Introduce MinidumpWritable, its dependencies, and their tests

util/file/string_file_writer.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/file/string_file_writer.h"
+
+#include <string.h>
+
+#include "base/logging.h"
+#include "base/numerics/safe_math.h"
+
+namespace crashpad {
+
+StringFileWriter::StringFileWriter() : string_(), offset_(0) {
+}
+
+StringFileWriter::~StringFileWriter() {
+}
+
+void StringFileWriter::Reset() {
+  string_.clear();
+  offset_ = 0;
+}
+
+bool StringFileWriter::Write(const void* data, size_t size) {
+  DCHECK(offset_.IsValid());
+
+  size_t offset = offset_.ValueOrDie();

[Robert Sesek, 2014/08/01 14:38:04]

Mark this const so it isn't accidentally used as a destination for arithmetic
outside its safety harness.

[Mark Mentovai, 2014/08/01 16:09:35]

rsesek wrote:
Yeah, I’d actually like to use more and more const for safety in all of this
code.

+  if (offset > string_.size()) {
+    string_.resize(offset);
+  }
+
+  base::CheckedNumeric<ssize_t> new_offset = offset_;
+  new_offset += size;
+  if (!new_offset.IsValid()) {
+    LOG(ERROR) << "Write(): file too large";
+    return false;
+  }
+
+  string_.replace(offset, size, reinterpret_cast<const char*>(data), size);
+  offset_ = new_offset;
+
+  return true;
+}
+
+bool StringFileWriter::WriteIoVec(std::vector<WritableIoVec>* iovecs) {
+  DCHECK(offset_.IsValid());
+
+  if (iovecs->empty()) {
+    LOG(ERROR) << "WriteIoVec(): no iovecs";
+    return false;
+  }
+
+  // Avoid writing anything at all if it would cause an overflow.
+  base::CheckedNumeric<ssize_t> new_offset = offset_;
+  for (const WritableIoVec& iov : *iovecs) {
+    new_offset += iov.iov_len;
+    if (!new_offset.IsValid()) {
+      LOG(ERROR) << "WriteIoVec(): file too large";
+      return false;
+    }
+  }
+
+  for (const WritableIoVec& iov : *iovecs) {
+    if (!Write(iov.iov_base, iov.iov_len)) {
+      return false;
+    }
+  }
+
+#ifndef NDEBUG
+  // The interface says that |iovecs| is not sacred, so scramble it to make sure
+  // that nobody depends on it.
+  memset(&(*iovecs)[0], 0xa5, sizeof((*iovecs)[0]) * iovecs->size());
+#endif
+
+  return true;
+}
+
+off_t StringFileWriter::Seek(off_t offset, int whence) {
+  DCHECK(offset_.IsValid());
+
+  size_t base_offset;
+
+  switch (whence) {
+    case SEEK_SET:
+      base_offset = 0;
+      break;
+
+    case SEEK_CUR:
+      base_offset = offset_.ValueOrDie();
+      break;
+
+    case SEEK_END:
+      base_offset = string_.size();
+      break;
+
+    default:
+      LOG(ERROR) << "Seek(): invalid whence " << whence;
+      return -1;
+  }
+
+  if (!base::IsValueInRangeForNumericType<off_t>(base_offset)) {
+    LOG(ERROR) << "Seek(): base_offset " << base_offset << " invalid for off_t";
+    return -1;
+  }
+
+  base::CheckedNumeric<off_t> new_offset_checked(base_offset);

[Robert Sesek, 2014/08/01 14:38:04]

Could use AssignIfInRange() for lines 112-117.

[Mark Mentovai, 2014/08/01 16:09:35]

rsesek wrote:
It actually works out being an extra line that way, because you can’t assign
right into a CheckedNumeric, but I made the change to leverage util anyway.

+  new_offset_checked += offset;
+  if (!new_offset_checked.IsValid()) {
+    LOG(ERROR) << "Seek(): new_offset invalid";
+    return -1;
+  }
+
+  off_t new_offset = new_offset_checked.ValueOrDie();
+  if (!base::IsValueInRangeForNumericType<size_t>(new_offset)) {

[Robert Sesek, 2014/08/01 14:38:04]

Same.

+    LOG(ERROR) << "Seek(): new_offset " << new_offset << " invalid for size_t";
+    return -1;
+  }
+
+  offset_ = new_offset;
+
+  return offset_.ValueOrDie();
+}
+
+}  // namespace crashpad