ANL.XmlComparer 2.0.3

XmlComparer

XmlComparer is a zero-dependency .NET library for structural XML comparison with an HTML side-by-side diff report.

Table of Contents

• Installation
• Basic Concepts
• Quickstart (CLI)
• Library Usage
• Which API Should I Use?
• Advanced Topics
• Performance
• Error Handling
• JSON Output Schema
• Projects

Installation

.NET CLI

dotnet add package XmlComparer.Core

Package Manager Console

Install-Package XmlComparer.Core

NuGet Package Manager

Search for XmlComparer.Core in the NuGet Package Manager.

Requirements

• .NET 9.0 or later
• Zero external dependencies

Basic Concepts

Key Attributes

Key attributes uniquely identify elements among siblings. When specified, the library uses these attributes to match elements even when their order changes.

Example:

<users>
  <user><name>Alice</name></user>
  <user><name>Bob</name></user>
</users>


<users>
  <user id="2"><name>Bob</name></user>
  <user id="1"><name>Alice</name></user>
</users>

Configure key attributes:

options.WithKeyAttributes("id", "code", "sku");

Diff Types

The library detects five types of changes:

Quickstart (CLI)

Run the runner against two XML files and generate an HTML report:

dotnet run --project XmlComparer.Runner -- .\original.xml .\new.xml --out diff.html --json diff.json --key id,code

Options:

The HTML report embeds the JSON diff in a <script type="application/json" id="xml-diff-json"> tag for single-file portability. If schema validation is requested, the JSON includes a Validation block alongside Diff, and the HTML shows a validation status panel.

Library Usage

Basic File Comparison

using XmlComparer.Core;

var diff = XmlComparer.CompareFiles("old.xml", "new.xml");

if (diff.Type != DiffType.Unchanged)
{
    Console.WriteLine($"Documents differ: {diff.Type}");
}

With Configuration

using XmlComparer.Core;

var result = XmlComparer.CompareFilesWithReport(
    "old.xml",
    "new.xml",
    options => options
        .WithKeyAttributes("id", "code")
        .ExcludeAttributes("timestamp")
        .ExcludeNodes(excludeSubtree: true, "metadata")
        .NormalizeWhitespace()
        .IncludeHtml()
        .IncludeJson());

File.WriteAllText("diff.html", result.Html!);
File.WriteAllText("diff.json", result.Json!);

Using XmlComparerService

using XmlComparer.Core;

var config = new XmlDiffConfig
{
    IgnoreValues = false
};
config.KeyAttributeNames.Add("id");
config.ExcludedNodeNames.Add("metadata");
config.ExcludedAttributeNames.Add("timestamp");

var service = new XmlComparerService(config);
var diff = service.Compare(@"C:\path\old.xml", @"C:\path\new.xml");
string html = service.GenerateHtml(diff);

Which API Should I Use?

Choose the API that best fits your scenario:

Advanced Topics

Custom Matching Strategies

Implement IMatchingStrategy for custom element matching:

public class CustomStrategy : IMatchingStrategy
{
    public double Score(XElement? e1, XElement? e2, XmlDiffConfig config)
    {
        if (e1 == null || e2 == null) return 0.0;
        if (e1.Name != e2.Name) return 0.0;

        var name1 = e1.Attribute("name")?.Value;
        var name2 = e2.Attribute("name")?.Value;

        return name1 == name2 && name1 != null ? 100.0 : 0.0;
    }
}

// Use your strategy
var result = XmlComparer.CompareFilesWithReport("a.xml", "b.xml",
    options => options.UseMatchingStrategy(new CustomStrategy()));

Performance Considerations

• Small files (< 1MB): Use synchronous methods for simplicity
• Large files (> 10MB): Use async methods to avoid blocking
• Memory usage: Entire documents are loaded into memory
• HTML generation: Can be memory-intensive for large diffs

Limits:

• Maximum file size: 100MB
• Maximum recursion depth: 1000 levels
• Maximum children per node: 10,000

Options Persistence

Save and load comparison options:

var options = new XmlComparisonOptions()
    .WithKeyAttributes("id")
    .ExcludeAttributes("timestamp")
    .IncludeHtml();

// Save to file
options.SaveToFile("options.json");

// Load from file
var loaded = XmlComparisonOptions.LoadFromFile("options.json");

