[release/3.1] Handle shortened JSON file in dotnet openapi

src/Tools/Microsoft.dotnet-openapi/src/Commands/BaseCommand.cs

@@ -569,7 +569,7 @@ private async Task WriteToFileAsync(Stream content, string destinationPath, bool
 
                 // Create or overwrite the destination file.
                 reachedCopy = true;
-                using var fileStream = new FileStream(destinationPath, FileMode.OpenOrCreate, FileAccess.Write);
+                using var fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write);
                 fileStream.Seek(0, SeekOrigin.Begin);
                 if (content.CanSeek)
                 {

src/Tools/Microsoft.dotnet-openapi/test/OpenApiRefreshTests.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.IO;
-using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.DotNet.OpenApi.Tests;
 using Xunit;
@@ -20,29 +19,90 @@ public async Task OpenApi_Refresh_Basic()
         {
             CreateBasicProject(withOpenApi: false);
 
+            // Add <OpenApiReference/> to the project. Ignore initial filename.json content.
             var app = GetApplication();
             var run = app.Execute(new[] { "add", "url", FakeOpenApiUrl });
 
-            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error.ToString()}");
+            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error}");
             Assert.Equal(0, run);
 
+            // File will grow after the refresh.
             var expectedJsonPath = Path.Combine(_tempDir.Root, "filename.json");
-            var json = await File.ReadAllTextAsync(expectedJsonPath);
-            json += "trash";
-            await File.WriteAllTextAsync(expectedJsonPath, json);
+            await File.WriteAllTextAsync(expectedJsonPath, "trash");
 
             var firstWriteTime = File.GetLastWriteTime(expectedJsonPath);
 
-            Thread.Sleep(TimeSpan.FromSeconds(1));
+            await Task.Delay(TimeSpan.FromSeconds(1));
 
             app = GetApplication();
             run = app.Execute(new[] { "refresh", FakeOpenApiUrl });
 
-            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error.ToString()}");
+            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error}");
             Assert.Equal(0, run);
 
             var secondWriteTime = File.GetLastWriteTime(expectedJsonPath);
             Assert.True(firstWriteTime < secondWriteTime, $"File wasn't updated! {firstWriteTime} {secondWriteTime}");
+            Assert.Equal(Content, await File.ReadAllTextAsync(expectedJsonPath), ignoreLineEndingDifferences: true);
+        }
+
+        // Regression test for #35767 scenario.
+        [Fact]
+        public async Task OpenApi_Refresh_MuchShorterFile()
+        {
+            CreateBasicProject(withOpenApi: false);
+
+            // Add <OpenApiReference/> to the project. Ignore initial filename.json content.
+            var app = GetApplication();
+            var run = app.Execute(new[] { "add", "url", FakeOpenApiUrl });
+
+            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error}");
+            Assert.Equal(0, run);
+
+            // File will shrink after the refresh.
+            var expectedJsonPath = Path.Combine(_tempDir.Root, "filename.json");
+            await File.WriteAllTextAsync(expectedJsonPath, PackageUrlContent);
+
+            var firstWriteTime = File.GetLastWriteTime(expectedJsonPath);
+
+            await Task.Delay(TimeSpan.FromSeconds(1));
+
+            app = GetApplication();
+            run = app.Execute(new[] { "refresh", FakeOpenApiUrl });
+
+            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error}");
+            Assert.Equal(0, run);
+
+            var secondWriteTime = File.GetLastWriteTime(expectedJsonPath);
+            Assert.True(firstWriteTime < secondWriteTime, $"File wasn't updated! {firstWriteTime} {secondWriteTime}");
+            Assert.Equal(Content, await File.ReadAllTextAsync(expectedJsonPath), ignoreLineEndingDifferences: true);
+        }
+
+        [Fact]
+        public async Task OpenApi_Refresh_UnchangedFile()
+        {
+            CreateBasicProject(withOpenApi: false);
+
+            // Add <OpenApiReference/> to the project and write the filename.json file.
+            var app = GetApplication();
+            var run = app.Execute(new[] { "add", "url", FakeOpenApiUrl });
+
+            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error}");
+            Assert.Equal(0, run);
+
+            var expectedJsonPath = Path.Combine(_tempDir.Root, "filename.json");
+            var firstWriteTime = File.GetLastWriteTime(expectedJsonPath);
+
+            await Task.Delay(TimeSpan.FromSeconds(1));
+
+            app = GetApplication();
+            run = app.Execute(new[] { "refresh", FakeOpenApiUrl });
+
+            Assert.True(string.IsNullOrEmpty(_error.ToString()), $"Threw error: {_error}");
+            Assert.Equal(0, run);
+
+            var secondWriteTime = File.GetLastWriteTime(expectedJsonPath);
+            Assert.Equal(firstWriteTime, secondWriteTime);
+            Assert.Equal(Content, await File.ReadAllTextAsync(expectedJsonPath));
         }
     }
 }