add FALLBACK_IP_TLS explanation and bash example
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243
docs/fallback-ip-curl-example.sh
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243
docs/fallback-ip-curl-example.sh
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#!/usr/bin/env bash
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set -u
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usage() {
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cat <<'USAGE'
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Usage:
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bash docs/fallback-ip-curl-example.sh --base-url URL --fallback-ip IP [options]
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Required:
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--base-url URL Server root URL, for example https://monitor.example.com
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--fallback-ip IP Fallback address for the URL host. Can be repeated.
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--fallback-ips "LIST" Comma or space separated fallback addresses.
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Options:
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--endpoint PATH Monitor endpoint path. Default: /monitor/api
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--token TOKEN Send TOKEN as X-Monitor-Token.
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--basic-auth USER:PASS Send HTTP Basic Auth credentials.
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--connect-timeout SEC Curl connection timeout. Default: 8
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--max-time SEC Curl total request timeout. Default: 20
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-h, --help Show this help.
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Example:
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bash docs/fallback-ip-curl-example.sh \
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--base-url https://monitor.example.com \
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--fallback-ip 192.168.1.20 \
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--fallback-ip 10.0.0.5 \
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--token secret
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The fallback keeps the URL host as monitor.example.com and only overrides DNS
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with curl --resolve. For HTTPS, curl still sends SNI for that host and verifies
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the certificate against that host.
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USAGE
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}
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die() {
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printf '%s\n' "$1" >&2
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printf '\n' >&2
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usage >&2
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exit 2
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}
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add_fallback_ips() {
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local values ip
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values="${1//,/ }"
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for ip in $values; do
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fallback_list+=("$ip")
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done
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}
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base_url=""
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endpoint="/monitor/api"
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token=""
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basic_auth=""
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connect_timeout="8"
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max_time="20"
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fallback_list=()
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while (($# > 0)); do
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case "$1" in
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--base-url)
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(($# >= 2)) || die "--base-url requires a value"
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base_url="$2"
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shift 2
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;;
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--base-url=*)
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base_url="${1#*=}"
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shift
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;;
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--fallback-ip)
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(($# >= 2)) || die "--fallback-ip requires a value"
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add_fallback_ips "$2"
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shift 2
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;;
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--fallback-ip=*)
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add_fallback_ips "${1#*=}"
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shift
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;;
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--fallback-ips)
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(($# >= 2)) || die "--fallback-ips requires a value"
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add_fallback_ips "$2"
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shift 2
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;;
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--fallback-ips=*)
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add_fallback_ips "${1#*=}"
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shift
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;;
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--endpoint)
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(($# >= 2)) || die "--endpoint requires a value"
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endpoint="$2"
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shift 2
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;;
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--endpoint=*)
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endpoint="${1#*=}"
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shift
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;;
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--token)
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(($# >= 2)) || die "--token requires a value"
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token="$2"
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shift 2
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;;
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--token=*)
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token="${1#*=}"
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shift
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;;
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--basic-auth)
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(($# >= 2)) || die "--basic-auth requires a value"
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basic_auth="$2"
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shift 2
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;;
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--basic-auth=*)
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basic_auth="${1#*=}"
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shift
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;;
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--connect-timeout)
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(($# >= 2)) || die "--connect-timeout requires a value"
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connect_timeout="$2"
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shift 2
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;;
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--connect-timeout=*)
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connect_timeout="${1#*=}"
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shift
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;;
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--max-time)
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(($# >= 2)) || die "--max-time requires a value"
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max_time="$2"
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shift 2
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;;
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--max-time=*)
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max_time="${1#*=}"
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shift
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;;
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-h|--help)
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usage
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exit 0
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;;
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*)
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die "Unknown argument: $1"
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;;
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esac
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done
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[[ -n "$base_url" ]] || die "--base-url is required"
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((${#fallback_list[@]} > 0)) || die "At least one --fallback-ip or --fallback-ips value is required"
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base_url="${base_url%/}"
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[[ "$endpoint" == /* ]] || endpoint="/$endpoint"
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url="${base_url}${endpoint}"
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if [[ "$base_url" =~ ^([A-Za-z][A-Za-z0-9+.-]*)://([^/]+) ]]; then
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scheme="${BASH_REMATCH[1]}"
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authority="${BASH_REMATCH[2]}"
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else
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die "--base-url must be an http or https URL"
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fi
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if [[ "$authority" == *"@"* ]]; then
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die "Put Basic Auth in --basic-auth USER:PASS, not in the URL"
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fi
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if [[ "$authority" =~ ^\[([^]]+)\](:([0-9]+))?$ ]]; then
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host="${BASH_REMATCH[1]}"
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port="${BASH_REMATCH[3]:-}"
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elif [[ "$authority" =~ ^([^:]+)(:([0-9]+))?$ ]]; then
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host="${BASH_REMATCH[1]}"
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port="${BASH_REMATCH[3]:-}"
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else
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die "Could not parse host and port from $authority"
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fi
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case "$scheme" in
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[Hh][Tt][Tt][Pp][Ss]) port="${port:-443}" ;;
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[Hh][Tt][Tt][Pp]) port="${port:-80}" ;;
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*) die "Only http and https URLs are supported" ;;
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esac
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curl_args=(
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--silent
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--show-error
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--location
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--connect-timeout "$connect_timeout"
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--max-time "$max_time"
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--header "Accept: application/json"
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)
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if [[ -n "$token" ]]; then
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curl_args+=(--header "X-Monitor-Token: $token")
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fi
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if [[ -n "$basic_auth" ]]; then
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curl_args+=(--user "$basic_auth")
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fi
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request_once() {
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local body_file http_code rc
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body_file="$(mktemp)"
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http_code="$(curl "${curl_args[@]}" "$@" --output "$body_file" --write-out '%{http_code}' "$url")"
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rc=$?
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if ((rc != 0)); then
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rm -f "$body_file"
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return "$rc"
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fi
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cat "$body_file"
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rm -f "$body_file"
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if [[ "$http_code" == 2* ]]; then
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return 0
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fi
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printf '\nHTTP %s from monitor endpoint\n' "$http_code" >&2
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return 22
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}
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printf 'Trying normal DNS for %s\n' "$host" >&2
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if request_once; then
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exit 0
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fi
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rc=$?
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if ((rc == 22)); then
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exit "$rc"
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fi
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printf 'Normal request failed before a usable HTTP response; trying fallback IPs\n' >&2
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last_rc="$rc"
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for ip in "${fallback_list[@]}"; do
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[[ -n "$ip" ]] || continue
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resolve_ip="$ip"
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if [[ "$resolve_ip" == *:* && "$resolve_ip" != \[*\] ]]; then
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resolve_ip="[$resolve_ip]"
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fi
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printf 'Trying %s via --resolve %s:%s:%s\n' "$ip" "$host" "$port" "$resolve_ip" >&2
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if request_once --resolve "${host}:${port}:${resolve_ip}"; then
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exit 0
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fi
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last_rc=$?
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done
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exit "$last_rc"
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