cmd, docker: Updates for infrastructure

These are some changes to the relay pool server, upgrade server, and
crash receiver to run under Kubernetes. It's been in production for a
while.

lib/httpcache/httpcache.go

@@ -0,0 +1,124 @@
+package httpcache
+
+import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"fmt"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+)
+
+type SinglePathCache struct {
+	next http.Handler
+	keep time.Duration
+
+	mut  sync.RWMutex
+	resp *recordedResponse
+}
+
+func SinglePath(next http.Handler, keep time.Duration) *SinglePathCache {
+	return &SinglePathCache{
+		next: next,
+		keep: keep,
+	}
+}
+
+type recordedResponse struct {
+	status int
+	header http.Header
+	data   []byte
+	gzip   []byte
+	when   time.Time
+	keep   time.Duration
+}
+
+func (resp *recordedResponse) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	for k, v := range resp.header {
+		w.Header()[k] = v
+	}
+
+	w.Header().Set("Cache-Control", fmt.Sprintf("public, max-age=%d", int(resp.keep.Seconds())))
+
+	if strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
+		w.Header().Set("Content-Encoding", "gzip")
+		w.Header().Set("Content-Length", fmt.Sprint(len(resp.gzip)))
+		w.WriteHeader(resp.status)
+		_, _ = w.Write(resp.gzip)
+		return
+	}
+
+	w.Header().Set("Content-Length", fmt.Sprint(len(resp.data)))
+	w.WriteHeader(resp.status)
+	_, _ = w.Write(resp.data)
+}
+
+type responseRecorder struct {
+	resp *recordedResponse
+}
+
+func (r *responseRecorder) WriteHeader(status int) {
+	r.resp.status = status
+}
+
+func (r *responseRecorder) Write(data []byte) (int, error) {
+	r.resp.data = append(r.resp.data, data...)
+	return len(data), nil
+}
+
+func (r *responseRecorder) Header() http.Header {
+	return r.resp.header
+}
+
+func (s *SinglePathCache) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		s.next.ServeHTTP(w, r)
+		return
+	}
+
+	w.Header().Set("X-Cache", "MISS")
+
+	s.mut.RLock()
+	ok := s.serveCached(w, r)
+	s.mut.RUnlock()
+	if ok {
+		return
+	}
+
+	s.mut.Lock()
+	defer s.mut.Unlock()
+	if s.serveCached(w, r) {
+		return
+	}
+
+	rec := &recordedResponse{status: http.StatusOK, header: make(http.Header), when: time.Now(), keep: s.keep}
+	childRec := r.Clone(context.Background())
+	childRec.Header.Del("Accept-Encoding") // don't let the client dictate the encoding
+	s.next.ServeHTTP(&responseRecorder{resp: rec}, childRec)
+
+	if rec.status == http.StatusOK {
+		buf := new(bytes.Buffer)
+		gw := gzip.NewWriter(buf)
+		_, _ = gw.Write(rec.data)
+		gw.Close()
+		rec.gzip = buf.Bytes()
+
+		s.resp = rec
+	}
+
+	rec.ServeHTTP(w, r)
+}
+
+func (s *SinglePathCache) serveCached(w http.ResponseWriter, r *http.Request) bool {
+	if s.resp == nil || time.Since(s.resp.when) > s.keep {
+		return false
+	}
+
+	w.Header().Set("X-Cache", "HIT")
+	w.Header().Set("X-Cache-From", s.resp.when.Format(time.RFC3339))
+
+	s.resp.ServeHTTP(w, r)
+	return true
+}