Bound no-arg list operations to prevent unbounded pagination - #1100
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Bound no-arg list operations to prevent unbounded pagination#1100ZYZ666-RGB wants to merge 1 commit into
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The no-arg listTools(), listResources(), listResourceTemplates() and listPrompts() follow the server-provided nextCursor chain via Mono.expand with no page limit, no duplicate-cursor detection and no total deadline. A server that returns an endless stream of non-empty cursors makes the client issue an unbounded number of requests, accumulate unbounded memory, and block synchronous callers forever. Add a client-side pagination guard: each no-arg list operation now tracks the cursors it has already seen and the number of pages fetched, and aborts with a new McpPaginationException when the configured maxPaginationPages (default 100) or paginationTimeout (disabled by default) is exceeded, or when a cursor is returned more than once. The bounds are configurable on both McpClient.SyncSpec and McpClient.AsyncSpec (maxPaginationPages(int), paginationTimeout(Duration)); existing behavior and APIs are unchanged for servers that terminate pagination normally. Adds McpAsyncClientPaginationTests covering normal multi-page aggregation, duplicate-cursor loops, ever-changing cursor loops (page limit and total timeout) and the synchronous client path. Fixes modelcontextprotocol#1084 Signed-off-by: zhaoyuzhe <1991039819@qq.com>
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Motivation and Context
The no-arg list operations (listTools(), listResources(), listResourceTemplates(),
listPrompts()) follow the server-provided nextCursor chain via Mono.expand with
no page limit, no duplicate-cursor detection and no total deadline. A server that
returns an endless stream of non-empty cursors makes the client:
requestTimeout does not help: it bounds each individual request, not the number of
requests. The existing #954 fix only stops servers that signal the end with an empty
cursor. Fixes #1084.
Changes
Add a client-side pagination guard applied to all four no-arg list operations:
caps the total number of pages fetched. 0 disables the limit.
the operation aborts immediately — an unambiguous sign of a loop.
bounds the wall-clock time of the whole list operation.
When a bound is exceeded the operation fails with a new
McpPaginationException carrying a clear message. Configuration is exposed on both
McpClient.SyncSpec and McpClient.AsyncSpec (maxPaginationPages(int),
paginationTimeout(Duration)). No existing API or behavior changes for servers that
terminate pagination normally — the guard state is created per subscription, so shared
Monos can be subscribed multiple times safely.
How Has This Been Tested?
New McpAsyncClientPaginationTests (6 tests):
Verified locally: mvn -pl mcp-core test (360 tests) and the mcp-test client test
classes (17 tests) all pass, with spring-javaformat validation green.
Breaking Changes
None. The new builder options are additive; defaults keep the API source-compatible and
only add protection against misbehaving servers.
Types of changes
Checklist
Additional context
Design note: Mono.expand runs per subscription, so a shared list Mono subscribed
twice would otherwise share stale guard state; the guard is therefore created inside
Mono.defer per subscription.