Refactor reverse proxy and enhance API routing

- Replaced the existing reverse proxy implementation with a new alias forwarding mechanism, improving path handling and request normalization.
- Updated the gateway to utilize the new forwarding approach, ensuring consistent handling of API requests and proper error management.
- Enhanced tests to validate the new routing behavior, including handling of double slashes and user endpoint requests.
- Improved documentation in GATEWAY_RUN.md to clarify the updated API routing and configuration requirements.

internal/server/gateway.go

@@ -6,7 +6,6 @@ import (
 	"log/slog"
 	"net"
 	"net/http"
-	"net/http/httputil"
 	"net/url"
 	"strings"
 	"time"
@@ -23,7 +22,7 @@ import (
 // Gateway serves health, metrics, and proxied API routes.
 type Gateway struct {
 	parsed        *config.Parsed
-	proxies       map[string]*httputil.ReverseProxy
+	proxies       map[string]http.Handler
 	agg           *aggregate.Handler
 	geo           *geoip.Service
 	log           *slog.Logger
@@ -44,7 +43,7 @@ func NewGateway(p *config.Parsed, log *slog.Logger, geo *geoip.Service) (*Gatewa
 	t.ResponseHeaderTimeout = 120 * time.Second
 	g := &Gateway{
 		parsed:      p,
-		proxies:     make(map[string]*httputil.ReverseProxy),
+		proxies:     make(map[string]http.Handler),
 		geo:         geo,
 		log:         log,
 		transport:   t,
@@ -58,9 +57,7 @@ func NewGateway(p *config.Parsed, log *slog.Logger, geo *geoip.Service) (*Gatewa
 		}
 		auth := p.AuthByAlias[s.Alias]
 		strip := "/api/" + s.Alias
-		rp := proxy.NewReverseProxy(u, strip, s.PathPrefix, auth)
-		rp.Transport = t
-		rp.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
+		g.proxies[s.Alias] = proxy.NewAliasForward(u, strip, s.PathPrefix, auth, t, func(w http.ResponseWriter, r *http.Request, err error) {
 			log.Error("upstream error", "alias", s.Alias, "err", err)
 			w.Header().Set("Content-Type", "application/json; charset=utf-8")
 			w.WriteHeader(http.StatusBadGateway)
@@ -68,8 +65,7 @@ func NewGateway(p *config.Parsed, log *slog.Logger, geo *geoip.Service) (*Gatewa
 				"ok":    false,
 				"error": map[string]string{"code": "bad_gateway", "message": "upstream unreachable"},
 			})
-		}
-		g.proxies[s.Alias] = rp
+		})
 	}
 	var aggCacheTTL time.Duration
 	if p.Config.Aggregate != nil && p.Config.Aggregate.CacheTTLMs > 0 {