API¶

This documentation assumes that you’re somewhat familiar with WTForms, since Minform is intentionally similar to (and substantively derived from) that project.

Minform provides a BinaryForm class, which subclasses from wtforms.form.Form. Instead of subclassing Form with wtforms.fields.Field instances as class variables, you need to subclass BinaryForm, and give it BinaryItem instances as class variables. The result will be a Form with additional pack() and unpack() methods.

Note

This documentation will often refer to bytes objects. This mostly applies to Python 3; if you’re using Python 2, you can read bytes as str.

Python version	raw bytes type	unicode string type
Python 2	`str`	`unicode`
Python 3	`bytes`	`str`

Base Classes¶

class minform.BinaryForm(formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs)[source]¶

Form with the power to serialize to and deserialize from packed bytes!

A BinaryForm is used much like a wtforms.form.Form. Instead of wtforms.fields.Field instances, however, the class members should be instances of BinaryItem.

When the class is created, the BinaryItem class members will be used, in order, to generate a binary protocol for serializing and deserializing instances of the form. Using the BinaryForm subclass’s unpack() method will bind a form to the data represented by a buffer.

size¶

int

The number of bytes in a packed buffer of data for this class.

order¶

Byte ordering of numbers, etc. in corresponding buffers of packed data. See Byte Order for more.

pack(order=None)[source]¶

Serialize this form’s bound data into packed bytes.

Parameters: order – byte order constant dictating the endianness of packed integers. If self.order is set, this parameter will be ignored.

Returns: bytes object with length self.size

Return type: bytes

pack_into(buffer, offset, order=None)[source]¶

Pack data from this item into an existing buffer.

Parameters:

buffer – a mutable byte buffer (e.g. bytearray), into which the data will be written

offset (int) – the starting index of buffer to write data to

data – see pack()

order – see pack()

classmethod unpack(buffer, order=None)[source]¶

Parameters:

buffer (bytes) – bytes object of length size

order – byte order constant for integer endianness. If order is set, this parameter will be ignored.

Returns:
form bound to the data stored in the buffer

Return type:
BinaryForm

Raises:
ValueError – if buffer has the wrong size.

classmethod unpack_from(buffer, offset=0, order=None)[source]¶

Unpack data from a specific portion of a buffer.

Parameters:

buffer – a byte buffer (e.g. a bytes object) that contains the serialized data at some offset

offset (int) – the index in buffer where the serialized data starts

order – see unpack()

class minform.BinaryItem[source]¶

Item that occupies a block of bytes in a BinaryForm

A number of BinaryItem subclasses have already been provided; see items for more.

size¶

The number of bytes that will be used to store the item when the parent form is packed in a buffer.

Note

If you subclass BinaryItem, you need to ensure that the object will have an appropriate size property, since it is used by the form to split up buffer data for unpacking, and to assembled packed data.

form_field¶

This property is optional; for example, BlankBytes instances do not have a form_field. If present, it should be an instance of wtforms.Field. This field will then become a member of the form, just like a field in a wtforms.form.Form.

order¶

byte order constant that will override the order of the containing form or field. This will only be necessary if you need to serialize/deserialize with mixed byte ordering.

pack(data, order=None)[source]¶

Serialize a chunk of data into packed bytes.

Parameters:

data – data to serialize, e.g. stored by a corresponding form field

order – byte order constant dictating the endianness of packed integers. If self.order is set, this parameter will be ignored.

Returns:
bytes object with length size

Return type:
bytes

pack_into(buffer, offset, data, order=None)[source]¶

Pack data from this item into an existing buffer.

Parameters:

buffer – a mutable byte buffer (e.g. bytearray), into which the data will be written

offset (int) – the starting index of buffer to write data to

data – see pack()

order – see pack()

unpack(buffer, order=None)[source]¶

Deserialize packed bytes into data.

Parameters:

buffer – bytes object of length size

order – byte order constant for integer endianness. If self.order is set, this parameter will be ignored.

Returns:
data stored in the buffer

Raises:
ValueError – if buffer has the wrong size.

unpack_from(buffer, offset=0, order=None)[source]¶

Unpack data from a specific portion of a buffer.

Parameters:

buffer – a byte buffer (e.g. a bytes object) that contains the serialized data at some offset

offset (int) – the index in buffer where the serialized data starts

order – see unpack()

Binary Items¶

Blank Bytes¶

class minform.BlankBytes(size)[source]¶

Add padding to a form when serialized.

