feat: implement pcap global header parsing

Author: devbyjitendra

src/main.py

@@ -1,20 +1,46 @@
 import sys
+import click
 from rich.console import Console
 from rich.panel import Panel
+from rich.table import Table
+from pcap_reader import PcapReader
 
 console = Console()
 
-def main():
+@click.command()
+@click.argument('filepath', required=False)
+def main(filepath):
     welcome_message = Panel.fit(
         "[bold blue]WireSpectra DPI Engine[/bold blue]\n"
         "[white]System Initialized[/white]",
         border_style="bright_magenta"
     )
     console.print(welcome_message)
-    
-    console.print(f"[green]✔[/green] Python {sys.version.split()[0]} detected.")
-    console.print("[yellow]![/yellow] Initializing project modules...")
-    console.print("[green]✔[/green] Project structure ready.")
+
+    if not filepath:
+        console.print("[yellow]Usage: python src/main.py <path_to_pcap>[/yellow]")
+        return
+
+    reader = PcapReader()
+    try:
+        console.print(f"[*] Opening file: [cyan]{filepath}[/cyan]...")
+        reader.open(filepath)
+        
+        # Display Header Information in a nice table
+        table = Table(title="PCAP Global Header")
+        table.add_column("Field", style="cyan")
+        table.add_column("Value", style="green")
+        
+        table.add_row("Magic Number", hex(reader.magic_number))
+        table.add_row("Version", f"{reader.version_major}.{reader.version_minor}")
+        table.add_row("Snap Length", str(reader.snaplen))
+        table.add_row("Network Type", "Ethernet (1)" if reader.network == 1 else str(reader.network))
+        
+        console.print(table)
+        reader.close()
+        
+    except Exception as e:
+        console.print(f"[bold red]Error:[/bold red] {str(e)}")
 
 if __name__ == "__main__":
     main()

src/pcap_reader.py

@@ -0,0 +1,56 @@
+import struct
+import os
+
+class PcapReader:
+    def __init__(self):
+        self.file = None
+        self.magic_number = None
+        self.version_major = None
+        self.version_minor = None
+        self.snaplen = None
+        self.network = None
+
+    def open(self, filepath: str):
+        """
+        Opens a PCAP file and parses the 24-byte global header.
+        """
+        if not os.path.exists(filepath):
+            raise FileNotFoundError(f"File not found: {filepath}")
+
+        self.file = open(filepath, 'rb')
+        
+        # PCAP Global Header is exactly 24 bytes
+        header_data = self.file.read(24)
+        if len(header_data) < 24:
+            self.file.close()
+            raise ValueError("Invalid PCAP file: Global header too short")
+
+        # Unpack the 24 bytes using struct
+        # I: uint32, H: uint16
+        # < for little-endian (standard PCAP)
+        (
+            self.magic_number,
+            self.version_major,
+            self.version_minor,
+            self.thiszone,     # GMT to local correction (ignored)
+            self.sigfigs,      # Accuracy of timestamps (ignored)
+            self.snaplen,      # Max length of captured packets
+            self.network       # Data link type (1 = Ethernet)
+        ) = struct.unpack('<IHHIIII', header_data)
+
+        # Verify magic number (0xa1b2c3d4 is standard PCAP)
+        if self.magic_number != 0xa1b2c3d4:
+            # Check for big-endian version
+            if self.magic_number == 0xd4c3b2a1:
+                raise ValueError("Big-endian PCAP files not supported yet")
+            raise ValueError(f"Not a valid PCAP file. Magic: {hex(self.magic_number)}")
+
+        return True
+
+    def close(self):
+        if self.file:
+            self.file.close()
+
+    def __repr__(self):
+        return (f"PcapReader(Version={self.version_major}.{self.version_minor}, "
+                f"Snaplen={self.snaplen}, Network={self.network})")