From 0eb3be96319e554cf3e34cadb501de464eacdd8d Mon Sep 17 00:00:00 2001
From: Mathias <mthbqv@gmail.com>
Date: Sat, 3 Oct 2026 20:57:31 +0200
Subject: [PATCH] test(uploads): concurrent receives are bounded in total and
 per user (#47), red

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 internal/uploads/intake_concurrency_test.go | 118 ++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 internal/uploads/intake_concurrency_test.go

diff --git a/internal/uploads/intake_concurrency_test.go b/internal/uploads/intake_concurrency_test.go
new file mode 100644
index 0000000..5a1b56e
--- /dev/null
+++ b/internal/uploads/intake_concurrency_test.go
@@ -0,0 +1,118 @@
+package uploads_test
+
+// Observes how many request bodies Accept will read at once (#47). HasRoom and the
+// per-user queue cap act before and after the receive; N parallel POSTs all pass
+// HasRoom while the queue is still empty, so the receive itself is bounded.
+
+import (
+	"context"
+	"errors"
+	"io"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"git.d-ma.be/mathias/tapir/internal/uploads"
+)
+
+// slowReceive starts an Accept whose body stays open until the returned writer is closed,
+// and waits until it holds a spool file, which proves it is inside the receive.
+type slowReceive struct {
+	w    *io.PipeWriter
+	done chan error
+}
+
+func startSlowReceive(t *testing.T, r *rig, in *uploads.Intake, user string, wantFiles int) *slowReceive {
+	t.Helper()
+	pr, pw := io.Pipe()
+	s := &slowReceive{w: pw, done: make(chan error, 1)}
+	go func() {
+		_, err := in.Accept(context.Background(), user, "t", pr)
+		s.done <- err
+	}()
+	require.Eventually(t, func() bool { return len(r.tmpFiles(t)) == wantFiles }, 2*time.Second, 5*time.Millisecond,
+		"the receive for %s should have started", user)
+	t.Cleanup(func() { _ = pw.Close() })
+	return s
+}
+
+func (s *slowReceive) finish(t *testing.T) error {
+	t.Helper()
+	_, _ = s.w.Write([]byte("data"))
+	require.NoError(t, s.w.Close())
+	select {
+	case err := <-s.done:
+		return err
+	case <-time.After(2 * time.Second):
+		t.Fatal("Accept did not return after its body ended")
+		return nil
+	}
+}
+
+func requireBusy(t *testing.T, err error) {
+	t.Helper()
+	var rej *uploads.RejectError
+	require.True(t, errors.As(err, &rej), "want a busy rejection, got %v", err)
+	assert.Equal(t, uploads.ReasonBusy, rej.Reason)
+}
+
+func TestAccept_APerUserLimitOnConcurrentReceivesRefusesTheNextBodyBeforeSpoolingIt(t *testing.T) {
+	r := newRig(t)
+	in := uploads.NewIntake(r.st, r.pr, r.sub, uploads.Limits{MaxBytes: 1024, MaxDuration: time.Hour}, r.tmp)
+	in.MaxReceivesPerUser = 2
+	in.MaxReceives = 10
+	startSlowReceive(t, r, in, "user-1", 1)
+	startSlowReceive(t, r, in, "user-1", 2)
+
+	_, err := in.Accept(context.Background(), "user-1", "t", strings.NewReader("data"))
+
+	requireBusy(t, err)
+	assert.Len(t, r.tmpFiles(t), 2, "the refused body was never spooled")
+	// Another user is not blocked by user-1's two receives.
+	other := startSlowReceive(t, r, in, "user-2", 3)
+	require.NoError(t, other.finish(t))
+}
+
+func TestAccept_AnOverallLimitOnConcurrentReceivesRefusesTheNextUser(t *testing.T) {
+	r := newRig(t)
+	in := uploads.NewIntake(r.st, r.pr, r.sub, uploads.Limits{MaxBytes: 1024, MaxDuration: time.Hour}, r.tmp)
+	in.MaxReceivesPerUser = 5
+	in.MaxReceives = 3
+	for i, u := range []string{"a", "b", "c"} {
+		startSlowReceive(t, r, in, u, i+1)
+	}
+
+	_, err := in.Accept(context.Background(), "d", "t", strings.NewReader("data"))
+
+	requireBusy(t, err)
+	assert.Len(t, r.tmpFiles(t), 3)
+}
+
+func TestAccept_AFinishedReceiveFreesItsSlot(t *testing.T) {
+	r := newRig(t)
+	in := uploads.NewIntake(r.st, r.pr, r.sub, uploads.Limits{MaxBytes: 1024, MaxDuration: time.Hour}, r.tmp)
+	in.MaxReceivesPerUser = 1
+	in.MaxReceives = 5
+	first := startSlowReceive(t, r, in, "user-1", 1)
+	require.NoError(t, first.finish(t))
+
+	_, err := in.Accept(context.Background(), "user-1", "t", strings.NewReader("data"))
+
+	require.NoError(t, err, "the slot is released when Accept returns")
+}
+
+func TestAccept_AFailedReceiveFreesItsSlot(t *testing.T) {
+	r := newRig(t)
+	in := uploads.NewIntake(r.st, r.pr, r.sub, uploads.Limits{MaxBytes: 1024, MaxDuration: time.Hour}, r.tmp)
+	in.MaxReceivesPerUser = 1
+	in.MaxReceives = 5
+	_, err := in.Accept(context.Background(), "user-1", "t", &brokenBody{n: 1})
+	require.ErrorIs(t, err, uploads.ErrClientRead)
+
+	_, err = in.Accept(context.Background(), "user-1", "t", strings.NewReader("data"))
+
+	require.NoError(t, err, "a dropped client must not leak a slot")
+}