Implement commit parsing/formatting

To be able to support git commits with multiple signature
headers, we have to implement our own parsing and formatting.

Signed-off-by: Alexis Sellier <alexis@radicle.xyz>

radicle/src/git.rs

@@ -274,3 +274,180 @@ pub fn run<P: AsRef<Path>, S: AsRef<std::ffi::OsStr>>(
         String::from_utf8_lossy(&output.stderr),
     ))
 }
+
+/// Parsing and formatting of commit objects.
+/// This module exists to work with commits that have multiple signature headers.
+pub mod commit {
+    use std::str::FromStr;
+
+    /// A parsed commit object.
+    /// Contains the full commit header and body.
+    ///
+    /// Can be created with the [`FromStr`] instance, and formatted with the [`ToString`]
+    /// instance.
+    #[derive(Debug)]
+    pub struct CommitObject {
+        headers: Vec<(String, String)>,
+        message: String,
+    }
+
+    impl CommitObject {
+        /// Get the commit message.
+        pub fn message(&self) -> &str {
+            self.message.as_str()
+        }
+
+        /// Iterate over the headers, in order.
+        pub fn headers(&self) -> impl Iterator<Item = (&str, &str)> {
+            self.headers.iter().map(|(k, v)| (k.as_str(), v.as_str()))
+        }
+
+        /// Iterate over matching header values.
+        pub fn values<'a>(&'a self, name: &'a str) -> impl Iterator<Item = &'a str> + '_ {
+            self.headers
+                .iter()
+                .filter(move |(k, _)| k == name)
+                .map(|(_, v)| v.as_str())
+        }
+
+        /// Push a header to the end of the headers section.
+        pub fn push_header(&mut self, name: &str, value: &str) {
+            self.headers
+                .push((name.to_owned(), value.trim().to_owned()));
+        }
+    }
+
+    #[derive(thiserror::Error, Debug)]
+    pub enum ParseError {
+        #[error("invalid git commit object format")]
+        InvalidFormat,
+    }
+
+    impl FromStr for CommitObject {
+        type Err = ParseError;
+
+        fn from_str(buffer: &str) -> Result<Self, Self::Err> {
+            let mut headers = Vec::new();
+            let (header, message) = buffer.split_once("\n\n").ok_or(ParseError::InvalidFormat)?;
+
+            for line in header.lines() {
+                if let Some(rest) = line.strip_prefix(' ') {
+                    let value: &mut String = headers
+                        .last_mut()
+                        .map(|(_, v)| v)
+                        .ok_or(ParseError::InvalidFormat)?;
+                    value.push('\n');
+                    value.push_str(rest);
+                } else if let Some((name, value)) = line.split_once(' ') {
+                    headers.push((name.to_owned(), value.to_owned()));
+                } else {
+                    return Err(ParseError::InvalidFormat);
+                }
+            }
+
+            Ok(Self {
+                headers,
+                message: message.to_owned(),
+            })
+        }
+    }
+
+    impl ToString for CommitObject {
+        fn to_string(&self) -> String {
+            let mut buf = String::new();
+
+            for (name, value) in &self.headers {
+                buf.push_str(name);
+                buf.push(' ');
+                buf.push_str(value.replace('\n', "\n ").as_str());
+                buf.push('\n');
+            }
+            buf.push('\n');
+            buf.push_str(self.message.as_str());
+            buf
+        }
+    }
+
+    #[cfg(test)]
+    mod test {
+        use super::*;
+
+        const UNSIGNED: &str = "\
+tree c66cc435f83ed0fba90ed4500e9b4b96e9bd001b
+parent af06ad645133f580a87895353508053c5de60716
+author Alexis Sellier <alexis@radicle.xyz> 1664467633 +0200
+committer Alexis Sellier <alexis@radicle.xyz> 1664786099 +0200
+
+Add SSH functionality with new `radicle-ssh`
+
+We borrow code from `thrussh`, refactored to be runtime-less.
+";
+
+        const SIGNATURE: &str = "\
+-----BEGIN SSH SIGNATURE-----
+U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgvjrQogRxxLjzzWns8+mKJAGzEX
+4fm2ALoN7pyvD2ttQAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5
+AAAAQIQvhIewOgGfnXLgR5Qe1ZEr2vjekYXTdOfNWICi6ZiosgfZnIqV0enCPC4arVqQg+
+GPp0HqxaB911OnSAr6bwU=
+-----END SSH SIGNATURE-----
+";
+
+        const SIGNED: &str = "\
+tree c66cc435f83ed0fba90ed4500e9b4b96e9bd001b
+parent af06ad645133f580a87895353508053c5de60716
+author Alexis Sellier <alexis@radicle.xyz> 1664467633 +0200
+committer Alexis Sellier <alexis@radicle.xyz> 1664786099 +0200
+other e6fe3c97619deb8ab4198620f9a7eb79d98363dd
+gpgsig -----BEGIN SSH SIGNATURE-----
+ U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgvjrQogRxxLjzzWns8+mKJAGzEX
+ 4fm2ALoN7pyvD2ttQAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5
+ AAAAQIQvhIewOgGfnXLgR5Qe1ZEr2vjekYXTdOfNWICi6ZiosgfZnIqV0enCPC4arVqQg+
+ GPp0HqxaB911OnSAr6bwU=
+ -----END SSH SIGNATURE-----
+gpgsig -----BEGIN SSH SIGNATURE-----
+ U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgvjrQogRxxLjzzWns8+mKJAGzEX
+ 4fm2ALoN7pyvD2ttQAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5
+ AAAAQIQvhIewOgGfnXLgR5Qe1ZEr2vjekYXTdOfNWICi6ZiosgfZnIqV0enCPC4arVqQg+
+ GPp0HqxaB911OnSAr6bwU=
+ -----END SSH SIGNATURE-----
+
+Add SSH functionality with new `radicle-ssh`
+
+We borrow code from `thrussh`, refactored to be runtime-less.
+";
+
+        #[test]
+        fn test_push_header() {
+            let mut commit = CommitObject::from_str(UNSIGNED).unwrap();
+            commit.push_header("other", "e6fe3c97619deb8ab4198620f9a7eb79d98363dd");
+            commit.push_header("gpgsig", SIGNATURE);
+            commit.push_header("gpgsig", SIGNATURE);
+
+            assert_eq!(commit.to_string(), SIGNED);
+        }
+
+        #[test]
+        fn test_get_header() {
+            let commit = CommitObject::from_str(SIGNED).unwrap();
+
+            assert_eq!(
+                commit.values("gpgsig").collect::<Vec<_>>(),
+                vec![SIGNATURE.trim(), SIGNATURE.trim()]
+            );
+            assert_eq!(
+                commit.values("parent").collect::<Vec<_>>(),
+                vec![String::from("af06ad645133f580a87895353508053c5de60716")],
+            );
+            assert!(commit.values("unknown").next().is_none());
+        }
+
+        #[test]
+        fn test_conversion() {
+            assert_eq!(CommitObject::from_str(SIGNED).unwrap().to_string(), SIGNED);
+            assert_eq!(
+                CommitObject::from_str(UNSIGNED).unwrap().to_string(),
+                UNSIGNED
+            );
+        }
+    }
+}