korni

An ultra-fast, nearly stateless, and failure-tolerant parser for .env files, written in Rust.

Designed for high-performance tooling (LSPs, linters, formatters) and applications that need deep introspection into environment configuration files.

Features

• 🚀 Blazingly Fast: Heavily optimized using nearly zero-copy parsing (Cow strings) and SIMD-friendly slice iterators.
• 📍 Introspective: Tracks exact line and column positions (spans) for keys, values, and comments.
• 💬 Comment Support: First-class support for parsing and preserving comments, including commented-out key-value pairs.
• 🛡️ Failure Tolerant: Continues parsing after errors, collecting all issues instead of halting on the first one.
• 📦 Zero Runtime Dependencies: Lightweight and easy to drop into any project.

Installation

[dependencies]
korni = "0.1.3"

Quick Start

use korni::{parse, ParseOptions};

fn main() {
    let input = r#"
# Database Configuration
DB_HOST=localhost
DB_PORT=5432
"#;

    // Simple parsing (fast mode)
    let entries = parse(input);

    for entry in entries {
        if let Some(pair) = entry.as_pair() {
            println!("Key: {}, Value: {}", pair.key, pair.value);
        }
    }

    // Advanced parsing with positions and comments
    let full_entries = korni::parse_with_options(input, ParseOptions::full());
}

API Reference

Core Types

Entry<'a>

The main parsing result type representing a single line in an .env file:

pub enum Entry<'a> {
    Comment(Span),           // A comment line (# ...)
    Pair(KeyValuePair<'a>),  // A key-value pair (KEY=value)
    Error(Error),            // A parsing error
}

KeyValuePair<'a>

Represents a parsed key-value pair with full introspection:

pub struct KeyValuePair<'a> {
    pub key: Cow<'a, str>,              // The key name
    pub key_span: Option<Span>,         // Span of the key
    pub value: Cow<'a, str>,            // The parsed value
    pub value_span: Option<Span>,       // Span of the value
    pub quote: QuoteType,               // Single, Double, or None
    pub open_quote_pos: Option<Position>,
    pub close_quote_pos: Option<Position>,
    pub equals_pos: Option<Position>,   // Position of the '='
    pub is_exported: bool,              // Whether 'export' keyword was used
    pub is_comment: bool,               // Whether this was in a comment (# KEY=value)
}

ParseOptions

Configure parsing behavior:

pub struct ParseOptions {
    pub include_comments: bool,  // Parse & include comments in output
    pub track_positions: bool,   // Track line/col/offset positions
}

// Presets
ParseOptions::fast()  // Default: no comments, no positions
ParseOptions::full()  // Comments + positions enabled

Position and Span

For precise location tracking:

pub struct Position {
    pub line: usize,    // 0-indexed line number
    pub col: usize,     // 0-indexed column number
    pub offset: usize,  // Byte offset from file start
}

pub struct Span {
    pub start: Position,
    pub end: Position,
}

QuoteType

Indicates how a value was quoted:

pub enum QuoteType {
    Single,  // 'value'
    Double,  // "value"
    None,    // value (unquoted)
}

Parsing Functions

parse(input: &str) -> Vec<Entry>

Fast parsing - returns key-value pairs only, no position tracking:

let entries = korni::parse("KEY=value");

parse_with_options(input: &str, options: ParseOptions) -> Vec<Entry>

Configurable parsing with custom options:

let entries = korni::parse_with_options(input, ParseOptions::full());

Builder API

The builder API provides a fluent interface for parsing from various sources:

From String

use korni::Korni;

let env = Korni::from_str("KEY=value")
    .preserve_comments()
    .track_positions()
    .parse()?;

println!("{}", env.get("KEY").unwrap());

From File

let env = Korni::from_file(".env")
    .preserve_comments()
    .parse()?;

Auto-discover File

Searches current directory and ancestors for the file:

let env = Korni::find_file(".env")?
    .parse()?;

From Bytes

let bytes = b"KEY=value";
let env = Korni::from_bytes(bytes).parse()?;

From Reader

use std::io::Cursor;

let reader = Cursor::new("KEY=value");
let env = Korni::from_reader(reader).parse()?;

Environment API

The Environment struct provides a HashMap-like interface:

use korni::Korni;

let env = Korni::from_str("
    DB_HOST=localhost
    DB_PORT=5432
").parse()?;

// Get a value
let host = env.get("DB_HOST");           // Option<&str>
let port = env.get_or("DB_PORT", "3306"); // &str with default

// Get full entry with metadata
if let Some(entry) = env.get_entry("DB_HOST") {
    println!("Quoted: {:?}", entry.quote);
    println!("Exported: {}", entry.is_exported);
}

