Characteristic read response is limited to 19 bytes when reading by UUID

[exocron]

When reading a characteristic by type/UUID, if the length of the response is greater than 19 bytes, the server will respond with Unlikely Error. This limitation does not exist when reading by handle. According to the Core Specification, the maximum length for a single attribute response when reading by type can be up to 253 bytes, provided that the MTU is large enough to handle it.

This line calls ble_att_svr_read_flat with a fixed size buffer, and is likely the culprit:

mynewt-nimble/nimble/host/src/ble_att_svr.c

Line 1318 in 5baa3f4

rc = ble_att_svr_read_flat(conn_handle, entry, 0, sizeof buf, buf,

To the access_cb function, reading a characteristic this way appears to be successful. There's no obvious indication that it will actually return an error to the client.