[NaCl SDK] Expose Google Drive to nacl_io.

native_client_sdk/src/libraries/nacl_io/googledrivefs/googledrivefs_node.cc

+// Copyright 2016 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.
+
+#include "nacl_io/googledrivefs/googledrivefs_node.h"
+
+#include <stdio.h>
+#include <time.h>
+
+#include <algorithm>
+
+#include "ppapi/c/pp_completion_callback.h"
+
+#include "nacl_io/error.h"
+#include "nacl_io/filesystem.h"
+#include "nacl_io/getdents_helper.h"
+#include "nacl_io/hash.h"
+#include "nacl_io/kernel_handle.h"
+#include "nacl_io/pepper_interface.h"
+#include "nacl_io/statuscode.h"
+#include "nacl_io/googledrivefs/googledrivefs.h"
+#include "nacl_io/googledrivefs/googledrivefs_util.h"
+
+namespace nacl_io {
+
+GoogleDriveFsNode::GoogleDriveFsNode(Filesystem* filesystem, Path path)
+    : Node(filesystem), path_(path) {}
+
+Error GoogleDriveFsNode::GetDents(size_t offs,
+                                  struct dirent* pdir,
+                                  size_t size,
+                                  int* out_bytes) {
+  *out_bytes = 0;
+
+  if (!IsaDir()) {
+    return ENOTDIR;
+  }
+
+  const ino_t kCurDirIno = -1;
+  const ino_t kParentDirIno = -2;
+  GetDentsHelper helper(kCurDirIno, kParentDirIno);
+
+  std::vector<std::string> dirent_names;
+  Error error = RequestDirent(&dirent_names);
+  if (error) {
+    return error;
+  }
+
+  for (size_t i = 0; i < dirent_names.size(); ++i) {
+    Path child_path(path_);
+    child_path = child_path.Append("/" + dirent_names[i]);
+    ino_t child_ino = HashPath(child_path);
+
+    helper.AddDirent(child_ino, dirent_names[i].c_str(),
+                     dirent_names[i].size());
+  }
+
+  return helper.GetDents(offs, pdir, size, out_bytes);
+}
+
+Error GoogleDriveFsNode::GetStat(struct stat* pstat) {
+  Error error = GetSize(&pstat->st_size);
+  if (error) {
+    return error;
+  }
+
+  error = GetModifiedTime(&pstat->st_mtime);
+  if (error) {
+    return error;
+  }
+
+  pstat->st_atime = 0;
+  pstat->st_ctime = 0;
+
+  pstat->st_mode = stat_.st_mode;
+
+  return 0;
+}
+
+Error GoogleDriveFsNode::Write(const HandleAttr& attr,
+                               const void* buf,
+                               size_t count,
+                               int* out_bytes) {
+  *out_bytes = 0;
+
+  if (IsaDir()) {
+    return EISDIR;
+  }
+  if ((GetMode() & S_IWRITE) == 0) {
+    return EACCES;
+  }
+
+  off_t file_size = 0;
+  Error error = GetSize(&file_size);
+  if (error) {
+    return error;
+  }
+
+  off_t file_buffer_size = std::max((unsigned long long int)file_size,

[binji, 2016/08/22 19:21:53]

use std::max<off_t> instead of casting the arguments

[chanpatorikku, 2016/08/29 17:14:03]

Done. std::max< 'C++ variable type' > is used in various places.

+                                    (unsigned long long int)attr.offs + count);
+
+  // use std::string for storing data in the heap, as the size of stack
+  // is measured in megabytes, disallowing files larger than that.
+  std::string file_buffer(file_buffer_size, '\0');
+
+  if (file_size > 0) {
+    int read_helper_out_bytes = 0;
+    error = ReadHelper(0, file_size - 1, &file_buffer, &read_helper_out_bytes);
+
+    if (error) {
+      return error;
+    }
+  }
+
+  char* pChar = (char*)buf;
+  for (size_t i = 0; i < count; ++i) {
+    file_buffer[attr.offs + i] = pChar[i];
+  }
+
+  error = WriteHelper(file_buffer.c_str(), file_buffer_size);

[binji, 2016/08/22 19:21:53]

Is there no better way than reading the entire file, modifying a small portion,
then writing it back?

[chanpatorikku, 2016/08/29 17:14:03]

No.  Google Drive API v3 supports only file overwrite.  

