fix: report canonicalized module path (#560)

In 31c0292 (#557), I improved the error message printed when the
module is outside of the root dir to include the file path of the
imported module. That's not enough to troubleshoot the problem,
because we print the non-canonical path, which is potentially different
from the string we use to check if the module path is within the root
dir.

In this commit, I refactored the method to make the code easier to
follow, and improved the error message to print the canonicalized
paths of the module and the root dir.

Signed-off-by: Miroslav Bajtoš <[email protected]>

runtime/module_loader.rs

@@ -72,52 +72,52 @@ impl ModuleLoader for ZinniaModuleLoader {
         async move {
             let spec_str = module_specifier.as_str();
 
-            let code = {
-                let is_module_local = match module_specifier.to_file_path() {
-                    Err(()) => false,
-                    Ok(module_path) => {
-                        match &module_root {
-                            None => true,
-                            Some(root) => module_path
-                                // Resolve any symlinks inside the path to prevent modules from escaping our sandbox
-                                .canonicalize()
-                                // Check that the module path is inside the module root directory
-                                .map(|p| p.starts_with(root))
-                                .unwrap_or(false),
-                        }
-                    },
-                };
-                if is_module_local {
-                    read_file_to_string(module_specifier.to_file_path().unwrap()).await?
-                } else if spec_str == "https://deno.land/[email protected]/testing/asserts.ts" || spec_str == "https://deno.land/[email protected]/testing/asserts.ts" {
+            let details = || {
+                let mut msg = format!("\nModule URL: {spec_str}");
+                if let Some(referrer) = &maybe_referrer {
+                    msg.push_str("\nImported from: ");
+                    msg.push_str(referrer.as_str());
+                }
+                msg
+            };
+
+            if spec_str == "https://deno.land/[email protected]/testing/asserts.ts" || spec_str == "https://deno.land/[email protected]/testing/asserts.ts" {
+                return Err(anyhow!("Zinnia bundles Deno asserts as 'zinnia:assert`. Please update your imports accordingly.{}", details()));
+            }
+
+            if module_specifier.scheme() != "file" {
+                return Err(anyhow!(
+                    "Unsupported scheme: {}. Zinnia can import local modules only.{}",
+                     module_specifier.scheme(),
+                     details()
+                ))
+            }
+
+            let module_path = module_specifier.to_file_path().map_err(|_|
+               anyhow!("Module specifier cannot be converted to a filepath.{}", details())
+            )?;
+
+            // Check that the module path is inside the module root directory
+            if let Some(canonical_root) = &module_root {
+                // Resolve any symlinks inside the path to prevent modules from escaping our sandbox
+                let canonical_module = module_path.canonicalize().map_err(|err|
+                   anyhow!("Cannot canonicalize module path: {err}.{}", details())
+                )?;
+
+                if !canonical_module.starts_with(canonical_root) {
                     return Err(anyhow!(
-                        "Zinnia bundles Deno asserts as 'zinnia:assert`. Please update your imports accordingly.\nModule URL: {spec_str}\nImported from: {}",
-                        maybe_referrer.map(|u| u.to_string()).unwrap_or("(none)".into())
+                        "Cannot import files outside of the module root directory.\n\
+                         Root directory (canonical): {}\n\
+                         Module file path (canonical): {}\
+                         {}",
+                        canonical_root.display(),
+                        canonical_module.display(),
+                        details()
                     ));
-                } else {
-                    let mut msg = if module_specifier.scheme() == "file" && module_root.is_some() {
-                        let module_desc = match module_specifier.to_file_path() {
-                            Ok(m) => format!("Module file path: {}", m.display()),
-                            Err(_) => "(Cannot convert the module specifier to a file path)".to_string(),
-                        };
-                        format!(
-                            "Cannot import files outside of module root directory {}\n{}",
-                            module_root.unwrap().display(),
-                            module_desc
-                        )
-                    } else {
-                        "Zinnia supports importing from relative paths only. ".to_string()
-                    };
-                    msg.push_str("\nModule URL: ");
-                    msg.push_str(spec_str);
-                    if let Some(referrer) = &maybe_referrer {
-                        msg.push_str("\nImported from: ");
-                        msg.push_str(referrer.as_str());
-                    }
-                    return Err(anyhow!(msg));
                 }
             };
 
+            let code = read_file_to_string(module_path).await?;
             let module = ModuleSource::new(ModuleType::JavaScript, code.into(), &module_specifier);
             Ok(module)
         }.boxed_local()
@@ -196,7 +196,7 @@ mod tests {
             Err(err) => {
                 let msg = format!("{err}");
                 assert!(
-                    msg.contains("Cannot import files outside of module root directory"),
+                    msg.contains("Cannot import files outside of the module root directory"),
                     "Expected import to fail with the sandboxing error, it failed with a different error instead:\n{}",
                     msg,
                 );

runtime/tests/js/module_loader_tests.js

@@ -18,5 +18,5 @@ test("can import files outside the main module directory", async () => {
 
 test("cannot import files over http", async () => {
   let err = await assertRejects(() => import("https://deno.land/[email protected]/version.ts"));
-  assertMatch(err.message, /Zinnia supports importing from relative paths only/);
+  assertMatch(err.message, /Zinnia can import local modules only/);
 });