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feat: add pagination support for listRoots operation #336

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feat: add pagination support for listRoots operation #336

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555c16a
feat: add pagination support for listRoots operation
tzolov Jun 24, 2025
4aeeb1f
refactor: make listRoots() return unmodifiable list and add comprehen…
tzolov Jun 24, 2025
7bc8726
test: add mock verification to McpAsyncServerExchangeTests
tzolov Jun 26, 2025
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17 changes: 16 additions & 1 deletion mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServerExchange.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,9 @@

package io.modelcontextprotocol.server;

import java.util.ArrayList;
import java.util.Collections;

import com.fasterxml.jackson.core.type.TypeReference;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
Expand Down Expand Up @@ -126,7 +129,19 @@ public Mono<McpSchema.ElicitResult> createElicitation(McpSchema.ElicitRequest el
* @return A Mono that emits the list of roots result.
*/
public Mono<McpSchema.ListRootsResult> listRoots() {
return this.listRoots(null);

// @formatter:off
return this.listRoots(McpSchema.FIRST_PAGE)
.expand(result -> (result.nextCursor() != null) ?
this.listRoots(result.nextCursor()) : Mono.empty())
.reduce(new McpSchema.ListRootsResult(new ArrayList<>(), null),
(allRootsResult, result) -> {
allRootsResult.roots().addAll(result.roots());
return allRootsResult;
})
.map(result -> new McpSchema.ListRootsResult(Collections.unmodifiableList(result.roots()),
result.nextCursor()));
// @formatter:on
}

/**
Expand Down
10 changes: 9 additions & 1 deletion mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java
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Expand Up @@ -1615,11 +1615,19 @@ public record Root( // @formatter:off
*
* @param roots An array of Root objects, each representing a root directory or file
* that the server can operate on.
* @param nextCursor An optional cursor for pagination. If present, indicates there
* are more roots available. The client can use this cursor to request the next page
* of results by sending a roots/list request with the cursor parameter set to this
*/
@JsonInclude(JsonInclude.Include.NON_ABSENT)
@JsonIgnoreProperties(ignoreUnknown = true)
public record ListRootsResult( // @formatter:off
@JsonProperty("roots") List<Root> roots) {
@JsonProperty("roots") List<Root> roots,
@JsonProperty("nextCursor") String nextCursor) {

public ListRootsResult(List<Root> roots) {
this(roots, null);
}
} // @formatter:on

}
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