Implement HTTP proxy option (#515). (#521)

This commit adds a "Proxy" field to the network settings screen, which
can be used to specify a HTTP proxy for any outgoing requests from the
device.

internal/confparser/confparser.go

@@ -3,6 +3,7 @@ package confparser
 import (
 	"fmt"
 	"net"
+	"net/url"
 	"reflect"
 	"slices"
 	"strconv"
@@ -372,6 +373,10 @@ func (f *FieldConfig) validateField() error {
 			if _, err := idna.Lookup.ToASCII(val); err != nil {
 				return fmt.Errorf("field `%s` is not a valid hostname: %s", f.Name, val)
 			}
+		case "proxy":
+			if url, err := url.Parse(val); err != nil || (url.Scheme != "http" && url.Scheme != "https") || url.Host == "" {
+				return fmt.Errorf("field `%s` is not a valid HTTP proxy URL: %s", f.Name, val)
+			}
 		default:
 			return fmt.Errorf("field `%s` cannot use validate_type: unsupported validator: %s", f.Name, validateType)
 		}

internal/network/config.go

@@ -3,6 +3,8 @@ package network
 import (
 	"fmt"
 	"net"
+	"net/http"
+	"net/url"
 	"time"
 
 	"github.com/guregu/null/v6"
@@ -32,8 +34,9 @@ type IPv6StaticConfig struct {
 	DNS     []string    `json:"dns,omitempty" validate_type:"ipv6" required:"true"`
 }
 type NetworkConfig struct {
-	Hostname null.String `json:"hostname,omitempty" validate_type:"hostname"`
-	Domain   null.String `json:"domain,omitempty" validate_type:"hostname"`
+	Hostname  null.String `json:"hostname,omitempty" validate_type:"hostname"`
+	HTTPProxy null.String `json:"http_proxy,omitempty" validate_type:"proxy"`
+	Domain    null.String `json:"domain,omitempty" validate_type:"hostname"`
 
 	IPv4Mode   null.String       `json:"ipv4_mode,omitempty" one_of:"dhcp,static,disabled" default:"dhcp"`
 	IPv4Static *IPv4StaticConfig `json:"ipv4_static,omitempty" required_if:"IPv4Mode=static"`
@@ -71,6 +74,18 @@ func (c *NetworkConfig) GetMDNSMode() *mdns.MDNSListenOptions {
 
 	return listenOptions
 }
+
+func (s *NetworkConfig) GetTransportProxyFunc() func(*http.Request) (*url.URL, error) {
+	return func(*http.Request) (*url.URL, error) {
+		if s.HTTPProxy.String == "" {
+			return nil, nil
+		} else {
+			proxyUrl, _ := url.Parse(s.HTTPProxy.String)
+			return proxyUrl, nil
+		}
+	}
+}
+
 func (s *NetworkInterfaceState) GetHostname() string {
 	hostname := ToValidHostname(s.config.Hostname.String)
 

internal/timesync/http.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"math/rand"
 	"net/http"
+	"net/url"
 	"strconv"
 	"time"
 )
@@ -57,6 +58,7 @@ func (t *TimeSync) queryMultipleHttp(urls []string, timeout time.Duration) (now
 				ctx,
 				url,
 				timeout,
+				t.networkConfig.GetTransportProxyFunc(),
 			)
 			duration := time.Since(startTime)
 
@@ -122,10 +124,16 @@ func queryHttpTime(
 	ctx context.Context,
 	url string,
 	timeout time.Duration,
+	proxyFunc func(*http.Request) (*url.URL, error),
 ) (now *time.Time, response *http.Response, err error) {
+	transport := http.DefaultTransport.(*http.Transport).Clone()
+	transport.Proxy = proxyFunc
+
 	client := http.Client{
-		Timeout: timeout,
+		Transport: transport,
+		Timeout:   timeout,
 	}
+
 	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
 	if err != nil {
 		return nil, nil, err