeBytes(pageState);
+        return buffer.bytes();
+    }
+
+    public static PageInfo fromString(String page) {
+        byte[] bytes;
+        try {
+            bytes = Base64.getDecoder().decode(page);
+        } catch (Exception e) {
+            throw new HugeException("Invalid page: '%s'", e, page);
+        }
+        return fromBytes(bytes);
+    }
+
+    public static PageInfo fromBytes(byte[] bytes) {
+        if (bytes.length == 0) {
+            // The first page
+            return new PageInfo(0, PAGE_NONE);
+        }
+        try {
+            BytesBuffer buffer = BytesBuffer.wrap(bytes);
+            int offset = buffer.readInt();
+            byte[] pageState = buffer.readBytes();
+            String page = PageState.toString(pageState);
+            return new PageInfo(offset, page);
+        } catch (Exception e) {
+            throw new HugeException("Invalid page: '0x%s'",
+                                    e, Bytes.toHex(bytes));
+        }
+    }
+
+    public static String page(Iterator<?> iterator) {
+        E.checkState(iterator instanceof Metadatable,
+                     "Invalid paging iterator: %s", iterator.getClass());
+        Object page = ((Metadatable) iterator).metadata(PAGE);
+        return (String) page;
+    }
+}