.\" zip_source_function.mdoc -- create data source from function
.\" Copyright (C) 2004-2017 Dieter Baron and Thomas Klausner
.\"
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.\" The authors can be contacted at <libzip@nih.at>
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.Dd December 18, 2017
.Dt ZIP_SOURCE_FUNCTION 3
.Os
.Sh NAME
.Nm zip_source_function ,
.Nm zip_source_function_create
.Nd create data source from function
.Sh LIBRARY
libzip (-lzip)
.Sh SYNOPSIS
.In zip.h
.Ft zip_source_t *
.Fn zip_source_function "zip_t *archive" "zip_source_callback fn" "void *userdata"
.Ft zip_source_t *
.Fn zip_source_function_create "zip_source_callback fn" "void *userdata" "zip_error_t *error"
.Sh DESCRIPTION
The functions
.Fn zip_source_function
and
.Fn zip_source_function_create
creates a zip source from the user-provided function
.Ar fn ,
which must be of the following type:
.Pp
.Ft typedef zip_int64_t
.Fo \fR(*\fPzip_source_callback\fR)\fP
.Fa "void *userdata" "void *data" "zip_uint64_t len" "zip_source_cmd_t cmd"
.Fc
.Pp
.Ar archive
or
.Ar error
are used for reporting errors and can be
.Dv NULL .
.Pp
When called by the library, the first argument is the
.Ar userdata
argument supplied to the function.
The next two arguments are a buffer
.Ar data
of size
.Ar len
when data is passed in or expected to be returned, or else
.Dv NULL
and 0.
The last argument,
.Ar cmd ,
specifies which action the function should perform.
.Pp
Depending on the uses, there are three useful sets of commands to be supported by a
.Fn zip_source_callback :
.Bl -tag -width seekable-read-sourceXX
.It read source
Providing streamed data (for file data added to archives).
Must support
.Dv ZIP_SOURCE_OPEN ,
.Dv ZIP_SOURCE_READ ,
.Dv ZIP_SOURCE_CLOSE ,
.Dv ZIP_SOURCE_STAT ,
and
.Dv ZIP_SOURCE_ERROR .
.It seekable read source
Same as previous, but from a source allowing reading from arbitrary
offsets (also for read-only zip archive).
Must additionally support
.Dv ZIP_SOURCE_SEEK ,
.Dv ZIP_SOURCE_TELL ,
and
.Dv ZIP_SOURCE_SUPPORTS .
.It read/write source
Same as previous, but additionally allowing writing (also for writable
zip archives).
Must additionally support
.Dv ZIP_SOURCE_BEGIN_WRITE ,
.Dv ZIP_SOURCE_COMMIT_WRITE ,
.Dv ZIP_SOURCE_ROLLBACK_WRITE ,
.Dv ZIP_SOURCE_SEEK_WRITE ,
.Dv ZIP_SOURCE_TELL_WRITE ,
and
.Dv ZIP_SOURCE_REMOVE .
.El
.Ss Dv ZIP_SOURCE_BEGIN_WRITE
Prepare the source for writing.
Use this to create any temporary file(s).
.Ss Dv ZIP_SOURCE_BEGIN_WRITE_CLONING
Prepare the source for writing, keeping the first
.Ar len
bytes of the original file.
Only implement this command if it is more efficient than copying the
data, and if it does not destructively overwrite the original file
(you still have to be able to execute
.Dv ZIP_SOURCE_ROLLBACK_WRITE ) .
.Pp
The next write should happen at byte
.Ar offset .
.Ss Dv ZIP_SOURCE_CLOSE
Reading is done.
.Ss Dv ZIP_SOURCE_COMMIT_WRITE
Finish writing to the source.
Replace the original data with the newly written data.
Clean up temporary files or internal buffers.
Subsequently opening and reading from the source should return the
newly written data.
.Ss Dv ZIP_SOURCE_ERROR
Get error information.
.Ar data
points to an array of two ints, which should be filled with the libzip
error code and the corresponding system error code for the error that
occurred.
See
.Xr zip_errors 3
for details on the error codes.
If the source stores error information in a zip_error_t, use
.Xr zip_error_to_data 3
and return its return value.
Otherwise, return 2 * sizeof(int).
.Ss Dv ZIP_SOURCE_FREE
Clean up and free all resources, including
.Ar userdata .
The callback function will not be called again.
.Ss Dv ZIP_SOURCE_OPEN
Prepare for reading.
.Ss Dv ZIP_SOURCE_READ
Read data into the buffer
.Ar data
of size
.Ar len .
Return the number of bytes placed into
.Ar data
on success, and zero for end-of-file.
.Ss Dv ZIP_SOURCE_REMOVE
Remove the underlying file.
This is called if a zip archive is empty when closed.
.Ss Dv ZIP_SOURCE_ROLLBACK_WRITE
Abort writing to the source.
Discard written data.
Clean up temporary files or internal buffers.
Subsequently opening and reading from the source should return the
original data.
.Ss Dv ZIP_SOURCE_SEEK
Specify position to read next byte from, like
.Xr fseek 3 .
