WIP - Non working struct encoding

* structs can't be encoded this way, they need to have one child array
per struct member.
* i.e. struct of arrays, rather than an array of structs.

src/PIL/Image.py

@@ -746,9 +746,11 @@ class Image:
 
 
     def __arrow_c_schema__(self) -> object:
+        self.load()
         return self.im.__arrow_c_schema__()
 
     def __arrow_c_array__(self, requested_schema: object | None = None) -> Tuple[object, object]:
+        self.load()
         return (self.im.__arrow_c_schema__(), self.im.__arrow_c_array__())
 
     def __getstate__(self) -> list[Any]:

src/_imaging.c

@@ -239,8 +239,8 @@ void ReleaseArrowSchemaPyCapsule(PyObject* capsule) {
 
 PyObject* ExportArrowSchemaPyCapsule(ImagingObject *self) {
     struct ArrowSchema* schema =
-        (struct ArrowSchema*)malloc(sizeof(struct ArrowSchema));
-    export_uint32_type(schema);
+      (struct ArrowSchema*)calloc(1, sizeof(struct ArrowSchema));
+    export_imaging_schema(self->image, schema);
     return PyCapsule_New(schema, "arrow_schema", ReleaseArrowSchemaPyCapsule);
 }
 
@@ -255,7 +255,7 @@ void ReleaseArrowArrayPyCapsule(PyObject* capsule) {
 
 PyObject* ExportArrowArrayPyCapsule(ImagingObject *self) {
     struct ArrowArray* array =
-        (struct ArrowArray*)malloc(sizeof(struct ArrowArray));
+      (struct ArrowArray*)calloc(1, sizeof(struct ArrowArray));
     export_imaging_array(self->image, array);
     return PyCapsule_New(array, "arrow_array", ReleaseArrowArrayPyCapsule);
 }

src/libImaging/Arrow.c

@@ -1,6 +1,7 @@
 
 #include "Arrow.h"
 #include "Imaging.h"
+#include <string.h>
 
 /* struct ArrowSchema* */
 /* _arrow_schema_channel(char* channel, char* format) { */
@@ -12,6 +13,18 @@ ReleaseExportedSchema(struct ArrowSchema* array) {
   // This should not be called on already released array
   //assert(array->release != NULL);
 
+  if (!array->release) {
+    return;
+  }
+  if (array->format) {
+    free((void*)array->format);
+    array->format = NULL;
+  }
+  if (array->name) {
+    free((void*)array->name);
+    array->name = NULL;
+  }
+
   // Release children
   for (int64_t i = 0; i < array->n_children; ++i) {
     struct ArrowSchema* child = array->children[i];
@@ -36,7 +49,80 @@ ReleaseExportedSchema(struct ArrowSchema* array) {
 }
 
 
-static void release_uint32_type(struct ArrowSchema* schema) {
+
+int export_named_type(struct ArrowSchema* schema,
+                       char* format,
+                       char* name) {
+
+  char* formatp;
+  char* namep;
+  size_t format_len = strlen(format) + 1;
+  size_t name_len = strlen(name) + 1;
+
+  formatp = calloc(format_len, 1);
+
+  if (!formatp) {
+    return 1;
+  }
+
+  namep = calloc(name_len, 1);
+  if (!namep){
+    free(formatp);
+    return 1;
+  }
+
+  strlcpy(formatp, format, format_len);
+  strlcpy(namep, name, name_len);
+
+  *schema = (struct ArrowSchema) {
+    // Type description
+    .format = formatp,
+    .name = namep,
+    .metadata = NULL,
+    .flags = 0,
+    .n_children = 0,
+    .children = NULL,
+    .dictionary = NULL,
+    // Bookkeeping
+    .release = &ReleaseExportedSchema
+  };
+  return 0;
+}
+
+int export_imaging_schema(Imaging im, struct ArrowSchema* schema) {
+  int retval = 0;
+
+  if (strcmp(im->arrow_band_format, "") == 0) {
+    return 1;
+  }
+
+  if (im->bands == 1) {
+    return export_named_type(schema, im->arrow_band_format, im->band_names[0]);
+  }
+
+  retval = export_named_type(schema, "+s", "");
+  if (retval) {
+    return retval;
+  }
+  // if it's not 1 band, it's an int32 at the moment. 4 unint8 bands.
+  schema->n_children = 4;
+  schema->children = calloc(4, sizeof(struct ArrowSchema*));
+  for (int i=0; i<4; i++) {
+    schema->children[i] =
+      (struct ArrowSchema*)calloc(1, sizeof(struct ArrowSchema));
+    if (export_named_type(schema->children[i], im->arrow_band_format, im->band_names[i])) {
+      /* error recovery */
+      for (int j=i-1; i>=0; i--) {
+        schema->children[j]->release(schema->children[j]);
+        free(schema->children[j]);
+      }
+      return 2;
+    }
+  }
+  return 0;
+}
+
+static void release_simple_type(struct ArrowSchema* schema) {
    // Mark released
    schema->release = NULL;
 }
@@ -52,10 +138,11 @@ void export_uint32_type(struct ArrowSchema* schema) {
       .children = NULL,
       .dictionary = NULL,
       // Bookkeeping
-      .release = &release_uint32_type
+      .release = &release_simple_type
    };
 }
 
