http_monitor

#!/bin/sh

# http_monitor
#
# HTTP monitor test
# Continuously probe given address:port destinations using given HTTP request.
# Checks the response using the given regex (resp_regex) like in F5 HTTP monitor.

# TODO
# - check exact response matching on F5
# - add CLI arguments and/or config file

destinations='10.60.1.41:9080 10.60.1.42:9080'

# printf formatted request
# shellcheck disable=SC2016  # Characters $ are part of the string.
request='GET /IBS/blank.htm HTTP/1.1\r\n$WSSN: ibs.q-bank.loc\r\n$WSSP: 443\r\n$WSIS: true\r\nConnection: close\r\n\r\n'
resp_regex='^HTTP/1.1\s[2-3]'

interval=1
log_file=http_monitor.log

resp_file=tmp-resp.txt
ncat_out_file=tmp-ncat-out.txt

ncat='nc'
prog_name=http_monitor

# ---

handle_req () {
    dst_ip="${1%:*}"
    dst_port="${1##*:}"
    # shellcheck disable=SC2059  # $request uses printf escape sequences
    printf "$request" | "$ncat" -v "$dst_ip" "$dst_port" >"$resp_file" 2>"$ncat_out_file"
}

test_resp () {
    grep -Eq "$resp_regex" "$resp_file"
}

cleanup () {
    date +"%FT%T --- Stopping $prog_name, probes: $probes, ncat errors: $ncat_errs, response errors: $resp_errs" | tee -a "$log_file"
    trap - EXIT HUP INT
    exit 0
}

probes=1
ncat_errs=0
resp_errs=0
trap cleanup EXIT HUP INT

date +"%FT%T --- Starting $prog_name, targets: $destinations, interval: $interval s" |
    tee -a "$log_file"
while true ; do
    printf '%d\r' "$probes"
    for dst in $destinations ; do
        if ! handle_req "$dst" ; then
            # sending the request failed
            date +"%FT%T Failed sending the request to $dst, netcat output:" | tee -a "$log_file"
            tee -a "$log_file" <"$ncat_out_file"
            ncat_errs=$((ncat_errs + 1))
        else
            if ! test_resp ; then
                # the response did not match
                date +"%FT%T Failed test response from $dst follows" | tee -a "$log_file"
                tee -a "$log_file" <"$resp_file"
                printf '%s\n' '------ response end ------' | tee -a "$log_file"
                resp_errs=$((resp_errs + 1))
            fi
        fi
    done
    probes=$((probes + 1))
    sleep "$interval"
done