Parsing HTTP User Agents with .NET

NuGet

string userAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36";
HttpUserAgentInformation info = HttpUserAgentParser.Parse(userAgent); // alias HttpUserAgentInformation.Parse()

returns

UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36"
Type = HttpUserAgentType.Browser
Platform = {
    Name = "Windows 10",
    PlatformType = HttpUserAgentPlatformType.Windows
}
Name = "Chrome"
Version = "90.0.4430.212"
MobileDeviceType = null

For dependency injection mechanisms, the IHttpUserAgentParserProvider interface exists, for which built-in or custom caching mechanisms can be used. The use is always:

private IHttpUserAgentParserProvider _parser;
public void MyMethod(string userAgent)
{
    HttpUserAgentInformation info = _parser.Parse(userAgent);
}

If no cache is required but dependency injection is still desired, the default cache provider can simply be used. This registers the HttpUserAgentParserDefaultProvider, which does not cache at all.

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpUserAgentParser(); // uses HttpUserAgentParserDefaultProvider and does not cache
}

Likewise, an In Process Cache mechanism is provided, based on a ConcurrentDictionary.

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpUserAgentCachedParser(); // uses `HttpUserAgentParserCachedProvider`
    // or
    // services.AddHttpUserAgentParser<HttpUserAgentParserCachedProvider>();
}

This is especially recommended for tests. For web applications, the IMemoryCache implementation should be used, which offers a timed expiration of the entries.

The package MyCSharp.HttpUserAgentParser.MemoryCache is required to use the IMemoryCache. This enables the registration of the IMemoryCache implementation:

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpUserAgentMemoryCachedParser();

    // or use options

    services.AddHttpUserAgentMemoryCachedParser(options =>
    {
        options.CacheEntryOptions.SlidingExpiration = TimeSpan.FromMinutes(60); // default is 1 day

        // limit the total entries in the MemoryCache
        //   each unique user agent string counts as one entry
        options.CacheOptions.SizeLimit = 1024; // default is null (= no limit)
    });
}

AddHttpUserAgentMemoryCachedParser registers HttpUserAgentParserMemoryCachedProvider as singleton which contains an isolated MemoryCache object.

For ASP.NET Core applications, an accessor pattern (IHttpUserAgentParserAccessor) implementation can be registered additionally that independently retrieves the user agent based on the HttpContextAccessor. This requires the package MyCSharp.HttpUserAgentParser.AspNetCore

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddHttpUserAgentMemoryCachedParser() // registers Parser, returns HttpUserAgentParserDependencyInjectionOptions
        // or use any other Parser registration like services.AddHttpUserAgentParser<TParser>(); above
        .AddHttpUserAgentParserAccessor(); // registers IHttpUserAgentParserAccessor, uses IHttpUserAgentParserProvider
}

Now you can use

public void MyMethod(IHttpUserAgentParserAccessor parserAccessor)
{
    HttpUserAgentInformation info = parserAccessor.Get();
}

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
.NET Core SDK=5.0.300-preview.21228.15
  [Host]     : .NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT
  DefaultJob : .NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT

More benchmark results can be found in this comment.

This library is inspired by UserAgentService by DannyBoyNg and contains optimizations for our requirements on myCSharp.de. We decided to fork the project, because we want a general restructuring with corresponding breaking changes.

by @BenjaminAbt and @gfoidl

MIT License

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