Class: Aspera::Cli::McpTool

Inherits:
MCP::Tool
  • Object
show all
Defined in:
lib/aspera/cli/mcp_tool.rb

Overview

MCP Tool: executes an ascli command in-process.

Constant Summary collapse

DEFAULT_MAX_TEXT_BYTES =

Default maximum byte size of the JSON text content returned for list results. Items are appended whole until the limit is reached; the full list is always available in structuredContent.

100_000
DEFAULT_EXTRA_ARGS =

Default extra arguments automatically prepended to every ascli call. Keeps the AI from having to remember mandatory flags on every invocation.

['--interactive=no', '--transfer.asynchronous=true'].freeze

Class Attribute Summary collapse

Class Method Summary collapse

Class Attribute Details

.extra_args ⇒ Object

Returns the value of attribute extra_args.



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# File 'lib/aspera/cli/mcp_tool.rb', line 144

def extra_args
  @extra_args
end

.max_text_bytes ⇒ Object

Returns the value of attribute max_text_bytes.



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# File 'lib/aspera/cli/mcp_tool.rb', line 144

def max_text_bytes
  @max_text_bytes
end

Class Method Details

.call(args:, server_context: nil) ⇒ Object 



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# File 'lib/aspera/cli/mcp_tool.rb', line 146

def call(args:, server_context: nil)
  effective_args = Array(extra_args || DEFAULT_EXTRA_ARGS) + args
  Log.dump(:mcp_execute, effective_args)
  runner = Runner.new(effective_args)
  result = runner.run_with_result
  case result
  when Result::Nothing, Result::Empty, NilClass
    MCP::Tool::Response.new([{type: 'text', text: ''}])
  when Result::SingleObject, Result::ObjectList, Result::ValueList
    # Apply --select filter in place (affects both text and structuredContent).
    runner.context.formatter.filter_columns_on_select(result.data) if result.data.is_a?(Array)
    # MCP spec requires structuredContent to be a JSON object (not an array).
    structured = result.data.is_a?(Array) ? {items: result.data} : result.data
    content = if result.data.is_a?(Array)
      text_limit = max_text_bytes || DEFAULT_MAX_TEXT_BYTES
      truncated_items = truncate_items_by_bytes(result.data, text_limit)
      total = result.data.size
      if truncated_items.size < total
        [
          {type: 'text', text: JSON.generate(truncated_items)},
          {type: 'text', text: "WARNING: result truncated to #{truncated_items.size} of #{total} items. Full dataset available in structuredContent."}
        ]
      else
        [{type: 'text', text: JSON.generate(result.data)}]
      end
    else
      [{type: 'text', text: JSON.generate(result.data)}]
    end
    MCP::Tool::Response.new(content, structured_content: structured)
  else
    MCP::Tool::Response.new([{type: 'text', text: result.data.to_s}])
  end
rescue SystemExit => e
  MCP::Tool::Response.new([{type: 'text', text: "exited with status #{e.status}"}], error: !e.status.zero?)
rescue => e
  MCP::Tool::Response.new([{type: 'text', text: "#{e.class}: #{e.message}"}], error: true)
end

.truncate_items_by_bytes(items, max_bytes) ⇒ Object

Returns the largest prefix of items whose JSON serialization fits within max_bytes. Items are appended whole — no item is ever split mid-JSON.



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# File 'lib/aspera/cli/mcp_tool.rb', line 186

def truncate_items_by_bytes(items, max_bytes)
  buf = +''
  items.each_with_index do |item, i|
    fragment = (i.zero? ? '[' : ',') + JSON.generate(item)
    break if buf.bytesize + fragment.bytesize + 1 > max_bytes # +1 for closing ']'
    buf << fragment
  end
  buf.empty? ? [] : JSON.parse("#{buf}]")
end