Question about otSrpClientSetHostName()

[OlivierGre]

I have a question concerning this code in SrpClient::Process():

openthread/src/cli/cli_srp_client.cpp

Lines 134 to 149 in 24d633d

	VerifyOrExit(aArgs[2].IsEmpty(), error = OT_ERROR_INVALID_ARGS);
	hostName = otSrpClientBuffersGetHostNameString(GetInstancePtr(), &size);
	len = aArgs[1].GetLength();
	VerifyOrExit(len + 1 <= size, error = OT_ERROR_INVALID_ARGS);
	// We first make sure we can set the name, and if so
	// we copy it to the persisted string buffer and set
	// the host name again now with the persisted buffer.
	// This ensures that we do not overwrite a previous
	// buffer with a host name that cannot be set.
	SuccessOrExit(error = otSrpClientSetHostName(GetInstancePtr(), aArgs[1].GetCString()));
	memcpy(hostName, aArgs[1].GetCString(), len + 1);
	IgnoreError(otSrpClientSetHostName(GetInstancePtr(), hostName));

In the second part of this code, why do we have to retrieve a pointer to the persisted butter, memcpy the data to it and then call otSrpClientSetHostName() ?
This is strange to me because it is like if the update of the host name was done by the memcpy, that means outside otSrpClientSetHostName().

Thanks for your information

[jwhui]

The SRP Client only maintains a pointer to the host name provided by the caller. As a result, the caller must maintain the buffer while the host name is in use. As the comment mentions, the first call to otSrpClientSetHostName() simply checks whether we can set the host name successfully.

openthread/src/cli/cli_srp_client.cpp

Lines 140 to 144 in 0756d1e

	// We first make sure we can set the name, and if so
	// we copy it to the persisted string buffer and set
	// the host name again now with the persisted buffer.
	// This ensures that we do not overwrite a previous
	// buffer with a host name that cannot be set.

However, the first call will set the pointer to a buffer that the client cannot maintain (i.e. aArgs[1].GetCString()).

openthread/src/cli/cli_srp_client.cpp

Line 146 in 0756d1e

SuccessOrExit(error = otSrpClientSetHostName(GetInstancePtr(), aArgs[1].GetCString()));

The memcpy() copies that data into a buffer that the client can maintain and the second call to otSrpClientSetHostName() updates the SRP Client with that new buffer (i.e. hostName).

openthread/src/cli/cli_srp_client.cpp

Line 149 in 0756d1e

IgnoreError(otSrpClientSetHostName(GetInstancePtr(), hostName));

[OlivierGre]

Ok thank you Jonathan