@azure/functions/src/converters/toMcpPromptTriggerOptionsToRpc.ts

Microsoft Azure Functions NodeJS Framework

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the MIT License.

import {
    McpPromptArgument,
    McpPromptArguments,
    McpPromptTriggerOptions,
    McpPromptTriggerOptionsToRpc,
} from '../../types/mcpPrompt';
import { McpPromptArgumentBuilder } from '../mcp/McpPromptArgumentBuilder';

/**
 * Converts an {@link McpPromptTriggerOptions} object to the wire-format
 * {@link McpPromptTriggerOptionsToRpc} the Functions host expects.
 *
 * - `promptName` is required.
 * - `promptArguments` is serialized to a compact JSON string (always present on the wire).
 * - `metadata` and `icons` are validated as JSON strings when supplied.
 */
export function convertToMcpPromptTriggerOptionsToRpc(options: McpPromptTriggerOptions): McpPromptTriggerOptionsToRpc {
    if (!options.promptName || typeof options.promptName !== 'string' || options.promptName.trim() === '') {
        throw new Error('MCP Prompt trigger requires a valid "promptName" property.');
    }

    const promptArgumentsJson = serializePromptArguments(options.promptArguments);

    const result: McpPromptTriggerOptionsToRpc = {
        promptName: options.promptName,
        promptArguments: promptArgumentsJson,
    };

    if (options.title !== undefined) {
        result.title = options.title;
    }

    if (options.description !== undefined) {
        result.description = options.description;
    }

    if (options.metadata !== undefined && typeof options.metadata === 'string' && options.metadata.trim() !== '') {
        try {
            JSON.parse(options.metadata);
        } catch {
            throw new Error('MCP Prompt trigger "metadata" must be a valid JSON string.');
        }
        result.metadata = options.metadata;
    }

    if (options.icons !== undefined && typeof options.icons === 'string' && options.icons.trim() !== '') {
        try {
            JSON.parse(options.icons);
        } catch {
            throw new Error('MCP Prompt trigger "icons" must be a valid JSON string.');
        }
        result.icons = options.icons;
    }

    return result;
}

function serializePromptArguments(args: McpPromptArguments | undefined): string {
    if (!args) {
        return '[]';
    }

    const list: McpPromptArgument[] = Array.isArray(args)
        ? args
        : Object.entries(args).map(([name, builder]) => {
              if (!(builder instanceof McpPromptArgumentBuilder)) {
                  throw new Error(
                      'MCP Prompt trigger "promptArguments" record values must be created with `promptArg.describe(...)`.'
                  );
              }
              return builder.toPromptArgument(name);
          });

    if (list.length === 0) {
        return '[]';
    }

    const normalized = list.map((a) => {
        if (!a.name || typeof a.name !== 'string' || a.name.trim() === '') {
            throw new Error('MCP Prompt trigger "promptArguments" entries require a non-empty "name".');
        }
        return {
            name: a.name,
            description: a.description ?? null,
            required: a.required === true,
        };
    });

    return JSON.stringify(normalized);
}