The size argument will set the size.

A BlankBytes instance can be placed anywhere in the list of fields in a BinaryForm definition. It doesn’t matter what name you give it; when the form’s fields are processed, the BlankBytes object itself will be removed from the class’s namespace.

The corresponding bytes will be null when the form is packed, and ignored when a data buffer is unpacked. Likewise, the bytes in a packed buffer will be ignored, and unpacking blank bytes will always return None.

Because BlankBytes objects lack a form_field attribute, there will be no corresponding attribute in a parent BinaryForm‘s data.

Basic Binary Fields¶

class minform.BinaryField[source]¶

BinaryItem that corresponds to a form field.

Note

This class should not be instantiated directly. Instead, use one of its subclasses, described below.

The following classes all have form_field attributes, and their constructors accept a superset of the construction parameters for a wtforms.fields.Field. In general, constructor arguments whose names correspond to BinaryItem construction parameters will be passed in to the constructor for the corresponding wtforms.fields.Field. So, for example, you can set a label for HTML rendering, or add extra validators.

The only notable exceptions are the order and length parameters, which are used to set the byte order and length policy, and will not be passed through to the Field.

class minform.BinaryBooleanField(label='', validators=None, order=None, **kwargs)[source]¶

Store either True or False as b'\x01' or b'\x00' (respectively).

size¶

always 1

form_field¶

A wtforms.fields.BooleanField instance.

class minform.CharField(label='', validators=None, order=None, **kwargs)[source]¶

Store a single byte as a one-character str (in Python 2) or bytes object (in Python 3).

size¶

always 1

form_field¶

A wtforms.fields.StringField instance.

class minform.BinaryIntegerField(label='', validators=None, order=None, **kwargs)[source]¶

This class should not be instantiated directly; instead, you should use one of its subclasses, which determine what kind of int is stored, and how. Those subclasses are:

Name size Min Max

Int8Field 1 -128 127

UInt8Field 1 0 255

Int16Field 2 -32768 32767

UInt16Field 2 0 65535

Int32Field 4 -2³¹ 2³¹ - 1

UInt32Field 4 0 2³² - 1

Int64Field 8 -2⁶³ 2⁶³ - 1

UInt64Field 8 0 2⁶⁴ - 1

form_field¶

A wtforms.fields.Integerfield instance.

class minform.Float32Field(label='', validators=None, order=None, **kwargs)[source]¶

Store a float in four bytes.

size¶

Always 4.

form_field¶

A wtforms.fields.FloatField instance.

class minform.Float64Field(label='', validators=None, order=None, **kwargs)[source]¶

Store a float in eight bytes.

size¶

Always 8.

form_field¶

A wtforms.fields.FloatField instance.

class minform.BytesField(label='', validators=None, max_length=None, length='automatic', order=None, **kwargs)[source]¶

Store N bytes.

max_length¶

Maximum number of bytes in the stored string. Note that this may not be equal to size.

size¶

The size of a BytesField with max_length N varies based on the length argument used to construct it.

If length is FIXED or AUTOMATIC, size will be N.

If length is EXPLICIT, there will be one or more extra bytes at the beginning of the packed data, which store the number of bytes used by the string. This will be the smallest number of bytes needed to store a number up to max_length. So, size can be N+1, N+2, N+4, or N+8. (For more information, see the documentation for EXPLICIT.)

form_field¶

A wtforms.fields.StringField instance.

Compound Binary Fields¶

These fields allow data to be nested. If your data may include several items with the same type, you can use a BinaryFieldList to manage them. If you want to re-use a set of items (or nest a more complicated data type in a BinaryFieldList), you can use a BinaryFormField to do so.

class minform.BinaryFieldList(inner_field, label='', validators=None, max_entries=None, length='explicit', order=None, **kwargs)[source]¶

Store a homogeneous list of information.

inner_field¶

A BinaryField instance.

max_entries¶

The maximum number of items that can be stored in the list.

length¶

A Length constant.

size¶

If length is minform.FIXED, size will be equal to max_size * inner_field.length.