Because only file overwrite is available in Google Drive API v3, and
UrlRequestInfoInterface::AppendDataToBody(..) can write data up to the max
number of uint32_t, a file written from GoogleDriveFs can be at most UINT_MAX
bytes.

For further information, a stackoverflow post confirmed that the Drive API dealt
with files as a whole and there was only file overwrite.

http://stackoverflow.com/questions/19478354/add-lines-to-a-file-without-overw...

+  if (error) {
+    return error;
+  }
+
+  *out_bytes = count;
+
+  return 0;
+}
+
+Error GoogleDriveFsNode::FTruncate(off_t length) {
+  if (IsaDir()) {
+    return EISDIR;
+  }
+
+  off_t file_size = 0;
+  Error error = GetSize(&file_size);
+  if (error) {
+    return error;
+  }
+
+  std::string file_buffer(length, '\0');
+
+  if (file_size > 0) {
+    int read_helper_out_bytes = 0;
+    off_t read_end = std::min(length, file_size);
+    error = ReadHelper(0, read_end - 1, &file_buffer, &read_helper_out_bytes);
+
+    if (error) {
+      return error;
+    }
+  }
+
+  error = WriteHelper(file_buffer.c_str(), length);
+  if (error) {
+    return error;
+  }
+
+  return 0;
+}
+
+Error GoogleDriveFsNode::Read(const HandleAttr& attr,
+                              void* buf,
+                              size_t count,
+                              int* out_bytes) {
+  *out_bytes = 0;
+
+  if (IsaDir()) {
+    return EISDIR;
+  }
+  if ((GetMode() & S_IREAD) == 0) {
+    return EACCES;
+  }
+
+  std::string file_buffer(count, '\0');
+
+  Error error =
+      ReadHelper(attr.offs, attr.offs + count - 1, &file_buffer, out_bytes);
+  if (error) {
+    return error;
+  }
+
+  char* pChar = (char*)buf;
+  for (size_t i = 0; i < count; ++i) {
+    pChar[i] = file_buffer[i];

[binji, 2016/08/22 19:21:53]

why not read directly into buf?

[chanpatorikku, 2016/08/29 17:14:03]

buf has to be copied from a std::string object at some time of the function
calls before GoogleDriveFsNode::Read(..) returns buf.  The copying has to be
there, so in patch set 2, buf was not read directly into.

The function calls in patch set 2 were
GoogleDriveFsNode::Read(.. void* buf ..), 
GoogleDriveFsNode::ReadHelper(.. std::string* out_helper_buffer), 
and GoogleDriveFsUtil::ReadResponseBody(.. std::string* out_body_buffer).

out_helper_buffer copies from out_body_buffer, and buf copies from
out_helper_buffer.

GoogleDriveFsUtil::ReadResponseBody(..) can read a response body string with
both an unknown length and a known length.  The length can be unknown because
the response body can be the contents of an arbitrary Google Drive file that has
an arbitrary length.

GoogleDriveFsNode::ReadHelper(..) can be designed to read just a string with
known length.

To simplify the code, ReadHelper is modified to become
GoogleDriveFsNode::ReadHelper(.. char* out_buffer).

The function calls in patch set 3 becomes GoogleDriveFsNode::Read(.. void* buf
..), GoogleDriveFsNode::ReadHelper(.. char* out_helper_buffer), and
GoogleDriveFsUtil::ReadResponseBody(.. std::string* out_body_buffer).

out_helper_buffer copies from out_body_buffer, and buf is passed as
out_helper_buffer.

