Bsky short link service (#4542)

* bskylink: scaffold service w/ initial config and schema

* bskylink: implement link creation and redirects

* bskylink: tidy

* bskylink: tests

* bskylink: tidy, add error handler

* bskylink: add dockerfile

* bskylink: add build

* bskylink: fix some express plumbing

* bskyweb: proxy fallthrough routes to link service redirects

* bskyweb: build w/ link proxy

* Add AASA to bskylink (#4588)

---------

Co-authored-by: Hailey <me@haileyok.com>

bskyweb/cmd/bskyweb/main.go

@@ -35,7 +35,7 @@ func run(args []string) {
 			Flags: []cli.Flag{
 				&cli.StringFlag{
 					Name:  "appview-host",
-					Usage: "method, hostname, and port of PDS instance",
+					Usage: "scheme, hostname, and port of PDS instance",
 					Value: "http://localhost:2584",
 					// retain old PDS env var for easy transition
 					EnvVars: []string{"ATP_APPVIEW_HOST", "ATP_PDS_HOST"},
@@ -47,6 +47,13 @@ func run(args []string) {
 					Value:    ":8100",
 					EnvVars:  []string{"HTTP_ADDRESS"},
 				},
+				&cli.StringFlag{
+					Name:     "link-host",
+					Usage:    "scheme, hostname, and port of link service",
+					Required: false,
+					Value:    "",
+					EnvVars:  []string{"LINK_HOST"},
+				},
 				&cli.BoolFlag{
 					Name:     "debug",
 					Usage:    "Enable debug mode",

bskyweb/cmd/bskyweb/server.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io/fs"
 	"net/http"
+	"net/url"
 	"os"
 	"os/signal"
 	"strings"
@@ -36,6 +37,7 @@ func serve(cctx *cli.Context) error {
 	debug := cctx.Bool("debug")
 	httpAddress := cctx.String("http-address")
 	appviewHost := cctx.String("appview-host")
+	linkHost := cctx.String("link-host")
 
 	// Echo
 	e := echo.New()
@@ -221,6 +223,14 @@ func serve(cctx *cli.Context) error {
 	e.GET("/profile/:handleOrDID/post/:rkey/liked-by", server.WebGeneric)
 	e.GET("/profile/:handleOrDID/post/:rkey/reposted-by", server.WebGeneric)
 
+	if linkHost != "" {
+		linkUrl, err := url.Parse(linkHost)
+		if err != nil {
+			return err
+		}
+		e.Group("/:linkId", server.LinkProxyMiddleware(linkUrl))
+	}
+
 	// Start the server.
 	log.Infof("starting server address=%s", httpAddress)
 	go func() {
@@ -292,6 +302,30 @@ func (srv *Server) Download(c echo.Context) error {
 	return c.Redirect(http.StatusFound, "/")
 }
 
+// Handler for proxying top-level paths to link service, which ends up serving a redirect
+func (srv *Server) LinkProxyMiddleware(url *url.URL) echo.MiddlewareFunc {
+	return middleware.ProxyWithConfig(
+		middleware.ProxyConfig{
+			Balancer: middleware.NewRoundRobinBalancer(
+				[]*middleware.ProxyTarget{{URL: url}},
+			),
+			Skipper: func(c echo.Context) bool {
+				req := c.Request()
+				if req.Method == "GET" &&
+					strings.LastIndex(strings.TrimRight(req.URL.Path, "/"), "/") == 0 && // top-level path
+					!strings.HasPrefix(req.URL.Path, "/_") { // e.g. /_health endpoint
+					return false
+				}
+				return true
+			},
+			RetryCount: 2,
+			ErrorHandler: func(c echo.Context, err error) error {
+				return c.Redirect(302, "/")
+			},
+		},
+	)
+}
+
 // handler for endpoint that have no specific server-side handling
 func (srv *Server) WebGeneric(c echo.Context) error {
 	data := pongo2.Context{}