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Prefix layers with sequential numbers starting at `0001_<name>`. To support this it assumes any layers on disk with a number prefix is equivalent i.e. changing the order of layers will not invalidate the cache. This has the benefit that: - Layers can be named something semantic without side effects. - Build and launch layer behavior is guaranteed to be the same (provided `read_env` is called and applied for every layer in main).
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,68 @@ | ||
| use libcnb::data::layer::LayerName; | ||
| use std::path::{Path, PathBuf}; | ||
| use std::sync::atomic::{AtomicUsize, Ordering}; | ||
|
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||
| /// As layers are created this is incremented | ||
| static LAYER_COUNT: AtomicUsize = AtomicUsize::new(1); | ||
| /// Formatting for number of leanding zeros. Max number of layers is 1024 (as of 2025). Four digits allows | ||
| /// one buildpack to meet or exceed that value | ||
| static DIGITS: usize = 4; | ||
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| fn prefix(value: usize) -> String { | ||
| format!("{value:0DIGITS$}_") | ||
| } | ||
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| fn next_count() -> usize { | ||
| LAYER_COUNT.fetch_add(1, Ordering::Acquire) | ||
| } | ||
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| /// Removes the `NNNN_` prefix if there is one | ||
| pub(crate) fn strip_order_prefix(name: &str) -> String { | ||
| let re = regex::Regex::new(&format!("^\\d{{{DIGITS}}}_")) | ||
| .expect("internal code bugs caught by unit tests"); | ||
| re.replace(name, "").to_string() | ||
| } | ||
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| /// Searches the given dir for an entry with the exact name or any NNNN_ prefix and returns Ok(Some(PathBuf)) | ||
| pub(crate) fn contains_entry_with_name_or_pattern( | ||
| dir: &Path, | ||
| name: &str, | ||
| ) -> Result<Option<PathBuf>, std::io::Error> { | ||
| let name = strip_order_prefix(name); | ||
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| let pattern = format!("^\\d{{{DIGITS}}}_{}$", regex::escape(&name)); | ||
| let re = regex::Regex::new(&pattern).expect("internal error if this fails to compile"); | ||
|
|
||
| for entry in fs_err::read_dir(dir)?.flatten() { | ||
| if let Some(file_name) = entry.file_name().to_str() { | ||
| if file_name == name || re.is_match(file_name) { | ||
| return Ok(Some(entry.path().clone())); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| Ok(None) | ||
| } | ||
|
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||
| /// Gets and increments the next name | ||
| /// | ||
| /// # Panics | ||
| /// | ||
| /// Assumes that prepending a value to a valid layer name is a valid operation | ||
| #[must_use] | ||
| pub(crate) fn ordered_layer_name(name: LayerName) -> LayerName { | ||
| let prefix = prefix(next_count()); | ||
| prefix_layer_name(&prefix, name) | ||
| } | ||
|
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||
| /// # Panics | ||
| /// | ||
| /// Assumes that prepending a value to a valid layer name is a valid operation | ||
| #[must_use] | ||
| #[allow(clippy::needless_pass_by_value)] | ||
| fn prefix_layer_name(prefix: impl AsRef<str>, name: LayerName) -> LayerName { | ||
| let prefix = prefix.as_ref(); | ||
| format!("{prefix}{}", name.as_str()) | ||
| .parse() | ||
| .expect("Prepending to a valid layer name is valid") | ||
| } |