add base layer.rs

Cargo.toml

@@ -13,3 +13,7 @@ semver = { version = "0.11", features = ["serde"] }
 serde = { version = "1.0", features = ["derive"] }
 thiserror = "1.0"
 toml = "0.5.8"
+
+[dev-dependencies]
+anyhow = "1"
+tempfile = "3"

src/data/layer.rs

@@ -12,3 +12,14 @@ pub struct Layer {
     pub cache: bool,
     pub metadata: Table,
 }
+
+impl Layer {
+    pub fn new() -> Self {
+        Layer {
+            launch: false,
+            build: false,
+            cache: false,
+            metadata: Table::new(),
+        }
+    }
+}

src/error.rs

@@ -1,4 +1,4 @@
-#[derive(thiserror::Error, Debug, PartialEq)]
+#[derive(thiserror::Error, Debug)]
 pub enum Error {
     #[error("Found `{0}` but value MUST be in form <major>.<minor> or <major>, where <major> is equivalent to <major>.0.")]
     InvalidBuildpackApi(String),
@@ -12,4 +12,10 @@ pub enum Error {
         "Found `{0}` but value MUST only contain numbers, letters, and the characters ., /, and -."
     )]
     InvalidStackId(String),
+    #[error("could not serialize into TOML")]
+    TomlSerError(#[from] toml::ser::Error),
+    #[error("could not deserialize from TOML")]
+    TomlDeError(#[from] toml::de::Error),
+    #[error("I/O Error: {0}")]
+    IoError(#[from] std::io::Error),
 }

src/layer.rs

@@ -0,0 +1,123 @@
+use crate::{data::layer::Layer as ContentMetadata, Error};
+use std::{
+    fs,
+    path::{Path, PathBuf},
+};
+
+/// CNB Layer
+pub struct Layer {
+    pub name: String,
+    path: PathBuf,
+    content_metadata_path: PathBuf,
+    content_metadata: ContentMetadata,
+}
+
+impl Layer {
+    /// Layer Constructor that makes a ready to go layer:
+    /// * create `/<layers_dir>/<layer> if it doesn't exist
+    /// * `/<layers_dir>/<layer>.toml` will be read and parsed from disk if found. If not found an
+    /// empty [`crate::data::layer::Layer`] will be constructed.
+    ///
+    /// # Errors
+    /// This function will return an error when:
+    /// * if it can not create the layer dir
+    /// * if it can not deserialize Layer Content Metadata to [`crate::data::layer::Layer`]
+    ///
+    /// # Examples
+    /// ```
+    /// # use tempfile::tempdir;
+    /// use libcnb::layer::Layer;
+    ///
+    /// # fn main() -> Result<(), libcnb::Error> {
+    /// # let layers_dir = tempdir().unwrap().path().to_owned();
+    /// let layer = Layer::new("foo", layers_dir)?;
+    ///
+    /// assert!(layer.as_path().exists());
+    /// assert_eq!(layer.content_metadata().launch, false);
+    /// assert_eq!(layer.content_metadata().build, false);
+    /// assert_eq!(layer.content_metadata().cache, false);
+    /// assert!(layer.content_metadata().metadata.is_empty());
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn new(name: impl Into<String>, layers_dir: impl AsRef<Path>) -> Result<Self, Error> {
+        let name = name.into();
+        let layers_dir = layers_dir.as_ref();
+        let path = layers_dir.join(&name);
+
+        fs::create_dir_all(&path)?;
+
+        let content_metadata_path = layers_dir.join(format!("{}.toml", &name));
+        let content_metadata = if let Ok(contents) = fs::read_to_string(&content_metadata_path) {
+            toml::from_str(&contents)?
+        } else {
+            ContentMetadata::new()
+        };
+
+        Ok(Layer {
+            name,
+            path,
+            content_metadata,
+            content_metadata_path,
+        })
+    }
+
+    /// Returns the path to the layer contents `/<layers_dir>/<layer>/`.
+    pub fn as_path(&self) -> &Path {
+        self.path.as_path()
+    }
+
+    /// Returns a reference to the [`crate::data::layer::Layer`]
+    pub fn content_metadata(&self) -> &ContentMetadata {
+        &self.content_metadata
+    }
+
+    /// Returns a mutable reference to the [`crate::data::layer::Layer`]
+    pub fn mut_content_metadata(&mut self) -> &mut ContentMetadata {
+        &mut self.content_metadata
+    }
+
+    /// Write [`crate::data::layer::Layer`] to `<layer>.toml`
+    pub fn write_content_metadata(&self) -> Result<(), crate::Error> {
+        fs::write(
+            &self.content_metadata_path,
+            toml::to_string(&self.content_metadata)?,
+        )?;
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+    use tempfile::tempdir;
+
+    #[test]
+    fn new_reads_layer_toml_metadata() -> Result<(), anyhow::Error> {
+        let layers_dir = tempdir()?.path().to_owned();
+        fs::create_dir_all(&layers_dir)?;
+        fs::write(
+            layers_dir.join("foo.toml"),
+            r#"
+[metadata]
+bar = "baz"
+"#,
+        )?;
+
+        let layer = Layer::new("foo", &layers_dir)?;
+        assert_eq!(
+            layer
+                .content_metadata()
+                .metadata
+                .get::<str>("bar")
+                .unwrap()
+                .as_str()
+                .unwrap(),
+            "baz"
+        );
+
+        Ok(())
+    }
+}

src/lib.rs

@@ -3,5 +3,6 @@ pub mod data;
 mod error;
 pub use error::Error;
 pub mod detect;
+pub mod layer;
 pub mod platform;
 pub mod shared;