Struct NdjsonWriter 

pub struct NdjsonWriter { /* private fields */ }

Available on crate feature io only.

NDJSON file writer with automatic rotation and metrics.

Each line written is expected to be a complete JSON object (NDJSON format). The writer handles file rotation, optional compression, and age-based cleanup.

Implementations

impl NdjsonWriter

pub fn new( config: &FileWriterConfig, subdir: &str, filename: &str, label: &str, ) -> Result<Self, Error>

Create a new NDJSON writer.

Creates {config.path}/{subdir}/ and writes to {filename} within it. Files are rotated according to the config’s rotation period.

Arguments

• config – Shared file writer settings (path, rotation, compression)
• subdir – Subdirectory under config.path (e.g. service name)
• filename – Output filename (e.g. “dlq.ndjson”, “events.ndjson”)
• label – Human label for log messages (e.g. “dlq”, “output”)

Errors

Returns std::io::Error if the output directory cannot be created.

pub fn write_line(&self, line: &[u8]) -> Result<(), Error>

Write a single line (must include trailing newline or caller appends it).

The data is written as-is – caller is responsible for serialisation and newline termination.

pub fn write_buf(&self, buf: &[u8], count: u64) -> Result<(), Error>

Write a pre-serialised buffer containing multiple newline-delimited lines.

The buffer should already have newlines between entries. The count parameter is used for metrics tracking.

pub fn flush(&self) -> Result<(), Error>

Flush any in-memory buffer through the rotating writer.

Note: file-rotate does not expose the underlying File handle, so this can only call flush() (which pushes buffered bytes from the writer’s in-memory buffer to the kernel page cache). It does NOT guarantee on-disk durability – a power-loss event between the page cache and the platter can still lose data. This is a limitation of the rotation library, not the API: when file-rotate gains a sync hook, this method will gain fsync-level semantics.

For DLQ flush callers: this is the strongest durability the file backend can express today. Producers running with high write rates plus an acks=all sibling Kafka backend will get real durability from the Kafka path.

Errors

Returns the underlying std::io::Error if the flush fails. The internal write_errors counter is incremented.

pub fn lines_written(&self) -> u64

Number of lines successfully written.

pub fn write_errors(&self) -> u64

Number of write errors encountered.

pub fn label(&self) -> &str

Human label for this writer (e.g. “dlq”, “output”).

pub fn output_path(&self) -> &PathBuf

Output directory path.

Trait Implementations

impl Debug for NdjsonWriter

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.