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Extend McpMetricsObserver with completion, error, and tools/list callbacks #1142

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Extend McpMetricsObserver with completion, error, and tools/list callbacks #1142

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57 changes: 56 additions & 1 deletion mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/McpMetricsObserver.java
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@

package software.amazon.smithy.java.mcp.server;

import java.time.Duration;
import software.amazon.smithy.utils.SmithyUnstableApi;

/**
Expand All @@ -27,10 +28,64 @@ void onInitialize(
);

/**
* Called when tool/call request is received.
* Called when tool/call request is received. Fires at the start of the call,
* before execution begins. Paired with {@link #onToolCallComplete} which fires after.
*
* @param method the JSON-RPC method name (e.g. {@code "tools/call"})
* @param toolName the name of the tool being invoked, or {@code null} if not available
*/
void onToolCall(
String method,
String toolName
);

/**
* Called after a tool call completes, whether it succeeded or failed.
* Every {@link #onToolCall} is guaranteed a matching {@code onToolCallComplete}.
*
* @param method the JSON-RPC method name (e.g. {@code "tools/call"})
* @param toolName the name of the tool that was invoked, or {@code null} if not available
* @param serverId the MCP server that handled the call (e.g. {@code "aws-lambda-mcp"}),
* or {@code null} if the tool was not found
* @param latency wall-clock time from request receipt to response
* @param success {@code true} if the tool call returned a successful result,
* {@code false} if it returned an error or threw an exception
* @param isProxy {@code true} if the call was forwarded to a proxy (StdioProxy or HttpMcpProxy),
* {@code false} if it was handled in-process by a local Smithy service
*/
default void onToolCallComplete(
String method,
String toolName,
String serverId,
Duration latency,
boolean success,
boolean isProxy
Comment thread
psp65 marked this conversation as resolved.
) {}

/**
* Called when a tool call results in an error. Always preceded by
* {@link #onToolCallComplete} with {@code success=false} for the same call.
*
* @param method the JSON-RPC method name (e.g. {@code "tools/call"})
* @param toolName the name of the tool that failed, or {@code null} if not available
* @param serverId the MCP server that handled the call, or {@code null} if the tool was not found
* @param errorMessage a description of the error
*/
default void onToolCallError(
String method,
String toolName,
String serverId,
String errorMessage
) {}

/**
* Called when a {@code tools/list} request is received.
*
* @param method the JSON-RPC method name (e.g. {@code "tools/list"})
* @param toolCount the number of tools returned after filtering
*/
default void onToolsList(
String method,
int toolCount
) {}
}
204 changes: 155 additions & 49 deletions mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/McpService.java
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
import java.io.StringWriter;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Base64;
import java.util.HashMap;
Expand Down Expand Up @@ -156,37 +157,39 @@ yield switch (method) {

private JsonRpcResponse handleInitialize(JsonRpcRequest req) {
if (metricsObserver != null) {
var params = req.getParams();
var clientInfo = params.getMember("clientInfo");
var capabilities = params.getMember("capabilities");

String extractedProtocolVersion = params.getMember("protocolVersion") != null
? params.getMember("protocolVersion").asString()
: null;

String clientName = clientInfo != null && clientInfo.getMember("name") != null
? clientInfo.getMember("name").asString()
: null;

String clientTitle = clientInfo != null && clientInfo.getMember("title") != null
? clientInfo.getMember("title").asString()
: null;

boolean rootsListChanged = capabilities != null
&& capabilities.getMember("roots") != null
&& capabilities.getMember("roots").getMember("listChanged") != null
&& capabilities.getMember("roots").getMember("listChanged").asBoolean();

boolean sampling = capabilities != null && capabilities.getMember("sampling") != null;
boolean elicitation = capabilities != null && capabilities.getMember("elicitation") != null;

metricsObserver.onInitialize("initialize",
extractedProtocolVersion,
rootsListChanged,
sampling,
elicitation,
clientName,
clientTitle);
safeObserve(() -> {
var params = req.getParams();
var clientInfo = params.getMember("clientInfo");
var capabilities = params.getMember("capabilities");

String extractedProtocolVersion = params.getMember("protocolVersion") != null
? params.getMember("protocolVersion").asString()
: null;

String clientName = clientInfo != null && clientInfo.getMember("name") != null
? clientInfo.getMember("name").asString()
: null;

String clientTitle = clientInfo != null && clientInfo.getMember("title") != null
? clientInfo.getMember("title").asString()
: null;

boolean rootsListChanged = capabilities != null
&& capabilities.getMember("roots") != null
&& capabilities.getMember("roots").getMember("listChanged") != null
&& capabilities.getMember("roots").getMember("listChanged").asBoolean();

boolean sampling = capabilities != null && capabilities.getMember("sampling") != null;
boolean elicitation = capabilities != null && capabilities.getMember("elicitation") != null;

metricsObserver.onInitialize("initialize",
extractedProtocolVersion,
rootsListChanged,
sampling,
elicitation,
clientName,
clientTitle);
});
}

this.initializeRequest.compareAndSet(null, req);
Expand Down Expand Up @@ -251,10 +254,17 @@ private JsonRpcResponse handlePromptsGet(JsonRpcRequest req) {
}

private JsonRpcResponse handleToolsList(JsonRpcRequest req, ProtocolVersion protocolVersion) {
var filteredTools = tools.values()
.stream()
.filter(t -> toolFilter.allowTool(t.serverId(), t.toolInfo().getName()))
.toList();

