rpc: add gzip response compression

sei-cosmos/server/api/server.go

@@ -116,12 +116,12 @@ func (s *Server) Start(cfg config.Config, apiMetrics *telemetry.Metrics) error {
 	if cfg.API.EnableUnsafeCORS {
 		allowAllCORS := handlers.CORS(handlers.AllowedHeaders([]string{"Content-Type"}))
 		s.mtx.Unlock()
-		return tmrpcserver.Serve(context.Background(), s.listener, allowAllCORS(h), tmCfg)
+		return tmrpcserver.Serve(context.Background(), s.listener, tmrpcserver.NewGzipHandler(allowAllCORS(h)), tmCfg)
 	}
 
 	logger.Info("starting API server...")
 	s.mtx.Unlock()
-	return tmrpcserver.Serve(context.Background(), s.listener, s.Router, tmCfg)
+	return tmrpcserver.Serve(context.Background(), s.listener, tmrpcserver.NewGzipHandler(s.Router), tmCfg)
 }
 
 // Close closes the API server.

sei-tendermint/internal/inspect/rpc/rpc.go

@@ -74,7 +74,7 @@ func Handler(rpcConfig *config.RPCConfig, routes core.RoutesMap) http.Handler {
 	if rpcConfig.IsCorsEnabled() {
 		rootHandler = addCORSHandler(rpcConfig, mux)
 	}
-	return rootHandler
+	return server.NewGzipHandler(rootHandler)
 }
 
 func addCORSHandler(rpcConfig *config.RPCConfig, h http.Handler) http.Handler {

sei-tendermint/internal/rpc/core/env.go

@@ -362,6 +362,7 @@ func (env *Environment) StartService(ctx context.Context, conf *config.Config) (
 			})
 			rootHandler = corsMiddleware.Handler(mux)
 		}
+		rootHandler = rpcserver.NewGzipHandler(rootHandler)
 		if conf.RPC.IsTLSEnabled() {
 			go func() {
 				if err := rpcserver.ServeTLS(

