Add wrappers around getxattr() and setxattr().

util/mac/xattr.cc

+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/mac/xattr.h"
+
+#include <errno.h>
+#include <sys/xattr.h>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/numerics/safe_conversions.h"
+#include "base/strings/stringprintf.h"
+#include "base/strings/string_number_conversions.h"
+
+namespace crashpad {
+
+bool ReadXattr(const base::FilePath& file,
+               const base::StringPiece& name,
+               std::string* value) {
+  value->resize(128);
+  ssize_t rv = 0;
+  do {

[Mark Mentovai, 2014/12/30 19:19:15]

Hmm…

The man page says
Maybe that’s better than the loop altogether.

[Robert Sesek, 2014/12/30 21:59:04]

Oh, I missed that. Yes, that's better.

+    // getxattr() has a |position| argument, but it is only used for resource
+    // fork attributes. If reading the attribute filled up to |value|'s
+    // capacity, resize the buffer and try to read the entire attribute again.
+    rv = getxattr(file.value().c_str(), name.data(), &(*value)[0],
+        value->size(), 0, 0);
+    if (rv < 0) {
+      if (errno == ERANGE) {
+        value->resize(value->size() * 2);

[Mark Mentovai, 2014/12/30 19:19:15]

…or if you keep this, just make sure there’s no way for it to logically
overflow.

+      } else {
+        PLOG(ERROR) << "getxattr " << name << " on file " << file.value();
+        return false;
+      }
+    } else {
+      // Resize the buffer to be the length of the read string.
+      value->resize(rv);
+    }
+  } while (rv < 0 && errno == ERANGE);
+
+  return true;
+}
+
+bool WriteXattr(const base::FilePath& file,
+                const base::StringPiece& name,
+                const std::string& value) {
+  int rv = setxattr(file.value().c_str(), name.data(), value.c_str(),
+      value.length(), 0, 0);
+  PLOG_IF(ERROR, rv != 0) << "setxattr " << name << " on file "
+                          << file.value();
+  return rv == 0;
+}
+
+bool ReadXattrBool(const base::FilePath& file,
+                   const base::StringPiece& name,
+                   bool* value) {
+  std::string tmp;
+  if (!ReadXattr(file, name, &tmp))
+    return false;
+  if (tmp == "1") {
+    *value = true;
+    return true;
+  } else if (tmp == "0") {
+    *value = false;
+    return true;
+  } else {
+    LOG(ERROR) << "ReadXattrBool " << name << " on file " << file.value()
+               << " could not be interpreted as boolean";
+    return false;
+  }
+}
+
+bool WriteXattrBool(const base::FilePath& file,
+                    const base::StringPiece& name,
+                    bool value) {
+  return WriteXattr(file, name, (value ? "1" : "0"));
+}
+
+bool ReadXattrInt(const base::FilePath& file,
+                  const base::StringPiece& name,
+                  int* value) {
+  std::string tmp;
+  if (!ReadXattr(file, name, &tmp))
+    return false;
+  return base::StringToInt(tmp, value);
+}
+
+bool WriteXattrInt(const base::FilePath& file,
+                   const base::StringPiece& name,
+                   int value) {
+  std::string tmp = base::StringPrintf("%d", value);
+  return WriteXattr(file, name, tmp);
+}
+
+bool ReadXattrTimeT(const base::FilePath& file,
+                    const base::StringPiece& name,
+                    time_t* value) {
+  // time_t on OS X is defined as a long, but it will be read into an
+  // int64_t here, since there is no string conversion method for long.
+  std::string tmp;
+  if (!ReadXattr(file, name, &tmp))
+    return false;
+
+  int64_t encoded_value;

[Mark Mentovai, 2014/12/30 19:19:15]

#include <stdint.h>.

[Robert Sesek, 2014/12/30 21:59:04]

Done.

+  if (!base::StringToInt64(tmp, &encoded_value))
+    return false;
+
+  *value = base::saturated_cast<time_t, int64_t>(encoded_value);
+  if (!base::IsValueInRangeForNumericType<time_t, int64_t>(encoded_value)) {

[Mark Mentovai, 2014/12/30 19:19:15]

You can leave out the int64_t template parameters on this and the
saturated_cast, because it’s implied by the type of encoded_value. Using the
implicit value means that if the type changes, there are fewer things to clean
up.

For the same reason, you could use decltype(*value) instead of time_t as the
template parameter.

[Robert Sesek, 2014/12/30 21:59:04]

Done.

+    LOG(ERROR) << "ReadXattrTimeT " << name << " on file " << file.value()
+               << " read over-sized value and will saturate";
+    return false;
+  }
+
+  return true;
+}
+
+bool WriteXattrTimeT(const base::FilePath& file,
+                     const base::StringPiece& name,
+                     time_t value) {
+  std::string tmp = base::StringPrintf("%ld", value);
+  return WriteXattr(file, name, tmp);
+}
+
+}  // namespace crashpad