Add support for YAML-based config

DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs

@@ -0,0 +1,259 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using DevProxy.Abstractions.Utils;
+using YamlDotNet.RepresentationModel;
+
+#pragma warning disable IDE0130
+namespace Microsoft.Extensions.Configuration;
+#pragma warning restore IDE0130
+
+/// <summary>
+/// A YAML file configuration source.
+/// </summary>
+public sealed class YamlConfigurationSource : FileConfigurationSource
+{
+    /// <inheritdoc/>
+    public override IConfigurationProvider Build(IConfigurationBuilder builder)
+    {
+        EnsureDefaults(builder);
+        return new YamlConfigurationProvider(this);
+    }
+}
+
+/// <summary>
+/// A YAML file configuration provider that supports anchors and merge keys.
+/// </summary>
+public sealed class YamlConfigurationProvider : FileConfigurationProvider
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="YamlConfigurationProvider"/> class.
+    /// </summary>
+    /// <param name="source">The configuration source.</param>
+    public YamlConfigurationProvider(YamlConfigurationSource source) : base(source)
+    {
+    }
+
+    /// <inheritdoc/>
+    public override void Load(Stream stream)
+    {
+        using var reader = new StreamReader(stream);
+        var yamlContent = reader.ReadToEnd();
+
+        // Parse the YAML using RepresentationModel which handles anchors/aliases natively
+        var yaml = new YamlStream();
+        using var stringReader = new StringReader(yamlContent);
+        yaml.Load(stringReader);
+
+        Data = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
+
+        if (yaml.Documents.Count == 0 || yaml.Documents[0].RootNode is null)
+        {
+            return;
+        }
+
+        if (yaml.Documents[0].RootNode is YamlMappingNode mappingNode)
+        {
+            FlattenYamlNode(mappingNode, string.Empty);
+        }
+    }
+
+    private void FlattenYamlNode(YamlNode node, string prefix)
+    {
+        switch (node)
+        {
+            case YamlMappingNode mappingNode:
+                FlattenMappingNode(mappingNode, prefix);
+                break;
+            case YamlSequenceNode sequenceNode:
+                FlattenSequenceNode(sequenceNode, prefix);
+                break;
+            case YamlScalarNode scalarNode:
+                Data[prefix] = scalarNode.Value;
+                break;
+        }
+    }
+
+    private void FlattenMappingNode(YamlMappingNode mappingNode, string prefix)
+    {
+        // First, collect all merge key values
+        var mergedValues = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
+
+        foreach (var entry in mappingNode.Children)
+        {
+            var key = GetScalarValue(entry.Key);
+            if (key is null)
+            {
+                continue;
+            }
+
+            // Handle YAML merge key (<<)
+            if (key == "<<")
+            {
+                if (entry.Value is YamlMappingNode mergeMapping)
+                {
+                    CollectMergedValues(mergeMapping, string.Empty, mergedValues);
+                }
+                else if (entry.Value is YamlSequenceNode mergeSequence)
+                {
+                    foreach (var item in mergeSequence.Children)
+                    {
+                        if (item is YamlMappingNode itemMapping)
+                        {
+                            CollectMergedValues(itemMapping, string.Empty, mergedValues);
+                        }
+                    }
+                }
+            }
+        }
+
+        // Add merged values first (they can be overridden by explicit values)
+        foreach (var kvp in mergedValues)
+        {
+            var fullKey = string.IsNullOrEmpty(prefix)
+                ? kvp.Key
+                : $"{prefix}{ConfigurationPath.KeyDelimiter}{kvp.Key}";
+            Data[fullKey] = kvp.Value;
+        }
+
+        // Then process regular keys (they override merged values)
+        foreach (var entry in mappingNode.Children)
+        {
+            var key = GetScalarValue(entry.Key);
+            if (key is null)
+            {
+                continue;
+            }
+
+            // Skip merge key
+            if (key == "<<")
+            {
+                continue;
+            }
+
+            var newPrefix = string.IsNullOrEmpty(prefix)
+                ? key
+                : $"{prefix}{ConfigurationPath.KeyDelimiter}{key}";
+
+            FlattenYamlNode(entry.Value, newPrefix);
+        }
+    }
+
+    private static string? GetScalarValue(YamlNode node)
+    {
+        return node is YamlScalarNode scalarNode ? scalarNode.Value : null;
+    }
+
+    private void CollectMergedValues(YamlMappingNode mappingNode, string prefix, Dictionary<string, string?> values)
+    {
+        foreach (var entry in mappingNode.Children)
+        {
+            var key = GetScalarValue(entry.Key);
+            if (key is null)
+            {
+                continue;
+            }
+
+            // Skip nested merge keys in merged content
