shecan.ir configurator.

configure_dns.sh

#! /bin/bash -e

#####################################################
#                  DNS configurator                 #
#####################################################

# Responds to a list of syscall.
trap "error 'Exiting now...'" SIGINT SIGQUIT

# CLI options (IRREPLACEABLE).
readonly bold=`tput bold`
readonly reset=`tput sgr0`
readonly red=`tput setaf 1`
readonly blue=`tput setaf 4`
readonly cyan=`tput setaf 6`
readonly grey=`tput setaf 8`

# Prints out a given message.
# Arguments:
#   $1 - Message to print
#   $2 - Optional flag to determine if the message should be suffixed with \r
function out {
    if [[ $2 ]]; then
        echo -ne "${1}\r"
    else
        echo -ne "${1}\n"
    fi
}

# Modifies a success message.
# Arguments:
#   $1 - Success message
#   $2 - Optional flag to determine if the message should be prefixed
#   $3 - Optional flag for line ending
function success {
    local prefix='[+] '

    if [[ $2 ]]; then
        msg="${cyan}${bold}${prefix}${reset}${blue}${1}${reset}"
    else
        msg="${blue}${1}${reset}"
    fi

    out "$msg" $3 >> /dev/stdout
}

# Modifies an info message.
# Arguments:
#   $1 - Info message
#   $2 - Optional flag to determine if the message should be prefixed
#   $3 - Optional flag for line ending
function info {
    local prefix='[*] '

    if [[ $2 ]]; then
        msg="${cyan}${bold}${prefix}${reset}${grey}${1}${reset}"
    else
        msg="${grey}${1}${reset}"
    fi

    out "$msg" $3 >> /dev/stdout
}

# Modifies an error message.
# Arguments:
#   $1 - Error message
#   $2 - Optional flag to determine if the message should be prefixed
#   $3 - Optional flag for line ending
function error {
    local prefix='[-] '

    if [[ $2 ]]; then
        msg="${cyan}${bold}${prefix}${reset}${red}${1}${reset}"
    else
        msg="${red}${1}${reset}"
    fi

    out "$msg" $3 >> /dev/stderr \
    && exit 1
}

# Prints out the usage guide of this script.
function usage {
    echo -e "Usage: $0 OPTION ARGUMENT [OPTION ARGUMENT]...
    -a\tRead configurations from specified address.
    -f\tChoose file to extract configurations from.
    -i\tSpecify hook to extract configurations with.
    -m\tChange application flow. [${FLOW_ADD}, ${FLOW_REMOVE}, ${FLOW_UPDATE}, ${FLOW_STATUS}]" >> /dev/stdout
}

# Makes print functions irreplaceable.
readonly -f usage success error info out

# RegEx pattern for validating IPv4. (IRREPLACEABLE)
readonly ipRegEx="((1?[0-9][0-9]?|2[0-4][0-9]|25[0-5])\.){3}(1?[0-9][0-9]?|2[0-4][0-9]|25[0-5])"

# Default path to DNS configurations.
readonly configFilePath="/etc/resolv.conf"

# DNS configurator's identifier. (IRREPLACEABLE)
readonly appFlag='#DNS_CONFIGURATOR'

# Key for configuring a DNS.
readonly configKey="nameserver"

# This section holds keys of application's flow.
#    status: Checks if any configurations are already applied by this script.
#    update: Removes old configurations and adds new configurations.
#    remove: Removes old configurations.
#    add:    Adds new configurations.
readonly FLOW_STATUS="status"
readonly FLOW_UPDATE="update"
readonly FLOW_REMOVE="remove"
readonly FLOW_ADD="add"

# This section holds keys of application's source of configurations.
#    file: Reads configurations from file.
#    url:  Extracts configurations from url.
readonly SOURCE_FILE="file"
readonly SOURCE_URL="url"

