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Add MCP proxy server support for prompts #1004

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Add MCP proxy server support for prompts #1004

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0e80b4d
Add MCP proxy server support for prompts
sanskritipatole Dec 20, 2025
5a6e4e9
Merge branch 'main' into mcp-service
sanskritipatole Dec 23, 2025
a6b8e64
Merge branch 'main' into mcp-service
sanskritipatole Dec 23, 2025
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37 changes: 32 additions & 5 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 @@ -220,8 +220,23 @@ private JsonRpcResponse handleInitialize(JsonRpcRequest req) {
}

private JsonRpcResponse handlePromptsList(JsonRpcRequest req) {
var allPrompts = new ArrayList<>(prompts.values().stream().map(Prompt::promptInfo).toList());

// Add prompts from proxy servers
for (McpServerProxy proxy : proxies.values()) {
try {
var response = proxy.rpc(req).join();
if (response.getError() == null) {
var proxyPrompts = response.getResult().asShape(ListPromptsResult.builder()).getPrompts();
allPrompts.addAll(proxyPrompts);
}
} catch (Exception e) {
LOG.error("Failed to fetch prompts from proxy: " + proxy.name(), e);
}
Comment on lines +233 to +235
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@adwsingh adwsingh Dec 23, 2025

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We should not silently swallow. Don't do anything, if there is an exception let it bubble up.

}

var result = ListPromptsResult.builder()
.prompts(prompts.values().stream().map(Prompt::promptInfo).toList())
.prompts(allPrompts)
.build();
return createSuccessResponse(req.getId(), result);
}
Expand All @@ -232,12 +247,24 @@ private JsonRpcResponse handlePromptsGet(JsonRpcRequest req) {

var prompt = prompts.get(normalize(promptName));

if (prompt == null) {
throw new RuntimeException("Prompt not found: " + promptName);
if (prompt != null) {
var result = promptProcessor.buildPromptResult(prompt, promptArguments);
return createSuccessResponse(req.getId(), result);
}

var result = promptProcessor.buildPromptResult(prompt, promptArguments);
return createSuccessResponse(req.getId(), result);
// Try proxy servers
for (McpServerProxy proxy : proxies.values()) {
try {
var response = proxy.rpc(req).join();
if (response.getError() == null) {
return createSuccessResponse(req.getId(), response.getResult());
}
} catch (Exception e) {
LOG.error("Failed to get prompt from proxy: " + proxy.name(), e);
}
}

throw new RuntimeException("Prompt not found: " + promptName);
Comment on lines +256 to +267
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@adwsingh adwsingh Dec 23, 2025

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Why try again from the Proxy? This goes against the MCP spec too, if a prompt wasn't broadcasted as a part of list/prompts then it should not be returned.

}

private JsonRpcResponse handleToolsList(JsonRpcRequest req, ProtocolVersion protocolVersion) {
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