iolimit: Add ExpectLengthReader

1 files changed, 70 insertions, 0 deletions

diff --git a/internal/iolimit/expect_length_reader_test.go b/internal/iolimit/expect_length_reader_test.go
new file mode 100644
index 00000000..503c88ed
--- /dev/null
+++ b/internal/iolimit/expect_length_reader_test.go
@@ -0,0 +1,70 @@
+package iolimit_test
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"testing"
+
+	"codeberg.org/lindenii/furgit/internal/iolimit"
+)
+
+func TestExpectLengthReaderExact(t *testing.T) {
+	t.Parallel()
+
+	r := iolimit.ExpectLengthReader(bytes.NewReader([]byte("hello")), 5)
+	got, err := io.ReadAll(r)
+	if err != nil {
+		t.Fatalf("ReadAll error: %v", err)
+	}
+	if !bytes.Equal(got, []byte("hello")) {
+		t.Fatalf("ReadAll = %q, want %q", got, "hello")
+	}
+
+	buf := make([]byte, 1)
+	n, err := r.Read(buf)
+	if n != 0 || !errors.Is(err, io.EOF) {
+		t.Fatalf("post-boundary Read = (%d,%v), want (0,EOF)", n, err)
+	}
+}
+
+func TestExpectLengthReaderShort(t *testing.T) {
+	t.Parallel()
+
+	r := iolimit.ExpectLengthReader(bytes.NewReader([]byte("hey")), 5)
+	_, err := io.ReadAll(r)
+	if !errors.Is(err, io.ErrUnexpectedEOF) {
+		t.Fatalf("ReadAll error = %v, want ErrUnexpectedEOF", err)
+	}
+}
+
+func TestExpectLengthReaderLongDetectedOnNextRead(t *testing.T) {
+	t.Parallel()
+
+	r := iolimit.ExpectLengthReader(bytes.NewReader([]byte("hello!")), 5)
+	buf := make([]byte, 5)
+	n, err := io.ReadFull(r, buf)
+	if err != nil {
+		t.Fatalf("ReadFull error: %v", err)
+	}
+	if n != 5 || !bytes.Equal(buf, []byte("hello")) {
+		t.Fatalf("ReadFull = (%d,%q), want (5,hello)", n, buf)
+	}
+
+	probe := make([]byte, 1)
+	n, err = r.Read(probe)
+	if n != 0 || !errors.Is(err, iolimit.ErrExpectedLengthExceeded) {
+		t.Fatalf("overflow Read = (%d,%v), want (0,ErrExpectedLengthExceeded)", n, err)
+	}
+}
+
+func TestExpectLengthReaderEmptyExpected(t *testing.T) {
+	t.Parallel()
+
+	r := iolimit.ExpectLengthReader(bytes.NewReader(nil), 0)
+	buf := make([]byte, 1)
+	n, err := r.Read(buf)
+	if n != 0 || !errors.Is(err, io.EOF) {
+		t.Fatalf("Read = (%d,%v), want (0,EOF)", n, err)
+	}
+}