Add a BigEndian::Reader to be the equivalent for LittleEndian::Reader (project-chip#36195)

* Add a big endian reader since we seem to potentially want this

* Minor re-arrange

* Fix includes

* Restyled by clang-format

* make some compilers happy

* Update src/lib/support/BufferReader.h

Co-authored-by: Boris Zbarsky <bzbarsky@apple.com>

---------

Co-authored-by: Andrei Litvin <andreilitvin@google.com>
Co-authored-by: Restyled.io <commits@restyled.io>
Co-authored-by: Boris Zbarsky <bzbarsky@apple.com>

Author: 4 people

src/lib/support/BufferReader.cpp

@@ -18,12 +18,29 @@
 #include "BufferReader.h"
 
 #include <lib/core/CHIPEncoding.h>
+#include <lib/core/CHIPError.h>
 
+#include <cstdint>
 #include <string.h>
 #include <type_traits>
 
 namespace chip {
 namespace Encoding {
+
+BufferReader & BufferReader::ReadBytes(uint8_t * dest, size_t size)
+{
+    static_assert(CHAR_BIT == 8, "Our various sizeof checks rely on bytes and octets being the same thing");
+
+    if (EnsureAvailable(size))
+    {
+        memcpy(dest, mReadPtr, size);
+        mReadPtr += size;
+        mAvailable -= size;
+    }
+
+    return *this;
+}
+
 namespace LittleEndian {
 
 namespace {
@@ -58,37 +75,12 @@ void Reader::RawReadLowLevelBeCareful(T * retval)
 
     constexpr size_t data_size = sizeof(T);
 
-    if (mAvailable < data_size)
-    {
-        mStatus = CHIP_ERROR_BUFFER_TOO_SMALL;
-        // Ensure that future reads all fail.
-        mAvailable = 0;
-        return;
-    }
-
-    ReadHelper(mReadPtr, retval);
-    mReadPtr += data_size;
-
-    mAvailable = static_cast<uint16_t>(mAvailable - data_size);
-}
-
-Reader & Reader::ReadBytes(uint8_t * dest, size_t size)
-{
-    static_assert(CHAR_BIT == 8, "Our various sizeof checks rely on bytes and octets being the same thing");
-
-    if ((size > UINT16_MAX) || (mAvailable < size))
+    if (EnsureAvailable(data_size))
     {
-        mStatus = CHIP_ERROR_BUFFER_TOO_SMALL;
-        // Ensure that future reads all fail.
-        mAvailable = 0;
-        return *this;
+        ReadHelper(mReadPtr, retval);
+        mReadPtr += data_size;
+        mAvailable -= data_size;
     }
-
-    memcpy(dest, mReadPtr, size);
-
-    mReadPtr += size;
-    mAvailable = static_cast<uint16_t>(mAvailable - size);
-    return *this;
 }
 
 // Explicit Read instantiations for the data types we want to support.
@@ -104,5 +96,46 @@ template void Reader::RawReadLowLevelBeCareful(uint32_t *);
 template void Reader::RawReadLowLevelBeCareful(uint64_t *);
 
 } // namespace LittleEndian
+
+namespace BigEndian {
+
+Reader & Reader::Read16(uint16_t * dest)
+{
+    if (!EnsureAvailable(sizeof(uint16_t)))
+    {
+        return *this;
+    }
+
+    static_assert(sizeof(*dest) == 2);
+
+    *dest = static_cast<uint16_t>((mReadPtr[0] << 8) + mReadPtr[1]);
+    mReadPtr += 2;
+    mAvailable -= 2;
+    return *this;
+}
+
+Reader & Reader::Read32(uint32_t * dest)
+{
+    if (!EnsureAvailable(sizeof(uint32_t)))
+    {
+        return *this;
+    }
+
+    static_assert(sizeof(*dest) == 4);
+
+    *dest = 0;
+    for (unsigned i = 0; i < sizeof(uint32_t); i++)
+    {
+        *dest <<= 8;
+        *dest += mReadPtr[i];
+    }
+
+    mReadPtr += sizeof(uint32_t);
+    mAvailable -= sizeof(uint32_t);
+    return *this;
+}
+
+} // namespace BigEndian
+
 } // namespace Encoding
 } // namespace chip