Rewrite of the entrypoint in Golang (#71)

- General improvements
    - Parallel download of only needed files at start
    - Prettier console output with all streams merged (openvpn, unbound, shadowsocks etc.)
    - Simplified Docker final image
    - Faster bootup
- DNS over TLS
    - Finer grain blocking at DNS level: malicious, ads and surveillance
    - Choose your DNS over TLS providers
    - Ability to use multiple DNS over TLS providers for DNS split horizon
    - Environment variables for DNS logging
    - DNS block lists needed are downloaded and built automatically at start, in parallel
- PIA
    - A random region is selected if the REGION parameter is left empty (thanks @rorph for your PR)
    - Routing and iptables adjusted so it can work as a Kubernetes pod sidecar (thanks @rorph for your PR)

internal/settings/dns.go

@@ -0,0 +1,108 @@
+package settings
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/models"
+	"github.com/qdm12/private-internet-access-docker/internal/params"
+)
+
+// DNS contains settings to configure Unbound for DNS over TLS operation
+type DNS struct {
+	Enabled               bool
+	Providers             []models.DNSProvider
+	AllowedHostnames      []string
+	PrivateAddresses      []string
+	BlockMalicious        bool
+	BlockSurveillance     bool
+	BlockAds              bool
+	VerbosityLevel        uint8
+	VerbosityDetailsLevel uint8
+	ValidationLogLevel    uint8
+}
+
+func (d *DNS) String() string {
+	if !d.Enabled {
+		return "DNS over TLS settings: disabled"
+	}
+	blockMalicious, blockSurveillance, blockAds := "disabed", "disabed", "disabed"
+	if d.BlockMalicious {
+		blockMalicious = "enabled"
+	}
+	if d.BlockSurveillance {
+		blockSurveillance = "enabled"
+	}
+	if d.BlockAds {
+		blockAds = "enabled"
+	}
+	var providersStr []string
+	for _, provider := range d.Providers {
+		providersStr = append(providersStr, string(provider))
+	}
+	settingsList := []string{
+		"DNS over TLS settings:",
+		"DNS over TLS provider: \n  |--" + strings.Join(providersStr, "\n  |--"),
+		"Block malicious: " + blockMalicious,
+		"Block surveillance: " + blockSurveillance,
+		"Block ads: " + blockAds,
+		"Allowed hostnames: " + strings.Join(d.AllowedHostnames, ", "),
+		"Private addresses:\n  |--" + strings.Join(d.PrivateAddresses, "\n  |--"),
+		"Verbosity level: " + fmt.Sprintf("%d/5", d.VerbosityLevel),
+		"Verbosity details level: " + fmt.Sprintf("%d/4", d.VerbosityDetailsLevel),
+		"Validation log level: " + fmt.Sprintf("%d/2", d.ValidationLogLevel),
+	}
+	return strings.Join(settingsList, "\n |--")
+}
+
+// GetDNSSettings obtains DNS over TLS settings from environment variables using the params package.
+func GetDNSSettings(params params.ParamsReader) (settings DNS, err error) {
+	settings.Enabled, err = params.GetDNSOverTLS()
+	if err != nil || !settings.Enabled {
+		return settings, err
+	}
+	settings.Providers, err = params.GetDNSOverTLSProviders()
+	if err != nil {
+		return settings, err
+	}
+	settings.AllowedHostnames, err = params.GetDNSUnblockedHostnames()
+	if err != nil {
+		return settings, err
+	}
+	settings.BlockMalicious, err = params.GetDNSMaliciousBlocking()
+	if err != nil {
+		return settings, err
+	}
+	settings.BlockSurveillance, err = params.GetDNSSurveillanceBlocking()
+	if err != nil {
+		return settings, err
+	}
+	settings.BlockAds, err = params.GetDNSAdsBlocking()
+	if err != nil {
+		return settings, err
+	}
+	settings.VerbosityLevel, err = params.GetDNSOverTLSVerbosity()
+	if err != nil {
+		return settings, err
+	}
+	settings.VerbosityDetailsLevel, err = params.GetDNSOverTLSVerbosityDetails()
+	if err != nil {
+		return settings, err
+	}
+	settings.ValidationLogLevel, err = params.GetDNSOverTLSValidationLogLevel()
+	if err != nil {
+		return settings, err
+	}
+	settings.PrivateAddresses = []string{ // TODO make env variable
+		"127.0.0.1/8",
+		"10.0.0.0/8",
+		"172.16.0.0/12",
+		"192.168.0.0/16",
+		"169.254.0.0/16",
+		"::1/128",
+		"fc00::/7",
+		"fe80::/10",
+		"::ffff:0:0/96",
+	}
+	return settings, nil
+}