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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System;
using System.Collections.Concurrent;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text.Json;
using System.Text.Json.Nodes;
using System.Text.Json.Schema;
using Microsoft.Shared.Diagnostics;
#pragma warning disable S1121 // Assignments should not be made from within sub-expressions
#pragma warning disable S107 // Methods should not have too many parameters
#pragma warning disable S1075 // URIs should not be hardcoded
using FunctionParameterKey = (
System.Type? Type,
string? ParameterName,
string? Description,
bool HasDefaultValue,
object? DefaultValue,
bool IncludeSchemaUri,
bool DisallowAdditionalProperties,
bool IncludeTypeInEnumSchemas);
namespace Microsoft.Extensions.AI;
/// <summary>Provides a collection of utility methods for marshalling JSON data.</summary>
public static partial class AIJsonUtilities
{
/// <summary>The uri used when populating the $schema keyword in inferred schemas.</summary>
private const string SchemaKeywordUri = "https://json-schema.org/draft/2020-12/schema";
/// <summary>Soft limit for how many items should be stored in the dictionaries in <see cref="_schemaCaches"/>.</summary>
private const int CacheSoftLimit = 4096;
/// <summary>Caches of generated schemas for each <see cref="JsonSerializerOptions"/> that's employed.</summary>
private static readonly ConditionalWeakTable<JsonSerializerOptions, ConcurrentDictionary<FunctionParameterKey, JsonElement>> _schemaCaches = new();
/// <summary>Gets a JSON schema accepting all values.</summary>
private static readonly JsonElement _trueJsonSchema = ParseJsonElement("true"u8);
/// <summary>Gets a JSON schema only accepting null values.</summary>
private static readonly JsonElement _nullJsonSchema = ParseJsonElement("""{"type":"null"}"""{"type":"null"}"""u8);
/// <summary>
/// Determines a JSON schema for the provided parameter metadata.
/// </summary>
/// <param name="parameterMetadata">The parameter metadata from which to infer the schema.</param>
/// <param name="functionMetadata">The containing function metadata.</param>
/// <param name="serializerOptions">The options used to extract the schema from the specified type.</param>
/// <param name="inferenceOptions">The options controlling schema inference.</param>
/// <returns>A JSON schema document encoded as a <see cref="JsonElement"/>.</returns>
public static JsonElement ResolveParameterJsonSchema(
AIFunctionParameterMetadata parameterMetadata,
AIFunctionMetadata functionMetadata,
JsonSerializerOptions? serializerOptions = null,
AIJsonSchemaCreateOptions? inferenceOptions = null)
{
_ = Throw.IfNull(parameterMetadata);
_ = Throw.IfNull(functionMetadata);
serializerOptions ??= functionMetadata.JsonSerializerOptions ?? DefaultOptions;
if (ReferenceEquals(serializerOptions, functionMetadata.JsonSerializerOptions) &&
parameterMetadata.Schema is JsonElement schema)
{
// If the resolved options matches that of the function metadata,
// we can just return the precomputed JSON schema value.
return schema;
}
return CreateParameterJsonSchema(
parameterMetadata.ParameterType,
parameterMetadata.Name,
description: parameterMetadata.Description,
hasDefaultValue: parameterMetadata.HasDefaultValue,
defaultValue: parameterMetadata.DefaultValue,
serializerOptions,
inferenceOptions);
}
/// <summary>
/// Creates a JSON schema for the provided parameter metadata.