Use
.Xr ZIP_SOURCE_GET_ARGS 3
to decode the arguments into the following struct:
.Bd -literal
struct zip_source_args_seek {
    zip_int64_t offset;
    int whence;
};
.Ed
.Pp
If the size of the source's data is known, use
.Xr zip_source_seek_compute_offset 3
to validate the arguments and compute the new offset.
.Ss Dv ZIP_SOURCE_SEEK_WRITE
Specify position to write next byte to, like
.Xr fseek 3 .
See
.Dv ZIP_SOURCE_SEEK
for details.
.Ss Dv ZIP_SOURCE_STAT
Get meta information for the input data.
.Ar data
points to an allocated
.Vt struct zip_stat ,
which should be initialized using
.Xr zip_stat_init 3
and then filled in.
.Pp
For uncompressed, unencrypted data, all information is optional.
However, fill in as much information as is readily available. 
.Pp
If the data is compressed,
.Dv ZIP_STAT_COMP_METHOD ,
.Dv ZIP_STAT_SIZE ,
and
.Dv ZIP_STAT_CRC
must be filled in.
.Pp
If the data is encrypted,
.Dv ZIP_STAT_ENCRYPTION_METHOD ,
.Dv ZIP_STAT_COMP_METHOD ,
.Dv ZIP_STAT_SIZE ,
and
.Dv ZIP_STAT_CRC
must be filled in.
.Pp
Information only available after the source has been read (e.g., size)
can be omitted in an earlier call.
.Em NOTE :
.Fn zip_source_function
may be called with this argument even after being called with
.Dv ZIP_SOURCE_CLOSE .
.Pp
Return sizeof(struct zip_stat) on success.
.Ss Dv ZIP_SOURCE_SUPPORTS
Return bitmap specifying which commands are supported.
Use
.Xr zip_source_make_command_bitmap 3 .
If this command is not implemented, the source is assumed to be a
read source without seek support.
.Ss Dv ZIP_SOURCE_TELL
Return the current read offset in the source, like
.Xr ftell 3 .
.Ss Dv ZIP_SOURCE_TELL_WRITE
Return the current write offset in the source, like
.Xr ftell 3 .
.Ss Dv ZIP_SOURCE_WRITE
Write data to the source.
Return number of bytes written.
.Ss Return Values
Commands should return \-1 on error.
.Dv ZIP_SOURCE_ERROR
will be called to retrieve the error code.
On success, commands return 0, unless specified otherwise in the
description above.
.Ss Calling Conventions
The library will always issue
.Dv ZIP_SOURCE_OPEN
before issuing
.Dv ZIP_SOURCE_READ ,
.Dv ZIP_SOURCE_SEEK ,
or
.Dv ZIP_SOURCE_TELL .
When it no longer wishes to read from this source, it will issue
.Dv ZIP_SOURCE_CLOSE .
If the library wishes to read the data again, it will issue
.Dv ZIP_SOURCE_OPEN
a second time.
If the function is unable to provide the data again, it should
return \-1.
.Pp
.Dv ZIP_SOURCE_BEGIN_WRITE
or
.Dv ZIP_SOURCE_BEGIN_WRITE_CLONING
will be called before
.Dv ZIP_SOURCE_WRITE ,
.Dv ZIP_SOURCE_SEEK_WRITE ,
or
.Dv ZIP_SOURCE_TELL_WRITE .
When writing is complete, either
.Dv ZIP_SOURCE_COMMIT_WRITE
or
.Dv ZIP_SOURCE_ROLLBACK_WRITE
will be called.
.Pp
.Dv ZIP_SOURCE_STAT
can be issued at any time.
.Pp
.Dv ZIP_SOURCE_ERROR
will only be issued in response to the function
returning \-1.
.Pp
.Dv ZIP_SOURCE_FREE
will be the last command issued;
if
.Dv ZIP_SOURCE_OPEN
was called and succeeded,
.Dv ZIP_SOURCE_CLOSE
will be called before
.Dv ZIP_SOURCE_FREE ,
and similarly for
.Dv ZIP_SOURCE_BEGIN_WRITE
or
.Dv ZIP_SOURCE_BEGIN_WRITE_CLONING
and
.Dv ZIP_SOURCE_COMMIT_WRITE
or
.Dv ZIP_SOURCE_ROLLBACK_WRITE .
.Sh RETURN VALUES
Upon successful completion, the created source is returned.
Otherwise,
.Dv NULL
is returned and the error code in
.Ar archive
or
.Ar error
is set to indicate the error (unless
it is
.Dv NULL ) .
.Sh ERRORS
.Fn zip_source_function
fails if:
.Bl -tag -width Er
.It Bq Er ZIP_ER_MEMORY
Required memory could not be allocated.
.El
.Sh SEE ALSO
.Xr libzip 3 ,
.Xr zip_add 3 ,
.Xr zip_replace 3 ,
.Xr zip_source 3 ,
.Xr zip_stat_init 3
.Sh HISTORY
.Fn zip_source_function
and
.Fn zip_source_function_create
were added in libzip 1.0.
.Sh AUTHORS
.An -nosplit
.An Dieter Baron Aq Mt dillo@nih.at
and
.An Thomas Klausner Aq Mt tk@giga.or.at