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Merged
Skobeltsyn merged 1 commit into from
May 30, 2026
+58 −62
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refactor(#2800): dedup MCP client list/text-block parsing and Skills … #80

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120 changes: 58 additions & 62 deletions src/main/kotlin/agents_engine/mcp/McpClient.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,35 @@ import java.util.concurrent.atomic.AtomicLong
* See `src/main/resources/internals-agent/mcp/McpClient.md`
* (#1837 / #1880).
*/
// #2800 — small dedup helpers used by every MCP RPC endpoint that follows
// the same "result.<key> is a List<Map>" shape (listPrompts, listResources,
// loadTools) or the same "join all text blocks with \n" shape (getPrompt,
// readResource, call).
private fun resultArray(result: Any?, key: String): List<*> {
val map = result as? Map<*, *> ?: return emptyList<Any?>()
return map[key] as? List<*> ?: emptyList<Any?>()
}

private fun joinTextContent(blocks: List<*>, contentKey: String = "text"): String =
blocks.mapNotNull { block ->
(block as? Map<*, *>)?.let { it[contentKey] as? String }
}.joinToString("\n")

private fun prefixed(prefix: String?, name: String): String =
if (prefix != null) "$prefix.$name" else name

private fun makeMcpSkill(
name: String,
description: String,
impl: (Map<String, Any?>) -> String,
): agents_engine.core.Skill<Map<String, Any?>, String> =
agents_engine.core.Skill<Map<String, Any?>, String>(
name = name,
description = description,
inType = Map::class,
outType = String::class,
).also { skill -> skill.implementedBy(impl) }

class McpClient internal constructor(private val transport: McpTransport) : AutoCloseable {

private var toolDescriptors: List<McpToolDescriptor> = emptyList()
Expand Down Expand Up @@ -108,31 +137,22 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
* Both surfaces ship; consumers pick the shape that matches their
* agent design.
*/
fun toolSkills(prefix: String? = null): List<agents_engine.core.Skill<Map<String, Any?>, String>> = toolDescriptors.map { t ->
val displayName = if (prefix != null) "$prefix.${t.name}" else t.name
agents_engine.core.Skill<Map<String, Any?>, String>(
name = displayName,
description = describeForLlm(t),
inType = Map::class,
outType = String::class,
).also { skill ->
skill.implementedBy { args -> call(t.name, args)?.toString() ?: "" }
fun toolSkills(prefix: String? = null): List<agents_engine.core.Skill<Map<String, Any?>, String>> =
toolDescriptors.map { t ->
makeMcpSkill(prefixed(prefix, t.name), describeForLlm(t)) { args ->
call(t.name, args)?.toString() ?: ""
}
}
}

/**
* #1796 — fetch prompt listings from the server (`prompts/list`).
* Returns the raw `McpPromptInfo` records; for the Skill view use
* [promptSkills].
*/
fun listPrompts(): List<McpPromptInfo> {
val result = post("prompts/list", emptyMap<String, Any?>())
val resultMap = result as? Map<*, *> ?: return emptyList()
val promptsList = resultMap["prompts"] as? List<*> ?: return emptyList()
return promptsList.mapNotNull { raw ->
fun listPrompts(): List<McpPromptInfo> =
resultArray(post("prompts/list", emptyMap<String, Any?>()), "prompts").mapNotNull { raw ->
val m = raw as? Map<*, *> ?: return@mapNotNull null
val name = m["name"] as? String ?: return@mapNotNull null
val description = m["description"] as? String
val args = (m["arguments"] as? List<*>)?.mapNotNull { a ->
val argMap = a as? Map<*, *> ?: return@mapNotNull null
val argName = argMap["name"] as? String ?: return@mapNotNull null
Expand All @@ -145,11 +165,10 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
McpPromptInfo(
name = name,
title = m["title"] as? String,
description = description,
description = m["description"] as? String,
arguments = args,
)
}
}

/**
* #1796 — render a server-side prompt template (`prompts/get`).
Expand All @@ -161,12 +180,13 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
val result = post("prompts/get", mapOf("name" to name, "arguments" to arguments))
val resultMap = result as? Map<*, *>
?: error("prompts/get returned non-object: $result")
val messages = resultMap["messages"] as? List<*> ?: emptyList<Any?>()
return messages.mapNotNull { msg ->
val m = msg as? Map<*, *> ?: return@mapNotNull null
val content = m["content"] as? Map<*, *> ?: return@mapNotNull null
content["text"] as? String
}.joinToString("\n")
// #2800 — prompts/get nests `text` one level deeper than tools/call:
// messages[].content.text instead of messages[].text. Pull the
// content map per message, then reuse joinTextContent.
val texts = resultArray(resultMap, "messages").mapNotNull { msg ->
(msg as? Map<*, *>)?.get("content") as? Map<*, *>
}
return joinTextContent(texts)
}

