support for readonly buffers (#863) (#1466)

tests/constructor_stats.h

@@ -180,7 +180,7 @@ public:
                 }
             }
         }
-        catch (const std::out_of_range &) {}
+        catch (const std::out_of_range&) {}
         if (!t1) throw std::runtime_error("Unknown class passed to ConstructorStats::get()");
         auto &cs1 = get(*t1);
         // If we have both a t1 and t2 match, one is probably the trampoline class; return whichever

tests/test_buffers.cpp

@@ -166,4 +166,30 @@ TEST_SUBMODULE(buffers, m) {
         .def_readwrite("value", (int32_t DerivedBuffer::*) &DerivedBuffer::value)
         .def_buffer(&DerivedBuffer::get_buffer_info);
 
+    struct BufferReadOnly {
+        const uint8_t value = 0;
+        BufferReadOnly(uint8_t value): value(value) {}
+
+        py::buffer_info get_buffer_info() {
+            return py::buffer_info(&value, 1);
+        }
+    };
+    py::class_<BufferReadOnly>(m, "BufferReadOnly", py::buffer_protocol())
+        .def(py::init<uint8_t>())
+        .def_buffer(&BufferReadOnly::get_buffer_info);
+
+    struct BufferReadOnlySelect {
+        uint8_t value = 0;
+        bool readonly = false;
+
+        py::buffer_info get_buffer_info() {
+            return py::buffer_info(&value, 1, readonly);
+        }
+    };
+    py::class_<BufferReadOnlySelect>(m, "BufferReadOnlySelect", py::buffer_protocol())
+        .def(py::init<>())
+        .def_readwrite("value", &BufferReadOnlySelect::value)
+        .def_readwrite("readonly", &BufferReadOnlySelect::readonly)
+        .def_buffer(&BufferReadOnlySelect::get_buffer_info);
+
 }

tests/test_buffers.py

@@ -1,8 +1,14 @@
+import io
 import struct
+import sys
+
 import pytest
+
 from pybind11_tests import buffers as m
 from pybind11_tests import ConstructorStats
 
+PY3 = sys.version_info[0] >= 3
+
 pytestmark = pytest.requires_numpy
 
 with pytest.suppress(ImportError):
@@ -85,3 +91,28 @@ def test_pointer_to_member_fn():
         buf.value = 0x12345678
         value = struct.unpack('i', bytearray(buf))[0]
         assert value == 0x12345678
+
+
+@pytest.unsupported_on_pypy
+def test_readonly_buffer():
+    buf = m.BufferReadOnly(0x64)
+    view = memoryview(buf)
+    assert view[0] == 0x64 if PY3 else b'd'
+    assert view.readonly
+
+
+@pytest.unsupported_on_pypy
+def test_selective_readonly_buffer():
+    buf = m.BufferReadOnlySelect()
+
+    memoryview(buf)[0] = 0x64 if PY3 else b'd'
+    assert buf.value == 0x64
+
+    io.BytesIO(b'A').readinto(buf)
+    assert buf.value == ord(b'A')
+
+    buf.readonly = True
+    with pytest.raises(TypeError):
+        memoryview(buf)[0] = 0 if PY3 else b'\0'
+    with pytest.raises(TypeError):
+        io.BytesIO(b'1').readinto(buf)