gRPC - raw requests

gRPC uses HTTP2 as based transport. The protocol is available here.

Capturing gRPC request with Wireshark

Here are steps to capture request:

run Wireshark and select an interface to capture traffic
run both gRPC server and client
trigger request in client
find packets sent in HTTP2 protocol that are identified as Magic, SETTINGS, HEADERS and DATA.
copy streams in these packets as a Hex Stream

Remember to choose a proper interface - select Loopback: lo0 for local server, tunnel interface (e.g. utun1) for server with VPN access, or Wi-Fi: en0 for server with public access.

If you don’t see packets in HTTP2 protocol, click “Analyze” -> “Decode As…”. Then, add TCP port X with HTTP2 protocol, where X is port of gRPC server (e.g. 8083).

wireshark

After the process you should have required data in hex:

Magic 505249202a20485454502f322e300d0a0d0a534d0d0a0d0a

SETTINGS 000000040000000000

HEADERS 0000570104000000018386458e629f43accbe8f50ebc8c632d141f418aa0e41d139d09b8f01e675f8b1d75d0620d263d4c4d65647a8d9acac8b4c7602bb6b81690bdff40027465864d833505b11f40899acac8b24d494f6a7f867df7df79d6ed

DATA 00000c00010000000100000000070a05576f726c64

Sending gRPC request

You can use many different tools to send a gRPC request as a client.

Node.js

var net = require('net');

var client = new net.Socket();

client.connect(8080, 'localhost', function() {
	console.log('Connected to server');

	var magic = new Buffer("505249202a20485454502f322e300d0a0d0a534d0d0a0d0a", "hex");
	client.write(magic);

	var settings = new Buffer("000000040000000000", "hex");
	client.write(settings);

	var headers = new Buffer("0000550104000000018386458c62919aa5e1d7918c65a283ff418aa0e41d139d09b8f01e075f8b1d75d0620d263d4c4d65647a8d9acac8b4c7602bb6b81690bdff40027465864d833505b11f40899acac8b24d494f6a7f867df7dd6dd7ad", "hex");
	client.write(headers);

	var data = new Buffer("00000c00010000000100000000070a05576f726c64", "hex");
	client.write(data);

});

client.on('data', function(data) {
	console.log('Received:\n' + data);
});

client.on('close', function() {
	console.log('Connection closed');
});

Go

package main

import (
	"encoding/hex"
	"fmt"
	"net"
	"os"
)

const APIURL = "localhost:8080"

func main() {
	conn, err := net.Dial("tcp", APIURL)
	if err != nil {
		fmt.Printf("Error: connect to server: %s\n", err)
		os.Exit(1)
	}

	magic := "505249202a20485454502f322e300d0a0d0a534d0d0a0d0a"
	settings := "000000040000000000"
	headers := "0000550104000000018386458c62919aa5e1d7918c65a283ff418aa0e41d139d09b8f01e075f8b1d75d0620d263d4c4d65647a8d9acac8b4c7602bb6b81690bdff40027465864d833505b11f40899acac8b24d494f6a7f867df7dd6dd7ad"
	data := "00000c00010000000100000000070a05576f726c64"

	packets := []string{magic, settings, headers, data}

	for _, p := range packets {
		raw, err := hex.DecodeString(p)
		if err != nil {
			fmt.Printf("Error: cannot decode hex string: %s\n", err)
			os.Exit(1)
		}

		if _, err := conn.Write(raw); err != nil {
			fmt.Printf("Error: cannot decode hex string: %s\n", err)
			os.Exit(1)
		}
	}

	buf := make([]byte, 1024)

	fmt.Print("Info: received:\n")

	for {
		n, err := conn.Read(buf)
		if err != nil {
			fmt.Printf("Error: cannot read from socket: %s\n", err)
			os.Exit(1)
		}
		fmt.Print(string(buf[:n]))
	}
}

netcat command

$ (echo -e "\x50\x52\x49\x20\x2a\x20\x48\x54\x54\x50\x2f\x32\x2e\x30\x0d\x0a\x0d\x0a\x53\x4d\x0d\x0a\x0d\x0a\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x55\x01\x04\x00\x00\x00\x01\x83\x86\x45\x8c\x62\x91\x9a\xa5\xe1\xd7\x91\x8c\x65\xa2\x83\xff\x41\x8a\xa0\xe4\x1d\x13\x9d\x09\xb8\xf0\x1e\x07\x5f\x8b\x1d\x75\xd0\x62\x0d\x26\x3d\x4c\x4d\x65\x64\x7a\x8d\x9a\xca\xc8\xb4\xc7\x60\x2b\xb6\xb8\x16\x90\xbd\xff\x40\x02\x74\x65\x86\x4d\x83\x35\x05\xb1\x1f\x40\x89\x9a\xca\xc8\xb2\x4d\x49\x4f\x6a\x7f\x86\x7d\xf7\xdd\x6d\xd7\xad\x00\x00\x0c\x00\x01\x00\x00\x00\x01\x00\x00\x00\x00\x07\x0a\x05\x57\x6f\x72\x6c\x64"; sleep 1) | nc localhost 8081

Sources:

http://www.juhonkoti.net/2015/11/26/using-haproxy-to-do-health-checks-to-grpc-services
https://linux.die.net/man/1/nc
https://njp.io/grpcc-a-simple-command-line-client-for-grpc-services/