Our team is working on a memory-constrained device which is connected to the internet. Being able to reduce MBEDTLS_SSL_MAX_CONTENT_LEN to 4096 would tremendously help us fitting everything we want on the chip. We know up front to which servers our device opens a connection, and which clients open a connection towards our device, so we will ensure that they will be able to deal with the smaller buffer sizes. The servers with which our device connects support the RFC 6066 max fragment length extension.
However, mbedTLS is not able to cope with fragmented handshake messages, which is a problem for us, since the certificates presented by the server are too large to be handled within frames of 4096 bytes.
I am aware that there is an MPS branch in the mbedTLS repository, and if I correctly understood, the code in this branch would support fragmented handshakes. Is there something you can say about the MPS branch? e.g. what is its status, will it indeed solve the fragmented handshake problems, what is needed before it is released? Is there something that our team can contribute to that branch, how much work would be needed to get it into a releasable status?