Struct Json 

pub struct Json {
    buf: String,
    comma: bool,
}

Incrementally built JSON. key before a value inside obj, bare values inside arr.

Fields

buf: String

comma: bool

Whether the next value needs a , in front of it. Reset on entering a container, set after every value.

Implementations

impl Json

pub fn new() -> Self

pub fn into_string(self) -> String

fn sep(&mut self)

pub fn obj(&mut self, f: impl FnOnce(&mut Self))

Write a {...}. Inside f, call key then a value.

pub fn arr(&mut self, f: impl FnOnce(&mut Self))

Write a [...].

pub fn key(&mut self, k: &str)

A member name. The value that follows attaches to it, so comma stays as it was rather than being armed here.

pub fn str(&mut self, s: &str)

pub fn i64(&mut self, v: i64)

pub fn u64(&mut self, v: u64)

pub fn i64_str(&mut self, v: i64)

A 64-bit integer as a JSON string, which is what OTLP/JSON says a 64-bit integer is.

Principle 3 decides this: where OTLP specifies an encoding, OTLP wins. The spec makes int64, sfixed64 and uint64 strings on the wire, the ingest decoder already reads them that way (section 0), and a response Mira cannot feed back to itself as a request body is not a round trip. The mechanical reason is the same in both directions: a JSON number is an IEEE754 double to a browser and to most parsers, time_unix_nano is ~1.7e18, and 2^53 is where a double stops counting. Bare-number output does not fail there, it silently rounds.

Only the 64-bit columns go through this. A severity_number, a status_code or a dropped_* is 32 bits or smaller, arithmetic on it is what a reader wants, and no double loses it.

pub fn u64_str(&mut self, v: u64)

fn quoted_digits(&mut self, digits: &str)

Quote without escaping: the input is to_string of an integer, so it is ASCII digits and at most a leading -.

pub fn f64(&mut self, v: f64)

Non-finite becomes null. JSON has no NaN or Infinity, and both turn up in real metrics — a histogram sum over no observations, a gauge from a division by zero. Emitting the bare token would produce a document that every strict parser, including the browser’s, rejects outright, taking the whole response down with it rather than the one field.

pub fn bool(&mut self, v: bool)

pub fn null(&mut self)

pub fn raw(&mut self, fragment: &str)

Splice in a fragment this writer produced earlier — a rendered value, or a run of "k":v,"k":v members inside an object.

The escape hatch for the one thing the closure API cannot express: caching. A metric’s descriptor and its resource attributes are identical across every point of a series, and re-rendering them per point is the difference between a chart query that costs one pass and one that costs two. Empty is a no-op so a cached fragment that turned out to be empty cannot emit a stray comma.

pub fn hex(&mut self, bytes: &[u8])

Lowercase hex of bytes, as one string. Trace and span ids are FixedSizeBinary on disk and hex everywhere a human or a W3C header sees them.

Trait Implementations

impl Default for Json

fn default() -> Self

Returns the “default value” for a type.