recover from panics during batch sub-requests (#86)

service/batchmdw/batch_processor.go

@@ -6,13 +6,16 @@ import (
 	"net/http"
 	"sync"
 
+	"github.com/kava-labs/kava-proxy-service/logging"
 	"github.com/kava-labs/kava-proxy-service/service/cachemdw"
 )
 
 // BatchProcessor makes multiple requests to the underlying handler and then combines all the
 // responses into a single response.
 // It assumes all individual responses are valid json. Each response is then marshaled into an array.
 type BatchProcessor struct {
+	*logging.ServiceLogger
+
 	handler   http.HandlerFunc
 	requests  []*http.Request
 	responses []*bytes.Buffer
@@ -23,14 +26,15 @@ type BatchProcessor struct {
 }
 
 // NewBatchProcessor creates a BatchProcessor for combining the responses of reqs to the handler
-func NewBatchProcessor(handler http.HandlerFunc, reqs []*http.Request) *BatchProcessor {
+func NewBatchProcessor(serviceLogger *logging.ServiceLogger, handler http.HandlerFunc, reqs []*http.Request) *BatchProcessor {
 	return &BatchProcessor{
-		handler:   handler,
-		requests:  reqs,
-		responses: make([]*bytes.Buffer, len(reqs)),
-		header:    nil,
-		status:    http.StatusOK,
-		mu:        sync.Mutex{},
+		ServiceLogger: serviceLogger,
+		handler:       handler,
+		requests:      reqs,
+		responses:     make([]*bytes.Buffer, len(reqs)),
+		header:        nil,
+		status:        http.StatusOK,
+		mu:            sync.Mutex{},
 	}
 }
 
@@ -42,6 +46,15 @@ func (bp *BatchProcessor) RequestAndServe(w http.ResponseWriter) error {
 		wg.Add(1)
 
 		go func(idx int, req *http.Request) {
+			// if a client closes the connection prematurely, it can cause panics from batch sub-requests.
+			// when that happens, log & discard the panic.
+			// https://github.com/golang/go/issues/28239
+			defer func() {
+				if recover() != nil {
+					wg.Done()
+					bp.Error().Int("sub-request index", idx).Msg("sub-request for batch panicked")
+				}
+			}()
 
 			buf := new(bytes.Buffer)
 			frw := newFakeResponseWriter(buf, bp.setErrStatus)

service/batchmdw/batchmdw.go

@@ -68,16 +68,18 @@ func CreateBatchProcessingMiddleware(
 			// build request as if it's the only one being requested.
 			req, err := http.NewRequestWithContext(singleRequestContext, r.Method, r.URL.String(), bytes.NewBuffer(body))
 			if err != nil {
-				panic(fmt.Sprintf("failed build sub-request: %s", err))
+				config.ServiceLogger.Error().Err(err).Any("req", single).Msg("failed to sub-request of batch")
+				continue
 			}
 			req.Host = r.Host
 			req.Header = r.Header
+			req.Close = true
 
 			reqs = append(reqs, req)
 		}
 
 		// process all requests and respond with results in an array
-		batchProcessor := NewBatchProcessor(singleRequestHandler, reqs)
+		batchProcessor := NewBatchProcessor(config.ServiceLogger, singleRequestHandler, reqs)
 		batchProcessor.RequestAndServe(w)
 	}
 }

service/shard.go

@@ -30,7 +30,7 @@ func (hsp HeightShardingProxies) ProxyForRequest(r *http.Request) (*httputil.Rev
 	_, _, found := hsp.pruningProxies.ProxyForRequest(r)
 	// if the host isn't in the pruning proxies, short circuit fallback to default
 	if !found {
-		hsp.Debug().Msg(fmt.Sprintf("no pruning host backend configured for %s", r.Host))
+		hsp.Trace().Msg(fmt.Sprintf("no pruning host backend configured for %s", r.Host))
 		return hsp.defaultProxies.ProxyForRequest(r)
 	}