Allow new-style buffer interfaces to be read/write when mapped that way

src/PIL/Image.py

@@ -2639,7 +2639,7 @@ def frombuffer(mode, size, data, decoder_name="raw", *args):
         if args[0] in _MAPMODES:
             im = new(mode, (1, 1))
             im = im._new(core.map_buffer(data, size, decoder_name, 0, args))
-            im.readonly = 1
+            im.readonly = im.im.readonly
             return im
 
     return frombytes(mode, size, data, decoder_name, args)

src/PIL/ImageFile.py

@@ -196,7 +196,7 @@ class ImageFile(Image.Image):
                         self.im = Image.core.map_buffer(
                             self.map, self.size, decoder_name, offset, args
                         )
-                    readonly = 1
+                    readonly = self.im.readonly
                     # After trashing self.im,
                     # we might need to reload the palette data.
                     if self.palette:

src/_imaging.c

@@ -3391,6 +3391,11 @@ _getattr_unsafe_ptrs(ImagingObject* self, void* closure)
                         );
 };
 
+static PyObject*
+_getattr_readonly(ImagingObject* self, void* closure)
+{
+    return PyInt_FromLong(self->image->readonly);
+}
 
 static struct PyGetSetDef getsetters[] = {
     { "mode",   (getter) _getattr_mode },
@@ -3399,6 +3404,7 @@ static struct PyGetSetDef getsetters[] = {
     { "id",     (getter) _getattr_id },
     { "ptr",    (getter) _getattr_ptr },
     { "unsafe_ptrs", (getter) _getattr_unsafe_ptrs },
+    { "readonly", (getter) _getattr_readonly },
     { NULL }
 };
 

src/libImaging/Imaging.h

@@ -89,6 +89,7 @@ struct ImagingMemoryInstance {
     int bands;          /* Number of bands (1, 2, 3, or 4) */
     int xsize;          /* Image dimension. */
     int ysize;
+    int readonly;
 
     /* Colour palette (for "P" images only) */
     ImagingPalette palette;

src/libImaging/Storage.c

@@ -64,6 +64,7 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size)
     im->xsize = xsize;
     im->ysize = ysize;
 
+    im->readonly = 0;
     im->type = IMAGING_TYPE_UINT8;
 
     if (strcmp(mode, "1") == 0) {

src/map.c

@@ -217,6 +217,7 @@ mapping_readimage(ImagingMapperObject* mapper, PyObject* args)
     if (!im)
         return NULL;
 
+    im->readonly = 1;
     /* setup file pointers */
     if (orientation > 0)
         for (y = 0; y < ysize; y++)
@@ -366,6 +367,7 @@ PyImaging_MapBuffer(PyObject* self, PyObject* args)
     if (!im)
         return NULL;
 
+    im->readonly = view.readonly;
     /* setup file pointers */
     if (ystep > 0)
         for (y = 0; y < ysize; y++)