Zstd Control

Properties   Methods   Events   Config Settings   Errors  

The Zstd control implements a Zstandard (zstd) compressor and decompressor.

Syntax

Zstd

Remarks

The Zstd control is compliant with RFC 8878, the Zstandard Compression Format specification. Data compressed by the control can be decompressed by any standard zstd-compatible tool or library, and the control can in turn decompress data produced by any standard zstd encoder.

The CompressionLevel property selects the compression level to use, from 1 (fastest) to 22 (most compact). The control favors speed and simplicity over maximum compression, so at very high levels it may not reach the same compression ratio as the reference zstd encoder; however, the resulting data is still fully standard and can be decompressed by any zstd decoder.

Data may be operated on in multiple ways as discussed below.

Compression and Decompression Streams

The GetDecompressionStream and GetCompressionStream methods are used to retrieve streams that read or write compressed data, as appropriate. The underlying stream should be passed to either method as a parameter.

CompressBlock and DecompressBlock

The CompressBlock and DecompressBlock methods operate on blocks (chunks) of data. The methods may be used to compress and decompress data as they become available.

Note that when using blocks of data, the OutputData property is not applicable. Instead, data are made available via the CompressedData and DecompressedData events.

If all data is available ahead of time, the CompressData and DecompressData methods may be called instead.

Compress Data

The InputData property should be set to the current block to be compressed. Next, the CompressBlock method should be called to compress the current block. Note that this method takes a LastBlock parameter; if the block of data is the final block to be compressed, it must be set to True. For all other blocks, it must remain False.

During compression, the CompressedData event will fire with the compressed data. Note that this event may not fire for every call to CompressBlock due to the way the compression algorithm operates.

zipstream.InputDataB = MyDecompressedData; zipstream.CompressBlock(); Data are accumulated inside the CompressedData event: private static void Zipstream_OnCompressedData(object sender, ZipstreamCompressedDataEventArgs e) { DoSomethingWith(e.DataB); }

Note that the OutputData property is not applicable when compressing block data.

Decompress Data

The InputData property should be set to the current block to be decompressed. Next, the DecompressBlock method should be called to decompress the current block.

During decompression, the DecompressedData event will fire with the decompressed data. Note that this event may not fire for every call to DecompressBlock due to the way the decompression algorithm operates.

zipstream.InputDataB = MyCompressedData; zipstream.DecompressBlock(); Data is accumulated inside the DecompressedData event: private static void Zipstream_OnDecompressedData(object sender, ZipstreamDecompressedDataEventArgs e) { DoSomethingWith(e.DataB); }

Note that the OutputData property is not applicable when decompressing block data.

CompressData and DecompressData

The CompressData and DecompressData methods operate on the complete blob of data. The entire compressed or decompressed data must be set to the InputData property before calling either method.

To compress and decompress data in blocks (chunks), refer to the CompressBlock and DecompressBlock methods.

Compress Data

The InputData property should be set to the decompressed data. This should be the entire data to be compressed. Next, the CompressData method should be called, after which the OutputData property will hold the compressed data.

zipstream.InputDataB = MyDecompressedData; zipstream.CompressData(); MyCompressedData = zipstream.OutputDataB;

In addition to OutputData, the compressed data may also be accumulated within the CompressedData event.

Decompress Data

The InputData property should be set to the compressed data. This should be the entire data to be decompressed. Next, the DecompressData method should be called, after which the OutputData property will hold the decompressed data.

zipstream.InputDataB = MyCompressedData; zipstream.DecompressData(); MyDecompressedData = zipstream.OutputDataB;

In addition to OutputData, the decompressed data may also be accumulated within the DecompressedData event.

Property List

---

The following is the full list of the properties of the control with short descriptions. Click on the links for further details.

Method List

---

The following is the full list of the methods of the control with short descriptions. Click on the links for further details.

Event List

---

The following is the full list of the events fired by the control with short descriptions. Click on the links for further details.

Config Settings

---

The following is a list of config settings for the control with short descriptions. Click on the links for further details.

CompressionLevel Property (Zstd Control)

The compression level to use.

Syntax

zstdcontrol.CompressionLevel[=integer]

Default Value

4

Remarks

This property dictates the compression level to use, from 1 to 22. Higher values will cause the control to compress better; lower values will cause the control to compress faster.

Note that some levels may produce functionally identical results to a neighboring level. A higher level will never compress worse than a lower one, but it is not guaranteed to compress better at every step.

Data Type

Integer

InputData Property (Zstd Control)

The data to compress or decompress.

