fix(build/oci): Propagate passAsFile files into the build sandbox.

fixes #87

Change-Id: Ia8109ae678bddb1072e15f6a3ed63e3e3c862b6a
Reviewed-on: https://cl.snix.dev/c/snix/+/30238
Autosubmit: Vova Kryachko <v.kryachko@gmail.com>
Reviewed-by: Florian Klink <flokli@flokli.de>
Tested-by: besadii
Reviewed-by: Yureka <snix@yuka.dev>

snix/build/src/oci/bundle.rs

@@ -1,7 +1,9 @@
 //! Module to create an OCI runtime bundle for a given [BuildRequest].
 use std::{
+    ffi::OsStr,
     fs,
-    path::{Path, PathBuf},
+    io::Write,
+    path::{Component, Path, PathBuf},
 };
 
 use super::scratch_name;
@@ -39,7 +41,33 @@ pub(crate) fn make_bundle<'a>(
     for p in request.scratch_paths.iter() {
         let scratch_path = scratch_root.join(scratch_name(p));
         debug!(scratch_path=?scratch_path, path=?p, "about to create scratch dir");
-        fs::create_dir_all(scratch_path).context("Unable to create scratch dir")?;
+        fs::create_dir_all(scratch_path.clone()).context("Unable to create scratch dir")?;
+
+        // TODO(#152): this is a hack, in the general case we may not have the "build" directory and additional files
+        // may not have /build prefix. But in practice today snix_build.rs is the only user of the builder and
+        // it always sets up a /build scratch and populates all additional_files with the /build prefix.
+        // For now this unblocks builds, but worth improving in the future.
+        if p == Path::new("build") {
+            for file in request.additional_files.iter() {
+                if file.path.components().count() < 2
+                    || file.path.components().next() != Some(Component::Normal(OsStr::new("build")))
+                {
+                    Err(std::io::Error::other(
+                        "Additional files must start with build/",
+                    ))?
+                }
+
+                // remove build/ prefix
+                let p = file.path.components().skip(1).collect::<PathBuf>();
+                if let Some(parent) = p.parent() {
+                    fs::create_dir_all(scratch_path.clone().join(parent))
+                        .context("Failed to create dir for additional file")?;
+                }
+                let p = scratch_path.join(p);
+                let mut out = std::fs::File::create(p).context("could not create file")?;
+                out.write_all(&file.contents)?;
+            }
+        }
     }
 
     Ok(())