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


Midware Components Reference