/**
Expand All @@ -175,30 +195,21 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
* `implementedBy` invokes [getPrompt] with the call-time args and
* returns the rendered text.
*/
fun promptSkills(prefix: String? = null): List<agents_engine.core.Skill<Map<String, Any?>, String>> {
return listPrompts().map { info ->
val displayName = if (prefix != null) "$prefix.${info.name}" else info.name
agents_engine.core.Skill<Map<String, Any?>, String>(
name = displayName,
fun promptSkills(prefix: String? = null): List<agents_engine.core.Skill<Map<String, Any?>, String>> =
listPrompts().map { info ->
makeMcpSkill(
name = prefixed(prefix, info.name),
description = info.description ?: "MCP prompt ${info.name}",
inType = Map::class,
outType = String::class,
).also { skill ->
skill.implementedBy { args -> getPrompt(info.name, args) }
}
) { args -> getPrompt(info.name, args) }
}
}

/**
* #1810 — fetch resource listings from the server (`resources/list`).
* Returns the raw `McpResourceInfo` records. For the Skill view, use
* [resourceSkills].
*/
fun listResources(): List<McpResourceInfo> {
val result = post("resources/list", emptyMap<String, Any?>())
val resultMap = result as? Map<*, *> ?: return emptyList()
val resourcesList = resultMap["resources"] as? List<*> ?: return emptyList()
return resourcesList.mapNotNull { raw ->
fun listResources(): List<McpResourceInfo> =
resultArray(post("resources/list", emptyMap<String, Any?>()), "resources").mapNotNull { raw ->
val m = raw as? Map<*, *> ?: return@mapNotNull null
val uri = m["uri"] as? String ?: return@mapNotNull null
val name = m["name"] as? String ?: return@mapNotNull null
Expand All @@ -211,7 +222,6 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
size = (m["size"] as? Number)?.toLong(),
)
}
}

/**
* #1810 — read a resource's content (`resources/read`). Joins all
Expand All @@ -223,11 +233,7 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
val result = post("resources/read", mapOf("uri" to uri))
val resultMap = result as? Map<*, *>
?: error("resources/read returned non-object: $result")
val contents = resultMap["contents"] as? List<*> ?: emptyList<Any?>()
return contents.mapNotNull { c ->
val m = c as? Map<*, *> ?: return@mapNotNull null
m["text"] as? String
}.joinToString("\n")
return joinTextContent(resultArray(resultMap, "contents"))
}

/**
Expand All @@ -237,30 +243,20 @@ class McpClient internal constructor(private val transport: McpTransport) : Auto
* captured URI. Skill args are ignored — resources are addressed
* by URI, not by call-time parameters.
*/
fun resourceSkills(prefix: String? = null): List<agents_engine.core.Skill<Map<String, Any?>, String>> {
return listResources().map { info ->
val displayName = if (prefix != null) "$prefix.${info.name}" else info.name
agents_engine.core.Skill<Map<String, Any?>, String>(
name = displayName,
fun resourceSkills(prefix: String? = null): List<agents_engine.core.Skill<Map<String, Any?>, String>> =
listResources().map { info ->
makeMcpSkill(
name = prefixed(prefix, info.name),
description = info.description ?: "MCP resource ${info.uri}",
inType = Map::class,
outType = String::class,
).also { skill ->
skill.implementedBy { _ -> readResource(info.uri) }
}
) { _ -> readResource(info.uri) }
}
}

fun call(toolName: String, args: Map<String, Any?>): Any? {
val result = post("tools/call", mapOf("name" to toolName, "arguments" to args))
val resultMap = result as? Map<*, *>
?: error("tools/call returned non-object: $result")
val content = resultMap["content"] as? List<*>
?: error("tools/call result missing 'content' array: $resultMap")
val isError = resultMap["isError"] as? Boolean ?: false
val text = content.mapNotNull { block ->
(block as? Map<*, *>)?.let { it["text"] as? String }
}.joinToString("\n")
val text = joinTextContent(resultArray(result, "content"))
if (isError) error("MCP tool '$toolName' failed: $text")
return text
}
Expand Down
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