Safe File

Part of the Using JSON Schema project.

Robust storage using text files is enhanced with support for automated recovery should an update fail.

This library provides support for reading and writing files in a recoverable mode, allowing automated recovery when the program restarts. Normal file read / write is also supported, enabling a common interface for both files using automated recovery capabilities and those not using them.

API

readFile

Read a file synchronously from a file system.

readFile (filename)

data = readFile (filename)

writeFile

Write a file synchronously to a file system.

writeFile (filename, data)

writeFile (filename, data)

safeReadFile

Read a file synchronously from a file system, inspecting the file system state and performing recovery processing if needed.

safeReadFile (filename)

data = safeReadFile (filename)

safeWriteFile

Write data to a file synchronously, using a recoverable set of steps. Should the write processing fail to complete, auto-recovery can perform the steps required to bring the file content back to a stable state.

safeWriteFile (filename, data)

safeWriteFile (filename, data)

safeGetState

Get the current state of the set of files representing the current file system contents. Returns one of,

• SAFE_NORMAL, normal state, base and backup files only present
• SAFE_RECOVERABLE, partial write condition that is automatically recoverable the next time a read, write or recover function is called
• SAFE_INTERVENE, last write failed before the data being written reached a recoverable state. Manual intervention is required if recovery of the last write is required, otherwise auto-recovery will recover to the prior stable state.

safeGetState (filename)

state = safeGetState (filename)

safeRecover

Initiate the auto-recovery process. This follows the same steps as safeReadFile follows, but can be called independently.

safeRecover (filename)

safeRecover (file)

SafeFileError

SafeFileError (code, message)

Constants for the error codes,

• NO_ERROR
• INVALID_NAME
• DOES_NOT_EXIST
• IS_NOT_A_FILE
• READ_ERROR
• WRITE_ERROR
• SAFE_NORMAL
• SAFE_RECOVERABLE
• SAFE_INTERVENE

Installation

The program can be installed using pip, with the command,

pip install ujs-safefile

License

MIT