JSON Number(double) Insufficient for Long NodeID

[wangyoucao577]

We use annotations=true to output nodes in route response, then we found the output nodes may invalid sometimes.
After investigate, it's caused by the JSON util only has one number type Number, which defined as double:

osrm-backend/include/util/json_container.hpp

Lines 89 to 94 in 15f0ca8

	struct Number
	{
	Number() = default;
	Number(double value_) : value{value_} {}
	double value;
	};

It means whatever the internal number type is, it will be converted to double before output. For some long std::uint64_t, the value will be cut in this conversion.

In our test, the nodeID 9280805980001101 will be cut to 9280805980001100, which results invalid nodeID.
Here's some test code:

// Example program
#include <iostream>
#include <string>
#include <cstdint>
#include <iomanip>

int main()
{
  std::uint64_t id = 9280805980001101;
  double d_id = static_cast<double>(id);
  std::uint64_t convert_back_id = static_cast<std::uint64_t>(d_id);
  
  std::cout << id << std::endl;
  std::cout << std::fixed << std::setprecision(6) << d_id << std::endl;
  std::cout << convert_back_id << std::endl;
}

// output: 
9280805980001101
9280805980001100.000000
9280805980001100

Full story please refer to Telenav#276

Any suggestion? Is it possible to have more Number types in the JSON util?
Many thanks in advance!

[awgrover]

The JSON spec does not appear to limit the range of a number at all(!) https://www.json.org/json-en.html. JSON Schema seems to, I think, as 32 bit signed: -2,147,483,648 ... 2,147,483,647 . Google notes a work around of

a 64-bit integer must be represented as a string in JSON requests/responses. The type property will be set to "string", but the format property will be set to "int64" to indicate that it is a 64-bit integer

As a workaround in this case, is it possible for you to use a string-id instead (i.e. trivially convert to-string for osrm, then convert to-int on return)?

[wangyoucao577]

@awgrover Actually I already returned string id as a workaround(see Telenav#276 (comment) and Telenav#285).
However, refer to https://stackoverflow.com/questions/13502398/json-integers-limit-on-size, the number seems unlimited by JSON spec. I think return correctly uint64 still will be better.

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