feat: add IsReadOnly to the client Options

ServiceNow.Api.Test/ReadOnlyOptionTests.cs

@@ -0,0 +1,107 @@
+using AwesomeAssertions;
+using Newtonsoft.Json.Linq;
+using System.Net;
+using Xunit;
+
+namespace ServiceNow.Api.Test;
+
+/// <summary>
+/// Credential-free: a refused write throws before any request reaches the handler.
+/// </summary>
+public class ReadOnlyOptionTests
+{
+	private static CancellationToken Ct => TestContext.Current.CancellationToken;
+
+	private sealed class RecordingHandler : HttpMessageHandler
+	{
+		public List<HttpMethod> Methods { get; } = [];
+
+		protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+		{
+			cancellationToken.ThrowIfCancellationRequested();
+			Methods.Add(request.Method);
+			return Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)
+			{
+				Content = new StringContent("{\"result\":{\"sys_id\":\"abc\"}}")
+			});
+		}
+	}
+
+	private static ServiceNowClient CreateClient(RecordingHandler handler, bool isReadOnly)
+		=> new(handler, new Options { IsReadOnly = isReadOnly });
+
+	[Fact]
+	public void IsReadOnly_DefaultsToFalse()
+		=> new Options().IsReadOnly.Should().BeFalse();
+
+	[Fact]
+	public async Task Create_IsRefused_WhenIsReadOnly()
+	{
+		using var handler = new RecordingHandler();
+		using var client = CreateClient(handler, isReadOnly: true);
+
+		var act = () => client.CreateAsync("incident", new JObject { ["short_description"] = "x" }, Ct);
+
+		await act.Should().ThrowAsync<InvalidOperationException>();
+		handler.Methods.Should().BeEmpty();
+	}
+
+	[Fact]
+	public async Task Update_IsRefused_WhenIsReadOnly()
+	{
+		using var handler = new RecordingHandler();
+		using var client = CreateClient(handler, isReadOnly: true);
+
+		var act = () => client.UpdateAsync("incident", new JObject { ["sys_id"] = "abc" }, Ct);
+
+		await act.Should().ThrowAsync<InvalidOperationException>();
+		handler.Methods.Should().BeEmpty();
+	}
+
+	[Fact]
+	public async Task Patch_IsRefused_WhenIsReadOnly()
+	{
+		using var handler = new RecordingHandler();
+		using var client = CreateClient(handler, isReadOnly: true);
+
+		var act = () => client.PatchAsync("incident", new JObject { ["sys_id"] = "abc" }, Ct);
+
+		await act.Should().ThrowAsync<InvalidOperationException>();
+		handler.Methods.Should().BeEmpty();
+	}
+
+	[Fact]
+	public async Task Delete_IsRefused_WhenIsReadOnly()
+	{
+		using var handler = new RecordingHandler();
+		using var client = CreateClient(handler, isReadOnly: true);
+
+		var act = () => client.DeleteAsync("incident", "abc", Ct);
+
+		await act.Should().ThrowAsync<InvalidOperationException>();
+		handler.Methods.Should().BeEmpty();
+	}
+
+	[Fact]
+	public async Task Delete_IsAllowed_WhenNotReadOnly()
+	{
+		using var handler = new RecordingHandler();
+		using var client = CreateClient(handler, isReadOnly: false);
+
+		await client.DeleteAsync("incident", "abc", Ct);
+
+		handler.Methods.Should().ContainSingle().Which.Should().Be(HttpMethod.Delete);
+	}
+
+	[Fact]
+	public async Task Get_IsAllowed_WhenIsReadOnly()
+	{
+		using var handler = new RecordingHandler();
+		using var client = CreateClient(handler, isReadOnly: true);
+
+		var result = await client.GetByIdAsync("incident", "abc", Ct);
+
+		result.Should().NotBeNull();
+		handler.Methods.Should().ContainSingle().Which.Should().Be(HttpMethod.Get);
+	}
+}

ServiceNow.Api/Options.cs

@@ -12,6 +12,11 @@ public class Options
 	/// </summary>
 	public ILogger? Logger { get; set; }
 
+	/// <summary>
+	/// Whether the client refuses every request other than GET, HEAD and OPTIONS
+	/// </summary>
+	public bool IsReadOnly { get; set; }
+
 	/// <summary>
 	/// The field that is used in the "GetAllByQueryInternalAsync" method in ServiceNowClient.
 	/// This can be set because it CAN happen that the table/view does NOT have this field,

ServiceNow.Api/ReadOnlyHandler.cs

@@ -0,0 +1,21 @@
+namespace ServiceNow.Api;
+
+/// <summary>
+/// Refuses every request other than GET, HEAD or OPTIONS while <see cref="Options.IsReadOnly"/> is set.
+/// The option is read on every request.
+/// </summary>
+internal sealed class ReadOnlyHandler(Options options, HttpMessageHandler innerHandler) : DelegatingHandler(innerHandler)
+{
+	protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+	{
+		if (options.IsReadOnly
+			&& request.Method != HttpMethod.Get
+			&& request.Method != HttpMethod.Head
+			&& request.Method != HttpMethod.Options)
+		{
+			throw new InvalidOperationException($"The client is read-only (IsReadOnly is true): {request.Method} {request.RequestUri?.AbsolutePath} is not allowed.");
+		}
+
+		return base.SendAsync(request, cancellationToken);
+	}
+}

ServiceNow.Api/ServiceNowClient.cs

@@ -42,7 +42,7 @@ public ServiceNowClient(
 			? $"https://{account}.servicenowservices.com"
 			: $"https://{account}.service-now.com";
 		var httpClientHandler = new HttpClientHandler();
-		_httpClient = new HttpClient(httpClientHandler)
+		_httpClient = new HttpClient(new ReadOnlyHandler(_options, httpClientHandler))
 		{
 			BaseAddress = new Uri(baseAddress),
 			DefaultRequestHeaders =
@@ -80,7 +80,7 @@ internal ServiceNowClient(
 		_logger = _options.Logger ?? new NullLogger<ServiceNowClient>();
 		AccountName = "test";
 
-		_httpClient = new HttpClient(httpMessageHandler)
+		_httpClient = new HttpClient(new ReadOnlyHandler(_options, httpMessageHandler))
 		{
 			BaseAddress = new Uri("https://test.service-now.com"),
 			DefaultRequestHeaders =