module: pkg exports validations and fallbacks

PR-URL: https://github.com/nodejs/node/pull/28949
Reviewed-By: Bradley Farias <bradley.meck@gmail.com>
Reviewed-By: Jan Krems <jan.krems@gmail.com>

1 files changed, 51 insertions, 15 deletions

diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index 9332c6c277..5d5767e0cf 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -24,6 +24,7 @@
 const {
   JSON,
   Object,
+  ObjectPrototype,
   Reflect,
   SafeMap,
   StringPrototype,
@@ -348,18 +349,18 @@ function resolveExports(nmPath, request, absoluteRequest) {
 
     const basePath = path.resolve(nmPath, name);
     const pkgExports = readExports(basePath);
+    const mappingKey = `.${expansion}`;
 
-    if (pkgExports != null) {
-      const mappingKey = `.${expansion}`;
-      const mapping = pkgExports[mappingKey];
-      if (typeof mapping === 'string') {
-        return fileURLToPath(new URL(mapping, `${pathToFileURL(basePath)}/`));
+    if (typeof pkgExports === 'object' && pkgExports !== null) {
+      if (ObjectPrototype.hasOwnProperty(pkgExports, mappingKey)) {
+        const mapping = pkgExports[mappingKey];
+        return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping, '',
+                                    basePath, mappingKey);
       }
 
       let dirMatch = '';
-      for (const [candidateKey, candidateValue] of Object.entries(pkgExports)) {
+      for (const candidateKey of Object.keys(pkgExports)) {
         if (candidateKey[candidateKey.length - 1] !== '/') continue;
-        if (candidateValue[candidateValue.length - 1] !== '/') continue;
         if (candidateKey.length > dirMatch.length &&
             StringPrototype.startsWith(mappingKey, candidateKey)) {
           dirMatch = candidateKey;
@@ -367,15 +368,13 @@ function resolveExports(nmPath, request, absoluteRequest) {
       }
 
       if (dirMatch !== '') {
-        const dirMapping = pkgExports[dirMatch];
-        const remainder = StringPrototype.slice(mappingKey, dirMatch.length);
-        const expectedPrefix =
-          new URL(dirMapping, `${pathToFileURL(basePath)}/`);
-        const resolved = new URL(remainder, expectedPrefix).href;
-        if (StringPrototype.startsWith(resolved, expectedPrefix.href)) {
-          return fileURLToPath(resolved);
-        }
+        const mapping = pkgExports[dirMatch];
+        const subpath = StringPrototype.slice(mappingKey, dirMatch.length);
+        return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping,
+                                    subpath, basePath, mappingKey);
       }
+    }
+    if (pkgExports != null) {
       // eslint-disable-next-line no-restricted-syntax
       const e = new Error(`Package exports for '${basePath}' do not define ` +
           `a '${mappingKey}' subpath`);
@@ -387,6 +386,43 @@ function resolveExports(nmPath, request, absoluteRequest) {
   return path.resolve(nmPath, request);
 }
 
+function resolveExportsTarget(pkgPath, target, subpath, basePath, mappingKey) {
+  if (typeof target === 'string') {
+    if (target.startsWith('./') &&
+        (subpath.length === 0 || target.endsWith('/'))) {
+      const resolvedTarget = new URL(target, pkgPath);
+      const pkgPathPath = pkgPath.pathname;
+      const resolvedTargetPath = resolvedTarget.pathname;
+      if (StringPrototype.startsWith(resolvedTargetPath, pkgPathPath) &&
+          StringPrototype.indexOf(resolvedTargetPath, '/node_modules/',
+                                  pkgPathPath.length - 1) === -1) {
+        const resolved = new URL(subpath, resolvedTarget);
+        const resolvedPath = resolved.pathname;
+        if (StringPrototype.startsWith(resolvedPath, resolvedTargetPath) &&
+            StringPrototype.indexOf(resolvedPath, '/node_modules/',
+                                    pkgPathPath.length - 1) === -1) {
+          return fileURLToPath(resolved);
+        }
+      }
+    }
+  } else if (Array.isArray(target)) {
+    for (const targetValue of target) {
+      if (typeof targetValue !== 'string') continue;
+      try {
+        return resolveExportsTarget(pkgPath, targetValue, subpath, basePath,
+                                    mappingKey);
+      } catch (e) {
+        if (e.code !== 'MODULE_NOT_FOUND') throw e;
+      }
+    }
+  }
+  // eslint-disable-next-line no-restricted-syntax
+  const e = new Error(`Package exports for '${basePath}' do not define a ` +
+      `valid '${mappingKey}' target${subpath ? 'for ' + subpath : ''}`);
+  e.code = 'MODULE_NOT_FOUND';
+  throw e;
+}
+
 Module._findPath = function(request, paths, isMain) {
   const absoluteRequest = path.isAbsolute(request);
   if (absoluteRequest) {