API Reference

Everything public is in the namespace IsImageUrlDotNet, in two static classes: ImageUrl (new in 2.0.0) and IsImageUrlDotNetLib (the 1.0.2 API, kept exactly). The verification program printed the surface of the net10.0 build by reflection:

static class IsImageUrlDotNet.ImageUrl [Extension]
  IReadOnlyList<string> ImageExtensions { get; }
  bool HasImageExtension(string url) [Extension]
  Task<bool> IsImageUrlAsync(string url) [Extension]
  Task<bool> IsImageUrlAsync(string url, CancellationToken cancellationToken) [Extension]
  Task<bool> IsImageUrlAsync(string url, HttpClient httpClient) [Extension]
  Task<bool> IsImageUrlAsync(string url, HttpClient httpClient, CancellationToken cancellationToken) [Extension]
static class IsImageUrlDotNet.IsImageUrlDotNetLib [Extension]
  FSharpList<string> ImageFileExtensions { get; }
  FSharpList<string> NonImageFileExtensions { get; }
  bool IsImageUrl(string opt) [Extension] [Obsolete("IsImageUrl keeps 1.0.2's answers, bugs included. Use ImageUrl.HasImageExtension (offline) or ImageUrl.IsImageUrlAsync (http and https only).", error: false)]

The url parameters are annotated as nullable (string? to C#), so passing null compiles without a warning and answers false. The three builds in the package (net10.0, net462, netstandard2.0) have the same public methods; see the builds.

ImageUrl

Member	Since	Returns	Throws
HasImageExtension(string? url)	2.0.0	true when the path of the URL ends in one of ImageExtensions, compared without regard to case or culture	never
IsImageUrlAsync(string? url)	2.0.0	a task of true when the URL is http or https and has an image extension, or else when a GET answers 2xx with an image/* media type	HttpRequestException, TaskCanceledException
IsImageUrlAsync(string? url, CancellationToken cancellationToken)	2.0.0	as above, cancellable	as above
IsImageUrlAsync(string? url, HttpClient httpClient)	2.0.0	as above, through your client (its handler, proxy, timeout and headers)	as above, and ArgumentNullException for a null client
IsImageUrlAsync(string? url, HttpClient httpClient, CancellationToken cancellationToken)	2.0.0	as above, cancellable	as above
ImageExtensions	2.0.0	the 16 extensions, lower case, read-only	never

All five methods are C# extension methods on string as well as static methods, and F# can call them either way. The exact rules are on How URLs are checked; every exception and its message is on Edge cases and errors.

ArgumentNullException for a null client is thrown by the call itself, before a task exists, so it escapes code that stores the task without awaiting it (example).

The overloads without a client use one shared HttpClient for the whole process. It times out after 10 seconds, sends the User-Agent IsImageUrlDotNet/2.0 (+https://github.com/m4bwav/IsImageUrlDotNet), follows no redirect by itself and uses the process's default proxy settings.

The extension lists

using IsImageUrlDotNet;

Console.WriteLine(string.Join(" ", ImageUrl.ImageExtensions));
Console.WriteLine(string.Join(" ", IsImageUrlDotNetLib.ImageFileExtensions));
Console.WriteLine(string.Join(" ", IsImageUrlDotNetLib.NonImageFileExtensions));

prints:

png jpg jpeg gif raw bmp svg psd webp avif apng ico tif tiff heic heif
png jpg gif raw bmp svg jpeg psd
exe pdf html htm txt mp3 wav odp

ImageExtensions is an IReadOnlyList<string>. The two old lists are F# lists (Microsoft.FSharp.Collections.FSharpList<string>), which C# can enumerate like any IEnumerable<string>.

IsImageUrlDotNetLib (obsolete)

Member	Since	Returns	Throws
IsImageUrl(string opt)	1.0.2 or earlier; obsolete since 2.0.0	1.0.2's answer on the runtime it runs on	whatever 1.0.2 threw: UriFormatException, WebException and more
ImageFileExtensions	1.0.2 or earlier	the eight extensions IsImageUrl treats as images without a request	never
NonImageFileExtensions	1.0.2 or earlier	the eight it treats as not images without a request	never

Versions before 1.0.2 were not examined. The obsolete attribute is a warning, not an error, so old code still builds. From C#, url.IsImageUrl() still works; from F#, only IsImageUrlDotNetLib.IsImageUrl url does. Its answers and requests match 1.0.2's in every recorded case (Versions and upgrading).

using IsImageUrlDotNet;

#pragma warning disable CS0618 // IsImageUrl is obsolete
Console.WriteLine("image.png".IsImageUrl());
Console.WriteLine("http://images.test/avatar".IsImageUrl());
#pragma warning restore CS0618

prints:

True
True

The first answer came from the extension; the second made a request that the stand-in answered with image/png.

Compiler messages

This file, with no #pragma:

using IsImageUrlDotNet;

var url = "http://images.test/avatar";
Console.WriteLine(url.IsImageUrl());
Console.WriteLine(await url.IsImageUrlAsync(default));

gives:

warning CS0618: 'IsImageUrlDotNetLib.IsImageUrl(string?)' is obsolete: 'IsImageUrl keeps 1.0.2's answers, bugs included. Use ImageUrl.HasImageExtension (offline) or ImageUrl.IsImageUrlAsync (http and https only).'
error CS0121: The call is ambiguous between the following methods or properties: 'IsImageUrlDotNet.ImageUrl.IsImageUrlAsync(string?, System.Threading.CancellationToken)' and 'IsImageUrlDotNet.ImageUrl.IsImageUrlAsync(string?, System.Net.Http.HttpClient)'

default fits both CancellationToken and HttpClient. Pass CancellationToken.None, a real token or a client.

The builds in the package

Read from each DLL's metadata in the published package:

lib/net10.0: 22016 bytes, 9 public methods, same public surface as the first; references FSharp.Core 6.0.0.0, netstandard 2.1.0.0, System.Collections 10.0.0.0, System.Net.Http 10.0.0.0, System.Net.Primitives 10.0.0.0, System.Net.Requests 10.0.0.0, System.Runtime 10.0.0.0
lib/net462: 22528 bytes, 9 public methods, same public surface as the first; references FSharp.Core 6.0.0.0, mscorlib 4.0.0.0, netstandard 2.0.0.0, System 4.0.0.0, System.Core 4.0.0.0, System.Net.Http 4.2.0.0
lib/netstandard2.0: 22016 bytes, 9 public methods, same public surface as the first; references FSharp.Core 6.0.0.0, netstandard 2.0.0.0

The package also ships XML documentation for each build, a README, an icon, and symbols in a separate snupkg.