ZIP_SOURCE_LAYERED(3) | Library Functions Manual | ZIP_SOURCE_LAYERED(3)

# NAME

`zip_source_layered`, `zip_source_layered_create` —
create layered data source from function

# LIBRARY

libzip (-lzip)

# SYNOPSIS

`#include <zip.h>`

zip_source_t *
`zip_source_layered`(zip_t *archive, zip_source_t *source, zip_source_layered_callback fn, void *userdata);

zip_source_t *
`zip_source_layered_create`(zip_source_t *source, zip_source_layered_callback fn, void *userdata, zip_error_t *error);

# DESCRIPTION

The functions `zip_source_layered`() and `zip_source_layered_create`() create a layered zip source from the user-provided function fn, which must be of the following type:

typedef zip_int64_t `(*p_source_layered_callback)`(zip_source_t *source, void *userdata, void *data, zip_uint64_t length, zip_source_cmd_t cmd);

archive or error are used for reporting errors and can be `NULL`.

When called by the library, the first argument is the source of the lower layer, the second argument is the userdata argument supplied to the function. The next two arguments are a buffer data of size length when data is passed in or expected to be returned, or else `NULL` and 0. The last argument, cmd, specifies which action the function should perform.

See zip_source_function(3) for a description of the commands.

A layered source transforms the data or metadata of the source below in some way. Layered sources can't support writing and are not sufficient to cleanly add support for additional compression or encryption methods. This may be revised in a later release of libzip.

On success, the layered source takes ownership of source. The caller should not free it.

The interaction with the lower layer depends on the command:

## `ZIP_SOURCE_ACCEPT_EMPTY`

If the layered source supports this command, the lower layer is not called automatically. Otherwise, the return value of the lower source is used.

## `ZIP_SOURCE_CLOSE`

The lower layer is closed after the callback returns.

## `ZIP_SOURCE_ERROR`

The lower layer is not called automatically. If you need to retrieve error information from the lower layer, use zip_error_set_from_source(3) or zip_source_pass_to_lower_layer(3).

## `ZIP_SOURCE_FREE`

The lower layer is freed after the callback returns.

## `ZIP_SOURCE_GET_FILE_ATTRIBUTES`

The attributes of the lower layer are merged with the attributes returned by the callback: information set by the callback wins over the lower layer, with the following exceptions: the higher version_needed is used, and general_purpose_bit_flags are only overwritten if the corresponding bit is set in general_purpose_bit_mask.

## `ZIP_SOURCE_OPEN`

The lower layer is opened before the callback is called.

## `ZIP_SOURCE_READ`

The lower layer is not called automatically.

## `ZIP_SOURCE_SEEK`

The lower layer is not called automatically.

## `ZIP_SOURCE_STAT`

data contains the stat information from the lower layer when the callback is called.

## `ZIP_SOURCE_SUPPORTS`

data contains the bitmap of commands supported by the lower layer when the callback is called. Since layered sources can't support writing, all commands related to writing are stripped from the returned support bitmap.

## `ZIP_SOURCE_TELL`

The lower layer is not called automatically.

# RETURN VALUES

Upon successful completion, the created source is returned. Otherwise, `NULL` is returned and the error code in archive or error is set to indicate the error (unless it is `NULL`).

# ERRORS

`zip_source_layered`() fails if:

[`ZIP_ER_MEMORY`]
  Required memory could not be allocated.

# SEE ALSO

libzip(3), zip_file_add(3), zip_file_attributes_init(3), zip_file_replace(3), zip_source(3), zip_source_function(3), zip_source_pass_to_lower_layer(3)

# HISTORY

`zip_source_layered`() and `zip_source_layered_create`() were added in libzip 1.10.

# AUTHORS

Dieter Baron <dillo@nih.at> and Thomas Klausner <tk@giga.or.at>

January 20, 2023 | NiH