+
 static void release_uint32_array(struct ArrowArray* array) {
    //assert(array->n_buffers == 2);
    // Free the buffers and the buffers array

src/libImaging/Imaging.h

@@ -109,6 +109,9 @@ struct ImagingMemoryInstance {
     int arrow_borrow; /* Number of arrow arrays that have been allocated */
     int blocks_count; /* Number of blocks that have been allocated */
     int lines_per_block; /* Number of lines in a block have been allocated */
+
+    char band_names[4][3]; /* names of bands, max 2 char + null terminator */
+    char arrow_band_format[2]; /* single character + null terminator */
 };
 
 #define IMAGING_PIXEL_1(im, x, y) ((im)->image8[(y)][(x)])
@@ -711,6 +714,7 @@ _imaging_tell_pyFd(PyObject *fd);
 
 #include "Arrow.h"
 extern void export_imaging_array(Imaging im, struct ArrowArray* array);
+extern int export_imaging_schema(Imaging im, struct ArrowSchema* schema);
 extern void export_uint32_type(struct ArrowSchema* schema);
 
 /* Errcodes */

src/libImaging/Storage.c

@@ -60,17 +60,20 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
     im->ysize = ysize;
 
     im->type = IMAGING_TYPE_UINT8;
+    strcpy(im->arrow_band_format, "C");
 
     if (strcmp(mode, "1") == 0) {
         /* 1-bit images */
         im->bands = im->pixelsize = 1;
         im->linesize = xsize;
+        strcpy(im->band_names[0],"1");
 
     } else if (strcmp(mode, "P") == 0) {
         /* 8-bit palette mapped images */
         im->bands = im->pixelsize = 1;
         im->linesize = xsize;
         im->palette = ImagingPaletteNew("RGB");
+        strcpy(im->band_names[0],"P");
 
     } else if (strcmp(mode, "PA") == 0) {
         /* 8-bit palette with alpha */
@@ -78,23 +81,36 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 4; /* store in image32 memory */
         im->linesize = xsize * 4;
         im->palette = ImagingPaletteNew("RGB");
+        strcpy(im->band_names[0],"P");
+        strcpy(im->band_names[1],"X");
+        strcpy(im->band_names[2],"X");
+        strcpy(im->band_names[3],"A");
 
     } else if (strcmp(mode, "L") == 0) {
         /* 8-bit grayscale (luminance) images */
         im->bands = im->pixelsize = 1;
         im->linesize = xsize;
+        strcpy(im->band_names[0],"L");
 
     } else if (strcmp(mode, "LA") == 0) {
         /* 8-bit grayscale (luminance) with alpha */
         im->bands = 2;
         im->pixelsize = 4; /* store in image32 memory */
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"L");
+        strcpy(im->band_names[1],"X");
+        strcpy(im->band_names[2],"X");
+        strcpy(im->band_names[3],"A");
 
     } else if (strcmp(mode, "La") == 0) {
         /* 8-bit grayscale (luminance) with premultiplied alpha */
         im->bands = 2;
         im->pixelsize = 4; /* store in image32 memory */
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"L");
+        strcpy(im->band_names[1],"X");
+        strcpy(im->band_names[2],"X");
+        strcpy(im->band_names[3],"a");
 
     } else if (strcmp(mode, "F") == 0) {
         /* 32-bit floating point images */
@@ -102,6 +118,8 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 4;
         im->linesize = xsize * 4;
         im->type = IMAGING_TYPE_FLOAT32;
+        strcpy(im->arrow_band_format , "f");
+        strcpy(im->band_names[0],"F");
 