/// </summary>
/// <param name="type">The type of the parameter.</param>
/// <param name="parameterName">The name of the parameter.</param>
/// <param name="description">The description of the parameter.</param>
/// <param name="hasDefaultValue">Whether the parameter is optional.</param>
/// <param name="defaultValue">The default value of the optional parameter, if applicable.</param>
/// <param name="serializerOptions">The options used to extract the schema from the specified type.</param>
/// <param name="inferenceOptions">The options controlling schema inference.</param>
/// <returns>A JSON schema document encoded as a <see cref="JsonElement"/>.</returns>
public static JsonElement CreateParameterJsonSchema(
Type? type,
string parameterName,
string? description = null,
bool hasDefaultValue = false,
object? defaultValue = null,
JsonSerializerOptions? serializerOptions = null,
AIJsonSchemaCreateOptions? inferenceOptions = null)
{
_ = Throw.IfNull(parameterName);
serializerOptions ??= DefaultOptions;
inferenceOptions ??= AIJsonSchemaCreateOptions.Default;
FunctionParameterKey key = (
type,
parameterName,
description,
hasDefaultValue,
defaultValue,
IncludeSchemaUri: false,
inferenceOptions.DisallowAdditionalProperties,
inferenceOptions.IncludeTypeInEnumSchemas);
return GetJsonSchemaCached(serializerOptions, key);
}
/// <summary>Creates a JSON schema for the specified type.</summary>
/// <param name="type">The type for which to generate the schema.</param>
/// <param name="description">The description of the parameter.</param>
/// <param name="hasDefaultValue">Whether the parameter is optional.</param>
/// <param name="defaultValue">The default value of the optional parameter, if applicable.</param>
/// <param name="serializerOptions">The options used to extract the schema from the specified type.</param>
/// <param name="inferenceOptions">The options controlling schema inference.</param>
/// <returns>A <see cref="JsonElement"/> representing the schema.</returns>
public static JsonElement CreateJsonSchema(
Type? type,
string? description = null,
bool hasDefaultValue = false,
object? defaultValue = null,
JsonSerializerOptions? serializerOptions = null,
AIJsonSchemaCreateOptions? inferenceOptions = null)
{
_ = Throw.IfNull(serializerOptions);
serializerOptions ??= DefaultOptions;
inferenceOptions ??= AIJsonSchemaCreateOptions.Default;
FunctionParameterKey key = (
type,
ParameterName: null,
description,
hasDefaultValue,
defaultValue,
inferenceOptions.IncludeSchemaKeyword,
inferenceOptions.DisallowAdditionalProperties,
inferenceOptions.IncludeTypeInEnumSchemas);
return GetJsonSchemaCached(serializerOptions, key);
}
private static JsonElement GetJsonSchemaCached(JsonSerializerOptions options, FunctionParameterKey key)
{
options.MakeReadOnly();
ConcurrentDictionary<FunctionParameterKey, JsonElement> cache = _schemaCaches.GetOrCreateValue(options);
if (cache.Count >= CacheSoftLimit)
{
return GetJsonSchemaCore(options, key);
}
return cache.GetOrAdd(
key: key,
#if NET
valueFactory: static (key, options) => GetJsonSchemaCore(options, key),
factoryArgument: options);
#else
valueFactory: key => GetJsonSchemaCore(options, key));
#endif
}
private static JsonElement GetJsonSchemaCore(JsonSerializerOptions options, FunctionParameterKey key)
{
_ = Throw.IfNull(options);
options.MakeReadOnly();
if (key.Type is null)
{
// For parameters without a type generate a rudimentary schema with available metadata.
JsonObject? schemaObj = null;
if (key.IncludeSchemaUri)
{
(schemaObj = [])["$schema"] = SchemaKeywordUri;
}
if (key.Description is not null)
{
(schemaObj ??= [])["description"] = key.Description;
}
if (key.HasDefaultValue)
{
JsonNode? defaultValueNode = key.DefaultValue is { } defaultValue
? JsonSerializer.Serialize(defaultValue, options.GetTypeInfo(defaultValue.GetType()))
: null;
(schemaObj ??= [])["default"] = defaultValueNode;
}
return schemaObj is null
? _trueJsonSchema
: JsonSerializer.SerializeToElement(schemaObj, JsonContext.Default.JsonNode);
}
if (key.Type == typeof(void))
{
return _nullJsonSchema;
}
JsonSchemaExporterOptions exporterOptions = new()
{
TreatNullObliviousAsNonNullable = true,
TransformSchemaNode = TransformSchemaNode,
};
JsonNode node = options.GetJsonSchemaAsNode(key.Type, exporterOptions);
return JsonSerializer.SerializeToElement(node, JsonContext.Default.JsonNode);
JsonNode TransformSchemaNode(JsonSchemaExporterContext ctx, JsonNode schema)
{
const string SchemaPropertyName = "$schema";
const string DescriptionPropertyName = "description";
const string NotPropertyName = "not";
const string TypePropertyName = "type";
const string EnumPropertyName = "enum";
const string PropertiesPropertyName = "properties";
const string AdditionalPropertiesPropertyName = "additionalProperties";
const string DefaultPropertyName = "default";
const string RefPropertyName = "$ref";
// Find the first DescriptionAttribute, starting first from the property, then the parameter, and finally the type itself.