if (metricsObserver != null) {
safeObserve(() -> metricsObserver.onToolsList("tools/list", filteredTools.size()));
}

var result = ListToolsResult.builder()
.tools(tools.values()
.stream()
.filter(t -> toolFilter.allowTool(t.serverId(), t.toolInfo().getName()))
.tools(filteredTools.stream()
.map(tool -> extractToolInfo(tool, protocolVersion))
.toList())
.build();
Expand All @@ -266,18 +276,36 @@ private JsonRpcResponse handleToolsCall(
Consumer<JsonRpcResponse> asyncResponseCallback,
ProtocolVersion protocolVersion
) {
String toolName = req.getParams().getMember("name") != null
? req.getParams().getMember("name").asString()
: null;

if (metricsObserver != null) {
String toolName = req.getParams().getMember("name") != null
? req.getParams().getMember("name").asString()
: null;
metricsObserver.onToolCall("tools/call", toolName);
safeObserve(() -> metricsObserver.onToolCall("tools/call", toolName));
}

var operationName = req.getParams().getMember("name").asString();
var tool = tools.get(operationName);
long startNanos = System.nanoTime();
var tool = tools.get(toolName);

if (tool == null) {
return createErrorResponse(req, "No such tool: " + operationName);
Duration latency = Duration.ofNanos(System.nanoTime() - startNanos);
if (metricsObserver != null) {
safeObserve(() -> {
metricsObserver.onToolCallComplete(
"tools/call",
toolName,
null,
latency,
false,
false);
metricsObserver.onToolCallError(
"tools/call",
toolName,
null,
"No such tool: " + toolName);
});
}
return createErrorResponse(req, "No such tool: " + toolName);
}

// Check if this tool should be dispatched to a proxy
Expand All @@ -291,8 +319,46 @@ private JsonRpcResponse handleToolsCall(
.build();

// Get response asynchronously and invoke callback
tool.proxy().rpc(proxyRequest).thenAccept(asyncResponseCallback).exceptionally(ex -> {
tool.proxy().rpc(proxyRequest).thenAccept(response -> {
Duration latency = Duration.ofNanos(System.nanoTime() - startNanos);
boolean success = response.getError() == null;
if (metricsObserver != null) {
safeObserve(() -> {
metricsObserver.onToolCallComplete("tools/call",
toolName,
tool.serverId(),
latency,
success,
true);
if (!success) {
String errMsg = response.getError().getMessage() != null
? response.getError().getMessage()
: "Unknown error";
metricsObserver.onToolCallError("tools/call",
toolName,
tool.serverId(),
errMsg);
}
});
}
asyncResponseCallback.accept(response);
}).exceptionally(ex -> {
Duration latency = Duration.ofNanos(System.nanoTime() - startNanos);
LOG.error("Error from proxy RPC", ex);
if (metricsObserver != null) {
safeObserve(() -> {
metricsObserver.onToolCallComplete("tools/call",
toolName,
tool.serverId(),
latency,
false,
true);
metricsObserver.onToolCallError("tools/call",
toolName,
tool.serverId(),
safeErrorMessage(ex));
});
}
asyncResponseCallback
.accept(createErrorResponse(req, new RuntimeException("Proxy error: " + ex.getMessage(), ex)));
return null;
Expand All @@ -302,16 +368,56 @@ private JsonRpcResponse handleToolsCall(
return null;
} else {
// Handle locally
var operation = tool.operation();
var argumentsDoc = req.getParams().getMember("arguments");
var adaptedDoc = adaptDocument(argumentsDoc, operation.getApiOperation().inputSchema());
var input = adaptedDoc.asShape(operation.getApiOperation().inputBuilder());
var output = operation.function().apply(input, null);
var result = formatStructuredContent(tool, (SerializableShape) output, protocolVersion);
return createSuccessResponse(req.getId(), result);
try {
var operation = tool.operation();
var argumentsDoc = req.getParams().getMember("arguments");
var adaptedDoc = adaptDocument(argumentsDoc, operation.getApiOperation().inputSchema());
var input = adaptedDoc.asShape(operation.getApiOperation().inputBuilder());
var output = operation.function().apply(input, null);
var result = formatStructuredContent(tool, (SerializableShape) output, protocolVersion);
Duration latency = Duration.ofNanos(System.nanoTime() - startNanos);
if (metricsObserver != null) {
safeObserve(() -> metricsObserver.onToolCallComplete("tools/call",
toolName,
tool.serverId(),
latency,
true,
false));
}
return createSuccessResponse(req.getId(), result);
} catch (Exception e) {
Duration latency = Duration.ofNanos(System.nanoTime() - startNanos);
if (metricsObserver != null) {
safeObserve(() -> {
metricsObserver.onToolCallComplete("tools/call",
toolName,
tool.serverId(),
latency,
false,
false);
metricsObserver.onToolCallError("tools/call",
toolName,
tool.serverId(),
safeErrorMessage(e));
});
}
throw e;
}
}
}

private void safeObserve(Runnable observation) {
try {
observation.run();
} catch (Exception e) {
LOG.warn("Metrics observer error", e);
}
}

private static String safeErrorMessage(Throwable t) {
return t.getMessage() != null ? t.getMessage() : t.getClass().getName();
}

/**
* Sets the notification writer for forwarding notifications from proxies.
*/
Expand Down
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