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Missing `@JsonIgnoreProperties(ignoreUnknown = true)` on capability sub-records

Abierto
#766 4 comentarios 0 reacciones 0 asignados Ver en GitHub

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Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
55/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Estancado
Stack tecnológico
java
Área
api

Línea de trabajo

Comienza en mcp-core/src/main/java/io/modelcontextprotocol/spec/McpSchema.java y revisa los capability records enumerados, comparándolos con ClientCapabilities y ServerCapabilities. Se considera terminado cuando los campos desconocidos de cada subregistro de capability afectado se ignoran durante la deserialización, incluidos los elicitation records anidados.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

bug P1
Bug description

The top-level ClientCapabilities and ServerCapabilities records have @JsonIgnoreProperties(ignoreUnknown = true), but their nested sub-records do not. Since the ObjectMapper is constructed with default settings (FAIL_ON_UNKNOWN_PROPERTIES = true), any unknown field on a capability sub-object causes a deserialization failure.

This already caused a real breakage when the elicitation capability gained form and url fields (#724, fixed in #731), but the systemic issue remains — the next spec addition to any capability sub-object will break older SDK versions again.

Affected records

In McpSchema.java:

Record Line Has annotation?
ClientCapabilities 383 Yes
RootCapabilities 397 Yes
Sampling 410 No
Elicitation 437 No
Elicitation.Form 443 No
Elicitation.Url 450 No
ServerCapabilities 535 Yes
CompletionCapabilities 548 No
LoggingCapabilities 555 No
PromptCapabilities 565 No
ResourceCapabilities 576 No
ToolCapabilities 587 No
Spec reference

The spec schema explicitly states capabilities are not a closed set:

"Known capabilities are defined here, in this schema, but this is not a closed set: any client can define its own, additional capabilities."

ClientCapabilities in schema.json — additionalProperties: false is never set on any capability object or sub-object. Several sub-capabilities (sampling, elicitation, completions, logging) explicitly set additionalProperties: true.

Expected behavior

Unknown fields on capability sub-objects should be silently ignored, matching the behavior of the top-level ClientCapabilities and ServerCapabilities records.

Related
  • #734 — reports the same issue for ToolCapabilities specifically
  • #724 / #731 — the elicitation breakage that was fixed by adding fields, not by adding the annotation

AI Disclaimer

Lenguaje dominante
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Forks
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