+  }
+
+  return 0;
+}
+
+Error GoogleDriveFsNode::GetSize(off_t* out_size) {
+  *out_size = 0;
+
+  GoogleDriveFs* googledrivefs = static_cast<GoogleDriveFs*>(filesystem_);
+
+  URLLoaderInterface* url_loader_iface =
+      googledrivefs->ppapi()->GetURLLoaderInterface();
+  PP_Resource url_loader_object =
+      url_loader_iface->Create(googledrivefs->instance());
+  URLRequestInfoInterface* url_request_info_iface =
+      googledrivefs->ppapi()->GetURLRequestInfoInterface();
+  PP_Resource url_request_info_object =
+      url_request_info_iface->Create(googledrivefs->instance());
+  PP_Resource url_response_info_object = 0;
+  Error error(0);
+  static const char base_url[] = "https://www.googleapis.com/drive/v3/files";
+  RequestUrlParams p;
+  std::string output;
+  std::string size_value;
+  int size_index;
+
+  if (IsaDir()) {
+    goto done;
+  }
+
+  p.url = base_url;
+  AddUrlPath(item_id_, &p.url);
+  AddUrlFirstQueryParameter("fields", "size", &p.url);
+
+  p.method = "GET";
+
+  p.headers = "";
+
+  AddHeaders("Content-type", "application/json", &p.headers);
+  AddHeaders("Authorization", "Bearer " + googledrivefs->token(), &p.headers);
+
+  error = MakeRequest(googledrivefs->ppapi(), url_loader_object,
+                      url_request_info_object, p);
+
+  if (error) {
+    goto done;
+  }
+
+  error = FinishPreparingResponse(googledrivefs->ppapi(), url_loader_object,
+                                  &url_response_info_object);
+
+  if (error) {
+    goto done;
+  }
+
+  if (ReadStatusCode(googledrivefs->ppapi(), url_response_info_object) !=
+      STATUSCODE_OK) {
+    error = EPERM;
+    goto done;
+  }
+
+  error = ReadResponseBody(googledrivefs->ppapi(), googledrivefs->instance(),
+                           url_response_info_object, INT_MAX, &output);
+  if (error) {
+    goto done;
+  }
+
+  GetValue(output, "size", 0, &size_value, &size_index);
+  if (size_index == -1) {
+    // in a STATUSCODE_OK response, size of a directory is not written.
+    size_value = "0";
+  }
+
+  *out_size = (off_t)atoi(size_value.c_str());
+
+done:
+  if (url_loader_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_loader_object);
+  }
+  if (url_request_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_request_info_object);
+  }
+  if (url_response_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_response_info_object);
+  }
+
+  return error;
+}
+
+Error GoogleDriveFsNode::Init(int open_flags) {
+  Error error = Node::Init(open_flags);
+
+  if (error) {
+    return error;
+  }
+
+  if (path_.Size() == 1) {
+    parent_dir_id_ = "";
+    item_id_ = "root";
+    SetType(S_IFDIR);
+    SetMode(S_IREAD);
+    return 0;
+  }
+
+  error = RequestParentDirId(path_, filesystem_, &parent_dir_id_);
+  if (error) {
+    return error;
+  }
+
+  // Request the ID of an item, which is a file or a directory
+  error =
+      RequestItemId(parent_dir_id_, path_.Basename(), filesystem_, &item_id_);
+
+  if (error == ENOENT) {
+    // Only files are open as mode O_CREAT
+    if ((open_flags & O_CREAT) != 0) {
+      error = CreateEmptyFile();
+      if (error) {
+        return error;
+      }
+      error = RequestItemId(parent_dir_id_, path_.Basename(), filesystem_,
+                            &item_id_);
+      if (error) {
+        return error;
+      }
+      SetType(S_IFREG);
+      if ((open_flags & O_RDWR) != 0) {
+        SetMode(S_IREAD | S_IWRITE);
+      } else if ((open_flags & O_WRONLY) != 0) {
+        SetMode(S_IWRITE);
+      } else {
+        SetMode(S_IREAD);
+      }
+    } else {
+      return ENOENT;
+    }
+  } else if (error) {
+    return error;
+  } else {
+    std::string dir_id = "";
+    error =
+        RequestDirId(parent_dir_id_, path_.Basename(), filesystem_, &dir_id);
+    if (error == ENOENT) {
+      SetType(S_IFREG);
+      if ((open_flags & O_RDWR) != 0) {
+        SetMode(S_IREAD | S_IWRITE);
+      } else if ((open_flags & O_WRONLY) != 0) {
+        SetMode(S_IWRITE);
+      } else {
+        SetMode(S_IREAD);
+      }
+    } else if (error) {
+      return error;
+    } else {
+      SetType(S_IFDIR);
+      SetMode(S_IREAD);
+    }
+
+    if (open_flags == 0) {
+      // open_flags == 0 for file opened on fopen with mode r and
+      // directory opened on opendir
+      return 0;
+    } else if (IsaDir()) {
+      return EPERM;
+    } else if ((open_flags & O_TRUNC) != 0) {
+      error = WriteHelper(NULL, 0);
+      if (error) {
+        return error;
+      }
+    }
+  }
+
+  return 0;
+}
+
+void GoogleDriveFsNode::Destroy() {
+  Node::Destroy();
+}
+
+Error GoogleDriveFsNode::ReadHelper(off_t start,
+                                    off_t end,
+                                    std::string* out_string_buffer,
+                                    int* out_bytes) {
+  (*out_string_buffer)[0] = '\0';
+  *out_bytes = 0;
+
+  GoogleDriveFs* googledrivefs = static_cast<GoogleDriveFs*>(filesystem_);
+
+  URLLoaderInterface* url_loader_iface =
+      googledrivefs->ppapi()->GetURLLoaderInterface();
+  PP_Resource url_loader_object =
+      url_loader_iface->Create(googledrivefs->instance());
+  URLRequestInfoInterface* url_request_info_iface =
+      googledrivefs->ppapi()->GetURLRequestInfoInterface();
+  PP_Resource url_request_info_object =
+      url_request_info_iface->Create(googledrivefs->instance());
+  PP_Resource url_response_info_object = 0;
+  Error error(EPERM);
+  static const char base_url[] =
+      "https://www.googleapis.com/download/drive/v3/files";
+  RequestUrlParams p;
+  char range_value_buffer[1024];
+  int char_written = 0;
+  int status_code = 0;
+  std::string output;
+
+  p.url = base_url;
+  AddUrlPath(item_id_, &p.url);
+  AddUrlFirstQueryParameter("alt", "media", &p.url);
+
+  p.method = "GET";
+
+  p.headers = "";
+
+  AddHeaders("Content-type", "application/json", &p.headers);
+  AddHeaders("Authorization", "Bearer " + googledrivefs->token(), &p.headers);
+
+  char_written = sprintf(range_value_buffer, "bytes=%lli-%lli",

