Midware TMWBuffer

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Overview

unit

RFormat.pas

TMWBuffer if a very important component in MidWare technology. TMWBuffer implement data storage and formatting for transmission. Data echanged between client and server is exactly TMWBuffer content, byte for byte.

TMWBuffer can be seen as a data table in memory. This table is organized as records made of variable field number, each field having a variable length.

TMWBuffer provides methods and properties to read, write and sort data. Data is stored in a very simple format: a buffer dynamically allocated from memory that contains all fields and records. Fields and records boundaries are marked with delimiters. If control characaters or delimiters are found within data, they are escaped. Three delimiters are used: escape delimiter, field delimiter and record delimiter. They are placed at start of buffer in order to consitute a kind of dictionnary.

By default, MidWare use those delimiters (decimal code): <syntaxhighlight lang="delphi">

  Field  18
  Record 20
  Escape 127

</syntaxhighlight> Escape delimiter is also used to mark meta data information within data buffer. Meta data is field type or general purpose meta data such as field layout.

If an escape character is followed by another escape character, then data contains a single character. Table below indicate the meaning of an escape character followed by another character: <syntaxhighlight lang="delphi">

 C  Carriage return
 L  Line feed
 F  Field delimiter
 R  Record delimiter
 N  Null character
 T  Field type follow (used for blobs: S=String)

</syntaxhighlight> Other uppercase characters are marking start of variable length general purpose meta data. End of meta data is marked with escape character and corresponding lower case letter.

Properties

AutoExpand		AutoExpand property tells the component if the data buffer can be expanded when it is too short for the data that needs to be written to it.
Bof		Bof property is TRUE when current position has reached begin of file.
DataBuffer		Gives access to the underlaying data buffer.
DataBufferCount		The size in bytes of the data present in the buffer.
DataBufferSize		The size in bytes of the current buffer.
Eof		Eof property is TRUE when current position has reached end of file.
FieldCount		Returns the number of fields in the current record.
Fields		The indexed Fields[] property gives access to the current record's fields.
FieldSize		Return field size in bytes.
FieldType		Read only indexed property returning filed type for a given field in current record.
HasData		HasData property is TRUE when TMWBuffer contains data.
HeaderSize		Size in byte of the header in the data buffer. Default to 0.
MetaData		Read only indexed MetaData property gives access to the current record's meta data (application defined).
RecordCount		Readonly property RecordCount retunrs the number of records stored in TMWBuffer. See also FieldCount.

Methods

AppendMetaData		AppendMetaData will add variable length, general purpose meta data at the end of current field.
Assign		The Assign method copies data from a TMWBuffer component to another.
AppendBinaryField		Write binary data as field content.
AppendFields		Append fields to the current record. See also WriteFields.
AppendRecord		Append a single record from another TMWBuffer.
AppendStreamField		Append a stream field to current record. See also WriteStreamField.
Delete		Delete the current record. Deleted records are physically lost.
ExpandBuffer		ExpandBuffer method check how much free space is left and will try to expand data buffer as needed.
First		First method makes the first record the current one.
FreeBookmark		Free resources used for bookmark keeping. See GetBookmark.
GetBookmark		Get a bookmark on current record.
GetStreamField		Get a stream (blob) field value from the buffer.
GotoBookmark		Return the current position to the bookmark setup by GetBookmark.
IsValidFields		IsValidFields check if a field number is valid for use with Fields indexed property.
Last		Last method will make the lsat record the current one.
LoadFromFile		Load TMWBuffer content from a files created with SaveToFile or SaveToStream.
LoadFromStream		Load TMWBuffer content from a stream created by SaveToStream or SaveToFile.
Locate		Locate a record by sequential search.
Next		Next method makes the next record the current one.
Prior		Prior method makes the previous record the current one.
RecordToString		Return the current record expressed as a string.
Rewrite		Clear buffer content and prepare for new writing.
SaveToFile		Save TMWBuffer data to a file.
SaveToStream		Save TMWBuffer data to a stream.
Seek		Set current record to the one indicated by nPos which results from a previous call to Tell method.
Sort		Sort will sort TMWBuffer content.
StringToRecord		Reverse operation for RecordToString.
StringToRecords		Same as StringToRecord, but applied for several records.
Tell		Return the internal position for the current record.
WriteDataBuffer		Append data from a buffer to the record buffer.
WriteFields		WriteFields will write fields to the next record or append fields to the current record as per NewRec argument.
WriteRecordMarker		Terminate the current record.
WriteStreamField		Write a single stream (blob) field.

How To

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