Syntax

zstdcontrol.InputData[=string]

Default Value

""

Remarks

This property specifies the data to compress or decompress.

When decompressing, this should be set to the compressed data before the DecompressData or DecompressBlock methods are called.

When compressing, this should be set to the decompressed data before the CompressData or CompressBlock methods are called.

Note that this property is not automatically cleared after each operation when performing operations on multiple chunks of data.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .InputDataB.

Data Type

Binary String

OutputData Property (Zstd Control)

The output data after compression or decompression.

Syntax

zstdcontrol.OutputData

Default Value

""

Remarks

This property holds the compressed or decompressed data after the CompressData or DecompressData methods are called.

This property is not applicable when calling the CompressBlock or DecompressBlock methods.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .OutputDataB.

This property is read-only and not available at design time.

Data Type

Binary String

CompressBlock Method (Zstd Control)

Compresses a block of data.

Syntax

zstdcontrol.CompressBlock LastBlock

Remarks

This method compresses the block of data specified by the InputData property.

The CompressBlock and DecompressBlock methods operate on blocks (chunks) of data. The methods may be used to compress and decompress data as they become available.

Note that when using blocks of data, the OutputData property is not applicable. Instead, data are made available via the CompressedData and DecompressedData events.

If all data is available ahead of time, the CompressData and DecompressData methods may be called instead.

Compress Data

The InputData property should be set to the current block to be compressed. Next, the CompressBlock method should be called to compress the current block. Note that this method takes a LastBlock parameter; if the block of data is the final block to be compressed, it must be set to True. For all other blocks, it must remain False.

During compression, the CompressedData event will fire with the compressed data. Note that this event may not fire for every call to CompressBlock due to the way the compression algorithm operates.

zipstream.InputDataB = MyDecompressedData; zipstream.CompressBlock(); Data are accumulated inside the CompressedData event: private static void Zipstream_OnCompressedData(object sender, ZipstreamCompressedDataEventArgs e) { DoSomethingWith(e.DataB); }

Note that the OutputData property is not applicable when compressing block data.

Decompress Data

The InputData property should be set to the current block to be decompressed. Next, the DecompressBlock method should be called to decompress the current block.

During decompression, the DecompressedData event will fire with the decompressed data. Note that this event may not fire for every call to DecompressBlock due to the way the decompression algorithm operates.

zipstream.InputDataB = MyCompressedData; zipstream.DecompressBlock(); Data is accumulated inside the DecompressedData event: private static void Zipstream_OnDecompressedData(object sender, ZipstreamDecompressedDataEventArgs e) { DoSomethingWith(e.DataB); }

Note that the OutputData property is not applicable when decompressing block data.

CompressData Method (Zstd Control)

Compresses the specified data.

Syntax

zstdcontrol.CompressData 

Remarks

This method compresses the data specified by the InputData property. After calling this method, the OutputData property holds the compressed data.

The CompressData and DecompressData methods operate on the complete blob of data. The entire compressed or decompressed data must be set to the InputData property before calling either method.

To compress and decompress data in blocks (chunks), refer to the CompressBlock and DecompressBlock methods.

Compress Data

The InputData property should be set to the decompressed data. This should be the entire data to be compressed. Next, the CompressData method should be called, after which the OutputData property will hold the compressed data.

zipstream.InputDataB = MyDecompressedData; zipstream.CompressData(); MyCompressedData = zipstream.OutputDataB;

In addition to OutputData, the compressed data may also be accumulated within the CompressedData event.

Decompress Data

The InputData property should be set to the compressed data. This should be the entire data to be decompressed. Next, the DecompressData method should be called, after which the OutputData property will hold the decompressed data.

zipstream.InputDataB = MyCompressedData; zipstream.DecompressData(); MyDecompressedData = zipstream.OutputDataB;

In addition to OutputData, the decompressed data may also be accumulated within the DecompressedData event.

Config Method (Zstd Control)

Sets or retrieves a configuration setting.

Syntax

zstdcontrol.Config ConfigurationString

Remarks

Config is a generic method available in every control. It is used to set and retrieve configuration settings for the control.

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the control, access to these internal properties is provided through the Config method.

To set a configuration setting named PROPERTY, you must call Config("PROPERTY=VALUE"), where VALUE is the value of the setting expressed as a string. For boolean values, use the strings "True", "False", "0", "1", "Yes", or "No" (case does not matter).

To read (query) the value of a configuration setting, you must call Config("PROPERTY"). The value will be returned as a string.

DecompressBlock Method (Zstd Control)

Decompresses a block of data.

