Mapping the Growth Hint

In a ZIP archive, the growth hint is used to reserve additional bytes that can be used to allow an item to grow in-place. The padding is stored in the Extra field, as defined in the ZIP file format specification. If a growth hint is used for an interleaved part, the package implementer should store the Extra field containing the growth hint padding with the item that represents the first piece of the part. [S3.2]

The format of the ZIP item's Extra field, when used for growth hints, is shown in Table 9–3, Structure of the Extra field for growth hints below.

Table 1. 9–3. Structure of the Extra field for growth hints

Field

Size

Value

Header ID

2 bytes

A220

Length of Extra field

2 bytes

The signature length (2 bytes) + the padding initial value length (2 bytes) + Length of the padding (variable)

Signature (for verification)

2 bytes

A028

Padding Initial Value

2 bytes

Hex number value is set by the producer when the item is created

<padding>

[Padding Length]

Should be filled with NULL characters