Activity - readFile

Activity Type: Indexed File

Description

Reads data from one or more binary or text files stored on the server. The file data is then written to an output which can be connected to another activity or delivered back to the user in the response document.

Examples

To read 9 bytes from the some/file.ext file, starting immediately after byte number 3, and to output the file data as a string without base-64 encoding it:

<readFile name="read">
  <file>some/file.ext</file>
  <bytes offset="3" length="9"/>
  <output name="fileAccessOutput" base64encode="false"/>
</readFile>

To read 5 lines from the some/file.ext text file, starting immediately after line number 2, and to output the data as a base-64 encoded string:

<readFile name="read">
  <file>some/file.ext</file>
  <lines offset="2" length="5"/>
  <output name="fileAccessOutput" base64encode="true"/>
</readFile>

To read data from one or more files and to base-64 encode the resulting data. The description of what data to read must be produced by another activity and connected to the fromLocal input:

<readFile name="read">
  <fromLocal from="searchOutput"/>
  <output name="fileAccessOutput" base64encode="true"/>
</readFile>

Specification

Element readFile:

• Attribute name - unique name for the activity within the scope of a request.
• One of the following element groups, either:
  • Element fromLocal - refers to the output stream of another activity.
    • Attribute from - name of an input stream providing the data to deliver.
• Or:
  • Element file - contains the path to the file to access. This path should be relative to the top-level directory exposed by the associated OGSA-DAI service and must not attempt to traverse up the directory hierarchy higher than this directory.
  • One of the following two elements (required):
    • Element bytes - access the contents of a file on a byte-by-byte basis.
      • Attribute offset - index of first byte to access, starting at 0.
      • Attribute length - number of bytes to access or -1 to read all bytes until the end of file.
    • Element lines - access the contents of a file on a line-by-line basis.
      • Attribute offset - index of first line to access, starting at 0.
      • Attribute length - number of lines to access or -1 to read all lines until the end of file.
• output (required) - output stream.
  • Attribute name - name of the activity's output stream.
  • Attribute base64encode - flag indicating whether the output will be base64 encoded (true) or not (false).

Input and Output Types

• Input: fromLocal (optional) — String of XML data where each block contains a <readFile> element conforming to the same specification described above. If used, this input allows the readFile activity to perfrom multiple file reading operations.
• Output: output — String or byte[] data containing the requested file contents. If the contents have been accessed on a line-by-line basis then each data block is a plain string or base-64 encoded string, depending on the value of the base64encode attribute for the activity. If the contents have been accessed on a byte-by-byte bases the data is a plain byte array or a base-64 encoded byte array, depending on the value of the base64encode attribute for the activity. If multiple file reading operations are performed, the output will contain a sequence of data from multiple files.

Warning to Service Deployers

This activity can be used by clients to potentially access any directory on your server below that exposed by the associated OGSA-DAI service.

Data Resource Accessor

This activity requires a data resource accessor that implements the following interface: uk.org.ogsadai.dataresource.FileAccessProvider

XML Schema

OGSA-DAI/schema/ogsadai/xsd/activities/file_reading.xsd

Class

uk.org.ogsadai.activity.indexedfiles.FileReadingActivity

Client Toolkit Class

uk.org.ogsadai.client.toolkit.activity.indexedfiles.ReadFile