Gzip Component

Properties   Methods   Events   Config Settings   Errors  

The Gzip component implements a gzip compressor and decompressor. It is compliant with RFC 1952 and compatible with the UNIX gzip and gunzip utilities.

Syntax

TipzGzip

Remarks

The gzip file format is typically used only to archive a single file. Accordingly, the operation of the component is simpler than that of the other components.

To compress with the component, set ArchiveFile to the name of the gzip file to be created, and FileDecompressedName to the name of the file to be compressed. Finally, invoke Compress. To extract the file, first set ArchiveFile. FileDecompressedName may then be set; if not, it will automatically be set from the gzip file headers. Finally, invoke the Extract or Compress method.

.tar.gz files may be created or extracted in one step by using the Tar component. See the documentation for Tar for more details.

Example (Creating a Gzip File)

ZipControl.ArchiveFile = "c:\test.gz" ZipControl.FileDecompressedName = "c:\test.txt" ZipControl.Compress() Example (Extracting from a Gzip File)

ZipControl.ArchiveFile = "c:\test.gz" ZipControl.Scan() ZipControl.FileDecompressedName = "c:\test.txt" ZipControl.Extract()

Property List

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

Method List

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

Event List

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

Config Settings

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

ArchiveFile Property (Gzip Component)

The name of the zip, gzip, tar, or jar archive.

Syntax

property ArchiveFile: String read get_ArchiveFile write set_ArchiveFile;

Default Value

''

Remarks

This property specifies the name of the archive to be read or written. This property is required when extracting files.

When Scan, Extract, or ExtractAll is invoked, the file specified by ArchiveFile will be opened for read. If the file does not exist, a trappable error will be generated.

When Compress is called, the file named by ArchiveFile will be written; if a file of this name already exists the Overwrite event will be fired. If ArchiveFile is set to the empty string (''), the archive will not be written to disk, and will be provided only through the Progress event.

The filename may be specified with or without a path. Paths may be relative or absolute, and should be specified in the format native to the host operating system. The filename should be specified with the appropriate extension (such as 'zip'); an extension will not automatically be appended by the component.

If the file cannot be read, or written, as appropriate, a trappable error will be generated.

Example (Creating an Archive)

ZipControl.ArchiveFile = "c:\test.zip" ZipControl.RecurseSubdirectories = true ZipControl.IncludeFiles("c:\foo\*") ZipControl.Compress()

Note: an archive already open for read may be closed by setting ArchiveFile to the empty string ('').

CompressionLevel Property (Gzip Component)

The compression level to use.

Syntax

property CompressionLevel: Integer read get_CompressionLevel write set_CompressionLevel;

Default Value

4

Remarks

This property specifies the level of compression to be used, between 1 and 6. Higher values will cause the component to compress better; lower values will cause the component to compress faster.

Storing without compression is not supported for Gzip.

CompressionMethod Property (Gzip Component)

The compression method for the component to use.

Syntax

property CompressionMethod: TipzTCompressionMethods read get_CompressionMethod write set_CompressionMethod;

TipzTCompressionMethods = (
  cmgDeflate,
  cmgLZCCompress
);

Default Value

cmgDeflate

Remarks

By default, the component uses the Deflate compression method described in rfc 1952. When set to LZC compress method, the component will use a variation of the method described by the LZW (Lempel-Ziv-Welch) algorithm that is compatible with Unix's compress utility.

ExtractToPath Property (Gzip Component)

A base path to decompress to.

Syntax

property ExtractToPath: String read get_ExtractToPath write set_ExtractToPath;

Default Value

''

Remarks

Setting the ExtractToPath property affects the operation of the Extract and ExtractAll methods. Setting this property to a nonempty string will cause all decompressed files to be written to the specified path. If pathnames are given in the values of FileDecompressedName they will be regarded as relative to ExtractToPath.

If the specified directory does not exist, it will be created when extraction is done.

ExtractToPath should always be specified in the format native to the host operating system, and with a trailing slash or backslash. If the path is specified otherwise, it will be immediately converted and stored in the converted format. For example, '/temp' would be immediately converted to '\temp\' on a Windows system.

Example (Extracting from an Archive)

ZipControl.ArchiveFile = "c:\temp.zip" ZipControl.ExtractToPath = "c:\extracted\" ZipControl.ExtractAll()

FileCompressedDate Property (Gzip Component)

The date and time of the compressed file, as stored within the gzip archive.

Syntax

property FileCompressedDate: Int64 read get_FileCompressedDate;

Default Value

0

Remarks

FileCompressedDate contains the last modified date of the file, as stored within the archive (it does not generally correspond to when the file was compressed).

FileCompressedDate is returned in a platform-specific format. The Java and other editions will return the number of milliseconds since January 1, 1970, 00:00:00. This value may be passed directly to the java.util.Date constructor to create a java.util.Date object representing this date.

