mcpcap

Instructions

Implementation Reference

• src/mcpcap/modules/capinfos.py:20-39 (handler)

  The primary handler function for the 'analyze_capinfos' tool. It delegates to analyze_packets for processing local or remote PCAP files.

  def analyze_capinfos(self, pcap_file: str) -> dict[str, Any]:
      """
      Return metadata from a PCAP file, similar to Wireshark's capinfos utility.
  
      IMPORTANT: This tool expects a FILE PATH or URL, not file content.
      - For local files: "/path/to/capture.pcap"
      - For remote files: "https://example.com/capture.pcap"
      - File uploads are NOT supported - save the file locally first
  
      Args:
          pcap_file: Path to local PCAP file or HTTP URL to remote PCAP file
                    (NOT file content - must be a path or URL)
  
      Returns:
          A structured dictionary containing PCAP metadata including:
          - File information (size, name, encapsulation type)
          - Packet statistics (count, data size, average sizes)
          - Temporal data (duration, timestamps, rates)
      """
      return self.analyze_packets(pcap_file)

• src/mcpcap/core/server.py:56-57 (registration)

  Registration of the analyze_capinfos tool with the FastMCP server instance.

  elif module_name == "capinfos":
      self.mcp.tool(module.analyze_capinfos)

• src/mcpcap/modules/capinfos.py:41-62 (helper)

  Implements the core PCAP analysis logic specific to capinfos, reading packets with rdpcap, generating stats, and collecting file metadata.

  def _analyze_protocol_file(self, pcap_file: str) -> dict[str, Any]:
      """Perform the actual information gathering on a local PCAP file."""
      try:
          packets = rdpcap(pcap_file)
  
          # Generate statistics
          stats = self._generate_statistics(packets)
  
          results = {
              "file_size_bytes": os.path.getsize(pcap_file),
              "filename": os.path.basename(pcap_file),
              "file_encapsulation": self._detect_linktype(pcap_file),
          }
  
          return results | stats
  
      except Exception as e:
          return {
              "error": f"Error reading PCAP file '{pcap_file}': {str(e)}",
              "file": pcap_file,
          }

• src/mcpcap/modules/capinfos.py:63-92 (helper)

  Helper function to detect and map the PCAP linktype (encapsulation type) to a human-readable name.

  def _detect_linktype(self, path: str) -> str:
      """Detect the linktype and try to map it to a human-readable encapsulation type.
  
      Args:
          path: Path to the packet capture
  
      Returns:
          Detected link-layer header (linktype)
  
      """
      # mapping based on pcap-linktype(7) and https://github.com/wireshark/wireshark/blob/master/wiretap/wtap.c#L656
      LINKTYPE_MAP = {
          1: "Ethernet",
          101: "Raw IP",
          105: "IEEE 802.11 Wireless LAN",
          113: "Linux cooked-mode capture v1",
          228: "Raw IPv4",
          229: "Raw IPv6",
          276: "Linux cooked-mode capture v2",
      }
      try:
          with PcapReader(path) as reader:
              linktype = getattr(reader, "linktype", None)
      except Exception:
          linktype = None
  
      return LINKTYPE_MAP.get(
          linktype, f"Unknown ({linktype})" if linktype else "Unknown"
      )

• src/mcpcap/modules/capinfos.py:93-119 (helper)

  Helper function to compute packet statistics like count, sizes, rates, and timestamps from packet list.

  def _generate_statistics(self, packet_details: list) -> dict[str, Any]:
      """Return metadata about the capture file, similar to capinfos(1) utility."""
      if not packet_details:
          return {"error": "No packets found"}
  
      packet_count = len(packet_details)
      data_size = sum(len(pkt) for pkt in packet_details)
      first_time = float(packet_details[0].time)
      last_time = float(packet_details[-1].time)
      duration = max(last_time - first_time, 0.000001)
      data_byte_rate = data_size / duration if duration > 0 else 0
      data_bit_rate = (data_size * 8) / duration if duration > 0 else 0
      avg_packet_size = data_size / packet_count if packet_count > 0 else 0
      avg_packet_rate = packet_count / duration if duration > 0 else 0
  
      return {
          "packet_count": packet_count,
          "data_size_bytes": data_size,
          "capture_duration_seconds": duration,
          "first_packet_time": first_time,
          "last_packet_time": last_time,
          "data_rate_bytes": data_byte_rate,
          "data_rate_bits": data_bit_rate,
          "average_packet_size_bytes": avg_packet_size,
          "average_packet_rate": avg_packet_rate,
      }

• src/mcpcap/modules/base.py:43-57 (helper)

  Base class helper method dispatched by the handler; handles local/remote PCAP files and calls protocol-specific analysis.

  def analyze_packets(self, pcap_file: str) -> dict[str, Any]:
      """Analyze packets from a PCAP file (local or remote).
  
      Args:
          pcap_file: Path to local PCAP file or HTTP URL to remote PCAP file
  
      Returns:
          A structured dictionary containing packet analysis results
      """
      # Check if this is a remote URL or local file
      if pcap_file.startswith(("http://", "https://")):
          return self._handle_remote_analysis(pcap_file)
      else:
          return self._handle_local_analysis(pcap_file)