     } else if (strcmp(mode, "I") == 0) {
         /* 32-bit integer images */
@@ -109,6 +127,8 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 4;
         im->linesize = xsize * 4;
         im->type = IMAGING_TYPE_INT32;
+        strcpy(im->arrow_band_format , "i");
+        strcpy(im->band_names[0],"I");
 
     } else if (strcmp(mode, "I;16") == 0 || strcmp(mode, "I;16L") == 0 ||
                strcmp(mode, "I;16B") == 0 || strcmp(mode, "I;16N") == 0) {
@@ -118,12 +138,18 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 2;
         im->linesize = xsize * 2;
         im->type = IMAGING_TYPE_SPECIAL;
+        strcpy(im->arrow_band_format , "s");
+        strcpy(im->band_names[0],"I");
 
     } else if (strcmp(mode, "RGB") == 0) {
         /* 24-bit true colour images */
         im->bands = 3;
         im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"R");
+        strcpy(im->band_names[1],"G");
+        strcpy(im->band_names[2],"B");
+        strcpy(im->band_names[3],"X");
 
     } else if (strcmp(mode, "BGR;15") == 0) {
         /* EXPERIMENTAL */
@@ -132,6 +158,8 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 2;
         im->linesize = (xsize * 2 + 3) & -4;
         im->type = IMAGING_TYPE_SPECIAL;
+        /* not allowing arrow due to line length packing */
+        strcpy(im->arrow_band_format , "");
 
     } else if (strcmp(mode, "BGR;16") == 0) {
         /* EXPERIMENTAL */
@@ -140,6 +168,8 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 2;
         im->linesize = (xsize * 2 + 3) & -4;
         im->type = IMAGING_TYPE_SPECIAL;
+        /* not allowing arrow due to line length packing */
+        strcpy(im->arrow_band_format , "");
 
     } else if (strcmp(mode, "BGR;24") == 0) {
         /* EXPERIMENTAL */
@@ -148,32 +178,54 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->pixelsize = 3;
         im->linesize = (xsize * 3 + 3) & -4;
         im->type = IMAGING_TYPE_SPECIAL;
+        /* not allowing arrow due to line length packing */
+        strcpy(im->arrow_band_format , "");
 
     } else if (strcmp(mode, "RGBX") == 0) {
         /* 32-bit true colour images with padding */
         im->bands = im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"R");
+        strcpy(im->band_names[1],"G");
+        strcpy(im->band_names[2],"B");
+        strcpy(im->band_names[3],"X");
 
     } else if (strcmp(mode, "RGBA") == 0) {
         /* 32-bit true colour images with alpha */
         im->bands = im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"R");
+        strcpy(im->band_names[1],"G");
+        strcpy(im->band_names[2],"B");
+        strcpy(im->band_names[3],"A");
 
     } else if (strcmp(mode, "RGBa") == 0) {
         /* 32-bit true colour images with premultiplied alpha */
         im->bands = im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"R");
+        strcpy(im->band_names[1],"G");
+        strcpy(im->band_names[2],"B");
+        strcpy(im->band_names[3],"a");
 
     } else if (strcmp(mode, "CMYK") == 0) {
         /* 32-bit colour separation */
         im->bands = im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"C");
+        strcpy(im->band_names[1],"M");
+        strcpy(im->band_names[2],"Y");
+        strcpy(im->band_names[3],"K");
 
     } else if (strcmp(mode, "YCbCr") == 0) {
         /* 24-bit video format */
         im->bands = 3;
         im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"Y");
+        strcpy(im->band_names[1],"Cb");
+        strcpy(im->band_names[2],"Cr");
+        strcpy(im->band_names[3],"X");
 
     } else if (strcmp(mode, "LAB") == 0) {
         /* 24-bit color, luminance, + 2 color channels */
@@ -181,6 +233,10 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->bands = 3;
         im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"L");
+        strcpy(im->band_names[1],"a");
+        strcpy(im->band_names[2],"b");
+        strcpy(im->band_names[3],"X");
 
     } else if (strcmp(mode, "HSV") == 0) {
         /* 24-bit color, luminance, + 2 color channels */
@@ -188,6 +244,10 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize, int size) {
         im->bands = 3;
         im->pixelsize = 4;
         im->linesize = xsize * 4;
+        strcpy(im->band_names[0],"H");
+        strcpy(im->band_names[1],"S");
+        strcpy(im->band_names[2],"V");
+        strcpy(im->band_names[3],"X");
 
     } else {
         free(im);