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      1 /*
      2  * Copyright (C) 2010 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ANDROID_UTILS_FLATTENABLE_H
     18 #define ANDROID_UTILS_FLATTENABLE_H
     19 
     20 
     21 #include <stdint.h>
     22 #include <sys/types.h>
     23 #include <utils/Errors.h>
     24 
     25 namespace android {
     26 
     27 /*
     28  * The Flattenable interface allows an object to serialize itself out
     29  * to a byte-buffer and an array of file descriptors.
     30  */
     31 
     32 class Flattenable
     33 {
     34 public:
     35     // size in bytes of the flattened object
     36     virtual size_t getFlattenedSize() const = 0;
     37 
     38     // number of file descriptors to flatten
     39     virtual size_t getFdCount() const = 0;
     40 
     41     // flattens the object into buffer.
     42     // size should be at least of getFlattenedSize()
     43     // file descriptors are written in the fds[] array but ownership is
     44     // not transfered (ie: they must be dupped by the caller of
     45     // flatten() if needed).
     46     virtual status_t flatten(void* buffer, size_t size,
     47             int fds[], size_t count) const = 0;
     48 
     49     // unflattens the object from buffer.
     50     // size should be equal to the value of getFlattenedSize() when the
     51     // object was flattened.
     52     // unflattened file descriptors are found in the fds[] array and
     53     // don't need to be dupped(). ie: the caller of unflatten doesn't
     54     // keep ownership. If a fd is not retained by unflatten() it must be
     55     // explicitly closed.
     56     virtual status_t unflatten(void const* buffer, size_t size,
     57             int fds[], size_t count) = 0;
     58 
     59 protected:
     60     virtual ~Flattenable() = 0;
     61 
     62 };
     63 
     64 /*
     65  * LightFlattenable is a protocol allowing object to serialize themselves out
     66  * to a byte-buffer.
     67  *
     68  * LightFlattenable objects must implement this protocol.
     69  *
     70  * LightFlattenable doesn't require the object to be virtual.
     71  */
     72 template <typename T>
     73 class LightFlattenable {
     74 public:
     75     // returns whether this object always flatten into the same size.
     76     // for efficiency, this should always be inline.
     77     inline bool isFixedSize() const;
     78 
     79     // returns size in bytes of the flattened object. must be a constant.
     80     inline size_t getSize() const;
     81 
     82     // flattens the object into buffer.
     83     inline status_t flatten(void* buffer) const;
     84 
     85     // unflattens the object from buffer of given size.
     86     inline status_t unflatten(void const* buffer, size_t size);
     87 };
     88 
     89 template <typename T>
     90 inline bool LightFlattenable<T>::isFixedSize() const {
     91     return static_cast<T const*>(this)->T::isFixedSize();
     92 }
     93 template <typename T>
     94 inline size_t LightFlattenable<T>::getSize() const {
     95     return static_cast<T const*>(this)->T::getSize();
     96 }
     97 template <typename T>
     98 inline status_t LightFlattenable<T>::flatten(void* buffer) const {
     99     return static_cast<T const*>(this)->T::flatten(buffer);
    100 }
    101 template <typename T>
    102 inline status_t LightFlattenable<T>::unflatten(void const* buffer, size_t size) {
    103     return static_cast<T*>(this)->T::unflatten(buffer, size);
    104 }
    105 
    106 /*
    107  * LightFlattenablePod is an implementation of the LightFlattenable protocol
    108  * for POD (plain-old-data) objects.
    109  */
    110 template <typename T>
    111 class LightFlattenablePod : public LightFlattenable<T> {
    112 public:
    113     inline bool isFixedSize() const {
    114         return true;
    115     }
    116 
    117     inline size_t getSize() const {
    118         return sizeof(T);
    119     }
    120     inline status_t flatten(void* buffer) const {
    121         *reinterpret_cast<T*>(buffer) = *static_cast<T const*>(this);
    122         return NO_ERROR;
    123     }
    124     inline status_t unflatten(void const* buffer, size_t) {
    125         *static_cast<T*>(this) = *reinterpret_cast<T const*>(buffer);
    126         return NO_ERROR;
    127     }
    128 };
    129 
    130 
    131 }; // namespace android
    132 
    133 
    134 #endif /* ANDROID_UTILS_FLATTENABLE_H */
    135