WasmFS JS API: Implement readlink (#19587)

Author: jameshu15869

emcc.py

@@ -2348,6 +2348,7 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_lchmod',
         '_wasmfs_llseek',
         '_wasmfs_identify',
+        '_wasmfs_readlink',
         '_wasmfs_readdir_start',
         '_wasmfs_readdir_get',
         '_wasmfs_readdir_finish',

src/library_wasmfs.js

@@ -228,12 +228,13 @@ FS.createPreloadedFile = FS_createPreloadedFile;
       _free(dataBuffer);
       return ret;
     }),
-    symlink: (target, linkpath) => withStackSave(() => {
-      var targetBuffer = stringToUTF8OnStack(target);
-      var linkpathBuffer = stringToUTF8OnStack(linkpath);
-      return __wasmfs_symlink(targetBuffer, linkpathBuffer);
-    }),
-    // TODO: readlink
+    symlink: (target, linkpath) => withStackSave(() => (
+      __wasmfs_symlink(stringToUTF8OnStack(target), stringToUTF8OnStack(linkpath))
+    )),
+    readlink: (path) => {
+      var readBuffer = FS.handleError(withStackSave(() => __wasmfs_readlink(stringToUTF8OnStack(path))));
+      return UTF8ToString(readBuffer);
+    },
     statBufToObject : (statBuf) => {
       // i53/u53 are enough for times and ino in practice.
       return {

system/lib/wasmfs/js_api.cpp

@@ -147,6 +147,16 @@ int _wasmfs_symlink(char* old_path, char* new_path) {
   return __syscall_symlink((intptr_t)old_path, (intptr_t)new_path);
 }
 
+intptr_t _wasmfs_readlink(char* path) {
+  static thread_local void* readBuf = nullptr;
+  readBuf = realloc(readBuf, PATH_MAX);
+  int err = __syscall_readlinkat(AT_FDCWD, (intptr_t)path, (intptr_t)readBuf, PATH_MAX);
+  if (err < 0) {
+    return err;
+  }
+  return (intptr_t)readBuf;
+}
+
 int _wasmfs_write(int fd, void *buf, size_t count) {
   __wasi_ciovec_t iovs[1];
   iovs[0].buf = (uint8_t*)buf;

test/fs/test_fs_js_api.c

@@ -1,9 +1,33 @@
 #include <emscripten/emscripten.h>
 #include <stdio.h>
+#include <unistd.h>
 #include <sys/stat.h>
 #include <assert.h>
 #include <fcntl.h>
 
+EM_JS(void, test_fs_readlink,(), {
+    FS.writeFile('/readlinktestfile', "");
+    FS.symlink('/readlinktestfile', '/readlinksymlink');
+
+    var symlinkString = FS.readlink('readlinksymlink');
+    assert(symlinkString === '/readlinktestfile');
+
+    var ex;
+    try {
+        FS.readlink('nonexistent');
+    } catch (err) {
+        ex = err;
+    }
+    assert(ex.name === "ErrnoError" && ex.errno === 44 /* ENOENT */);
+
+    try {
+        FS.readlink('readlinktestfile');
+    } catch (err) {
+        ex = err;
+    }
+    assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+});
+
 void test_fs_allocate() {
     EM_ASM(
         FS.writeFile("allocatetestfile", 'a=1\nb=2\n');
@@ -125,7 +149,7 @@ int main() {
         var ex;
         try {
             FS.open('filenothere', 'r');
-        } catch(err) {
+        } catch (err) {
             ex = err;
         }
         assert(ex.name === "ErrnoError" && ex.errno === 44 /* ENOENT */);
@@ -281,11 +305,11 @@ int main() {
         var ex;
         try {
             FS.close(file);
-        } catch(err) {
+        } catch (err) {
             ex = err;
         }
 
-        assert(ex.name === "ErrnoError" && ex.errno === 8 /* EBADF */)
+        assert(ex.name === "ErrnoError" && ex.errno === 8 /* EBADF */);
     );
 
     /********** test FS.mknod() **********/
@@ -305,7 +329,7 @@ int main() {
     assert(mknodStats.st_mode & 0400);
 
     test_fs_allocate();
-
+    test_fs_readlink();
     test_fs_truncate();
 
     remove("mknodtest");
@@ -314,6 +338,9 @@ int main() {
     remove("renametestfile");
     remove("readtestfile");
     remove("closetestfile");
+    remove("testfile");
+    remove("closetestfile");
+    remove("/testdir");
 
     puts("success");
 }