Add a Darwin framework utility to convert data-value dictionaries to …

…TLV in NSData. (#31666)

Not public API, just an internal utility.

src/darwin/Framework/CHIP/MTRBaseDevice.mm

@@ -743,6 +743,27 @@ static CHIP_ERROR MTREncodeTLVFromDataValueDictionary(id object, chip::TLV::TLVW
     return CHIP_ERROR_INVALID_ARGUMENT;
 }
 
+NSData * _Nullable MTREncodeTLVFromDataValueDictionary(NSDictionary<NSString *, id> * value, NSError * __autoreleasing * error)
+{
+    // A single data item cannot be bigger than a packet, so just use 1200 bytes
+    // as the max size of our buffer.  This assumes that lists will not be
+    // passed as-is to this method but will get chunked, with each list item
+    // passed to this method separately.
+    uint8_t buffer[1200];
+    TLV::TLVWriter writer;
+    writer.Init(buffer);
+
+    CHIP_ERROR err = MTREncodeTLVFromDataValueDictionary(value, writer, TLV::AnonymousTag());
+    if (err != CHIP_NO_ERROR) {
+        if (error) {
+            *error = [MTRError errorForCHIPErrorCode:err];
+        }
+        return nil;
+    }
+
+    return AsData(ByteSpan(buffer, writer.GetLengthWritten()));
+}
+
 // Callback type to pass data value as an NSObject
 typedef void (*MTRDataValueDictionaryCallback)(void * context, id value);
 

src/darwin/Framework/CHIP/MTRBaseDevice_Internal.h

@@ -230,4 +230,10 @@ static inline MTRTransportType MTRMakeTransportType(chip::Transport::Type type)
 // Convert TLV data into data-value dictionary as described in MTRDeviceResponseHandler
 NSDictionary<NSString *, id> * _Nullable MTRDecodeDataValueDictionaryFromCHIPTLV(chip::TLV::TLVReader * data);
 
+// Convert a data-value dictionary as described in MTRDeviceResponseHandler into
+// TLV Data with an anonymous tag.  This method assumes the encoding of the
+// value fits in a single UDP MTU; for lists this method might need to be used
+// on each list item separately.
+NSData * _Nullable MTREncodeTLVFromDataValueDictionary(NSDictionary<NSString *, id> * value, NSError * __autoreleasing * error);
+
 NS_ASSUME_NONNULL_END