implement read/write functionality of VarintPostingsList #19

Author: aligusnet

src/InformationRetrieval.Test/Indexing/PostingsList/VarintPostingsListTest.cs

@@ -1,19 +1,19 @@
-using System.IO;
+using System;
+using System.IO;
 using System.Linq;
 
 using Xunit;
 
 using Corpus;
 using InformationRetrieval.Indexing.PostingsList;
-using InformationRetrieval.Utility;
 
 
 namespace InformationRetrieval.Test.Indexing.PostingsList
 {
     public class VarintPostingsListTest
     {
         [Fact]
-        public void VarintPostingsListSmokeTest()
+        public void CreationTest()
         {
             var postingsList = new VarintPostingsList()
             {
@@ -26,5 +26,28 @@ public void VarintPostingsListSmokeTest()
 
             Assert.Equal(PostingsListTest.GetDocIds(1, 2, 11, 15, 119), postingsList.ToArray());
         }
+
+        [Fact]
+        public void ReadWriteTest()
+        {
+            var postingsList = new VarintPostingsList()
+            {
+                new DocumentId(1),
+                new DocumentId(2),
+                new DocumentId(11),
+                new DocumentId(15),
+                new DocumentId(119),
+            };
+
+            int size = postingsList.GetReadOnlySpan().Length;
+            var stream = new MemoryStream();
+            stream.Write(postingsList.GetReadOnlySpan());
+            stream.Seek(0, SeekOrigin.Begin);
+            var buffer = new byte[size];
+            stream.Read(buffer.AsSpan());
+            var restored = new VarintPostingsList(buffer);
+
+            Assert.Equal(postingsList, restored);
+        }
     }
 }

src/InformationRetrieval/Indexing/PostingsList/VarintPostingsList.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 
 using Corpus;
 using InformationRetrieval.Utility;
@@ -16,14 +17,26 @@ public class VarintPostingsList : IReadOnlyCollection<DocumentId>
         private int length;
         private uint prevInserted;
 
-        public VarintPostingsList()
+        public VarintPostingsList() : this(0) { }
+
+        public VarintPostingsList(int capacity)
         {
-            data = new byte[32];
+            data = capacity > 0 ? new byte[capacity] : Array.Empty<byte>();
             length = 0;
             prevInserted = 0;
             Count = 0;
         }
 
+        public VarintPostingsList(byte[] buffer) : this(buffer, buffer.Length) { }
+
+        public VarintPostingsList(byte[] buffer, int length)
+        {
+            data = buffer;
+            this.length = length;
+            Count = VarintEncoder.GetIntegerCount(buffer.AsSpan(0, length));
+            prevInserted = this.LastOrDefault().Id;
+        }
+
         public int Count { get; private set; }
 
         public void Add(DocumentId docId)
@@ -55,14 +68,13 @@ public IEnumerator<DocumentId> GetEnumerator()
             }
         }
 
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return GetEnumerator();
-        }
+        IEnumerator IEnumerable.GetEnumerator() 
+            => GetEnumerator();
 
-        private void Resize(int newSize)
-        {
-            Array.Resize(ref data, newSize);
-        }
+        public ReadOnlySpan<byte> GetReadOnlySpan() 
+            => data.AsSpan(0, length);
+
+        private void Resize(int newSize) 
+            => Array.Resize(ref data, newSize);
     }
 }