The BOINC storage model is based on files. The inputs and outputs of applications, and the application executables, are files.

The BOINC core client transfers files to and from data servers operated by the project, using HTTP.

A file is described by an XML element of the form

<file_info>
    <name>foobar</name>
    <url>http://a.b.c/foobar</url>
    <url>http://x.y.z/foobar</url>
    ...
    <md5_cksum>123123123123</md5_cksum>
    <nbytes>134423</nbytes>
    <max_nbytes>200000</max_nbytes>
    <status>1</status>
    [ <generated_locally/> ]
    [ <executable/> ]
    [ <upload_when_present/> ]
    [ <sticky/> ]
    [ <signature_required/> ]
</file_info>

• The <name> element gives the file's name, which must be unique within the project.
• Each <url> element gives a URL where the file is (or will be) located on a data server.
• The <md5_cksum> element is the MD5 checksum of the file.
• The <nbytes> element is the size of the file in bytes (may be greater than 2^32).
• The <max_nbytes> element is the maximum allowable size of the file in bytes (may be greater than 2^32). This is used to prevent flooding data servers with bogus data.
• The <status> element is 0 if the file is not present, 1 if the file is present, or a negative error code if there was a problem in downloading or generating the file.
• The <generated_locally> element, if present, indicates that the file will be generated by an application on the client, as opposed to being downloaded.
• The <executable> element, if present, indicates that the file protections should be set to allow execution.
• The <upload_when_present> element, if present, indicates that the file should be uploaded after it is created.
• The <sticky> element, if present, indicates that the file should be retained on the client after its initial use.
• The <signature_required> element, if present, indicates that the file should be verified with an RSA signature. This generally only applies to executable files.

Once a file is created (on a data server or a participant host) it is immutable.

File references

Files may be associated with workunits, results and application versions. Each such association is represented by an XML element of the form

<file_ref>
    <file_name>foobar</file_name>
    [ <open_name>input</open_name> ]
    [ <main_program/> ]
</file_ref>

• The <file_name> element specifies a file.
• The <open_name> element is the name by which the application will refer to the file.
• The <main_program/> element is used for files associated with application versions. It indicates that this file is the application's main program.