Make TLVReader getter const for ByteSpan and CharSpan (#28169)

* Move some TLV reader get methods to const (integers and bools)

* Move floating point getters to const

* Make use of new newly const support in protocol decoder printers

* Restyled by clang-format

* Another minor simplification

---------

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

src/lib/core/TLVReader.cpp

@@ -290,7 +290,7 @@ CHIP_ERROR TLVReader::Get(double & v) const
     return CHIP_NO_ERROR;
 }
 
-CHIP_ERROR TLVReader::Get(ByteSpan & v)
+CHIP_ERROR TLVReader::Get(ByteSpan & v) const
 {
     const uint8_t * val;
     ReturnErrorOnFailure(GetDataPtr(val));
@@ -304,7 +304,7 @@ constexpr int kUnicodeInformationSeparator1       = 0x1F;
 constexpr size_t kMaxLocalizedStringIdentifierLen = 2 * sizeof(LocalizedStringIdentifier);
 } // namespace
 
-CHIP_ERROR TLVReader::Get(CharSpan & v)
+CHIP_ERROR TLVReader::Get(CharSpan & v) const
 {
     if (!TLVTypeIsUTF8String(ElementType()))
     {
@@ -460,32 +460,22 @@ CHIP_ERROR TLVReader::DupString(char *& buf)
     return err;
 }
 
-CHIP_ERROR TLVReader::GetDataPtr(const uint8_t *& data)
+CHIP_ERROR TLVReader::GetDataPtr(const uint8_t *& data) const
 {
-    CHIP_ERROR err;
-
-    if (!TLVTypeIsString(ElementType()))
-        return CHIP_ERROR_WRONG_TLV_TYPE;
+    VerifyOrReturnError(TLVTypeIsString(ElementType()), CHIP_ERROR_WRONG_TLV_TYPE);
 
     if (GetLength() == 0)
     {
         data = nullptr;
         return CHIP_NO_ERROR;
     }
 
-    err = EnsureData(CHIP_ERROR_TLV_UNDERRUN);
-    if (err != CHIP_NO_ERROR)
-        return err;
-
     uint32_t remainingLen = static_cast<decltype(mMaxLen)>(mBufEnd - mReadPoint);
 
     // Verify that the entirety of the data is available in the buffer.
     // Note that this may not be possible if the reader is reading from a chain of buffers.
-    if (remainingLen < static_cast<uint32_t>(mElemLenOrVal))
-        return CHIP_ERROR_TLV_UNDERRUN;
-
+    VerifyOrReturnError(remainingLen >= static_cast<uint32_t>(mElemLenOrVal), CHIP_ERROR_TLV_UNDERRUN);
     data = mReadPoint;
-
     return CHIP_NO_ERROR;
 }
 
@@ -576,20 +566,19 @@ CHIP_ERROR TLVReader::VerifyEndOfContainer()
 
 CHIP_ERROR TLVReader::Next()
 {
-    CHIP_ERROR err;
-    TLVElementType elemType = ElementType();
+    ReturnErrorOnFailure(Skip());
+    ReturnErrorOnFailure(ReadElement());
 
-    err = Skip();
-    if (err != CHIP_NO_ERROR)
-        return err;
+    TLVElementType elemType = ElementType();
 
-    err = ReadElement();
-    if (err != CHIP_NO_ERROR)
-        return err;
+    VerifyOrReturnError(elemType != TLVElementType::EndOfContainer, CHIP_END_OF_TLV);
 
-    elemType = ElementType();
-    if (elemType == TLVElementType::EndOfContainer)
-        return CHIP_END_OF_TLV;
+    // Ensure that GetDataPtr calls can be called immediately after Next, so
+    // that `Get(ByteSpan&)` does not need to advance buffers and just works
+    if (TLVTypeIsString(elemType) && (GetLength() != 0))
+    {
+        ReturnErrorOnFailure(EnsureData(CHIP_ERROR_TLV_UNDERRUN));
+    }
 
     return CHIP_NO_ERROR;
 }

src/lib/core/TLVReader.h

@@ -440,7 +440,7 @@ class DLL_EXPORT TLVReader
      *                                      the reader is not positioned on an element.
      *
      */
-    CHIP_ERROR Get(ByteSpan & v);
+    CHIP_ERROR Get(ByteSpan & v) const;
 
     /**
      * Get the value of the current element as a FixedByteSpan
@@ -453,7 +453,7 @@ class DLL_EXPORT TLVReader
      *
      */
     template <size_t N>
-    CHIP_ERROR Get(FixedByteSpan<N> & v)
+    CHIP_ERROR Get(FixedByteSpan<N> & v) const
     {
         const uint8_t * val;
         ReturnErrorOnFailure(GetDataPtr(val));
@@ -472,7 +472,7 @@ class DLL_EXPORT TLVReader
      *                                      the reader is not positioned on an element.
      *
      */
-    CHIP_ERROR Get(CharSpan & v);
+    CHIP_ERROR Get(CharSpan & v) const;
 
     /**
      * Get the Localized String Identifier contained in the current element..
@@ -634,9 +634,8 @@ class DLL_EXPORT TLVReader
      * Get a pointer to the initial encoded byte of a TLV byte or UTF8 string element.
      *
      * This method returns a direct pointer to the encoded string value within the underlying input buffer
-     * if a non-zero length string payload is present. To succeed, the method requires that the entirety of the
-     * string value be present in a single buffer. Otherwise the method returns #CHIP_ERROR_TLV_UNDERRUN.
-     * This makes the method of limited use when reading data from multiple discontiguous buffers.
+     * as fetched by `Next`. To succeed, the method requires that the entirety of the
+     * string value be present in a single buffer.
      *
      * If no string data is present (i.e the length is zero), data shall be updated to point to null.
      *
@@ -653,7 +652,7 @@ class DLL_EXPORT TLVReader
      *                                      TLVBackingStore.
      *
      */
-    CHIP_ERROR GetDataPtr(const uint8_t *& data);
+    CHIP_ERROR GetDataPtr(const uint8_t *& data) const;
 
     /**
      * Prepares a TLVReader object for reading the members of TLV container element.

src/lib/format/protocol_decoder.cpp

@@ -45,7 +45,7 @@ class ByTag
     const Tag mTag;
 };
 
-CHIP_ERROR FormatCurrentValue(TLVReader & reader, chip::StringBuilderBase & out)
+CHIP_ERROR FormatCurrentValue(const TLVReader & reader, chip::StringBuilderBase & out)
 {
     switch (reader.GetType())
     {
@@ -105,7 +105,7 @@ CHIP_ERROR FormatCurrentValue(TLVReader & reader, chip::StringBuilderBase & out)
 }
 
 // Returns a null terminated string containing the current reader value
-void PrettyPrintCurrentValue(TLVReader & reader, chip::StringBuilderBase & out, PayloadDecoderBase::DecodePosition & position)
+void PrettyPrintCurrentValue(const TLVReader & reader, chip::StringBuilderBase & out, PayloadDecoderBase::DecodePosition & position)
 {
     CHIP_ERROR err = FormatCurrentValue(reader, out);