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fix(mcp): translate OpenAPI 3.0 nullable into JSON Schema

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The response schemas added yesterday made every paginated list tool fail. The
plugin's fields are documented as OpenAPI format and validated with a JSON
Schema validator, and `nullable: true` is not a JSON Schema keyword — so it is
ignored, `type: string` is enforced, and `previous: null` on the first page is
rejected as *null is not of type "string"*.

The failure lands after the backend has already done the work, surfaces to the
caller as a bare tool retry exhaustion, and appears nowhere in the gateway's own
logs. Found only because an orchestrating agent asked a question that paged.

The generator now rewrites `nullable: true` into `type: [T, "null"]` wherever it
inlines a schema, request bodies included. A 3.1 spec needs none of this.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Stéphane Tailland
2026-08-29 12:19:31 +02:00
parent 63d2d90107
commit 865a7376e3
1 changed files with 51 additions and 34 deletions
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kong/mcp/ai-mcp-proxy.yaml
+51 -34
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@@ -58,13 +58,15 @@ config:
type: integer type: integer
example: 123 example: 123
next: next:
type: string type:
nullable: true - string
- 'null'
format: uri format: uri
example: http://api.example.org/accounts/?page=4 example: http://api.example.org/accounts/?page=4
previous: previous:
type: string type:
nullable: true - string
- 'null'
format: uri format: uri
example: http://api.example.org/accounts/?page=2 example: http://api.example.org/accounts/?page=2
results: results:
@@ -93,33 +95,38 @@ config:
type: string type: string
maxLength: 50 maxLength: 50
addressline2: addressline2:
type: string type:
nullable: true - string
- 'null'
maxLength: 50 maxLength: 50
city: city:
type: string type: string
maxLength: 50 maxLength: 50
state: state:
type: string type:
nullable: true - string
- 'null'
maxLength: 50 maxLength: 50
postalcode: postalcode:
type: string type:
nullable: true - string
- 'null'
maxLength: 15 maxLength: 15
country: country:
type: string type: string
maxLength: 50 maxLength: 50
creditlimit: creditlimit:
type: string type:
- string
- 'null'
format: decimal format: decimal
pattern: ^-?\d{0,8}(?:\.\d{0,2})?$ pattern: ^-?\d{0,8}(?:\.\d{0,2})?$
nullable: true
salesrepemployeenumber: salesrepemployeenumber:
type: integer type:
- integer
- 'null'
maximum: 2147483647 maximum: 2147483647
minimum: -2147483648 minimum: -2147483648
nullable: true
required: required:
- addressline1 - addressline1
- city - city
@@ -183,33 +190,38 @@ config:
type: string type: string
maxLength: 50 maxLength: 50
addressline2: addressline2:
type: string type:
nullable: true - string
- 'null'
maxLength: 50 maxLength: 50
city: city:
type: string type: string
maxLength: 50 maxLength: 50
state: state:
type: string type:
nullable: true - string
- 'null'
maxLength: 50 maxLength: 50
postalcode: postalcode:
type: string type:
nullable: true - string
- 'null'
maxLength: 15 maxLength: 15
country: country:
type: string type: string
maxLength: 50 maxLength: 50
creditlimit: creditlimit:
type: string type:
- string
- 'null'
format: decimal format: decimal
pattern: ^-?\d{0,8}(?:\.\d{0,2})?$ pattern: ^-?\d{0,8}(?:\.\d{0,2})?$
nullable: true
salesrepemployeenumber: salesrepemployeenumber:
type: integer type:
- integer
- 'null'
maximum: 2147483647 maximum: 2147483647
minimum: -2147483648 minimum: -2147483648
nullable: true
required: required:
- addressline1 - addressline1
- city - city
@@ -304,33 +316,38 @@ config:
type: string type: string
maxLength: 50 maxLength: 50
addressline2: addressline2:
type: string type:
nullable: true - string
- 'null'
maxLength: 50 maxLength: 50
city: city:
type: string type: string
maxLength: 50 maxLength: 50
state: state:
type: string type:
nullable: true - string
- 'null'
maxLength: 50 maxLength: 50
postalcode: postalcode:
type: string type:
nullable: true - string
- 'null'
maxLength: 15 maxLength: 15
country: country:
type: string type: string
maxLength: 50 maxLength: 50
creditlimit: creditlimit:
type: string type:
- string
- 'null'
format: decimal format: decimal
pattern: ^-?\d{0,8}(?:\.\d{0,2})?$ pattern: ^-?\d{0,8}(?:\.\d{0,2})?$
nullable: true
salesrepemployeenumber: salesrepemployeenumber:
type: integer type:
- integer
- 'null'
maximum: 2147483647 maximum: 2147483647
minimum: -2147483648 minimum: -2147483648
nullable: true
required: required:
- addressline1 - addressline1
- city - city