If length is minform.EXPLICIT, size will be prefix_length + (max_size * inner_field.length). The value of prefix_length follows the documentation for Length.

form_field¶

A wtforms.fields.FieldList instance.

class minform.BinaryFormField(form_class, label='', validators=None, order=None, **kwargs)[source]¶

Nest one BinaryForm inside another.

form_class¶

The BinaryForm subclass that describes the contents of this field. A BinaryFormField instance will have the same size as its form_class, and will pack and unpack data in the same ways.

form_field¶

A wtforms.fields.FormField instance.

Custom BinaryItems¶

When creating a custom BinaryItem, you need to be sure to include:

A size attribute. This is used to determine how many bytes will be required by the unpack() method, and how many will be expected to be returned by the pack() method. This attribute is required even if you write custom pack() and BinaryItem.unpack() methods that don’t refer to it!

A pack() method. The type of data should be compatible with the type returned by the unpack() method (below).

An unpack() method. You can expect buf to have self.size bytes when the method is invoked in the course of using a BinaryForm.

Length¶

The following constants are used as the length argument when constructing a BytesField or a BinaryFieldList; they control whether and how the packed buffer signals the length of the data.

minform.FIXED¶

If the length is FIXED, all of the packed information, including terminal null bytes, will be considered part of the data.

fixed_bytes = BytesField(max_length=6, length=FIXED)
fixed_bytes.unpack(b'foobar\0\0\0\0') == b'foobar\0\0\0\0'

fixed_list = BinaryFieldList(UInt16Field(), max_entries=4, length=FIXED)
fixed_list.unpack(b'\x12\x34\x56\x78\x9a\x00\x00\x00') == \
    [0x1234, 0x5678, 0x9a00, 0x0000]

minform.EXPLICIT¶

If length is EXPLICIT, the packed buffer will start with an unsigned int that gives the length of the data (the number of bytes in a BytesField, or the number of entries in a BinaryFieldList). This prefix will be sized according to necessity; it will always be big enough to store the max_length or max_entries of the field:

maximum	prefix type	prefix size
up to 255	UInt8	1 byte
256 - 65535	UInt16	2 bytes
65535 - 4294967296	UInt32	4 bytes
larger	UInt64	8 bytes

If the max is larger than 2⁶⁴, a ValueError will be thrown. Here are some examples of the use of EXPLICIT length fields:

explicit_bytes = BytesField(max_length=9, length=EXPLICIT)

# The first byte is the length of the string.
explicit_bytes.pack(b'foobar') == b'\x06foobar\0\0\0'

# If you manually include the null bytes, they'll be preserved.
explicit_bytes.pack(b'foo\0\0\0') == b'\x06foo\0\0\0\0\0\0'

# The unpacking process respects the explicit size given.
explicit_bytes.unpack(b'\x05hey\0\0\0\0\0\0') == b'hey\0\0'
explicit_bytes.unpack(b'\x02hey\0\0\0\0\0\0') == b'he'

explicit_list = BinaryFieldList(UInt16Field, max_entries=4,
                                length=EXPLICIT)

explicit_list.pack([0x1234, 0x5678, 0x9abc, 0xdef0]) == \
    b'\x04\x12\x34\x56\x78\x9a\xbc\xde\xf0'
explicit_list.pack([0x1234, 0x5678]) == b'\x02\x12\x34\x56\x78\0\0\0\0'

minform.AUTOMATIC¶

The AUTOMATIC option is only available for BytesField, and has very simple semantics: strings shorter than max_length will be padded with null bytes when packed, and null bytes will be trimmed from the end when unpacking a buffer.

auto_bytes = BytesField(max_length=10, length=AUTOMATIC)

auto_bytes.pack(b'1234554321') == b'1234554321'
auto_bytes.pack(b'foobar') == b'foobar\0\0\0\0'

auto_bytes.unpack(b'abc\0def\0\0\0') == b'abc\0def'

Byte order¶

minform.NATIVE¶

minform.LITTLE_ENDIAN¶

minform.BIG_ENDIAN¶

minform.NETWORK¶

These constants operate according to the byte order constants from the struct module. The minform.NATIVE constant corresponds to the '=' prefix, rather than '@'.

Note

Setting the order property on a BinaryForm or BinaryItem will override the order argument of pack() and unpack() methods. For clarity, we recommend that you use either the attribute or the pack()/unpack() argument.

Likewise, the order of a BinaryItem will override the order of the form or field that contains it.

You can think of it as the order cascading down from the BinaryForm.unpack order argument, through the class, to each of that form’s items, and easy nested item, until it is overridden by an order attribute.