# Default url to get DNS configurations from.
url='https://shecan.ir'

# Default hook for catching DNS configurations.
hook='shecan-dns-ips'

# Default application's source form extracting configurations.
configSource=$SOURCE_URL

# Default application flow.
flow=$FLOW_ADD

# Gets the program's source of configurations based on input.
# Arguments:
#   $1 - Source value (URL or file path)
#   $2 - Source type (file or URL)
function getSource {
    configSource=$2

    if [[ $configSource == $SOURCE_FILE ]]; then
        configFile=$1
    elif [[ $configSource == $SOURCE_URL ]]; then
        url=$1
    fi
}

# Gets the program's flow based on input.
# Arguments:
#   $1 - Flow value (add, remove, update, status)
function getFlow {
    if grep -qE "\b(${FLOW_ADD}|${FLOW_REMOVE}|${FLOW_UPDATE}|${FLOW_STATUS})\b" <<< $1; then
        flow=$1
    else
        usage; exit 1
    fi
}

# Writes given addresses to the local DNS configuration file.
# Arguments:
#   $@ - List of DNS addresses
function write {
    for address in $@; do
        if ! grep -Exq "${configKey}\s+${address}\s+${appFlag}$" $configFilePath; then
            sudo sed -i "$(grep -n "${configKey}" ${configFilePath} | cut -f 1 -d ':' | head -n 1)i\\${configKey} ${address}  \\t${appFlag}" $configFilePath
        fi
    done
}

# Removes old DNS configurations from local DNS configuration file. (Identifies old configurations with app flag)
function remove {
    sudo sed -i "/${appFlag}$/d" $configFilePath
}

# Makes managing functions irreplaceable.
readonly -f getSource getFlow write remove

# Gets arguments from input.
while getopts "a:f:i:m:h" arg; do
    case $arg in
        a )
            getSource $OPTARG $SOURCE_URL
            ;;
        f )
            getSource $OPTARG $SOURCE_FILE
            ;;
        i )
            hook=$OPTARG
            ;;
        m )
            getFlow $OPTARG
            ;;
        h )
            usage; exit
            ;;
        * )
            usage; exit 1
            ;;
    esac
done

# Checks if the chosen flow requires removing old configurations.
if [[ $flow == $FLOW_UPDATE || $flow == $FLOW_REMOVE ]]; then
    { # This section removes old configurations from local DNS configuration file.
        remove \
        && success "Old configurations have been removed." true
    } || {
        error "Error on removing old configuration files." true
    }

    # If the flow is 'off' the application needs to be terminated.
    if [[ $flow == $FLOW_REMOVE ]]; then
        info "All configurations has been removed."; exit
    fi
elif [[ $flow == $FLOW_STATUS ]]; then
    if grep -Fq "${appFlag}" "${configFilePath}"; then
        info "Configurations are ${blue}active${reset}."; exit
    else
        info "Configurations are ${red}inactive${reset}."; exit
    fi
fi

# This section is responsible for chosing the source of configurations [URL, FILE].
if [[ $configSource == $SOURCE_FILE ]]; then
    { # This section fetches payload from FILE.
        info "Reading file..." true true \
        && payload=$(cat $configFile) \
        && success "File has been read." true
    } || {
        error "Error on reading file." true
    }
elif [[ $configSource == $SOURCE_URL ]]; then
    { # This section fetches payload from URL.
        info "Fetching payload..." true true \
        && payload=$(curl -sX GET ${url} | grep ${hook}) \
        && success "Payload has been fetched." true
    } || {
        error "Error on fetching payload." true
    }
fi

{ # This section extracts DNS configurations from payload.
    info "Extracting configurations..." true true \
    && addresses=$(grep -oE ${ipRegEx} <<< ${payload}) \
    && success "Configurations have been extracted." true
} || {
    error "Error on extracting configurations." true
}

{ # This section writes new configurations to the local DNS configuration file.
    write $addresses \
    && success "Local DNS configuration file has been updated." true
} || {
    error "Error on editing local DNS configuration file." true
}

info "Enjoy your freedom :)"