# Buggy code
def _open(self):
    # HEAD
    s = self.fp.read(32)
    if i32(s) != 0x59A66A95:
        raise SyntaxError("not an SUN raster file")

    offset = 32

    self.size = i32(s[4:8]), i32(s[8:12])

    depth = i32(s[12:16])
    if depth == 1:
        self.mode, rawmode = "1", "1;I"
    elif depth == 8:
        self.mode = rawmode = "L"
    elif depth == 24:
        self.mode, rawmode = "RGB", "BGR"
    else:
        raise SyntaxError("unsupported mode")

    compression = i32(s[20:24])

    if i32(s[24:28]) != 0:
        length = i32(s[28:32])
        offset = offset + length
        self.palette = ImagePalette.raw("RGB;L", self.fp.read(length))
        if self.mode == "L":
            self.mode = rawmode = "P"

    stride = (((self.size[0] * depth + 7) // 8) + 3) & (~3)

    if compression == 1:
        self.tile = [("raw", (0, 0) + self.size, offset, (rawmode, stride))]
    elif compression == 2:
        self.tile = [("sun_rle", (0, 0) + self.size, offset, rawmode)]


# Traceback (IOError)
from PIL import Image
im = Image.open('sunraster.im1')
print im.format,im.size, im.mode
SUN (640, 400) 1
im.load()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/rh/python27/root/usr/lib/python2.7/site-packages/PIL/ImageFile.py", line 240, in load
raise_ioerror(err_code)
File "/opt/rh/python27/root/usr/lib/python2.7/site-packages/PIL/ImageFile.py", line 59, in raise_ioerror
raise IOError(message + " when reading image file")
IOError: buffer overrun when reading image file


# Fixed code
def _open(self):
    # The Sun Raster file header is 32 bytes in length and has the following format:

    #     typedef struct _SunRaster
    #     {
    #         DWORD MagicNumber;      /* Magic (identification) number */
    #         DWORD Width;            /* Width of image in pixels */
    #         DWORD Height;           /* Height of image in pixels */
    #         DWORD Depth;            /* Number of bits per pixel */
    #         DWORD Length;           /* Size of image data in bytes */
    #         DWORD Type;             /* Type of raster file */
    #         DWORD ColorMapType;     /* Type of color map */
    #         DWORD ColorMapLength;   /* Size of the color map in bytes */
    #     } SUNRASTER;

    # HEAD
    s = self.fp.read(32)
    if i32(s) != 0x59A66A95:
        raise SyntaxError("not an SUN raster file")

    offset = 32

    self.size = i32(s[4:8]), i32(s[8:12])

    depth = i32(s[12:16])
    data_length = i32(s[16:20])  # unreliable, ignore.
    file_type = i32(s[20:24])
    palette_type = i32(s[24:28])  # 0: None, 1: RGB, 2: Raw/arbitrary
    palette_length = i32(s[28:32])

    if depth == 1:
        self.mode, rawmode = "1", "1;I"
    elif depth == 4:
        self.mode, rawmode = "L", "L;4"
    elif depth == 8:
        self.mode = rawmode = "L"
    elif depth == 24:
        if file_type == 3:
            self.mode, rawmode = "RGB", "RGB"
        else:
            self.mode, rawmode = "RGB", "BGR"
    elif depth == 32:
        if file_type == 3:
            self.mode, rawmode = "RGB", "RGBX"
        else:
            self.mode, rawmode = "RGB", "BGRX"
    else:
        raise SyntaxError("Unsupported Mode/Bit Depth")

    if palette_length:
        if palette_length > 1024:
            raise SyntaxError("Unsupported Color Palette Length")

        if palette_type != 1:
            raise SyntaxError("Unsupported Palette Type")

        offset = offset + palette_length
        self.palette = ImagePalette.raw("RGB;L", self.fp.read(palette_length))
        if self.mode == "L":
            self.mode = "P"
            rawmode = rawmode.replace("L", "P")

    # 16 bit boundaries on stride
    stride = ((self.size[0] * depth + 15) // 16) * 2

    # file type: Type is the version (or flavor) of the bitmap
    # file. The following values are typically found in the Type
    # field:
    # 0000h	Old
    # 0001h	Standard
    # 0002h	Byte-encoded
    # 0003h	RGB format
    # 0004h	TIFF format
    # 0005h	IFF format
    # FFFFh	Experimental

    # Old and standard are the same, except for the length tag.
    # byte-encoded is run-length-encoded
    # RGB looks similar to standard, but RGB byte order
    # TIFF and IFF mean that they were converted from T/IFF
    # Experimental means that it's something else.
    # (http://www.fileformat.info/format/sunraster/egff.htm)

    if file_type in (0, 1, 3, 4, 5):
        self.tile = [("raw", (0, 0) + self.size, offset, (rawmode, stride))]
    elif file_type == 2:
        self.tile = [("sun_rle", (0, 0) + self.size, offset, rawmode)]
    else:
        raise SyntaxError("Unsupported Sun Raster file type")