Apt - Minimum Viable Buildpack - 02 - Aptfile Parsing (#2)

The `Aptfile` is how an application can specify custom packages to install. Unlike the version from our [classic apt buildpack](https://github.com/heroku/heroku-buildpack-apt), this parser **does not support**:
- [Custom debian packages](https://github.com/heroku/heroku-buildpack-apt/blob/master/bin/compile#L84-L89)
- [Custom repositories](https://github.com/heroku/heroku-buildpack-apt/blob/master/bin/compile#L71-L72)

Only package names, comment lines, and blank lines are supported in this version. 

Package names are parsed according to the restrictions defined in the [Debian Manual](https://www.debian.org/doc/debian-policy/ch-controlfields.html#source).

Cargo.toml

@@ -4,10 +4,12 @@ edition = "2021"
 rust-version = "1.76"
 
 [dependencies]
+commons = { git = "https://github.com/heroku/buildpacks-ruby", branch = "main" }
 libcnb = "=0.18.0"
 
 [dev-dependencies]
 libcnb-test = "=0.18.0"
+indoc = "2"
 
 [lints.rust]
 unreachable_pub = "warn"

src/aptfile.rs

@@ -0,0 +1,136 @@
+use std::collections::HashSet;
+use std::str::FromStr;
+
+#[derive(Debug, Eq, PartialEq)]
+pub(crate) struct Aptfile {
+    packages: HashSet<DebianPackageName>,
+}
+
+impl FromStr for Aptfile {
+    type Err = ParseAptfileError;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        value
+            .lines()
+            .map(str::trim)
+            .filter(|line| !line.starts_with('#') && !line.is_empty())
+            .map(DebianPackageName::from_str)
+            .collect::<Result<HashSet<_>, _>>()
+            .map_err(ParseAptfileError)
+            .map(|packages| Aptfile { packages })
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub(crate) struct ParseAptfileError(ParseDebianPackageNameError);
+
+#[derive(Debug, Eq, PartialEq, Hash)]
+pub(crate) struct DebianPackageName(String);
+
+impl FromStr for DebianPackageName {
+    type Err = ParseDebianPackageNameError;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        // https://www.debian.org/doc/debian-policy/ch-controlfields.html#source
+        // Package names (both source and binary, see Package) must consist only of
+        // lower case letters (a-z), digits (0-9), plus (+) and minus (-) signs,
+        // and periods (.). They must be at least two characters long and must
+        // start with an alphanumeric character.
+        let is_valid_package_name = value
+            .chars()
+            .all(|c| matches!(c, 'a'..='z' | '0'..='9' | '+' | '-' | '.'))
+            && value.chars().count() >= 2
+            && value.starts_with(|c: char| c.is_ascii_alphanumeric());
+
+        if is_valid_package_name {
+            Ok(DebianPackageName(value.to_string()))
+        } else {
+            Err(ParseDebianPackageNameError(value.to_string()))
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub(crate) struct ParseDebianPackageNameError(String);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn parse_valid_debian_package_name() {
+        let valid_names = [
+            "a0",             // min length, starting with number
+            "0a",             // min length, starting with letter
+            "g++",            // alphanumeric to start followed by non-alphanumeric characters
+            "libevent-2.1-6", // just a mix of allowed characters
+            "a0+.-",          // all the allowed characters
+        ];
+        for valid_name in valid_names {
+            assert_eq!(
+                DebianPackageName::from_str(valid_name).unwrap(),
+                DebianPackageName(valid_name.to_string())
+            );
+        }
+    }
+
+    #[test]
+    fn parse_invalid_debian_package_name() {
+        let invalid_names = [
+            "a",               // too short
+            "+a",              // can't start with non-alphanumeric character
+            "ab_c",            // can't contain invalid characters
+            "aBc",             // uppercase is not allowed
+            "package=1.2.3-1", // versioning is not allowed, package name only
+        ];
+        for invalid_name in invalid_names {
+            assert_eq!(
+                DebianPackageName::from_str(invalid_name).unwrap_err(),
+                ParseDebianPackageNameError(invalid_name.to_string())
+            );
+        }
+    }
+
+    #[test]
+    fn parse_aptfile() {
+        let aptfile = Aptfile::from_str(indoc! { "
+           # comment line
+               # comment line with leading whitespace
+
+            package-name-1
+            package-name-2
+
+            # Package name has leading and trailing whitespace
+               package-name-3  \t
+            # Duplicates are allowed (at least for now)
+            package-name-1
+
+        " })
+        .unwrap();
+        assert_eq!(
+            aptfile,
+            Aptfile {
+                packages: HashSet::from([
+                    DebianPackageName("package-name-1".to_string()),
+                    DebianPackageName("package-name-2".to_string()),
+                    DebianPackageName("package-name-3".to_string()),
+                ])
+            }
+        );
+    }
+
+    #[test]
+    fn parse_invalid_aptfile() {
+        let error = Aptfile::from_str(indoc! { "
+           invalid package name!
+        " })
+        .unwrap_err();
+        assert_eq!(
+            error,
+            ParseAptfileError(ParseDebianPackageNameError(
+                "invalid package name!".to_string()
+            ))
+        );
+    }
+}

