Merge pull request emscripten-core#26 from rstz/add-realpath-support

Add realpath support

pthreadfs/examples/emscripten-tests/realpath.cpp

@@ -0,0 +1,65 @@
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <emscripten.h>
+
+void create_file(const char* path, const char* buffer, int mode) {
+  int fd = open(path, O_CREAT | O_TRUNC | O_RDWR, mode);
+  assert(fd >= 0);
+
+  int err = write(fd, buffer, sizeof(char) * strlen(buffer));
+  assert(err == (sizeof(char) * strlen(buffer)));
+
+  close(fd);
+}
+
+void setup() {
+  mkdir("persistent/folder", 0777);
+  mkdir("nonpersistent", 0777);
+  create_file("persistent/folder/file", "abcdef", 0777);
+  create_file("nonpersistent/file2", "ghijkl", 0777);
+}
+
+void cleanup() {
+  unlink("persistent/folder/file");
+  unlink("nonpersistent/file2");
+  rmdir("persistent/folder");
+  rmdir("nonpersistent");
+}
+
+bool test_path(const char* provided_path, const char* expected_path) {
+  char computed_path[PATH_MAX];
+  char* res = realpath(provided_path, computed_path);
+  int success = strcmp(expected_path, computed_path);
+  return res && success;
+}
+
+void test() {
+  const char* provided_paths[] = {"persistent/folder/../folder/file",
+    "persistent/../persistent/folder/file", "persistent/folder/./file", "/persistent/folder/file"};
+  const char* expected_paths[] = {"persistent/folder/file", "persistent/folder/file",
+    "persistent/folder/file", "persistent/folder/file"};
+  for (int i = 0; i < sizeof(provided_paths) / sizeof(char*); i++) {
+    if (!test_path(provided_paths[i], expected_paths[i])) {
+      char* errStr = strerror(errno);
+      printf("Realpath failed for path %d: %s. Error string: %s\n", i, provided_paths[i], errStr);
+      return;
+    }
+  }
+  puts("success");
+}
+
+int main() {
+  setup();
+  test();
+  cleanup();
+  return EXIT_SUCCESS;
+}

pthreadfs/pthreadfs.cpp

@@ -114,6 +114,18 @@ bool is_pthreadfs_file(std::string path) {
   return path.rfind("/" PTHREADFS_FOLDER_NAME, 0) == 0 || path.rfind(PTHREADFS_FOLDER_NAME, 0) == 0;
 }
 
+bool is_pthreadfs_fd_link(std::string path) {
+  if (path.rfind("/proc/self/fd/", 0) == 0) {
+    char* p;
+    long fd = strtol(path.substr(14).c_str(), &p, 10);
+    // As defined in library_asyncfs.js, the minimum fd for PThreadFS is 4097.
+    if (*p == 0 && fd >= 4097) {
+      return true;
+    }
+  }
+  return false;
+}
+
 } // namespace emscripten
 
 // Static functions calling resumFct and setting the return value.
@@ -235,8 +247,15 @@ SYS_CAPI_DEF(ioctl, 54, long fd, long request, ...) {
   SYS_SYNC_TO_ASYNC_FD(ioctl, fd, request, arg);
 }
 
+// The implementation of readlink includes special handling for the file descriptor's symlinks in
+// /proc/self/fd/. This is necessary for handling realpath.
 SYS_CAPI_DEF(readlink, 85, long path, long buf, long bufsize) {
-  SYS_SYNC_TO_ASYNC_PATH(readlink, path, buf, bufsize);
+  std::string pathname((char*)path);
+  if (emscripten::is_pthreadfs_file(pathname) || emscripten::is_pthreadfs_fd_link(pathname)) {
+    SYS_SYNC_TO_ASYNC_NORETURN(readlink, path, buf, bufsize);
+    return resume_result_long;
+  }
+  return __sys_readlink(path, buf, bufsize);
 }
 
 SYS_CAPI_DEF(fchmod, 94, long fd, long mode) { SYS_SYNC_TO_ASYNC_FD(fchmod, fd, mode); }

pthreadfs/pthreadfs.h

@@ -280,6 +280,9 @@ class sync_to_async {
 
 // Determines if `path` is a file in the special folder PTHREADFS_FOLDER.
 bool is_pthreadfs_file(std::string path);
+// Determines is `path` is a symlink in self/proc/fd/ that corresponds to a file in
+// PTHREADFS_FOLDER.
+bool is_pthreadfs_fd_link(std::string path);
 
 } // namespace emscripten