Implements DownloadBlock logic DynamicsValue/fake-xrm-easy#157

src/FakeXrmEasy.Core/FileStorage/Db/Exceptions/InvalidBlockLengthException.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace FakeXrmEasy.Core.FileStorage.Db.Exceptions
+{
+    /// <summary>
+    /// Exception raised when the BlockLength property is not valid
+    /// </summary>
+    public class InvalidBlockLengthException: Exception
+    {
+        /// <summary>
+        /// Default constructor
+        /// </summary>
+        public InvalidBlockLengthException() : base($"The BlockLength property must be greater than zero.")
+        {
+
+        }
+    }
+}

src/FakeXrmEasy.Core/FileStorage/Db/Exceptions/InvalidOffsetException.cs

@@ -0,0 +1,22 @@
+using System;
+using FakeXrmEasy.Core.FileStorage.Download;
+
+namespace FakeXrmEasy.Core.FileStorage.Db.Exceptions
+{
+    /// <summary>
+    /// Exception raised when an Offset property is not within the range of a given file length
+    /// </summary>
+    public class InvalidOffsetException: Exception
+    {
+        /// <summary>
+        /// Default constructor
+        /// </summary>
+        /// <param name="properties"></param>
+        /// <param name="actualLength"></param>
+        internal InvalidOffsetException(DownloadBlockProperties properties, long actualLength) 
+            : base($"The Offset '{properties.Offset.ToString()}' and block lengh '{properties.BlockLength.ToString()}' property values are not within the file's size of [0..{actualLength.ToString()}]")
+        {
+
+        }
+    }
+}

src/FakeXrmEasy.Core/FileStorage/Db/InMemoryFileDb.cs

@@ -239,9 +239,36 @@ public List<FileDownloadSession> GetAllFileDownloadSessions()
             return _fileDownloadSessions.Values.ToList();
         }
 
-        public byte[] DownloadFileBlock(DownloadBlockProperties uploadBlockProperties)
+        public byte[] DownloadFileBlock(DownloadBlockProperties downloadBlockProperties)
         {
-            throw new NotImplementedException();
+            var fileDownloadSession = GetFileDownloadSession(downloadBlockProperties.FileDownloadSessionId);
+            if (fileDownloadSession == null)
+            {
+                throw new FileTokenContinuationNotFoundException(downloadBlockProperties.FileDownloadSessionId);
+            }
+
+            if (downloadBlockProperties.BlockLength <= 0)
+            {
+                throw new InvalidBlockLengthException();
+            }
+
+            if (downloadBlockProperties.Offset < 0)
+            {
+                throw new InvalidOffsetException(downloadBlockProperties, fileDownloadSession.File.Content.Length);
+            }
+
+            if (downloadBlockProperties.BlockLength + downloadBlockProperties.Offset >
+                fileDownloadSession.File.Content.Length)
+            {
+                throw new InvalidOffsetException(downloadBlockProperties, fileDownloadSession.File.Content.Length);
+            }
+
+            var data = new byte[downloadBlockProperties.BlockLength];
+
+            Array.Copy(fileDownloadSession.File.Content, downloadBlockProperties.Offset, data,
+                0, downloadBlockProperties.BlockLength);
+
+            return data;
         }
         #endregion
     }

tests/FakeXrmEasy.Core.Tests/FileStorage/Db/InMemoryFileDbDownloaderTests.cs

@@ -17,7 +17,8 @@ public class InMemoryFileDbDownloaderTests
         private readonly FileDownloadProperties _fileDownloadProperties;
         private readonly Entity _entity;
         private readonly FileAttachment _file;
-
+        private readonly DownloadBlockProperties _downloadBlockProperties;
+
         public InMemoryFileDbDownloaderTests()
         {
             _db = new InMemoryDb();
@@ -43,6 +44,11 @@ public InMemoryFileDbDownloaderTests()
                 AttributeName = "dv_file",
                 Content = new byte[] { 1, 2, 3, 4 }
             };
+
+            _downloadBlockProperties = new DownloadBlockProperties()
+            {
+                FileDownloadSessionId = ""
+            };
         }
 
         [Fact]
@@ -93,5 +99,74 @@ public void Should_return_file_download_session_if_properties_are_valid()
             Assert.Equal(_fileDownloadProperties.Target.LogicalName, _entity.LogicalName);
             Assert.Equal(_fileDownloadProperties.Target.Id, _entity.Id);
         }
+
+        [Fact]
+        public void Should_throw_file_token_continuation_not_found_exception()
+        {
+            _downloadBlockProperties.FileDownloadSessionId = "invalid id";
+            Assert.Throws<FileTokenContinuationNotFoundException>(() =>
+                _fileDb.DownloadFileBlock(_downloadBlockProperties));
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(-23456)]
+        public void Should_throw_invalid_length_exception(long blockLength)
+        {
+            _fileDb.AddFile(_file);
+
+            _entity[_fileDownloadProperties.FileAttributeName] = _file.Id;
+            _db.AddEntityRecord(_entity);
+
+            var fileContinuationToken = _fileDb.InitFileDownloadSession(_fileDownloadProperties);
+            Assert.NotNull(fileContinuationToken);
+
+            _downloadBlockProperties.FileDownloadSessionId = fileContinuationToken;
+            _downloadBlockProperties.BlockLength = blockLength;
+            Assert.Throws<InvalidBlockLengthException>(() => _fileDb.DownloadFileBlock(_downloadBlockProperties));
+        }
+
+        [Theory]
+        [InlineData(-1, 2)]
+        [InlineData(0, 5)] 
+        [InlineData(2, 25)]
+        [InlineData(4, 2)]
+        public void Should_throw_invalid_offset_exception_if_exceeds_file_length(long offset, long blockLength)
+        {
+            _fileDb.AddFile(_file);
+
+            _entity[_fileDownloadProperties.FileAttributeName] = _file.Id;
+            _db.AddEntityRecord(_entity);
+
+            var fileContinuationToken = _fileDb.InitFileDownloadSession(_fileDownloadProperties);
+            Assert.NotNull(fileContinuationToken);
+
+            _downloadBlockProperties.FileDownloadSessionId = fileContinuationToken;
+            _downloadBlockProperties.Offset = offset;
+            _downloadBlockProperties.BlockLength = blockLength;
+            Assert.Throws<InvalidOffsetException>(() => _fileDb.DownloadFileBlock(_downloadBlockProperties));
+        }
+
+        [Theory]
+        [InlineData(0, 4)]
+        [InlineData(1, 3)] 
+        [InlineData(3, 1)]
+        public void Should_download_a_valid_file_block(long offset, long blockLength)
+        {
+            _fileDb.AddFile(_file);
+
+            _entity[_fileDownloadProperties.FileAttributeName] = _file.Id;
+            _db.AddEntityRecord(_entity);
+
+            var fileContinuationToken = _fileDb.InitFileDownloadSession(_fileDownloadProperties);
+            Assert.NotNull(fileContinuationToken);
+
+            _downloadBlockProperties.FileDownloadSessionId = fileContinuationToken;
+            _downloadBlockProperties.Offset = offset;
+            _downloadBlockProperties.BlockLength = blockLength;
+            var data = _fileDb.DownloadFileBlock(_downloadBlockProperties);
+
+            Assert.Equal(blockLength, data.Length);
+        }
     }
 }