+            if (key == "<<")
+            {
+                continue;
+            }
+
+            var newPrefix = string.IsNullOrEmpty(prefix)
+                ? key
+                : $"{prefix}{ConfigurationPath.KeyDelimiter}{key}";
+
+            CollectMergedValuesFromNode(entry.Value, newPrefix, values);
+        }
+    }
+
+    private void CollectMergedValuesFromNode(YamlNode node, string prefix, Dictionary<string, string?> values)
+    {
+        switch (node)
+        {
+            case YamlMappingNode mappingNode:
+                CollectMergedValues(mappingNode, prefix, values);
+                break;
+            case YamlSequenceNode sequenceNode:
+                for (int i = 0; i < sequenceNode.Children.Count; i++)
+                {
+                    var newPrefix = $"{prefix}{ConfigurationPath.KeyDelimiter}{i}";
+                    CollectMergedValuesFromNode(sequenceNode.Children[i], newPrefix, values);
+                }
+                break;
+            case YamlScalarNode scalarNode:
+                // Later values override earlier values within merged content
+                values[prefix] = scalarNode.Value;
+                break;
+        }
+    }
+
+    private void FlattenSequenceNode(YamlSequenceNode sequenceNode, string prefix)
+    {
+        for (int i = 0; i < sequenceNode.Children.Count; i++)
+        {
+            var newPrefix = $"{prefix}{ConfigurationPath.KeyDelimiter}{i}";
+            FlattenYamlNode(sequenceNode.Children[i], newPrefix);
+        }
+    }
+}
+
+/// <summary>
+/// Extension methods for adding YAML configuration.
+/// </summary>
+public static class YamlConfigurationExtensions
+{
+    /// <summary>
+    /// Adds a YAML configuration source to the configuration builder.
+    /// </summary>
+    /// <param name="builder">The configuration builder.</param>
+    /// <param name="path">The path to the YAML file.</param>
+    /// <param name="optional">Whether the file is optional.</param>
+    /// <param name="reloadOnChange">Whether to reload on change.</param>
+    /// <returns>The configuration builder.</returns>
+    public static IConfigurationBuilder AddYamlFile(
+        this IConfigurationBuilder builder,
+        string path,
+        bool optional = false,
+        bool reloadOnChange = false)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        ArgumentException.ThrowIfNullOrEmpty(path);
+
+        return builder.Add<YamlConfigurationSource>(s =>
+        {
+            s.FileProvider = null;
+            s.Path = path;
+            s.Optional = optional;
+            s.ReloadOnChange = reloadOnChange;
+            s.ResolveFileProvider();
+        });
+    }
+
+    /// <summary>
+    /// Adds a configuration file (JSON or YAML based on extension).
+    /// </summary>
+    /// <param name="builder">The configuration builder.</param>
+    /// <param name="path">The path to the configuration file.</param>
+    /// <param name="optional">Whether the file is optional.</param>
+    /// <param name="reloadOnChange">Whether to reload on change.</param>
+    /// <returns>The configuration builder.</returns>
+    public static IConfigurationBuilder AddConfigFile(
+        this IConfigurationBuilder builder,
+        string path,
+        bool optional = false,
+        bool reloadOnChange = false)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        ArgumentException.ThrowIfNullOrEmpty(path);
+
+        if (ProxyYaml.IsYamlFile(path))
+        {
+            return builder.AddYamlFile(path, optional, reloadOnChange);
+        }
+
+        return builder.AddJsonFile(path, optional, reloadOnChange);
+    }
+}

DevProxy.Abstractions/Plugins/BaseLoader.cs

@@ -120,11 +120,27 @@ private async Task LoadFileContentsAsync(CancellationToken cancellationToken)
         {
             using var stream = new FileStream(FilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
             using var reader = new StreamReader(stream);
-            var responsesString = await reader.ReadToEndAsync(cancellationToken);
+            var fileContents = await reader.ReadToEndAsync(cancellationToken);
 
-            if (!_validateSchemas || await ValidateFileContentsAsync(responsesString, cancellationToken))
+            // Convert YAML to JSON if needed
+            string jsonContents;
+            if (ProxyYaml.IsYamlFile(FilePath))
             {
-                LoadData(responsesString);
+                if (!ProxyYaml.TryConvertYamlToJson(fileContents, out var converted, out var error))
+                {
+                    Logger.LogError("Failed to parse YAML file {File}: {Error}", FilePath, error);
+                    return;
+                }
+                jsonContents = converted!;
+            }
+            else
+            {
+                jsonContents = fileContents;
+            }
+
+            if (!_validateSchemas || await ValidateFileContentsAsync(jsonContents, cancellationToken))
+            {
+                LoadData(jsonContents);
             }
         }
         catch (Exception ex)