[binji, 2016/08/22 19:21:53]

Use snprintf instead of sprintf

[chanpatorikku, 2016/08/29 17:14:03]

Done.

+                         (long long int)start, (long long int)end);
+  if (char_written < 0) {
+    error = EPERM;
+    goto done;
+  }
+
+  AddHeaders("Range", std::string(range_value_buffer), &p.headers);

[binji, 2016/08/22 19:21:53]

Remove std::string constructor, it will be automatically coerced when you pass
range_value_buffer.

[chanpatorikku, 2016/08/29 17:14:03]

Done.

+
+  error = MakeRequest(googledrivefs->ppapi(), url_loader_object,
+                      url_request_info_object, p);
+
+  if (error) {
+    goto done;
+  }
+
+  error = FinishPreparingResponse(googledrivefs->ppapi(), url_loader_object,
+                                  &url_response_info_object);
+
+  if (error) {
+    goto done;
+  }
+
+  status_code =
+      ReadStatusCode(googledrivefs->ppapi(), url_response_info_object);
+
+  if (status_code == STATUSCODE_OK ||
+      status_code == STATUSCODE_PARTIAL_CONTENT) {
+    error =
+        ReadResponseBody(googledrivefs->ppapi(), googledrivefs->instance(),
+                         url_response_info_object, end - start + 1, &output);
+
+    if (error) {
+      goto done;
+    }
+
+    for (size_t i = 0; i < output.size(); ++i) {
+      (*out_string_buffer)[i] = output[i];

[binji, 2016/08/22 19:21:53]

looks like you are assuming that out_string_buffer is large enough to fit this,
probably worth adding an assert.

[chanpatorikku, 2016/08/29 17:14:03]

Not adding assert here, but adding assert in various places.

The caller of ReadHelper makes sure that the buffer, whose size is end - start +
1, has enough space.  

ReadHelper(off_t start, off_t end ...) is changed to ReadHelper(uint32_t start,
uint32_t end …). The size of a Google Drive file is <= UINT_MAX when it is
written from nacl_io, so start and end are in uint32_t.

Start and end are made sure to be between 0 and UINT_MAX.

Before calling ReadHelper(..), the caller makes sure start and end are <=
UINT_MAX (KernelHandle makes sure HandleAttr.offs >= 0, and start and end >=
HandleAttr.offs),

The buffer size is therefore at most UINT_MAX.  The new, revised
ReadResponseBody(..), which ReadHelper(..) calls, returns at most UINT_MAX
number of bytes, so the buffer size does not have to be asserted.

