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//! Compression algorithm spec for PBF output blobs.
use std::str::FromStr;
/// Compression algorithm for PBF output blobs.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
#[non_exhaustive]
pub enum Compression {
/// No compression (raw bytes).
None,
/// Zlib compression at the given level (0-9).
/// Level 6 matches osmium's default (`Z_DEFAULT_COMPRESSION`).
Zlib(u32),
/// Zstd compression at the given level (1-22, default 3).
///
/// Zstd decompresses 3-5x faster than zlib at equivalent compression ratios,
/// making it ideal for read-heavy workflows (planet imports, tile generation).
/// Level 3 (zstd's default) provides a good balance of compression ratio and
/// speed. Higher levels (e.g. 19) compress ~10-15% better but are much slower
/// to write - use for archival PBFs that will be read many times.
///
/// **Compatibility warning:** Not all PBF consumers support zstd yet. As of
/// 2025, osmium, osm2pgsql, and most tools only read zlib-compressed PBFs.
/// Use zstd for internal pipelines where you control both writer and reader.
Zstd(i32),
}
impl Default for Compression {
fn default() -> Self {
Compression::Zlib(6)
}
}
/// Parse error for [`Compression`] string specs.
#[derive(Debug, Clone)]
pub struct ParseCompressionError(String);
impl std::fmt::Display for ParseCompressionError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str(&self.0)
}
}
impl std::error::Error for ParseCompressionError {}
impl FromStr for Compression {
type Err = ParseCompressionError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
match s {
"none" => Ok(Self::None),
"zlib" => Ok(Self::default()),
"zstd" => Ok(Self::Zstd(3)),
_ if s.starts_with("zlib:") => {
let level: u32 = s[5..]
.parse()
.map_err(|_| ParseCompressionError(format!("invalid zlib level: {s}")))?;
if level > 9 {
return Err(ParseCompressionError(format!(
"zlib level must be 0-9, got {level}"
)));
}
Ok(Self::Zlib(level))
}
_ if s.starts_with("zstd:") => {
let level: i32 = s[5..]
.parse()
.map_err(|_| ParseCompressionError(format!("invalid zstd level: {s}")))?;
if !(-7..=22).contains(&level) {
return Err(ParseCompressionError(format!(
"zstd level must be -7..22, got {level}"
)));
}
Ok(Self::Zstd(level))
}
_ => Err(ParseCompressionError(format!(
"unknown compression: {s} (expected none, zlib, zlib:LEVEL, zstd, zstd:LEVEL)"
))),
}
}
}