Add ReadAllAsync

Author: SteveSandersonMS

BlazorInputFile/BlazorInputFile.csproj

@@ -4,7 +4,7 @@
     <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
     <RazorLangVersion>3.0</RazorLangVersion>
     <LangVersion>preview</LangVersion>
-    <PackageVersion>0.1.0-preview</PackageVersion>
+    <PackageVersion>0.1.0-preview-00002</PackageVersion>
     <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
   </PropertyGroup>
 

BlazorInputFile/FileListEntryExtensions.cs

@@ -0,0 +1,38 @@
+using System;
+using System.IO;
+using System.Threading.Tasks;
+
+namespace BlazorInputFile
+{
+    public static class FileListEntryExtensions
+    {
+        /// <summary>
+        /// Reads the entire uploaded file into a <see cref="MemoryStream"/>. This will allocate
+        /// however much memory is needed to hold the entire file, or will throw if the client
+        /// tries to supply more than <paramref name="maxSizeBytes"/> bytes. Be careful not to
+        /// let clients allocate too much memory on the server.
+        /// </summary>
+        /// <param name="fileListEntry">The <see cref="IFileListEntry"/>.</param>
+        /// <param name="maxSizeBytes">The maximum amount of data to accept.</param>
+        public static async Task<MemoryStream> ReadAllAsync(this IFileListEntry fileListEntry, int maxSizeBytes = 1024*1024)
+        {
+            if (fileListEntry is null)
+            {
+                throw new ArgumentNullException(nameof(fileListEntry));
+            }
+
+            // We can trust .Length to be correct (and can't change later) because the implementation
+            // won't supply more bytes than this, even if the JS-side code would send more data.
+            var sourceData = fileListEntry.Data;
+            if (sourceData.Length > maxSizeBytes)
+            {
+                throw new ArgumentOutOfRangeException(nameof(fileListEntry), $"The maximum allowed size is {maxSizeBytes}, but the supplied file is of length {fileListEntry.Size}.");
+            }
+
+            var result = new MemoryStream();
+            await sourceData.CopyToAsync(result);
+            result.Seek(0, SeekOrigin.Begin);
+            return result;
+        }
+    }
+}