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use crate::{Key, Value};
use std::fmt::{self, Write};
use std::sync::atomic::{AtomicUsize, Ordering};
static ENCODER_ID_COUNTER: AtomicUsize = AtomicUsize::new(0);
/// Encoder is a mechanism for serializing an attribute set into a specific string
/// representation that supports caching, to avoid repeated serialization. An
/// example could be an exporter encoding the attribute set into a wire
/// representation.
pub trait Encoder: fmt::Debug {
/// Encode returns the serialized encoding of the attribute
/// set using its Iterator. This result may be cached.
fn encode(&self, attributes: &mut dyn Iterator<Item = (&Key, &Value)>) -> String;
/// A value that is unique for each class of attribute encoder. Attribute encoders
/// allocate these using `new_encoder_id`.
fn id(&self) -> EncoderId;
}
/// EncoderID is used to identify distinct Encoder
/// implementations, for caching encoded results.
#[derive(Debug)]
pub struct EncoderId(usize);
impl EncoderId {
/// Check if the id is valid
pub fn is_valid(&self) -> bool {
self.0 != 0
}
}
/// Default attribute encoding strategy
#[derive(Debug)]
pub struct DefaultAttributeEncoder;
impl Encoder for DefaultAttributeEncoder {
fn encode(&self, attributes: &mut dyn Iterator<Item = (&Key, &Value)>) -> String {
attributes
.enumerate()
.fold(String::new(), |mut acc, (idx, (key, value))| {
let offset = acc.len();
if idx > 0 {
acc.push(',')
}
if write!(acc, "{}", key).is_err() {
acc.truncate(offset);
return acc;
}
acc.push('=');
if write!(acc, "{}", value).is_err() {
acc.truncate(offset);
return acc;
}
acc
})
}
fn id(&self) -> EncoderId {
new_encoder_id()
}
}
/// Build a new default encoder
pub fn default_encoder() -> Box<dyn Encoder + Send + Sync> {
Box::new(DefaultAttributeEncoder)
}
/// Build a new encoder id
pub fn new_encoder_id() -> EncoderId {
let old_encoder_id = ENCODER_ID_COUNTER.fetch_add(1, Ordering::AcqRel);
EncoderId(old_encoder_id + 1)
}