The .NET Edition will return the number of ticks, or 100-nanosecond intervals, since January 1, 0001, 00:00:00. This value may be passed directly to the System.DateTime constructor to create a System.DateTime object representing this date.

Reading the value of this property will return a meaningful value only after a call to Scan or Extract. If a meaningful value is not available this property will return a value of 0.

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

FileCompressedName Property (Gzip Component)

Filename, as stored inside of the archive.

Syntax

property FileCompressedName: String read get_FileCompressedName write set_FileCompressedName;

Default Value

''

Remarks

FileCompressedName contains the name of the compressed file, as stored within the gzip header.

This field should generally be set with a relative path or with no path at all. The exact interpretation of the path is left to the decompression software; generally, pathnames will be interpreted as relative to a base directory, and these subdirectories will be created as needed. Absolute pathnames (paths beginning with a / character) will not be interpreted correctly by the component, and may or may not be interpreted correctly by other decompression software.

Paths should be specified in standard (UNIX) format. They may also be specified in the format native to the host operating system, in which case they will be immediately converted.

It is not usually necessary to manually set the value of this property; it will be assigned by Compress if it is not specified, and it will always be written by a call to Scan or Extract.

FileDecompressedName Property (Gzip Component)

File name to decompress to, or compress from.

Syntax

property FileDecompressedName: String read get_FileDecompressedName write set_FileDecompressedName;

Default Value

''

Remarks

FileDecompressedName contains the name of the file in the archive, as stored on the file system, outside the archive.

When compressing a file, this property should be specified with a path, if necessary, to allow the file to be found by the component. If the file cannot be found when Compress is called, a trappable error will be generated, and the archive will not be correctly written.

When decompressing files, this property may be set after calling Scan and prior to calling Extract. If this property is set to the empty string when Extract is called, Extract will automatically set this property to an appropriate value.

Note: If Scan is not called before Extract, the component will internally call the method and any value in FileDecompressedName will be overwritten.

Paths on the local file system should be specified in the format native to the host operating system. They may also be specified in standard (UNIX) format, in which case they will be immediately converted.

FileDecompressedSize Property (Gzip Component)

Gets the size of the file, as decompressed outside the archive.

Syntax

property FileDecompressedSize: Int64 read get_FileDecompressedSize;

Default Value

-1

Remarks

This property holds the decompressed size of the file. If an archive is open for read (i.e. has been scanned or decompressed), this information will be read from the archive headers. If an archive is not open for read, the component will retrieve the information for the corresponding value of DecompressedName from the local file system.

A value of -1 will be returned in case of an I/O error.

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

FileInputData Property (Gzip Component)

The data of the file to be compressed.

Syntax

property FileInputData: String read get_FileInputData write set_FileInputData;
property FileInputDataB: TBytes read get_FileInputDataB write set_FileInputDataB;

Default Value

''

Remarks

When this property is set, the component will read in the data from this property instead of reading from the file contained in the FileDecompressedName property.

This property is not available at design time.

GzipData Property (Gzip Component)

(Decompression only) The gzip file contents as a byte array.

Syntax

property GzipData: String write set_GzipData;
property GzipDataB: TBytes write set_GzipDataB;

Default Value

''

Remarks

Normally you should set ArchiveFile before invoking Scan or Extract. If you prefer to read the gzip file from memory you may set GzipData instead. GzipData should be set to the entire contents of the gzip file; this will allow you to read from the archive without writing any temporary files to disk.

If you would like to extract data from the archive without ever writing to disk you should also set WriteToProgressEvent to true, and after invoking Scan, you should set the value of FileDecompressedName to an empty string. Then, when you invoke Extract (or ExtractAll) the data will be provided in the Progress event.

This property is write-only. Note that modifying a gzip file stored in GzipData is not supported, so Append will throw exceptions.

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

HasMoreData Property (Gzip Component)

Shows whether or not there is more data in the gzip archive.

Syntax

property HasMoreData: Boolean read get_HasMoreData;

Default Value

false

Remarks

The Gzip format described in RFC 1952 allows multiple gzipped data members to be concatenated into a single file. However, due to the nature of the algorithm it is impossible to determine the number of data members until after the entire archive has been decompressed. The HasMoreData property can be used to cycle through the archive and extract each file.

Simply set the ArchiveFile and ExtractToPath properties, then call Extract as long as the component has available data.

Note: the component will not update FileDecompressedName unless you call Scan or manually set FileDecompressedName on each loop before calling Extract.

Example (Extracting Multiple Files)

ZipControl.ArchiveFile = "c:\temp.zip" ZipControl.ExtractToPath = "c:\extracted\" Do ZipControl.Scan() //here you may inspect the file name in FileDecompressedName prior to extraction ZipControl.Extract() While ZipControl.HasMoreData

This property is read-only.

