SERVER-17629 Implemented Bounded Data View/Cursor

Implements DataRange and DataRangeCursor, bounded Status returning
variants of DataView and DataCursor.

Implements DataType::Handler<> to allow for specialization by type.
* Endian specializations
* BSONObj specialization

Fix for endian conversions for floats and doubles to avoid some
signaling bit patterns.

1 files changed, 127 insertions, 0 deletions

diff --git a/src/mongo/base/data_range.h b/src/mongo/base/data_range.h
new file mode 100644
index 00000000000..a87a5b2bfb5
--- /dev/null
+++ b/src/mongo/base/data_range.h
@@ -0,0 +1,127 @@
+/*    Copyright 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#pragma once
+
+#include <cstring>
+#include <tuple>
+#include <type_traits>
+
+#include "mongo/base/data_type.h"
+#include "mongo/base/error_codes.h"
+#include "mongo/base/status_with.h"
+#include "mongo/platform/endian.h"
+#include "mongo/util/mongoutils/str.h"
+
+namespace mongo {
+
+    class ConstDataRange {
+
+    public:
+        // begin and end should point to the first and one past last bytes in
+        // the range you wish to view.
+        //
+        // debug_offset provides a way to indicate that the ConstDataRange is
+        // located at an offset into some larger logical buffer. By setting it
+        // to a non-zero value, you'll change the Status messages that are
+        // returned on failure to be offset by the amount passed to this
+        // constructor.
+        ConstDataRange(const char* begin, const char* end, std::ptrdiff_t debug_offset = 0)
+            : _begin(begin), _end(end), _debug_offset(debug_offset) {
+            invariant(end >= begin);
+        }
+
+        const char* data() const {
+            return _begin;
+        }
+
+        size_t length() const {
+            return _end - _begin;
+        }
+
+        template<typename T>
+        Status read(T* t, size_t offset = 0) const {
+            if (offset > length()) {
+                return makeOffsetStatus(offset);
+            }
+
+            return DataType::load(t, _begin + offset, length() - offset, nullptr,
+                                  offset + _debug_offset);
+        }
+
+        template<typename T>
+        StatusWith<T> read(std::size_t offset = 0) const {
+            T t(DataType::defaultConstruct<T>());
+            Status s = read(&t, offset);
+
+            if (s.isOK()) {
+                return StatusWith<T>(std::move(t));
+            } else {
+                return StatusWith<T>(std::move(s));
+            }
+        }
+
+        friend bool operator==(const ConstDataRange& lhs, const ConstDataRange& rhs) {
+            return std::tie(lhs._begin, lhs._end) == std::tie(rhs._begin, rhs._end);
+        }
+
+        friend bool operator!=(const ConstDataRange& lhs, const ConstDataRange& rhs) {
+            return !(lhs == rhs);
+        }
+
+
+    protected:
+        const char* _begin;
+        const char* _end;
+        std::ptrdiff_t _debug_offset;
+
+        Status makeOffsetStatus(size_t offset) const;
+
+    };
+
+    class DataRange : public ConstDataRange {
+
+    public:
+        typedef char* bytes_type;
+
+        DataRange(bytes_type begin, bytes_type end, std::ptrdiff_t debug_offset = 0)
+            : ConstDataRange(begin, end, debug_offset) {
+        }
+
+        template<typename T>
+        Status write(const T& value, std::size_t offset = 0) {
+            if (offset > length()) {
+                return makeOffsetStatus(offset);
+            }
+
+            return DataType::store(value, const_cast<char *>(_begin + offset), length() - offset,
+                                   nullptr, offset + _debug_offset);
+        }
+
+    };
+
+} // namespace mongo