+    }
+
+    *out_bytes = output.size();
+
+    error = 0;
+    goto done;
+  } else if (status_code == STATUSCODE_REQUESTED_RANGE_NOT_SATISFIABLE) {
+    error = 0;

[binji, 2016/08/22 19:21:53]

why isn't this an error?

[chanpatorikku, 2016/08/29 17:14:03]

Google Drive API v3, HttpFs, and Html5Fs do not show an error when the file read
range low and high has a low value >= file size, so ReadHelper(..) does not
return an error either.

When low value >= the file size, Google Drive API v3 returns an empty response
body in addition to the status code STATUSCODE_REQUESTED_RANGE_NOT_SATISFIABLE. 
When Google Drive API v3 returns an error, the response body is non empty and
shows an error description.  Since an empty response body but not an error
description is returned, it can be concluded that Google Drive API v3 does not
return an error.

Moreover, when low value >= the file size, HttpFsNode::Read(..) and
Html5FsNode::Read(..), are designed to return no error.  There are test cases in
http_fs_test.cc and html5_fs_test.cc testing the scenario.

+    goto done;
+  }
+
+done:
+  if (url_loader_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_loader_object);
+  }
+  if (url_request_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_request_info_object);
+  }
+  if (url_response_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_response_info_object);
+  }
+
+  return error;
+}
+
+Error GoogleDriveFsNode::WriteHelper(const char* body_data,
+                                     uint32_t body_size) {
+  GoogleDriveFs* googledrivefs = static_cast<GoogleDriveFs*>(filesystem_);
+
+  URLLoaderInterface* url_loader_iface =
+      googledrivefs->ppapi()->GetURLLoaderInterface();
+  PP_Resource url_loader_object =
+      url_loader_iface->Create(googledrivefs->instance());
+  URLRequestInfoInterface* url_request_info_iface =
+      googledrivefs->ppapi()->GetURLRequestInfoInterface();
+  PP_Resource url_request_info_object =
+      url_request_info_iface->Create(googledrivefs->instance());
+  PP_Resource url_response_info_object = 0;
+  Error error(0);
+  static const char base_url[] =
+      "https://www.googleapis.com/upload/drive/v3/files";
+  RequestUrlParams p;
+
+  p.url = base_url;
+  AddUrlPath(item_id_, &p.url);
+  AddUrlFirstQueryParameter("uploadType", "media", &p.url);
+
+  p.method = "PATCH";
+
+  p.headers = "";
+
+  AddHeaders("Content-type", "application/json", &p.headers);
+  AddHeaders("Authorization", "Bearer " + googledrivefs->token(), &p.headers);
+
+  p.body = std::string(body_data, body_size);
+
+  error = MakeRequest(googledrivefs->ppapi(), url_loader_object,
+                      url_request_info_object, p);
+
+  if (error) {
+    goto done;
+  }
+
+  error = FinishPreparingResponse(googledrivefs->ppapi(), url_loader_object,
+                                  &url_response_info_object);
+
+  if (error) {
+    goto done;
+  }
+
+  if (ReadStatusCode(googledrivefs->ppapi(), url_response_info_object) !=
+      STATUSCODE_OK) {
+    error = EPERM;
+    goto done;
+  }
+
+done:
+  if (url_loader_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_loader_object);
+  }
+  if (url_request_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_request_info_object);
+  }
+  if (url_response_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_response_info_object);
+  }
+
+  return error;
+}
+
+Error GoogleDriveFsNode::GetModifiedTime(time_t* out_mtime) {
+  GoogleDriveFs* googledrivefs = static_cast<GoogleDriveFs*>(filesystem_);
+
+  URLLoaderInterface* url_loader_iface =
+      googledrivefs->ppapi()->GetURLLoaderInterface();
+  PP_Resource url_loader_object =
+      url_loader_iface->Create(googledrivefs->instance());
+  URLRequestInfoInterface* url_request_info_iface =
+      googledrivefs->ppapi()->GetURLRequestInfoInterface();
+  PP_Resource url_request_info_object =
+      url_request_info_iface->Create(googledrivefs->instance());
+  PP_Resource url_response_info_object = 0;
+  Error error(0);
+  static const char base_url[] = "https://www.googleapis.com/drive/v3/files";
+  RequestUrlParams p;
+  std::string output;
+  std::string modified_time_value = "";
+  int modified_time_index = 0;
+  struct tm timeinfo;
+
+  p.url = base_url;
+  AddUrlPath(item_id_, &p.url);
+  AddUrlFirstQueryParameter("fields", "modifiedTime", &p.url);
+
+  p.method = "GET";
+
+  p.headers = "";
+
+  AddHeaders("Content-type", "application/json", &p.headers);
+  AddHeaders("Authorization", "Bearer " + googledrivefs->token(), &p.headers);
+
+  error = MakeRequest(googledrivefs->ppapi(), url_loader_object,
+                      url_request_info_object, p);
+
+  if (error) {
+    goto done;
+  }
+
+  error = FinishPreparingResponse(googledrivefs->ppapi(), url_loader_object,
+                                  &url_response_info_object);
+
+  if (error) {
+    goto done;
+  }
+
+  if (ReadStatusCode(googledrivefs->ppapi(), url_response_info_object) !=
+      STATUSCODE_OK) {
+    error = EPERM;
+    goto done;
+  }
+
+  error = ReadResponseBody(googledrivefs->ppapi(), googledrivefs->instance(),
+                           url_response_info_object, INT_MAX, &output);
+  if (error) {
+    goto done;
+  }
+
+  // the value of modifiedTime is assumed to be always in the STATUSCODE_OK
+  // response.
+  GetValue(output, "modifiedTime", 0, &modified_time_value,

