REST API design for data synchronization service - rest

Question

What is best practice for data synchronization operation between client and server?
We have 2 (or more) resources:
cars -> year, model, engine
toys -> color, brand, weight
And we need to get updated resources from server in case of any updates on them. For example: someone made changes from another client on the same data and we need to transfer those updates to our client application.
Request:
http://api.example.com/sync?data=cars,toys (verb?)
http://api.example.com/synchronizations?data=cars,toys (virtual resource "synchronizations")
Response with mixed data:
status code: 200
{
message: "ok",
data: {
cars: [
{
year: 2015,
model: "Fiat 500"
engine: 0.9
},
{
year: 2004,
model: "Nissan Sunny"
engine: 1.3
}
],
toys: [
{
color: "yellow",
brand: "Bruder"
weight: 2
}
],
}
}
or response with status code 204 if no updates available. In my opinion making separated http calls in not a good solution. What if we have 100 resources (=100 http calls)?

Answer 1

I am not an expert, but one method I have used in the past is to ask for a "signature" of the data, as opposed to always going and getting the data. The signature can be a hash of the data you are looking for. So, flow would be something like:
Get signature hash of the data
http://api.example.com/sync/signature/cars
Which returns the signature hash
Check if the signature is different from the last time you retrieved the data
If the signature is different, go and get the data
http://api.example.com/sync/cars
Have the REST also add the new signature to the data
{
message: "ok",
data: {
cars: [
{
year: 2015,
model: "Fiat 500"
engine: 0.9
},
{
year: 2004,
model: "Nissan Sunny"
engine: 1.3
},
],
signature: "570a90bfbf8c7eab5dc5d4e26832d5b1"
}
}