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Add a buffer reader helper class that can be used to read buffers saf…
…ely. The idea is to not have people doing ad-hoc, and often incorrect when they forget to update lengths, length checks. I did measure the codesize with the Read methods out-of-line, and it's larger than with the inline methods as far as I can tell. It might be worth re-measuring once we have more callers to see what things look like then.
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| /* | ||
| * | ||
| * Copyright (c) 2020 Project CHIP Authors | ||
| * | ||
| * 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. | ||
| */ | ||
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| /** | ||
| * @file | ||
| * Utility classes for safely reading from size-limited buffers. | ||
| */ | ||
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| #pragma once | ||
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| #include <climits> | ||
| #include <lib/core/CHIPEncoding.h> | ||
| #include <lib/core/CHIPError.h> | ||
| #include <lib/support/CodeUtils.h> | ||
| #include <stdint.h> | ||
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| namespace chip { | ||
| namespace Encoding { | ||
| namespace LittleEndian { | ||
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| /** | ||
| * @class Reader | ||
| * | ||
| * Simple reader for reading little-endian things out of buffers. | ||
| */ | ||
| class Reader | ||
| { | ||
| public: | ||
| /** | ||
| * Create a data model reader from a given buffer and length. | ||
| * | ||
| * @param buffer The octet buffer to read from. The caller must ensure | ||
| * (most simply by allocating the reader on the stack) that | ||
| * the buffer outlives the reader. The buffer is allowed to | ||
| * be null if buf_len is 0. | ||
| * @param buf_len The number of octets in the buffer. | ||
| */ | ||
| Reader(const uint8_t * buffer, uint16_t buf_len) : mBufStart(buffer), mReadPtr(buffer), mAvailable(buf_len) {} | ||
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| /** | ||
| * Number of octets we have read so far. This might be able to go away once | ||
| * we do less switching back and forth between DataModelReader and raw | ||
| * buffers. | ||
| */ | ||
| uint16_t OctetsRead() const { return static_cast<uint16_t>(mReadPtr - mBufStart); } | ||
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| /** | ||
| * Read a single 8-bit unsigned integer. | ||
| * | ||
| * @param [out] dest Where the 8-bit integer goes. | ||
| * | ||
| * @return Whether the read succeeded. The read can fail if there are not | ||
| * enough octets available. | ||
| */ | ||
| CHECK_RETURN_VALUE | ||
| CHIP_ERROR Read8(uint8_t * dest) { return Read(dest); } | ||
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| /** | ||
| * Read a single 16-bit unsigned integer. | ||
| * | ||
| * @param [out] dest Where the 16-bit integer goes. | ||
| * | ||
| * @return Whether the read succeeded. The read can fail if there are not | ||
| * enough octets available. | ||
| */ | ||
| CHECK_RETURN_VALUE | ||
| CHIP_ERROR Read16(uint16_t * dest) { return Read(dest); } | ||
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| /** | ||
| * Read a single 32-bit unsigned integer. | ||
| * | ||
| * @param [out] dest Where the 32-bit integer goes. | ||
| * | ||
| * @return Whether the read succeeded. The read can fail if there are not | ||
| * enough octets available. | ||
| */ | ||
| CHECK_RETURN_VALUE | ||
| CHIP_ERROR Read32(uint32_t * dest) { return Read(dest); } | ||
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| /** | ||
| * Read a single 64-bit unsigned integer. | ||
| * | ||
| * @param [out] dest Where the 64-bit integer goes. | ||
| * | ||
| * @return Whether the read succeeded. The read can fail if there are not | ||
| * enough octets available. | ||
| */ | ||
| CHECK_RETURN_VALUE | ||
| CHIP_ERROR Read64(uint64_t * dest) { return Read(dest); } | ||
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| protected: | ||
| template <typename T> | ||
| CHIP_ERROR Read(T * retval) | ||
| { | ||
| static_assert(CHAR_BIT == 8, "Our various sizeof checks rely on bytes and octets being the same thing"); | ||
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| static constexpr size_t data_size = sizeof(T); | ||
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| if (mAvailable < data_size) | ||
| { | ||
| return CHIP_ERROR_BUFFER_TOO_SMALL; | ||
| } | ||
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| Read(mReadPtr, retval); | ||
| mAvailable = static_cast<uint16_t>(mAvailable - data_size); | ||
| return CHIP_NO_ERROR; | ||
| } | ||
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| private: | ||
| // These helper methods return void and put the value being read into an | ||
| // outparam because that allows us to easily overload on the type of the | ||
| // thing being read. | ||
| void Read(const uint8_t *& p, uint8_t * dest) { *dest = Encoding::Read8(p); } | ||
| void Read(const uint8_t *& p, uint16_t * dest) { *dest = Encoding::LittleEndian::Read16(p); } | ||
| void Read(const uint8_t *& p, uint32_t * dest) { *dest = Encoding::LittleEndian::Read32(p); } | ||
| void Read(const uint8_t *& p, uint64_t * dest) { *dest = Encoding::LittleEndian::Read64(p); } | ||
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| /** | ||
| * Our buffer start. | ||
| */ | ||
| const uint8_t * const mBufStart; | ||
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| /** | ||
| * Our current read point. | ||
| */ | ||
| const uint8_t * mReadPtr; | ||
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| /** | ||
| * The number of octets we can still read starting at mReadPtr. | ||
| */ | ||
| uint16_t mAvailable; | ||
| }; | ||
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| } // namespace LittleEndian | ||
| } // namespace Encoding | ||
| } // namespace chip |
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