Fix hangs with large request payloads

handlers.go

@@ -23,6 +23,11 @@ const (
 // withAppHeaders adds application headers such as X-App-Version and X-App-Name.
 func withAppHeaders(c int, h http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
+		// Consume the request body before responding. This allows clients to finish
+		// sending large payloads instead of having net/http close the connection
+		// with unread request data.
+		_, _ = io.Copy(io.Discard, r.Body)
+
 		w.Header().Set(httpHeaderAppName, version.Name)
 		w.Header().Set(httpHeaderAppVersion, version.Version)
 		w.WriteHeader(c)

handlers_test.go

@@ -0,0 +1,51 @@
+// Copyright IBM Corp. 2016, 2026
+// SPDX-License-Identifier: MPL-2.0
+
+package main
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestRequestBodyIsDrained(t *testing.T) {
+	for _, test := range []struct {
+		name string
+		size int
+	}{
+		{name: "small", size: 1 << 10},
+		{name: "20 MiB", size: 20 << 20},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			body := &countingReader{reader: bytes.NewReader(make([]byte, test.size))}
+			request := httptest.NewRequest(http.MethodPost, "/", io.NopCloser(body))
+			response := httptest.NewRecorder()
+
+			httpLog(io.Discard, withAppHeaders(http.StatusOK, httpEcho("hello")))(response, request)
+
+			if body.read != test.size {
+				t.Fatalf("read %d request-body bytes, want %d", body.read, test.size)
+			}
+			if response.Code != http.StatusOK {
+				t.Fatalf("status = %d, want %d", response.Code, http.StatusOK)
+			}
+			if got, want := response.Body.String(), "hello\n"; got != want {
+				t.Fatalf("body = %q, want %q", got, want)
+			}
+		})
+	}
+}
+
+type countingReader struct {
+	reader io.Reader
+	read   int
+}
+
+func (r *countingReader) Read(p []byte) (int, error) {
+	n, err := r.reader.Read(p)
+	r.read += n
+	return n, err
+}