70 lines
2.9 KiB
C#
70 lines
2.9 KiB
C#
using System.Text.Json;
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using System.Text.Json.Serialization;
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namespace ModelContextProtocol.Protocol;
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/// <summary>
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/// Serializes <see cref="CacheScope"/> caching-scope hints, tolerating unknown or future values on read.
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/// </summary>
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/// <remarks>
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/// <para>
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/// SEP-2549 introduces <c>cacheScope</c> as a forward-looking caching hint. If a server sends an
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/// unrecognized scope string (for example, a value added in a later revision of the specification) or a
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/// non-string token, this converter maps it to <see langword="null"/> rather than throwing. This prevents
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/// a single unexpected hint from breaking deserialization of the entire result (for example, the whole
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/// tool list). A <see langword="null"/> result is the same as an absent field, which clients treat as
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/// <see cref="CacheScope.Public"/>.
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/// </para>
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/// <para>
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/// This converter is applied per-property on the cacheable result types. The <see cref="CacheScope"/>
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/// enum itself retains a standard string converter for any standalone serialization.
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/// </para>
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/// </remarks>
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internal sealed class CacheScopeConverter : JsonConverter<CacheScope?>
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{
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public override CacheScope? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
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{
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if (reader.TokenType is JsonTokenType.String)
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{
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string? value = reader.GetString();
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// Match case-insensitively so a non-conforming casing of "private" (a security-relevant hint)
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// is honored rather than falling through to null, which clients would treat as "public" and
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// could cache user-specific data in a shared cache. Genuinely unknown values still map to null.
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if (string.Equals(value, "public", StringComparison.OrdinalIgnoreCase))
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{
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return CacheScope.Public;
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}
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if (string.Equals(value, "private", StringComparison.OrdinalIgnoreCase))
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{
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return CacheScope.Private;
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}
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return null;
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}
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// Any non-string token (number, bool, object, array) is an unrecognized hint. Consume the whole
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// value, including the contents of an object or array, so the reader is left correctly positioned
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// before mapping to null. Skipping is required for container tokens: returning without consuming
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// them would leave the reader mispositioned and break deserialization of the enclosing result.
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reader.Skip();
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return null;
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}
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public override void Write(Utf8JsonWriter writer, CacheScope? value, JsonSerializerOptions options)
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{
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if (value is null)
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{
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writer.WriteNullValue();
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return;
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}
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writer.WriteStringValue(value switch
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{
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CacheScope.Public => "public",
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CacheScope.Private => "private",
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_ => throw new JsonException($"Unsupported {nameof(CacheScope)} value: {value}."),
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});
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}
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}
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