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import ( "context" "crypto/rand" "encoding/binary" "errors" "fmt" "io" "log/slog" "net" "net/http" "net/http/httputil" "net/url" "strings" "sync" "syscall" "time"
"github.com/mdlayher/vsock")
const ( readCacheProxyPortMin = 20000 readCacheProxyPortMax = 60000)
type ReadCacheProxy struct { port uint32
ln *vsock.Listener server *http.Server}
func StartReadCacheProxy(ctx context.Context, cid uint32, upstreams []CacheUpstream, logger *slog.Logger) (*ReadCacheProxy, error) { if logger == nil { logger = slog.Default() } logger = logger.With("where", "read_cache", "cid", cid)
if len(upstreams) == 0 { return nil, nil }
ln, port, err := listenRandomVsockPort(ctx) if err != nil { return nil, err }
proxy := &ReadCacheProxy{ port: port, ln: ln, } proxy.server = &http.Server{ Handler: cacheProxyHandler(upstreams, logger), Protocols: cacheProxyProtocols(), ReadHeaderTimeout: 10 * time.Second, }
filtered := &cidFilteredVsockListener{ Listener: ln, cid: cid, logger: logger, } go func() { if err := proxy.server.Serve(filtered); err != nil && !errors.Is(err, http.ErrServerClosed) && !errors.Is(err, net.ErrClosed) { logger.Warn("proxy stopped", "cid", cid, "port", port, "error", err) } }()
logger.Info("started proxy", "cid", cid, "port", port, "upstreams", len(upstreams)) return proxy, nil}
func (p *ReadCacheProxy) Port() uint32 { if p == nil { return 0 } return p.port}
func (p *ReadCacheProxy) Close() error { if p == nil { return nil }
var closeErr error if p.server != nil { ctx, cancel := context.WithTimeout(context.Background(), time.Second) closeErr = errors.Join(closeErr, p.server.Shutdown(ctx)) cancel() p.server = nil } if p.ln != nil { closeErr = errors.Join(closeErr, p.ln.Close()) p.ln = nil } return closeErr}
type cidFilteredVsockListener struct { *vsock.Listener cid uint32 logger *slog.Logger}
func (l *cidFilteredVsockListener) Accept() (net.Conn, error) { for { conn, err := l.Listener.Accept() if err != nil { return nil, err }
addr, ok := conn.RemoteAddr().(*vsock.Addr) if ok && addr.ContextID == l.cid { return conn, nil }
l.logger.Warn("dropping proxy connection from unexpected cid", "remote", conn.RemoteAddr(), "expectedCID", l.cid) _ = conn.Close() }}
func parseCacheUpstreams(raw []string) ([]*url.URL, error) { upstreams := make([]*url.URL, 0, len(raw)) seen := make(map[string]struct{}, len(raw)) for _, value := range raw { value = strings.TrimSpace(value) if value == "" { continue } if _, ok := seen[value]; ok { continue } seen[value] = struct{}{}
parsed, err := url.Parse(value) if err != nil { return nil, fmt.Errorf("parse URL %q: %w", value, err) } if parsed.Scheme != "http" && parsed.Scheme != "https" { return nil, fmt.Errorf("URL %q uses unsupported scheme %q", value, parsed.Scheme) } if parsed.Host == "" { return nil, fmt.Errorf("URL %q is missing host", value) } upstreams = append(upstreams, parsed) } return upstreams, nil}
type CacheUpstream struct { url *url.URL // guarded upstreams come from the workflow file // requests to them are refused for special-purpose address ranges guarded bool}
func BuildCacheUpstreams(rawTrusted, rawGuarded []string) ([]CacheUpstream, error) { trusted, err := parseCacheUpstreams(rawTrusted) if err != nil { return nil, err } guarded, err := parseCacheUpstreams(rawGuarded) if err != nil { return nil, err } return mergeCacheUpstreams(trusted, guarded), nil}
func mergeCacheUpstreams(trusted, guarded []*url.URL) []CacheUpstream { merged := make([]CacheUpstream, 0, len(trusted)+len(guarded)) seen := make(map[string]struct{}, len(trusted)+len(guarded)) for _, u := range trusted { if _, ok := seen[u.String()]; ok { continue } seen[u.String()] = struct{}{} merged = append(merged, CacheUpstream{url: u}) } for _, u := range guarded { if _, ok := seen[u.String()]; ok { continue } seen[u.String()] = struct{}{} merged = append(merged, CacheUpstream{url: u, guarded: true}) } return merged}
func listenRandomVsockPort(ctx context.Context) (*vsock.Listener, uint32, error) { var lastErr error for range 32 { port, err := randomVsockPort() if err != nil { return nil, 0, err } ln, err := vsock.Listen(port, nil) if err == nil { return ln, port, nil } lastErr = err
select { case <-ctx.Done(): return nil, 0, ctx.Err() default: } } return nil, 0, fmt.Errorf("listen on random vsock port: %w", lastErr)}
func randomVsockPort() (uint32, error) { var data [4]byte if _, err := rand.Read(data[:]); err != nil { return 0, fmt.Errorf("allocate read vsock port: %w", err) } span := uint32(readCacheProxyPortMax - readCacheProxyPortMin) return readCacheProxyPortMin + binary.BigEndian.Uint32(data[:])%span, nil}
var proxyTransport = &http.Transport{ Proxy: http.ProxyFromEnvironment, ForceAttemptHTTP2: true, MaxIdleConns: 100, IdleConnTimeout: 90 * time.Second, TLSHandshakeTimeout: 10 * time.Second, ExpectContinueTimeout: 1 * time.Second,}
