Commit `90ffcd3e9d`

90ffcd3e9d458bba371e2d640e75145af7e6b02e

parent: 276d65d64c

Verified · cmc ci/build: success ci/lint: success ci/test: success

cmc <hello@cleberg.net> · 2026-09-11 02:45 UTC

Serve DeviantArt API responses from the cache

The cache sits in front of the throttle, so a hit costs neither an
upstream request nor a throttle slot. On by default; api-cache.enabled
turns it off.

Closes #8

Layout: unified · split

app/httpclient.go +33 −4

	@@ -81,11 +81,40 @@ func tunedTransport() *http.Transport {
81	return t	81	return t
82	}	82	}
83		83
84	// InstallDAThrottle wraps http.DefaultTransport with the rate/concurrency limits and	84	// daCache is the API response cache shared by every transport, or nil when
85	// timeouts above. Call once at startup, before any DeviantArt request is made.	85	// api-cache.enabled is false.
		86	var daCache *apiCache
		87
		88	// chain wraps base with the throttle and, when enabled, the cache in front
		89	// of it, so a hit never spends a throttle slot.
		90	func chain(base http.RoundTripper) http.RoundTripper {
		91	rt := throttled(base)
		92	if daCache != nil {
		93	return daCache.transport(rt)
		94	}
		95	return rt
		96	}
		97
		98	// logCacheStatsForever prints one line an hour so an operator can see the
		99	// cache working without an endpoint. Run it in its own goroutine.
		100	func logCacheStatsForever(c *apiCache) {
		101	for {
		102	time.Sleep(time.Hour)
		103	hits, misses, entries, held := c.stats()
		104	println("api cache:", hits, "hits,", misses, "misses,", entries, "entries,", held>>20, "MB held")
		105	}
		106	}
		107
		108	// InstallDAThrottle wraps http.DefaultTransport with the rate/concurrency limits
		109	// and timeouts above, and with the API response cache when it is enabled. Call
		110	// once at startup, after ExecuteConfig and before any DeviantArt request.
86	func InstallDAThrottle() {	111	func InstallDAThrottle() {
87	baseTransport = tunedTransport()	112	baseTransport = tunedTransport()
88	http.DefaultTransport = throttled(baseTransport)	113	if CFG.APICache.Enabled {
		114	daCache = newAPICache(CFG.APICache.MaxSize<<20, apiCacheTTL)
		115	go logCacheStatsForever(daCache)
		116	}
		117	http.DefaultTransport = chain(baseTransport)
89	}	118	}
90		119
91	// throttled wraps base with the DeviantArt rate and concurrency limits.	120	// throttled wraps base with the DeviantArt rate and concurrency limits.
	@@ -104,5 +133,5 @@ func ProxiedTransport(proxy *url.URL) http.RoundTripper {
104	base = tunedTransport()	133	base = tunedTransport()
105	}	134	}
106	base.Proxy = http.ProxyURL(proxy)	135	base.Proxy = http.ProxyURL(proxy)
107	return throttled(base)	136	return chain(base)
108	}	137	}

app/httpclient_test.go +14 −4

 // InstallDAThrottle must preserve proxy-from-environment so HTTPS_PROXY (VPN
 // egress) keeps working, and must not panic on a repeat call.
 func TestInstallDAThrottlePreservesProxy(t *testing.T) {
-	orig := http.DefaultTransport
+	orig, origCache := http.DefaultTransport, daCache
-	defer func() { http.DefaultTransport = orig }()
+	defer func() { http.DefaultTransport, daCache = orig, origCache }()
 	InstallDAThrottle()
-	th, ok := http.DefaultTransport.(*daThrottle)
+	// With api-cache on (the default) the cache is outermost and the throttle
+	// sits inside it; with it off the throttle is outermost.
+	rt := http.DefaultTransport
+	if CFG.APICache.Enabled {
+		ct, ok := rt.(*cachedTransport)
+		if !ok {
+			t.Fatalf("DefaultTransport is not the cache, got %T", rt)
+		}
+		rt = ct.base
+	}
+	th, ok := rt.(*daThrottle)
 	if !ok {
-		t.Fatalf("DefaultTransport was not wrapped, got %T", http.DefaultTransport)
+		t.Fatalf("DefaultTransport was not wrapped by the throttle, got %T", rt)
 	}
 	base, ok := th.base.(*http.Transport)
 	if !ok {

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