Add working realpath implementation to glibc-compat

ports/glibc-compat/src/realpath.c

+/* Copyright 2014 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file. */
+
+/*
+ * Copied from native_client_sdk/src/libraries/nacl_io/
+ * TODO(sbc): remove this file once realpath.c is added to libnacl
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+char* realpath(const char* path, char* resolved_path) {
+  if (path == NULL) {
+    errno = EINVAL;
+    return NULL;
+  }
+
+  int needs_free = 0;
+  if (resolved_path == NULL) {
+    resolved_path = (char*)malloc(PATH_MAX);
+    needs_free = 1;
+  }
+
+  struct stat statbuf;
+  const char* in = path;
+  char* out = resolved_path;
+  char* out_end = resolved_path + PATH_MAX - 1;
+  int done = 0;
+
+  *out = 0;
+
+  if (*in == '/') {
+    // Absolute path.
+    strcat(out, "/");
+    in++;
+    out++;
+  } else {
+    // Relative path.
+    if (getcwd(out, out_end - out) == NULL)
+      goto fail;
+
+    out += strlen(out);
+  }
+
+  if (stat(resolved_path, &statbuf) != 0)
+    goto fail;
+
+  while (!done) {
+    const char* next_slash = strchr(in, '/');
+    size_t namelen;
+    const char* next_in;
+    if (next_slash) {
+      namelen = next_slash - in;
+      next_in = next_slash + 1;
+    } else {
+      namelen = strlen(in);
+      next_in = in + namelen;  // Move to the '\0'
+      done = 1;
+    }
+
+    if (namelen == 0) {
+      // Empty name, do nothing.
+    } else if (namelen == 1 && strncmp(in, ".", 1) == 0) {
+      // Current directory, do nothing.
+    } else if (namelen == 2 && strncmp(in, "..", 2) == 0) {
+      // Parent directory, find previous slash in resolved_path.
+      char* prev_slash = strrchr(resolved_path, '/');
+      assert(prev_slash != NULL);
+
+      out = prev_slash;
+      if (prev_slash == resolved_path) {
+        // Moved to the root. Keep the slash.
+        ++out;
+      }
+
+      *out = 0;
+    } else {
+      // Append a slash if not at root.
+      if (out != resolved_path + 1) {
+        if (out + 1 > out_end) {
+          errno = ENAMETOOLONG;
+          goto fail;
+        }
+
+        strncat(out, "/", namelen);
+        out++;
+      }
+
+      if (out + namelen > out_end) {
+        errno = ENAMETOOLONG;
+        goto fail;
+      }
+
+      strncat(out, in, namelen);
+      out += namelen;
+    }
+
+    in = next_in;
+
+    if (stat(resolved_path, &statbuf) != 0)
+      goto fail;
+
+    // If there is more to the path, then the current path must be a directory.
+    if (!done && !S_ISDIR(statbuf.st_mode)) {
+      errno = ENOTDIR;
+      goto fail;
+    }
+  }
+
+  return resolved_path;
+
+fail:
+  if (needs_free) {
+    free(resolved_path);
+  }
+  return NULL;
+}