net/http/internal: return unexpected EOF on incomplete chunk read

Fixes #48861

src/net/http/internal/chunked.go

@@ -81,6 +81,11 @@ func (cr *chunkedReader) Read(b []uint8) (n int, err error) {
 					cr.err = errors.New("malformed chunked encoding")
 					break
 				}
+			} else {
+				if cr.err == io.EOF {
+					cr.err = io.ErrUnexpectedEOF
+				}
+				break
 			}
 			cr.checkEnd = false
 		}
@@ -109,6 +114,8 @@ func (cr *chunkedReader) Read(b []uint8) (n int, err error) {
 		// bytes to verify they are "\r\n".
 		if cr.n == 0 && cr.err == nil {
 			cr.checkEnd = true
+		} else if cr.err == io.EOF {
+			cr.err = io.ErrUnexpectedEOF
 		}
 	}
 	return n, cr.err

src/net/http/internal/chunked_test.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"strings"
 	"testing"
+	"testing/iotest"
 )
 
 func TestChunk(t *testing.T) {
@@ -211,3 +212,30 @@ func TestChunkReadPartial(t *testing.T) {
 	}
 
 }
+
+// Issue 48861: ChunkedReader should report incomplete chunks
+func TestIncompleteChunk(t *testing.T) {
+	const valid = "4\r\nabcd\r\n" + "5\r\nabc\r\n\r\n" + "0\r\n"
+
+	for i := 0; i < len(valid); i++ {
+		incomplete := valid[:i]
+		r := NewChunkedReader(strings.NewReader(incomplete))
+		if _, err := io.ReadAll(r); err != io.ErrUnexpectedEOF {
+			t.Errorf("expected io.ErrUnexpectedEOF for %q, got %v", incomplete, err)
+		}
+	}
+
+	r := NewChunkedReader(strings.NewReader(valid))
+	if _, err := io.ReadAll(r); err != nil {
+		t.Errorf("unexpected error for %q: %v", valid, err)
+	}
+}
+
+func TestChunkEndReadError(t *testing.T) {
+	readErr := fmt.Errorf("chunk end read error")
+
+	r := NewChunkedReader(io.MultiReader(strings.NewReader("4\r\nabcd"), iotest.ErrReader(readErr)))
+	if _, err := io.ReadAll(r); err != readErr {
+		t.Errorf("expected %v, got %v", readErr, err)
+	}
+}