Problem
Manually implementing EncodeLabelSet for a struct currently involves a lot of boilerplate:
pub struct MyLabels {
pub method: &'static str, // or String, Cow<'static, str>, etc.
pub status: u16
// many other fields
}
impl EncodeLabelSet for MyLabels {
fn encode(&self, encoder: &mut LabelSetEncoder) -> Result<(), fmt::Error> {
// label: method = self.method
{
let mut label = encoder.encode_label();
let mut key = label.encode_label_key()?;
// field name -> key string (handle raw-idents manually if you used them)
EncodeLabelKey::encode("method", &mut key)?;
let mut value = key.encode_label_value()?;
EncodeLabelValue::encode(&self.method, &mut value)?;
value.finish()?;
}
// label: status = self.status
{
let mut label = encoder.encode_label();
let mut key = label.encode_label_key()?;
EncodeLabelKey::encode("status", &mut key)?;
let mut value = key.encode_label_value()?;
EncodeLabelValue::encode(&self.status, &mut value)?;
value.finish()?;
}
// repeated for all other fields
Ok(())
}
}This can become a chore if you have to implement it manually (e.g. because you want conditional encoding).
Solution
A new LabelSetWriter struct that allows you to easily specify (key, value) pairs to encode.
Usage
pub struct MyLabels {
pub status: u16,
pub method: &'static str,
pub optional: Option<&'static str>,
// suppose we want to flatten these (like `#[prometheus(flatten)]`)
pub common: CommonLabels
}
impl EncodeLabelSet for MyLabels {
fn encode(&self, enc: &mut LabelSetEncoder) -> Result<(), fmt::Error> {
let mut writer = LabelSetWriter::new(enc);
.kv("status", &self.status)?
.kv("method", &self.method)?;
// allows for conditional encoding
if let Some(optional) = &self.optional {
writer.kv("optional", optional)?;
}
// allows flattening
writer.flatten(&self.common)?;
Ok(())
}
}Discussion
I've written the code for LabelSetWriter and it's helpful for me in reducing boilerplate.
Would anyone else find this useful? I'm open to making a PR if so.
Problem
Manually implementing
EncodeLabelSetfor a struct currently involves a lot of boilerplate:This can become a chore if you have to implement it manually (e.g. because you want conditional encoding).
Solution
A new
LabelSetWriterstruct that allows you to easily specify (key, value) pairs to encode.Usage
Discussion
I've written the code for
LabelSetWriterand it's helpful for me in reducing boilerplate.Would anyone else find this useful? I'm open to making a PR if so.