// Iterate all pairs
for pair in env.iter() {
    println!("{} = {}", pair.key, pair.value);
}

// Check for errors
if env.has_errors() {
    for error in env.errors() {
        eprintln!("Error: {}", error);
    }
}

// Export to HashMap<String, String>
let map = env.to_map();

Iterator API

Stream entries one at a time for memory efficiency:

use korni::{Parser, EnvIterator};

let parser = Parser::new("KEY1=a\nKEY2=b");
let iter = EnvIterator::new(parser);

for entry in iter {
    // Process entry
}

Error Types

All parsing errors include byte offsets for precise error reporting:

pub enum Error {
    InvalidUtf8 { offset: usize, reason: String },
    UnclosedQuote { quote_type: &'static str, offset: usize },
    InvalidKey { offset: usize, reason: String },
    ForbiddenWhitespace { location: &'static str, offset: usize },
    DoubleEquals { offset: usize },
    InvalidBom { offset: usize },
    Expected { offset: usize, expected: &'static str },
    Generic { offset: usize, message: String },
    Io(String),
}

// Get the byte offset of any error
let offset = error.offset();

Parsing Rules

Keys

• Must contain only ASCII alphanumeric characters and underscores ([A-Za-z0-9_])
• Must NOT start with a digit
• No whitespace allowed between key and =

VALID_KEY=value
_also_valid=value
# Invalid: 123_KEY=value (starts with digit)
# Invalid: KEY = value (whitespace around =)

Values

Unquoted Values

• Terminate at first whitespace or end of line
• Support line continuation with trailing backslash

KEY=simple_value
MULTI=line1\
line2

Single-Quoted Values

• Literal strings - no escape processing
• Must be closed on the same line

KEY='raw value with $VAR not expanded'

Double-Quoted Values

• Support escape sequences: \n, \r, \t, \\, \", \$
• Unknown escapes are preserved literally

KEY="line1\nline2"
ESCAPED="contains \"quotes\""

Comments

• Lines starting with # are comments
• Inline comments: KEY=value # comment (requires whitespace before #)
• Commented-out pairs (# KEY=value) are parsed with is_comment: true

Export Keyword

The optional export prefix is supported:

export DATABASE_URL=postgres://localhost/db

BOM Handling

• UTF-8 BOM (\xEF\xBB\xBF) at file start is silently skipped
• BOM in middle of file produces an error

Comparison with dotenvy

dotenvy is the standard, battle-tested crate for loading environment variables in Rust applications. korni serves a different, more specialized purpose.

Feature	dotenvy	korni
Primary Goal	Load env vars into std::env	Parse env files into structured data
Output	Modifies process environment	AST / Structured Iterators
Introspection	None (opaque loading)	Full (Spans, Line/Col, Offsets)
Comments	Ignored	Parsed & Preserved
Error Handling	Stops on first error	Failure-tolerant (collects all errors)
Modifies std::env	✅ Yes	❌ No (Pure parsing)
Use Case	Application Configuration	Tooling (IDEs, Linters), Complex Configs

When to use dotenvy

• You just want cargo run to pick up your .env file.
• You need standard, 12-factor app configuration.

When to use korni

• You are building an IDE plugin, linter, or formatter.
• You need to analyze the structure of an .env file (e.g. "where is DB_PORT defined?").
• You need performance-critical parsing of massive files.
• You want to manually control how environment variables are applied.

Specification & Compliance

EDF Specification

This parser implements the EDF (Ecolog Dotenv File Format) 1.0.0 specification.

Compliance Statement

korni aims for EDF 1.0.0 compliance. Per the specification's compliance requirements:

A parser implementation claiming EDF 1.0.0 Compliance MUST adhere to ALL requirements specified in the specification. This is a strict, all-or-nothing compliance model.

Requirements Implemented

• ✅ Parsing Rules: Keys, values (quoted/unquoted), comments, and multiline handling per Section 4
• ✅ Error Handling: Failure-tolerant parsing with detailed error messages including byte offsets
• ✅ Security: UTF-8 validation, BOM handling, error message safety
• ✅ Edge Cases: Empty values, escape sequences, line continuations

Allowed Variations (per spec)

This implementation varies in:

• Performance: Heavily optimized with focus on zero-copy parsing (but it is not absolutely zero-copy) and SIMD-friendly iterators
• API Design: Rust-idiomatic with Cow strings, builders, and iterators
• Additional Features: Position tracking, comment parsing, and is_comment flag for commented-out pairs

Version Compatibility

• Specification Version: EDF 1.0.0
• Semantic Versioning: This library follows semver. Major version bumps indicate potential parsing behavior changes.

License

MIT