Type descAttrType = typeof(DescriptionAttribute);
var descriptionAttribute =
GetAttrs(descAttrType, ctx.PropertyInfo?.AttributeProvider)?.FirstOrDefault() ??
GetAttrs(descAttrType, ctx.PropertyInfo?.AssociatedParameter?.AttributeProvider)?.FirstOrDefault() ??
GetAttrs(descAttrType, ctx.TypeInfo.Type)?.FirstOrDefault();
if (descriptionAttribute is DescriptionAttribute attr)
{
ConvertSchemaToObject(ref schema).Insert(0, DescriptionPropertyName, (JsonNode)attr.Description);
}
if (schema is JsonObject objSchema)
{
// The resulting schema might be a $ref using a pointer to a different location in the document.
// As JSON pointer doesn't support relative paths, parameter schemas need to fix up such paths
// to accommodate the fact that they're being nested inside of a higher-level schema.
if (key.ParameterName is not null && objSchema.TryGetPropertyValue(RefPropertyName, out JsonNode? paramName))
{
// Fix up any $ref URIs to match the path from the root document.
string refUri = paramName!.GetValue<string>();
Debug.Assert(refUri is "#" || refUri.StartsWith("#/", StringComparison.Ordinal), $"Expected {nameof(refUri)} to be either # or start with #/, got {refUri}");
refUri = refUri == "#"
? $"#/{PropertiesPropertyName}/{key.ParameterName}"
: $"#/{PropertiesPropertyName}/{key.ParameterName}/{refUri.AsMemory("#/".Length)}";
objSchema[RefPropertyName] = (JsonNode)refUri;
}
// Include the type keyword in enum types
if (key.IncludeTypeInEnumSchemas && ctx.TypeInfo.Type.IsEnum && objSchema.ContainsKey(EnumPropertyName) && !objSchema.ContainsKey(TypePropertyName))
{
objSchema.Insert(0, TypePropertyName, "string");
}
// Disallow additional properties in object schemas
if (key.DisallowAdditionalProperties && objSchema.ContainsKey(PropertiesPropertyName) && !objSchema.ContainsKey(AdditionalPropertiesPropertyName))
{
objSchema.Add(AdditionalPropertiesPropertyName, (JsonNode)false);
}
}
if (ctx.Path.IsEmpty)
{
// We are at the root-level schema node, append parameter-specific metadata
if (!string.IsNullOrWhiteSpace(key.Description))
{
JsonObject obj = ConvertSchemaToObject(ref schema);
JsonNode descriptionNode = (JsonNode)key.Description!;
int index = obj.IndexOf(DescriptionPropertyName);
if (index < 0)
{
// If there's no description property, insert it at the beginning of the doc.
obj.Insert(0, DescriptionPropertyName, (JsonNode)key.Description!);
}
else
{
// If there is a description property, just update it in-place.
obj[index] = (JsonNode)key.Description!;
}
}
if (key.HasDefaultValue)
{
JsonNode? defaultValue = JsonSerializer.Serialize(key.DefaultValue, options.GetTypeInfo(typeof(object)));
ConvertSchemaToObject(ref schema)[DefaultPropertyName] = defaultValue;
}
if (key.IncludeSchemaUri)
{
// The $schema property must be the first keyword in the object
ConvertSchemaToObject(ref schema).Insert(0, SchemaPropertyName, (JsonNode)SchemaKeywordUri);
}
}
return schema;
static object[]? GetAttrs(Type attrType, ICustomAttributeProvider? provider) =>
provider?.GetCustomAttributes(attrType, inherit: false);
static JsonObject ConvertSchemaToObject(ref JsonNode schema)
{
JsonObject obj;
JsonValueKind kind = schema.GetValueKind();
switch (kind)
{
case JsonValueKind.Object:
return (JsonObject)schema;
case JsonValueKind.False:
schema = obj = new() { [NotPropertyName] = true };
return obj;
default:
Debug.Assert(kind is JsonValueKind.True, $"Invalid schema type: {kind}");
schema = obj = [];
return obj;
}
}
}
}
private static JsonElement ParseJsonElement(ReadOnlySpan<byte> utf8Json)
{
Utf8JsonReader reader = new(utf8Json);
return JsonElement.ParseValue(ref reader);
}
}
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