Custom deserialization of JSON w/Serde

foo.rs

fn deserialize_images<'de, D>(de: D) -> Result<Vec<Image>, D::Error>
    where D: serde::Deserializer<'de>
{
    let value: serde_json::Value = serde::Deserialize::deserialize(de)?;
    let object = value
        .as_object()
        .ok_or(serde::de::Error::custom("expected an object of images"))?;
    let images = object
        .iter()
        .flat_map(|(k, v)| match (k.as_ref(), v) {
                      ("original", &serde_json::Value::Object(ref map)) => {
                          map.get("url")
                              .and_then(|v| v.as_str())
                              .and_then(|s| Url::parse(s).ok())
                              .map(|url| Image::Original(url))
                      }
                      ("fixed_width_small_still", &serde_json::Value::Object(ref map)) => {
                          map.get("url")
                              .and_then(|v| v.as_str())
                              .and_then(|s| Url::parse(s).ok())
                              .map(|url| Image::Thumbnail(url))
                      }
                      _ => None,
                  })
        .collect();
    Ok(images)
}