if values.is_empty() {
      fields.remove(field);
    }

    Some(value)
  }
}

fn remove_and_concatenate_field(
  fields: &mut BTreeMap<&[u8], Vec<&[u8]>>,
  field: &[u8],
) -> Option<Vec<u8>> {
  let value = fields.remove(field)?;

  if value.is_empty() {
    None
  } else {
    Some(value.into_iter().flatten().cloned().collect())
  }
}

impl From<RawEnvelope> for ParsedEnvelope {
  fn from(envelope: RawEnvelope) -> Self {
    let body = envelope
      .payload
      .iter()
      .enumerate()
      .position(|(i, push)| i % 2 == 0 && push.is_empty());

    let mut fields: BTreeMap<&[u8], Vec<&[u8]>> = BTreeMap::new();

    let mut incomplete_field = false;

    for item in envelope.payload[..body.unwrap_or(envelope.payload.len())].chunks(2) {
      match item {
        [key, value] => fields.entry(key).or_default().push(value),
        _ => incomplete_field = true,
      }
    }

    let duplicate_field = fields.iter().any(|(_key, values)| values.len() > 1);

    let content_encoding = remove_field(&mut fields, &CONTENT_ENCODING_TAG);