[chanpatorikku, 2016/08/07 02:41:03]

I don't know about how practical my implementation of GetValue() is.

GetValue() is called only at the time a response with status code 200 is there.

Response body is never cutoff in a response with status code 200.

GetValue() assumes that response body is never cutoff. When a response body is,
for example,

{

  “modifiedTime”: “2016-08-07T10:44:55.342Z”

}

, GetValue() never checks the case when there is not a second double quote after
the first double quote of the time value.

Could you please reply if the implementation is practical?

[binji, 2016/08/22 19:21:53]

You may want to specify the expected format below, and check that the length of
the response is what you expected as well. I think that will be a sufficient
test.

[chanpatorikku, 2016/08/29 17:14:03]

The comment becomes not applicable now.

GetValue(..) is redesigned to return an error when a second double quote is not
there.

GetValue(..) is renamed to GetValueStringAndValuePos(..) and becomes an usual
function that gets a key value from a key.  It returns an error when the key is
not there or the json body to look for the keys and values is not in the
expected format.

+           &modified_time_index);
+
+  timeinfo.tm_year = atoi(modified_time_value.substr(0, 4).c_str());
+  timeinfo.tm_mon = atoi(modified_time_value.substr(5, 2).c_str());
+  timeinfo.tm_mday = atoi(modified_time_value.substr(8, 2).c_str());
+  timeinfo.tm_hour = atoi(modified_time_value.substr(11, 2).c_str());
+  timeinfo.tm_min = atoi(modified_time_value.substr(14, 2).c_str());
+  timeinfo.tm_sec = atoi(modified_time_value.substr(17, 2).c_str());
+  timeinfo.tm_isdst = 0;
+
+  *out_mtime = mktime(&timeinfo);
+
+done:
+  if (url_loader_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_loader_object);
+  }
+  if (url_request_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_request_info_object);
+  }
+  if (url_response_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_response_info_object);
+  }
+
+  return error;
+}
+
+Error GoogleDriveFsNode::CreateEmptyFile() {
+  GoogleDriveFs* googledrivefs = static_cast<GoogleDriveFs*>(filesystem_);
+
+  URLLoaderInterface* url_loader_iface =
+      googledrivefs->ppapi()->GetURLLoaderInterface();
+  PP_Resource url_loader_object =
+      url_loader_iface->Create(googledrivefs->instance());
+  URLRequestInfoInterface* url_request_info_iface =
+      googledrivefs->ppapi()->GetURLRequestInfoInterface();
+  PP_Resource url_request_info_object =
+      url_request_info_iface->Create(googledrivefs->instance());
+  PP_Resource url_response_info_object = 0;
+  Error error(0);
+  static const char base_url[] =
+      "https://www.googleapis.com/upload/drive/v3/files";
+  RequestUrlParams p;
+  std::string BOUNDARY_VALUE = "foo_bar_baz";
+
+  p.url = base_url;
+  AddUrlFirstQueryParameter("uploadType", "multipart", &p.url);
+
+  p.method = "POST";
+
+  p.headers = "";
+
+  AddHeaders("Content-type", "multipart/related; boundary=" + BOUNDARY_VALUE,
+             &p.headers);
+  AddHeaders("Authorization", "Bearer " + googledrivefs->token(), &p.headers);
+
+  p.body = "";
+  AddBody("--" + BOUNDARY_VALUE, &p.body);
+  AddBody("Content-Type: application/json; charset=UTF-8", &p.body);
+  AddBody("", &p.body);