Abort Method (Gzip Component)

Aborts the current operation.

Syntax

procedure Abort();

Remarks

Abort may be used to immediately interrupt compression or decompression. Any files partially written by the component will be deleted.

Append Method (Gzip Component)

Adds specified file to an existing archive.

Syntax

procedure Append();

Remarks

The file contained in the FileDecompressedName property will be appended to the archive specified by ArchiveFile.

This method may only be used to add files to an existing archive. To add files to a new archive, Compress method should be used.

Compress Method (Gzip Component)

Creates the compressed gzip archive.

Syntax

procedure Compress();

Remarks

Invoking Compress creates the archive specified by ArchiveFile. When the method is called, the file specified by FileDecompressedName will be opened, and the file specified by ArchiveFile will contain the compressed output.

The filename to be stored within the archive is given by FileCompressedName. If this property is set to the empty string, it will be set to an appropriate value automatically; the component always writes a filename in the gzip headers.

As the data is compressed the Progress event will be fired at regular intervals. This event may be used to stream out the gzip file, or to display a progress bar to the user.

Config Method (Gzip Component)

Sets or retrieves a configuration setting.

Syntax

function Config(ConfigurationString: String): String;

Remarks

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

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the component, 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.

Extract Method (Gzip Component)

Extracts the compressed file from the gzip archive.

Syntax

procedure Extract();

Remarks

Invoking Extract decompresses the archive specified by ArchiveFile. The compressed file will be extracted, and written to disk. Also, FileCompressedName will be set to the filename found in the archive.

If FileDecompressedName is set to a nonempty string the file will be written there. Otherwise the component will automatically set FileDecompressedName to an appropriate value:

If a filename (i.e., FileCompressedName) is stored in the gzip headers, this filename will be used.

Otherwise, if ArchiveFile ends in '.gz', this filename, less the '.gz' extension will be used. If there are multiple files in the archive, the current 0-based file index will be appended to all files after the first file to differentiate between multiple files. For instance "test.gz" would become "test" for the first file and "test.gz" would become "test.1" for the second file in the archive.

If neither of these two conditions holds, '.unzipped' will be appended to ArchiveFile.

ExtractAll Method (Gzip Component)

Extracts all files from the compressed archive.

Syntax

procedure ExtractAll();

Remarks

ExtractAll extracts all files from the archive. The file(s) will be extracted to the directory specified by ExtractToPath, and given the names found in the archive or specified by FileDecompressedName.

If Scan has not been invoked when ExtractAll is called, Scan will automatically be invoked, and the FileCompressedName and FileDecompressedName properties will be set to the values found in the archive. To manually set the decompressed filenames, Scan should be invoked before setting FileDecompressedName.

The BeginFile and EndFile events will be fired before and after each file is extracted, and the Progress event will be fired as the data is extracted. If WriteToProgressEvent is set to true, the decompressed data will be streamed out through the Progress event.

Example (Extracting from an Archive)

ZipControl.ArchiveFile = "c:\temp.zip" ZipControl.ExtractToPath = "c:\extracted\" ZipControl.ExtractAll()

Reset Method (Gzip Component)

Resets the component.

Syntax

procedure Reset();

Remarks

Reset resets the state of the component. All properties will be set to their default values, and any files open will be closed.

Scan Method (Gzip Component)

Scans the compressed archive.

Syntax

procedure Scan();

Remarks

This method will scan the gzip archive specified by ArchiveFile. The archive will be read, the header will be checked, and the stored filename will be written to FileCompressedName.

Unlike in the Zip, Tar, and Jar components, it is never necessary to invoke this method, and it will not be automatically invoked by Extract. Suggested uses for this method would be to check that the file is a gzip file, or to determine an appropriate value for FileDecompressedName.

SetArchiveInputStream Method (Gzip Component)

The stream to read the zip, tar, jar, or gzip archive from.

Syntax

procedure SetArchiveInputStream(ArchiveStream: TStream);

Remarks

This method should be set when the archive is to be read from a stream when Extract is called.

By default, and when this is set to null, the component will read from the file specified by ArchiveFile. However, when this is a valid stream, the data will be read from the stream.

SetArchiveOutputStream Method (Gzip Component)

The stream to write the zip, tar, jar, or gzip archive to.

Syntax

procedure SetArchiveOutputStream(ArchiveStream: TStream);

Remarks

This method should be set when the archive is to be written to a stream when Compress is called.

By default, and when this is set to null, the component will write to the file specified by ArchiveFile. However, when this is a valid stream, the data will be written to the stream.

SetFileInputStream Method (Gzip Component)

The input stream to read the decompressed data from.

