get_image_info.py

import StringIO
import struct

def get_image_info(datastream):
#    datastream = ReseekFile(datastream)
    datastream.seek(0)
    data = str(datastream.read(30))
    size = len(data)
    height = -1
    width = -1
    content_type = ''

    # handle GIFs
    if (size >= 10) and data[:6] in ('GIF87a', 'GIF89a'):
        # Check to see if content_type is correct
        content_type = 'image/gif'
        w, h = struct.unpack("<HH", data[6:10])
        width = int(w)
        height = int(h)

    # See PNG 2. Edition spec (http://www.w3.org/TR/PNG/)
    # Bytes 0-7 are below, 4-byte chunk length, then 'IHDR'
    # and finally the 4-byte width, height
    elif ((size >= 24) and data.startswith('\211PNG\r\n\032\n')
          and (data[12:16] == 'IHDR')):
        content_type = 'image/png'
        w, h = struct.unpack(">LL", data[16:24])
        width = int(w)
        height = int(h)

    # Maybe this is for an older PNG version.
    elif (size >= 16) and data.startswith('\211PNG\r\n\032\n'):
        # Check to see if we have the right content type
        content_type = 'image/png'
        w, h = struct.unpack(">LL", data[8:16])
        width = int(w)
        height = int(h)

    # handle JPEGs
    elif (size >= 2) and data.startswith('\377\330'):
        content_type = 'image/jpeg'
#        jpeg = StringIO.StringIO(data)
        datastream.seek(0)
        jpeg = datastream
        jpeg.read(2)
        b = jpeg.read(1)
        try:
            while (b and ord(b) != 0xDA):
                while (ord(b) != 0xFF): b = jpeg.read(1)
                while (ord(b) == 0xFF): b = jpeg.read(1)
                if (ord(b) >= 0xC0 and ord(b) <= 0xC3):
                    jpeg.read(3)
                    h, w = struct.unpack(">HH", jpeg.read(4))
                    break
                else:
#                    int(struct.unpack(">H", jpeg.read(2))[0])-2
#                    length = struct.unpack(">H", jpeg.read(2))
#                    jpeg.read(int(length[0]) - 2)
                    jpeg.read(int(struct.unpack(">H", jpeg.read(2))[0])-2)
#                print 'Position now', jpeg.tell()
                b = jpeg.read(1)
            width = int(w)
            height = int(h)
        except struct.error:
            pass
        except ValueError:
            pass

    return content_type, width, height

def verify_jpeg(datastream):
    ENDING = [0xFF, 0xD9]
    try:
        datastream.seek(-2, 2)
    except IOError:
        return False
    for e in ENDING:
        b = datastream.read(1)
        if ord(b) == e:
            continue
        else:
            return False
    return True