1 files changed, 42 insertions, 0 deletions
diff --git a/internal/net/conn_bound_test.go b/internal/net/conn_bound_test.go
new file mode 100644
index 0000000..45b0f90
--- /dev/null
+++ b/internal/net/conn_bound_test.go
@@ -0,0 +1,42 @@
+package net
+
+import (
+	"bufio"
+	"strings"
+	"testing"
+)
+
+// Regression: the oversized-line handler drains the rest of the line before
+// returning. ReadSlice returns a slice into a reusable buffer, so the
+// truncated prefix must be copied out before draining or it gets overwritten
+// by the remainder of the client's input.
+func TestOversizedLineKeepsTruncatedPrefix(t *testing.T) {
+	oversized := strings.Repeat("A", maxLineLength*2) + strings.Repeat("Z", maxLineLength*3) + "\n"
+	c := &tcpConn{reader: bufio.NewReaderSize(strings.NewReader(oversized+"look\n"), maxLineLength*4)}
+
+	got, err := c.ReadMessage()
+	if err != nil {
+		t.Fatalf("oversized line produced an error: %v", err)
+	}
+	if got != strings.Repeat("A", maxLineLength) {
+		t.Fatalf("truncated prefix corrupted by buffer reuse: got %q...", got[:20])
+	}
+
+	next, err := c.ReadMessage()
+	if err != nil {
+		t.Fatalf("reader did not recover after an oversized line: %v", err)
+	}
+	if next != "look" {
+		t.Fatalf("subsequent line lost: got %q", next)
+	}
+}
+
+func TestNormalLinesUnaffected(t *testing.T) {
+	c := &tcpConn{reader: bufio.NewReaderSize(strings.NewReader("look\nsay hi\r\n"), maxLineLength*4)}
+	for _, want := range []string{"look", "say hi"} {
+		got, err := c.ReadMessage()
+		if err != nil || got != want {
+			t.Fatalf("ReadMessage()=(%q,%v), want (%q,nil)", got, err, want)
+		}
+	}
+}