Syntax

procedure SetFileInputStream(ArchiveStream: TStream);

Remarks

When this method is set to a valid stream, the component will read in the data from the stream as the current file instead of reading from the file contained in the FileDecompressedName property.

BeginFile Event (Gzip Component)

Fired before a file is processed.

Syntax

type TBeginFileEvent = procedure (
  Sender: TObject;
  Index: Integer;
  var Skip: Boolean
) of Object;

property OnBeginFile: TBeginFileEvent read FOnBeginFile write FOnBeginFile;

Remarks

BeginFile is fired before compression or decompression begins. Index will contain 0.

You may use the Skip parameter to tell the component to skip the file when appending or decompressing.

EndFile Event (Gzip Component)

Fired after a file is processed.

Syntax

type TEndFileEvent = procedure (
  Sender: TObject;
  Index: Integer
) of Object;

property OnEndFile: TEndFileEvent read FOnEndFile write FOnEndFile;

Remarks

EndFile is fired when compression or decompression finishes. Index will contain 0.

Error Event (Gzip Component)

Information about non-fatal errors.

Syntax

type TErrorEvent = procedure (
  Sender: TObject;
  const Description: String;
  ErrorCode: Integer;
  Index: Integer;
  const Filename: String;
  var Ignore: Boolean
) of Object;

property OnError: TErrorEvent read FOnError write FOnError;

Remarks

The Error event is fired when non-fatal errors occur during compression or decompression. Note that if this event is fired during decompression this may indicate that the archive is corrupt.

By default these errors will cause the component to fail with an exception. The exception may be overridden by setting Ignore to true. This will cause the error to be ignored, the file will be skipped if necessary, and the component will continue operation.

ErrorCode will correspond to one of the following errors:

Description contains a textual description of the error. Index and Filename contain the array index (where appropriate) and filename of the file being processed at the time of the error.

Overwrite Event (Gzip Component)

Fired whenever a file exists and may be overwritten.

Syntax

type TOverwriteEvent = procedure (
  Sender: TObject;
  var Filename: String;
  var Overwrite: Boolean
) of Object;

property OnOverwrite: TOverwriteEvent read FOnOverwrite write FOnOverwrite;

Remarks

Overwrite is fired when a file is about to be overwritten, and would overwrite an existing file. The event is fired during decompression.

Filename contains the full name of the file, specified with its pathname.

Overwrite specifies whether or not the file will be overwritten. For Zip, Jar, and Tar, this is equal by default to the value of the OverwriteFiles property. For Gzip, this value defaults to true.

Either of the parameters may be changed when the event is fired. Changing the value of Overwrite will override the default behavior of the component, and cause the file to be overwritten or not overwritten, depending on the value set. If Filename is changed, the value of Overwrite will be ignored, and the file will be written with the specified name. If a file of the new name also exists this file will be silently overwritten.

Progress Event (Gzip Component)

Fired as progress is made.

Syntax

type TProgressEvent = procedure (
  Sender: TObject;
  Data: String;
  DataB: TBytes;
  const Filename: String;
  BytesProcessed: Int64;
  PercentProcessed: Integer
) of Object;

property OnProgress: TProgressEvent read FOnProgress write FOnProgress;

Remarks

The Progress event is automatically fired as compression or decompression is performed. When WriteToProgressEvent is true, the output data is provided through the Data parameter, allowing for it to be streamed out.

Filename contains the name of the file being written. If no file is being written, Filename will contain an empty string, and the output data will be provided exclusively through this event.

BytesProcessed contains the total number of uncompressed bytes processed. PercentProcessed contains the percent of uncompressed bytes processed, corresponding roughly to the running time of the operation.

For Gzip extraction only, BytesProcessed and PercentProcessed will reflect the number of compressed bytes extracted, as it is generally impossible to predetermine the total uncompressed size.

If WriteToProgressEvent is false, Data will contain null.

Config Settings (Gzip Component)

The component 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 component, access to these internal properties is provided through the Config method.

Gzip Config Settings

Base Config Settings

Trappable Errors (Gzip Component)

Errors

The following errors may be generated by the component. Note that frequently the error message will contain more specific information than what is listed here.

Note that some non-fatal errors may be trapped and explicitly ignored in the Error event. This will allow the component to continue operation even in case of error.

Gzip Errors

	102   The gzip archive is of an invalid or unsupported format.
	111   Can't open file for read.
	112   Can't open file for write.
	113   Can't create directory.
	114   The file is too large.
	115   Can't create empty archive.
	116   The archive must be scanned prior to attempting this operation.
	117   The array index is out of range.
	118   The maximum size of the archive has been exceeded.
	119   The archive must be specified, or streaming must be enabled.
	120   The component is busy.
	124   Must specify the compressed name.
	127   Bad CRC-32 checksum.
	128   Unable to set file date.
	133   File already exists in the archive.
	150   An I/O error has occurred (details follow).