Add CORS support and response caching to aggregate endpoints

- Introduced CORS configuration options in config.example.yaml, allowing specification of allowed origins for cross-origin requests.
- Enhanced the aggregate handler to support response caching with a configurable TTL, improving performance for repeated requests.
- Updated the aggregate API to return a structured response indicating whether any upstream requests failed, enhancing error handling and response clarity.
- Modified documentation in AGGREGATE.md and README.md to reflect the new CORS and caching features.
- Added tests to validate the new functionality in the aggregate handler.

internal/config/config.go

@@ -15,13 +15,14 @@ var aliasRe = regexp.MustCompile(`^[a-z0-9][a-z0-9_-]*$`)
 
 // Config is the gateway YAML configuration.
 type Config struct {
-	Listen         string           `yaml:"listen"`
-	AllowAll       bool             `yaml:"allow_all"`
-	WhitelistCIDRs []string         `yaml:"whitelist_cidrs"`
-	TrustedProxies []string         `yaml:"trusted_proxies"`
-	Servers        []Server         `yaml:"servers"`
-	Aggregate      *AggregateConfig `yaml:"aggregate"`
-	GeoIP          *GeoIPConfig     `yaml:"geoip"`
+	Listen             string           `yaml:"listen"`
+	AllowAll           bool             `yaml:"allow_all"`
+	WhitelistCIDRs     []string         `yaml:"whitelist_cidrs"`
+	TrustedProxies     []string         `yaml:"trusted_proxies"`
+	CorsAllowedOrigins []string         `yaml:"cors_allowed_origins"`
+	Servers            []Server         `yaml:"servers"`
+	Aggregate          *AggregateConfig `yaml:"aggregate"`
+	GeoIP              *GeoIPConfig     `yaml:"geoip"`
 }
 
 // GeoIPConfig enables GeoLite2 lookups for /api/agg/unique-ips (optional).
@@ -38,6 +39,8 @@ type GeoIPConfig struct {
 type AggregateConfig struct {
 	// IncludeAliases limits aggregation to these server aliases; empty means all servers.
 	IncludeAliases []string `yaml:"include_aliases"`
+	// CacheTTLMs is in-memory cache TTL for successful GET /api/agg/* responses (milliseconds). 0 disables.
+	CacheTTLMs uint64 `yaml:"cache_ttl_ms"`
 }
 
 // Server maps a URL alias to an upstream base URL.
@@ -123,6 +126,9 @@ func (c *Config) Validate() error {
 				return fmt.Errorf("aggregate.include_aliases[%d]: unknown server alias %q", i, a)
 			}
 		}
+		if c.Aggregate.CacheTTLMs > 60000 {
+			return fmt.Errorf("aggregate.cache_ttl_ms must be within [0, 60000]")
+		}
 	}
 	return nil
 }

internal/config/config_test.go

@@ -98,3 +98,19 @@ func TestValidateAggregateIncludeAliases(t *testing.T) {
 		t.Fatal("expected error for unknown include alias")
 	}
 }
+
+func TestValidateAggregateCacheTTL(t *testing.T) {
+	c := &Config{
+		Servers: []Server{
+			{Alias: "a", BaseURL: "http://x:1"},
+		},
+		Aggregate: &AggregateConfig{CacheTTLMs: 60001},
+	}
+	if err := c.Validate(); err == nil {
+		t.Fatal("expected error for cache_ttl_ms > 60000")
+	}
+	c.Aggregate.CacheTTLMs = 1000
+	if err := c.Validate(); err != nil {
+		t.Fatal(err)
+	}
+}