sei-tendermint/rpc/jsonrpc/server/gzip.go

@@ -0,0 +1,215 @@
+package server
+
+import (
+	"bufio"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+const minCompressBytes = 1024
+
+var gzPool = sync.Pool{
+	New: func() any {
+		w, _ := gzip.NewWriterLevel(io.Discard, gzip.BestSpeed)
+		return w
+	},
+}
+
+type gzipResponseWriter struct {
+	resp http.ResponseWriter
+
+	gz            *gzip.Writer
+	contentLength uint64
+	hasLength     bool
+	inited        bool
+}
+
+func (w *gzipResponseWriter) init() {
+	if w.inited {
+		return
+	}
+	w.inited = true
+
+	hdr := w.resp.Header()
+	length := hdr.Get("content-length")
+	if len(length) > 0 {
+		if n, err := strconv.ParseUint(length, 10, 64); err == nil {
+			w.hasLength = true
+			w.contentLength = n
+		}
+	}
+
+	// Skip compression if the inner handler already encoded the response or
+	// explicitly opted out via Transfer-Encoding: identity.
+	if hdr.Get("content-encoding") != "" || hdr.Get("transfer-encoding") == "identity" {
+		return
+	}
+
+	// Skip compression for small responses with a known Content-Length; below
+	// the threshold the gzip overhead outweighs the savings and the CPU cost
+	// per byte is not worth it for unauthenticated callers.
+	if w.hasLength && w.contentLength < minCompressBytes {
+		return
+	}
+
+	w.gz = gzPool.Get().(*gzip.Writer)
+	w.gz.Reset(w.resp)
+	hdr.Del("content-length")
+	hdr.Set("content-encoding", "gzip")
+}
+
+func (w *gzipResponseWriter) Header() http.Header {
+	return w.resp.Header()
+}
+
+func (w *gzipResponseWriter) WriteHeader(status int) {
+	// Bodyless responses must not be compressed — gzip would write a stream
+	// terminator into what must be an empty body (RFC 7230 §3.3).
+	if status == http.StatusNoContent || status == http.StatusNotModified ||
+		(status >= 100 && status <= 199) {
+		w.inited = true // skip gzip setup
+		w.resp.WriteHeader(status)
+		return
+	}
+	w.init()
+	w.resp.WriteHeader(status)
+}
+
+func (w *gzipResponseWriter) Write(b []byte) (int, error) {
+	w.init()
+
+	if w.gz == nil {
+		return w.resp.Write(b)
+	}
+
+	return w.gz.Write(b)
+}
+
+func (w *gzipResponseWriter) Flush() {
+	// Decide the encoding before headers are committed: a bare Flush() before
+	// any Write() would otherwise commit identity-encoded headers, after which a
+	// later Write() sets Content-Encoding: gzip too late and emits gzip bytes
+	// under an identity encoding.
+	w.init()
+	if w.gz != nil {
+		_ = w.gz.Flush()
+	}
+	if f, ok := w.resp.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
+// Hijack implements http.Hijacker by forwarding to the inner ResponseWriter.
+// The gzip writer is closed first so the hijacked connection starts clean.
+func (w *gzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	h, ok := w.resp.(http.Hijacker)
+	if !ok {
+		return nil, nil, fmt.Errorf("gzip middleware: underlying ResponseWriter does not implement http.Hijacker")
+	}
+	w.close()
+	return h.Hijack()
+}
+
+func (w *gzipResponseWriter) close() {
+	if w.gz == nil {
+		return
+	}
+	_ = w.gz.Close()
+	gzPool.Put(w.gz)
+	w.gz = nil
+}
+
+// acceptsGzip reports whether the request advertises gzip encoding support,
+// respecting q-values and the "*" wildcard per RFC 7231 §5.3.4.
+func acceptsGzip(r *http.Request) bool {
+	gzipQ := -1.0
+	starQ := -1.0
+	for _, field := range r.Header["Accept-Encoding"] {
+		for part := range strings.SplitSeq(field, ",") {
+			part = strings.TrimSpace(part)
+			coding, params, _ := strings.Cut(part, ";")
+			coding = strings.ToLower(strings.TrimSpace(coding))
+			q := 1.0
+			for p := range strings.SplitSeq(params, ";") {
+				p = strings.TrimSpace(p)
+				if k, v, ok := strings.Cut(p, "="); ok && strings.ToLower(strings.TrimSpace(k)) == "q" {
+					if f, err := strconv.ParseFloat(strings.TrimSpace(v), 64); err == nil {
+						q = f
+					}
+				}
+			}
+			switch coding {
+			case "gzip":
+				gzipQ = q
+			case "*":
+				starQ = q
+			}
+		}
+	}
+	if gzipQ >= 0 {
+		return gzipQ > 0
+	}
+	if starQ >= 0 {
+		return starQ > 0
+	}
+	return false
+}
+
+// ensureVaryAcceptEncoding appends Accept-Encoding to the Vary header exactly
+// once, deduplicating against any value already set by the inner handler or
+// CORS middleware. Vary: * already implies Accept-Encoding, so it is left as-is.
+func ensureVaryAcceptEncoding(h http.Header) {
+	existing := h.Get("Vary")
+	for part := range strings.SplitSeq(existing, ",") {
+		v := strings.TrimSpace(part)
+		if strings.EqualFold(v, "Accept-Encoding") || v == "*" {
+			return
+		}
+	}
+	if existing == "" {
+		h.Set("Vary", "Accept-Encoding")
+	} else {
+		h.Set("Vary", existing+", Accept-Encoding")
+	}
+}
+
+// hasUpgradeToken reports whether the Upgrade header contains token (RFC 7230
+// §6.7 permits a comma-separated list; each token is matched case-insensitively).
+func hasUpgradeToken(r *http.Request, token string) bool {
+	for _, field := range r.Header["Upgrade"] {
+		for part := range strings.SplitSeq(field, ",") {
+			if strings.EqualFold(strings.TrimSpace(part), token) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// NewGzipHandler wraps next with gzip response compression. Compression is
+// skipped for clients that do not advertise gzip support via Accept-Encoding.
+// WebSocket upgrades are passed through unmodified; gzipResponseWriter also
+// implements http.Hijacker as defense-in-depth for non-canonical Upgrade values.
+func NewGzipHandler(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Vary must be set on every response — compressed or not — so that CDN
+		// caches key on Accept-Encoding and never serve a wrong variant.
+		ensureVaryAcceptEncoding(w.Header())
+
+		if !acceptsGzip(r) || hasUpgradeToken(r, "websocket") {
+			next.ServeHTTP(w, r)
+			return
+		}
+
+		wrapper := &gzipResponseWriter{resp: w}
+		defer wrapper.close()
+
+		next.ServeHTTP(wrapper, r)
+	})
+}