// JSON serialization
string json = options.ToJson();
var fromJson = XmlComparisonOptions.FromJson(json);

Performance

Benchmark results from .NET 9.0 (Release build, x64):

XML Comparison Performance

Output Format Generation

LCS Algorithm Performance

Memory Usage

• Small diff (100 elements): ~300 MB allocated
• Medium diff (5,000 elements): ~140 MB allocated
• GC Gen 2 collections: Minimal for typical workloads

Performance Tips

1. Use key attributes for better matching on reordered elements
2. Exclude attributes/nodes you don't need to compare
3. For very large files, consider using async methods
4. JSON generation is significantly faster than HTML

Benchmark Environment:

• Runtime: .NET 9.0.10 (x64 RyuJIT AVX2)
• Hardware: Intel/AMD x64 with AVX2 support
• Build: Release optimization enabled

Error Handling

The library may throw these exceptions:

Example Error Handling

try
{
    var result = XmlComparer.CompareFilesWithReport(
        "original.xml",
        "new.xml",
        options => options.IncludeHtml());
}
catch (FileNotFoundException ex)
{
    Console.WriteLine($"File not found: {ex.FileName}");
}
catch (ArgumentException ex)
{
    Console.WriteLine($"Invalid input: {ex.Message}");
}
catch (InvalidOperationException ex)
{
    Console.WriteLine($"Operation failed: {ex.Message}");
}

JSON Output Schema

The JSON output is an envelope:

{
  "Validation": {
    "IsValid": true,
    "Errors": []
  },
  "Summary": {
    "Total": 10,
    "Unchanged": 5,
    "Added": 2,
    "Deleted": 1,
    "Modified": 1,
    "Moved": 1
  },
  "Diff": {
    "Name": "root",
    "Type": "Modified",
    "Children": [...]
  }
}

The JSON Schema for the envelope is packaged as XmlDiff.schema.json in the NuGet package.

Projects

• XmlComparer.Core - Diff engine and HTML formatter
• XmlComparer.Runner - CLI/sample runner
• XmlComparer.Tests - Unit tests

Configuration Options

Async and Streams

using XmlComparer.Core;
using System.IO;
using System.Threading.Tasks;

// Async file comparison
var diff = await XmlComparer.CompareFilesAsync(@"C:\a.xml", @"C:\b.xml");

// Stream comparison
using var left = File.OpenRead(@"C:\a.xml");
using var right = File.OpenRead(@"C:\b.xml");
var diffFromStreams = XmlComparer.CompareStreams(left, right);

String Extension Methods

using XmlComparer.Core;

string xml1 = "<root><child>1</child></root>";
string xml2 = "<root><child>2</child></root>";

var diff = xml1.CompareXmlTo(xml2, options => options.IgnoreValues());
var report = xml1.CompareXmlToWithReport(xml2, options => options.IncludeHtml());

Dependency Injection Friendly Client

using XmlComparer.Core;

var client = new XmlComparerClient(
    new XmlDiffConfig(),
    new DefaultMatchingStrategy());

var result = client.CompareContentWithReport(
    "<root><child>1</child></root>",
    "<root><child>2</child></root>",
    options => options.IncludeJson());

Embedded XSD Usage

If your schemas are embedded resources:

using System.Reflection;
using XmlComparer.Core;

var assembly = Assembly.GetExecutingAssembly();
var resources = XmlSchemaSetFactory.ListEmbeddedSchemas(assembly);
var schemaSet = XmlSchemaSetFactory.FromEmbeddedResource(
    assembly,
    "Your.Assembly.Resources.SampleSchema.xsd");

var validator = new XmlSchemaValidator(schemaSet);
var result = validator.ValidateContent("<root><child>123</child></root>");

Matching Strategy Registry

Register strategies once and resolve by id:

XmlComparisonOptions.MatchingStrategyRegistry.TryRegister(
    "default",
    () => new DefaultMatchingStrategy());

loaded.ResolveMatchingStrategyFromRegistry();

if (XmlComparisonOptions.MatchingStrategyRegistry.TryResolve("default", out var strategy))
{
    // Use strategy
}

Registry lifecycle tip: Register strategies at app startup and clear/unregister on shutdown or in test teardown to avoid stale global state.