app service unix socket support (#3022)

This is the last part of unix socket support to talk to app servers, go
based app services already support unix sockets:

5a68173fe3
```
appservice:
  # The address that the homeserver can use to connect to this appservice.
  address: unix:///var/snap/matrix/current/whatsapp.socket

  # The hostname and port where this appservice should listen.
  hostname: /var/snap/matrix/current/whatsapp.socket
  port: 0
```

### Pull Request Checklist

<!-- Please read
https://matrix-org.github.io/dendrite/development/contributing before
submitting your pull request -->

* [x] I have added Go unit tests or [Complement integration
tests](https://github.com/matrix-org/complement) for this PR _or_ I have
justified why this PR doesn't need tests
* [x] Pull request includes a [sign off below using a legally
identifiable
name](https://matrix-org.github.io/dendrite/development/contributing#sign-off)
_or_ I have already signed off privately

Signed-off-by: `Boris Rybalkin <ribalkin@gmail.com>`

setup/config/config_appservice.go

@@ -15,16 +15,23 @@
 package config
 
 import (
+	"context"
+	"crypto/tls"
 	"fmt"
+	"net"
+	"net/http"
 	"os"
 	"path/filepath"
 	"regexp"
 	"strings"
+	"time"
 
 	log "github.com/sirupsen/logrus"
 	"gopkg.in/yaml.v2"
 )
 
+const UnixSocketPrefix = "unix://"
+
 type AppServiceAPI struct {
 	Matrix  *Global  `yaml:"-"`
 	Derived *Derived `yaml:"-"` // TODO: Nuke Derived from orbit
@@ -80,7 +87,41 @@ type ApplicationService struct {
 	// Whether rate limiting is applied to each application service user
 	RateLimited bool `yaml:"rate_limited"`
 	// Any custom protocols that this application service provides (e.g. IRC)
-	Protocols []string `yaml:"protocols"`
+	Protocols    []string `yaml:"protocols"`
+	HTTPClient   *http.Client
+	isUnixSocket bool
+	unixSocket   string
+}
+
+func (a *ApplicationService) CreateHTTPClient(insecureSkipVerify bool) {
+	client := &http.Client{
+		Timeout: time.Second * 30,
+		Transport: &http.Transport{
+			DisableKeepAlives: true,
+			TLSClientConfig: &tls.Config{
+				InsecureSkipVerify: insecureSkipVerify,
+			},
+			Proxy: http.ProxyFromEnvironment,
+		},
+	}
+	if strings.HasPrefix(a.URL, UnixSocketPrefix) {
+		a.isUnixSocket = true
+		a.unixSocket = "http://unix"
+		client.Transport = &http.Transport{
+			DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
+				return net.Dial("unix", strings.TrimPrefix(a.URL, UnixSocketPrefix))
+			},
+		}
+	}
+	a.HTTPClient = client
+}
+
+func (a *ApplicationService) RequestUrl() string {
+	if a.isUnixSocket {
+		return a.unixSocket
+	} else {
+		return a.URL
+	}
 }
 
 // IsInterestedInRoomID returns a bool on whether an application service's
@@ -152,7 +193,7 @@ func (a *ApplicationService) IsInterestedInRoomAlias(
 func loadAppServices(config *AppServiceAPI, derived *Derived) error {
 	for _, configPath := range config.ConfigFiles {
 		// Create a new application service with default options
-		appservice := ApplicationService{
+		appservice := &ApplicationService{
 			RateLimited: true,
 		}
 
@@ -169,13 +210,13 @@ func loadAppServices(config *AppServiceAPI, derived *Derived) error {
 		}
 
 		// Load the config data into our struct
-		if err = yaml.Unmarshal(configData, &appservice); err != nil {
+		if err = yaml.Unmarshal(configData, appservice); err != nil {
 			return err
 		}
-
+		appservice.CreateHTTPClient(config.DisableTLSValidation)
 		// Append the parsed application service to the global config
 		derived.ApplicationServices = append(
-			derived.ApplicationServices, appservice,
+			derived.ApplicationServices, *appservice,
 		)
 	}