Syntax

zstdcontrol.DecompressBlock 

Remarks

This method decompresses the block of data specified by the InputData property.

The CompressBlock and DecompressBlock methods operate on blocks (chunks) of data. The methods may be used to compress and decompress data as they become available.

Note that when using blocks of data, the OutputData property is not applicable. Instead, data are made available via the CompressedData and DecompressedData events.

If all data is available ahead of time, the CompressData and DecompressData methods may be called instead.

Compress Data

The InputData property should be set to the current block to be compressed. Next, the CompressBlock method should be called to compress the current block. Note that this method takes a LastBlock parameter; if the block of data is the final block to be compressed, it must be set to True. For all other blocks, it must remain False.

During compression, the CompressedData event will fire with the compressed data. Note that this event may not fire for every call to CompressBlock due to the way the compression algorithm operates.

zipstream.InputDataB = MyDecompressedData; zipstream.CompressBlock(); Data are accumulated inside the CompressedData event: private static void Zipstream_OnCompressedData(object sender, ZipstreamCompressedDataEventArgs e) { DoSomethingWith(e.DataB); }

Note that the OutputData property is not applicable when compressing block data.

Decompress Data

The InputData property should be set to the current block to be decompressed. Next, the DecompressBlock method should be called to decompress the current block.

During decompression, the DecompressedData event will fire with the decompressed data. Note that this event may not fire for every call to DecompressBlock due to the way the decompression algorithm operates.

zipstream.InputDataB = MyCompressedData; zipstream.DecompressBlock(); Data is accumulated inside the DecompressedData event: private static void Zipstream_OnDecompressedData(object sender, ZipstreamDecompressedDataEventArgs e) { DoSomethingWith(e.DataB); }

Note that the OutputData property is not applicable when decompressing block data.

DecompressData Method (Zstd Control)

Decompresses the specified data.

Syntax

zstdcontrol.DecompressData 

Remarks

This method decompresses the data specified by the InputData property. After calling this method, the OutputData property holds the decompressed data.

The CompressData and DecompressData methods operate on the complete blob of data. The entire compressed or decompressed data must be set to the InputData property before calling either method.

To compress and decompress data in blocks (chunks), refer to the CompressBlock and DecompressBlock methods.

Compress Data

The InputData property should be set to the decompressed data. This should be the entire data to be compressed. Next, the CompressData method should be called, after which the OutputData property will hold the compressed data.

zipstream.InputDataB = MyDecompressedData; zipstream.CompressData(); MyCompressedData = zipstream.OutputDataB;

In addition to OutputData, the compressed data may also be accumulated within the CompressedData event.

Decompress Data

The InputData property should be set to the compressed data. This should be the entire data to be decompressed. Next, the DecompressData method should be called, after which the OutputData property will hold the decompressed data.

zipstream.InputDataB = MyCompressedData; zipstream.DecompressData(); MyDecompressedData = zipstream.OutputDataB;

In addition to OutputData, the decompressed data may also be accumulated within the DecompressedData event.

Reset Method (Zstd Control)

Resets the control.

Syntax

zstdcontrol.Reset 

Remarks

This method is used to reset the state of the control. All properties are set to their default values, and any open files are closed.

CompressedData Event (Zstd Control)

Fires with compressed data.

Syntax

Sub zstdcontrol_CompressedData(Data As String)

Remarks

This event is fired one or more times as compressed data become available when the CompressData or CompressBlock methods are called.

Data holds the current block of compressed data.

DecompressedData Event (Zstd Control)

Fires with decompressed data.

Syntax

Sub zstdcontrol_DecompressedData(Data As String)

Remarks

This event is fired one or more times as decompressed data become available when the DecompressData or DecompressBlock methods are called.

Data holds the current block of decompressed data.

Error Event (Zstd Control)

Fires with information about errors during data delivery.

Syntax

Sub zstdcontrol_Error(ErrorCode As Integer, Description As String)

Remarks

This event is fired in case of exceptional conditions during message processing. Normally, the control fails with an error.

ErrorCode contains an error code and Description contains a textual description of the error. For a list of valid error codes and their descriptions, please refer to the Error Codes section.

Config Settings (Zstd Control)

The control accepts one or more of the following configuration settings. Configuration settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the control, access to these internal properties is provided through the Config method.

No configuration settings defined.

Base Config Settings

Trappable Errors (Zstd Control)

Note that the streams returned by GetCompressionStream and GetDecompressionStream will throw standard IOExceptions in case of error.

ZipStream Errors