How to get the request sent by my computer using tshark - tshark

Question

I ran tshark -V > file.log in my terminal and then in a separate terminal I ran curl 'www.google.com'. I then returned to the first terminal, shut off tshark and then looked at file.log. In it there are a number of 'frames'. For example, here is one of them:
Frame 42: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface en0, id 0
Interface id: 0 (en0)
Interface name: en0
Interface description: Wi-Fi
Encapsulation type: Ethernet (1)
Arrival Time: Nov 3, 2020 17:28:15.022217000 PST
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1604453295.022217000 seconds
[Time delta from previous captured frame: 0.000244000 seconds]
[Time delta from previous displayed frame: 0.000244000 seconds]
[Time since reference or first frame: 12.164253000 seconds]
Frame Number: 42
Frame Length: 66 bytes (528 bits)
Capture Length: 66 bytes (528 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ethertype:ip:tcp]
Ethernet II, Src: *****, Dst: *****
Destination: *****
Address: *****
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Source: Apple_81:82:2f (ac:bc:32:81:82:2f)
Address: Apple_81:82:2f (ac:bc:32:81:82:2f)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Type: IPv4 (0x0800)
Internet Protocol Version 4, Src: *****, Dst: *****
0100 .... = Version: 4
.... 0101 = Header Length: 20 bytes (5)
Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
0000 00.. = Differentiated Services Codepoint: Default (0)
.... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
Total Length: 52
Identification: 0x0000 (0)
Flags: 0x40, Don't fragment
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment Offset: 0
Time to Live: 64
Protocol: TCP (6)
Header Checksum: 0xabe8 [validation disabled]
[Header checksum status: Unverified]
Source Address: 134.87.182.156
Destination Address: 172.217.165.14
Transmission Control Protocol, Src Port: 55888, Dst Port: 80, Seq: 76, Ack: 530, Len: 0
Source Port: 55888
Destination Port: 80
[Stream index: 3]
[TCP Segment Len: 0]
Sequence Number: 76 (relative sequence number)
Sequence Number (raw): 2379446728
[Next Sequence Number: 76 (relative sequence number)]
Acknowledgment Number: 530 (relative ack number)
Acknowledgment number (raw): 278173922
1000 .... = Header Length: 32 bytes (8)
Flags: 0x010 (ACK)
000. .... .... = Reserved: Not set
...0 .... .... = Nonce: Not set
.... 0... .... = Congestion Window Reduced (CWR): Not set
.... .0.. .... = ECN-Echo: Not set
.... ..0. .... = Urgent: Not set
.... ...1 .... = Acknowledgment: Set
.... .... 0... = Push: Not set
.... .... .0.. = Reset: Not set
.... .... ..0. = Syn: Not set
.... .... ...0 = Fin: Not set
[TCP Flags: ·······A····]
Window: 2048
[Calculated window size: 131072]
[Window size scaling factor: 64]
Checksum: 0xc5b6 [unverified]
[Checksum Status: Unverified]
Urgent Pointer: 0
Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
TCP Option - No-Operation (NOP)
Kind: No-Operation (1)
TCP Option - No-Operation (NOP)
Kind: No-Operation (1)
TCP Option - Timestamps: TSval 190086814, TSecr 4203481592
Kind: Time Stamp Option (8)
Length: 10
Timestamp value: 190086814
Timestamp echo reply: 4203481592
[SEQ/ACK analysis]
[This is an ACK to the segment in frame: 41]
[The RTT to ACK the segment was: 0.000244000 seconds]
[iRTT: 0.064637000 seconds]
[Timestamps]
[Time since first frame in this TCP stream: 0.219685000 seconds]
[Time since previous frame in this TCP stream: 0.000244000 seconds]
I think each frame corresponds to a single request sent or received by my computer. I want to know how to reconstruct the exact request sent by my computer to googles server. Additionally, I want to know how to capture whatever was returned by the server.

Answer 1

During the packet capture you can use the -f (capture filter) option to extract only the packets linked to www.google.com
tshark -a duration:10 -T text -V -f "host www.google.com" > capture.txt
I set the -a (autostop) capture option to 10 seconds, because I was only doing the curl 'www.google.com' once.
The command above will capture all TCP and UDP related to the curl request.
If you want to reassemble the connection after a capture you need to create a pcap file during the capture:
# this is capturing all traffic
tshark -a duration:10 -w capture.pcap
You can query this pcap file in multiple ways:
tshark -r capture.pcap -Y http.request -T fields -e http.host -e http.user_agent
# output
www.google.com curl/7.64.1'
tshark -r capture.pcap -Y "(http.host == www.google.com)"
44 1.631029 192.168.86.35 → 64.233.177.105 HTTP 144 GET / HTTP/1.1
tshark -r capture.pcap -Y "dns.qry.name == www.google.com"
#output
36 1.546800 192.168.86.35 → 192.168.86.1 DNS 74 Standard query 0xe159 A www.google.com
39 1.587633 192.168.86.1 → 192.168.86.35 DNS 170 Standard query response 0xe159 A www.google.com A 64.233.177.105 A 64.233.177.104 A 64.233.177.103 A 64.233.177.99 A 64.233.177.147 A 64.233.177.106
# get the frame details for TCP packets associated with google
tshark -r capture.pcap -T fields -e tcp.stream -Y "tcp contains google"
#output frame number(s)
# get the frame details for UDP packets associated with google
tshark -r capture.pcap -T fields -e udp.stream -Y "udp contains google"
# follow the TCP frame
# this should return the curl request for www.google.com
tshark -r capture.pcap -q -z follow,tcp,ascii,frame_number
# follow the UDP frame
tshark -r capture.pcap -q -z follow,udp,ascii,frame_number
Hopefully, this answer helps solve your question.