// for guarded upstreams, this will refuse requests made to blocked addressesvar guardedProxyTransport = &http.Transport{ DialContext: (&net.Dialer{ Timeout: 30 * time.Second, KeepAlive: 30 * time.Second, Control: refuseSpecialPurposeAddrs, }).DialContext, ForceAttemptHTTP2: true, MaxIdleConns: 100, IdleConnTimeout: 90 * time.Second, TLSHandshakeTimeout: 10 * time.Second, ExpectContinueTimeout: 1 * time.Second,}
// this should run after dns resolution, so it should cover any rebinding tricksfunc refuseSpecialPurposeAddrs(network, address string, _ syscall.RawConn) error { host, _, err := net.SplitHostPort(address) if err != nil { return fmt.Errorf("split dial address %q: %w", address, err) } ip := net.ParseIP(host) if ip == nil { return fmt.Errorf("refusing to dial non-IP address %q", host) } bits := 128 if ip4 := ip.To4(); ip4 != nil { ip = ip4 bits = 32 } for _, ipnet := range blockedNamespaceNets { _, blockedBits := ipnet.Mask.Size() if blockedBits != bits { continue } if ipnet.Contains(ip) { return fmt.Errorf("refusing to dial %s: %s is blocked for workflow caches", ip, ipnet) } } return nil}
// the proxy is the cache as far as the guest is concerned, so we answer// /nix-cache-info ourselves instead of racing the upstreams for it. merging// those also doesn't make any sense (none of the options make sense for// merging)const nixCacheInfo = "StoreDir: /nix/store\nWantMassQuery: 1\nPriority: 40\n"
func cacheProxyHandler(upstreams []CacheUpstream, logger *slog.Logger) http.Handler { proxy := &httputil.ReverseProxy{ // nothing to do here: the racing transport builds the full URL per // upstream, it just needs the guest's path/query left intact Rewrite: func(*httputil.ProxyRequest) {}, ErrorLog: slog.NewLogLogger(logger.Handler(), slog.LevelError), Transport: ¶llelRacingTransport{ upstreams: upstreams, underlying: proxyTransport, guardedUnderlying: guardedProxyTransport, logger: logger, }, }
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { if r.URL.Path == "/nix-cache-info" { w.Header().Set("Content-Type", "text/x-nix-cache-info") _, _ = io.WriteString(w, nixCacheInfo) return } proxy.ServeHTTP(w, r) })}
func cacheProxyProtocols() *http.Protocols { protocols := new(http.Protocols) protocols.SetHTTP1(true) protocols.SetUnencryptedHTTP2(true) return protocols}
func mergeQuery(base, extra string) string { switch { case base == "": return extra case extra == "": return base default: return base + "&" + extra }}
type parallelRacingTransport struct { upstreams []CacheUpstream underlying http.RoundTripper guardedUnderlying http.RoundTripper logger *slog.Logger}
func (t *parallelRacingTransport) RoundTrip(req *http.Request) (*http.Response, error) { type result struct { resp *http.Response err error is404 bool idx int }
resCh := make(chan result, len(t.upstreams)) cancels := make([]context.CancelFunc, len(t.upstreams)) var wg sync.WaitGroup
for i, upstream := range t.upstreams { wg.Add(1) ctx, cancel := context.WithCancel(req.Context()) cancels[i] = cancel
go func(idx int, target CacheUpstream, uCtx context.Context) { defer wg.Done()
raceReq := req.Clone(uCtx) // rewrite to the target, joining the upstream's base path/query // with what the guest asked for raceReq.URL.Scheme = target.url.Scheme raceReq.URL.Host = target.url.Host raceReq.URL.Path = strings.TrimSuffix(target.url.Path, "/") + req.URL.Path raceReq.URL.RawQuery = mergeQuery(target.url.RawQuery, req.URL.RawQuery) // Host wins over URL.Host for the outgoing Host header, and the // reverse proxy preserves the guest's (127.0.0.1:<port>), which // host-routed upstreams like fastly reject with a 421 raceReq.Host = target.url.Host // the transport doesn't turn URL userinfo into basic auth, only // http.Client does, so do it ourselves if user := target.url.User; user != nil { password, _ := user.Password() raceReq.SetBasicAuth(user.Username(), password) }
rt := t.underlying if target.guarded { rt = t.guardedUnderlying } resp, err := rt.RoundTrip(raceReq) if err != nil { resCh <- result{err: err, idx: idx} return } if resp.StatusCode == http.StatusNotFound { _ = resp.Body.Close() // don't care about the body of a 404 resCh <- result{is404: true, idx: idx} return } if resp.StatusCode >= 400 { // an erroring upstream must not win over a healthy one _ = resp.Body.Close() resCh <- result{err: fmt.Errorf("upstream returned status %d", resp.StatusCode), idx: idx} return } // yay, ok resCh <- result{resp: resp, idx: idx} }(i, upstream, ctx) }
go func() { wg.Wait() close(resCh) }()
var total404s int for res := range resCh { if res.is404 { total404s++ if total404s == len(t.upstreams) { for _, cancel := range cancels { cancel() } return &http.Response{ StatusCode: http.StatusNotFound, Body: io.NopCloser(strings.NewReader("404 nix path not found")), Header: make(http.Header), Request: req, }, nil } continue }
if res.err != nil { if !errors.Is(res.err, context.Canceled) { t.logger.Warn("upstream failed", "path", req.URL.Path, "error", res.err, ) } continue }
// cancel other requests for i, cancel := range cancels { if i != res.idx { cancel() } } return res.resp, nil }
for _, cancel := range cancels { cancel() } return nil, errors.New("all upstreams failed or timed out")}