src/errors.rs

@@ -1,2 +1,15 @@
+use crate::aptfile::ParseAptfileError;
+
 #[derive(Debug)]
-pub(crate) enum AptBuildpackError {}
+#[allow(clippy::enum_variant_names)]
+pub(crate) enum AptBuildpackError {
+    DetectAptfile(std::io::Error),
+    ReadAptfile(std::io::Error),
+    ParseAptfile(ParseAptfileError),
+}
+
+impl From<AptBuildpackError> for libcnb::Error<AptBuildpackError> {
+    fn from(value: AptBuildpackError) -> Self {
+        Self::BuildpackError(value)
+    }
+}

src/main.rs

@@ -1,28 +1,54 @@
+use crate::aptfile::Aptfile;
 use crate::errors::AptBuildpackError;
-use libcnb::build::{BuildContext, BuildResult};
-use libcnb::detect::{DetectContext, DetectResult};
+use commons::output::build_log::{BuildLog, Logger};
+use libcnb::build::{BuildContext, BuildResult, BuildResultBuilder};
+use libcnb::detect::{DetectContext, DetectResult, DetectResultBuilder};
 use libcnb::generic::{GenericMetadata, GenericPlatform};
 use libcnb::{buildpack_main, Buildpack};
+use std::fs;
+use std::io::stdout;
 
 #[cfg(test)]
 use libcnb_test as _;
 
+mod aptfile;
 mod errors;
 
 buildpack_main!(AptBuildpack);
 
+const APTFILE_PATH: &str = "Aptfile";
+
 struct AptBuildpack;
 
 impl Buildpack for AptBuildpack {
     type Platform = GenericPlatform;
     type Metadata = GenericMetadata;
     type Error = AptBuildpackError;
 
-    fn detect(&self, _context: DetectContext<Self>) -> libcnb::Result<DetectResult, Self::Error> {
-        todo!()
+    fn detect(&self, context: DetectContext<Self>) -> libcnb::Result<DetectResult, Self::Error> {
+        let aptfile_exists = context
+            .app_dir
+            .join(APTFILE_PATH)
+            .try_exists()
+            .map_err(AptBuildpackError::DetectAptfile)?;
+
+        if aptfile_exists {
+            DetectResultBuilder::pass().build()
+        } else {
+            BuildLog::new(stdout())
+                .without_buildpack_name()
+                .announce()
+                .warning("No Aptfile found.");
+            DetectResultBuilder::fail().build()
+        }
     }
 
-    fn build(&self, _context: BuildContext<Self>) -> libcnb::Result<BuildResult, Self::Error> {
-        todo!()
+    fn build(&self, context: BuildContext<Self>) -> libcnb::Result<BuildResult, Self::Error> {
+        let _aptfile: Aptfile = fs::read_to_string(context.app_dir.join(APTFILE_PATH))
+            .map_err(AptBuildpackError::ReadAptfile)?
+            .parse()
+            .map_err(AptBuildpackError::ParseAptfile)?;
+
+        BuildResultBuilder::new().build()
     }
 }

tests/integration_test.rs

@@ -3,3 +3,33 @@
 
 // Required due to: https://github.com/rust-lang/rust/issues/95513
 #![allow(unused_crate_dependencies)]
+
+use libcnb_test::{assert_contains, BuildConfig, PackResult, TestRunner};
+
+#[test]
+#[ignore = "integration test"]
+fn test_successful_detection() {
+    TestRunner::default().build(
+        BuildConfig::new(get_integration_test_builder(), "tests/fixtures/basic")
+            .expected_pack_result(PackResult::Success),
+        |_| {},
+    );
+}
+
+#[test]
+#[ignore = "integration test"]
+fn test_failed_detection() {
+    TestRunner::default().build(
+        BuildConfig::new(get_integration_test_builder(), "tests/fixtures/no_aptfile")
+            .expected_pack_result(PackResult::Failure),
+        |ctx| {
+            assert_contains!(ctx.pack_stdout, "No Aptfile found.");
+        },
+    );
+}
+
+const DEFAULT_BUILDER: &str = "heroku/builder:22";
+
+fn get_integration_test_builder() -> String {
+    std::env::var("INTEGRATION_TEST_CNB_BUILDER").unwrap_or(DEFAULT_BUILDER.to_string())
+}