Adding ToDataUrlAsync extension method

BlazorInputFile/FileListEntryExtensions.cs

@@ -34,5 +34,32 @@ public static async Task<MemoryStream> ReadAllAsync(this IFileListEntry fileList
             result.Seek(0, SeekOrigin.Begin);
             return result;
         }
+
+        /// <summary>
+        /// Reads the entire uploaded file into a base64 encoded string. 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.  Default max 5mb
+        /// </summary>
+        /// <param name="fileListEntry">The <see cref="IFileListEntry"/>.</param>
+        /// <param name="maxSizeBytes">The maximum amount of data to accept.</param>
+        /// <returns></returns>
+        public static async Task<string> ToDataUrlAsync(this IFileListEntry fileListEntry, int maxSizeBytes = 5 * 1024 * 1024)
+        {
+            if (fileListEntry is null)
+            {
+                throw new ArgumentNullException(nameof(fileListEntry));
+            }
+
+            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}.");
+            }
+
+            using var result = new MemoryStream();
+            await sourceData.CopyToAsync(result);
+            return $"data:{fileListEntry.Type};base64, { Convert.ToBase64String(result.ToArray())}";
+        }
     }
 }

samples/Sample.Core/Pages/ImageFile.razor

@@ -25,13 +25,9 @@
             // Load as an image file in memory
             var format = "image/jpeg";
             var imageFile = await rawFile.ToImageFileAsync(format, 640, 480);
-            var ms = new MemoryStream();
-            await imageFile.Data.CopyToAsync(ms);
 
-            // Make a data URL so we can display it
-            imageDataUri = $"data:{format};base64,{Convert.ToBase64String(ms.ToArray())}";
-
-            status = $"Finished loading {ms.Length} bytes from {imageFile.Name}";
+            imageDataUri = await imageFile.ToDataUrlAsync();
+            status = $"Finished loading {imageFile.Data.Length} bytes from {imageFile.Name}";
         }
     }
 }