+  AddBody("{", &p.body);
+  AddBody(std::string("  \"name\": \"") + path_.Basename() + std::string("\","),
+          &p.body);
+  AddBody("  \"parents\": [", &p.body);
+  AddBody("    \"" + parent_dir_id_ + "\"", &p.body);
+  AddBody("  ]", &p.body);
+  AddBody("}", &p.body);
+  AddBody("", &p.body);
+  AddBody("--" + BOUNDARY_VALUE, &p.body);
+  AddBody("Content-Type: text/plain", &p.body);
+  AddBody("", &p.body);
+  AddBody("", &p.body);
+  AddBody("--" + BOUNDARY_VALUE + "--", &p.body);
+
+  error = MakeRequest(googledrivefs->ppapi(), url_loader_object,
+                      url_request_info_object, p);
+
+  if (error) {
+    goto done;
+  }
+
+  error = FinishPreparingResponse(googledrivefs->ppapi(), url_loader_object,
+                                  &url_response_info_object);
+
+  if (error) {
+    goto done;
+  }
+
+  if (ReadStatusCode(googledrivefs->ppapi(), url_response_info_object) !=
+      STATUSCODE_OK) {
+    error = EPERM;
+    goto done;
+  }
+
+done:
+  if (url_loader_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_loader_object);
+  }
+  if (url_request_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_request_info_object);
+  }
+  if (url_response_info_object) {
+    googledrivefs->ppapi()->ReleaseResource(url_response_info_object);
+  }
+
+  return error;
+}
+
+Error GoogleDriveFsNode::RequestDirentHelper(
+    const std::string& url,
+    std::vector<std::string>* out_dirent_names) {
+  std::string response_body;
+  Error error = GetListFileResponseBody(url, filesystem_, &response_body);
+  if (error) {
+    return error;
+  }
+
+  std::string name_value = "";
+  int name_index = 0;
+
+  GetValue(response_body, "name", name_index, &name_value, &name_index);
+
+  while (name_index != -1) {
+    out_dirent_names->push_back(name_value);
+
+    GetValue(response_body, "name", name_index, &name_value, &name_index);
+  }
+
+  std::string next_page_token_value = "";
+  int next_page_token_index = 0;
+  GetValue(response_body, "nextPageToken", 0, &next_page_token_value,
+           &next_page_token_index);
+  if (next_page_token_index != -1) {
+    return RequestDirentWithNextPageToken(next_page_token_value,
+                                          out_dirent_names);
+  }
+
+  return 0;
+}
+
+Error GoogleDriveFsNode::RequestDirentWithNextPageToken(
+    const std::string& next_page_token,
+    std::vector<std::string>* out_dirent_names) {
+  static const char base_url[] = "https://www.googleapis.com/drive/v3/files";
+
+  std::string url = base_url;
+  AddUrlFirstQueryParameter("pageToken", next_page_token, &url);
+  AddUrlNextQueryParameter("q", "%27" + item_id_ + "%27+in+parents", &url);
+
+  return RequestDirentHelper(url, out_dirent_names);
+}
+
+Error GoogleDriveFsNode::RequestDirent(
+    std::vector<std::string>* out_dirent_names) {
+  static const char base_url[] = "https://www.googleapis.com/drive/v3/files";
+
+  std::string url = base_url;
+  AddUrlFirstQueryParameter("q", "%27" + item_id_ + "%27+in+parents", &url);

[binji, 2016/08/22 19:21:53]

this expression ("%27" + ...) is very common, probably would be good to make a
helper function for it.

[chanpatorikku, 2016/08/29 17:14:03]

Done.

+
+  return RequestDirentHelper(url, out_dirent_names);
+}
+
+}  // namespace nacl_io