file-io

Overview ¶

Package main demonstrates format.File: the declarative typed file descriptor for reading, writing, and updating files with full codec validation.

Scenario: an IoT sensor data pipeline that:

• Loads a TOML service config on startup using a static format.File
• Applies a single env var override via format.FromEnvVar
• Writes and reads per-sensor JSON measurement files using a template path
• Validates path variables (date format) with a format.FilePathParam codec
• Handles all typed file errors with errors.As
• Wires a stats.FileObserver for per-operation metrics + slog for structured errors
• Writes and reads raw binary (PNG) files using format.Binary + validate.PNG

Key patterns shown:

• format.NewFile — declare once, use anywhere (mirrors rest.Route / events.Channel)
• format.File.BuildPath — pre-flight path validation without any I/O
• format.File.Update — atomic read-modify-write in one call
• format.FileOptions — wiring observer + custom file permission
• format.FilePathParamError, format.MissingFilePathVarError, format.FileReadError — navigate via errors.As
• format.Binary — raw binary file I/O with magic-byte validation

Run with: go run ./examples/file-io