Add support for listing image tags

src/api.rs

@@ -0,0 +1,78 @@
+use serde::Deserialize;
+
+use crate::config::Config;
+use crate::error::ApiError;
+
+/// Iterate over a paginated result set, collecting and returning the response
+/// set.
+///
+/// The Docker Registry API specifies that when making a GET request, the
+/// response will be paginated using a Link response header for the Next URI.
+/// The URL will be encoded using RFC5988. [https://tools.ietf.org/html/rfc5988]
+///
+/// This function will continuously request the "Next" link as long as it is
+/// returned, collecting and returning the deserialized response bodies as a
+/// Vec<T>.
+///
+/// # Errors:
+///
+/// Returns an `ApiError` if there is a problem constructing the URL from the
+/// configured `registry_url` base and the given `path`, or if there is an
+/// error deserializing the HTTP response body as JSON, or if there is an
+/// error parsing the `Link` header value as an RFC5988 URL.
+pub async fn fetch_all<T: for<'de> Deserialize<'de>>(
+    config: &Config,
+    path: &str,
+) -> Result<Vec<T>, ApiError> {
+    log::trace!("fetch_all({path:?})");
+
+    let mut responses: Vec<T> = Vec::default();
+    let mut uri = String::from(path);
+    loop {
+        log::debug!("GET {uri:?}");
+        let url = config.registry_url.join(&uri)?;
+
+        let resp = reqwest::get(url).await?;
+        let headers = resp.headers().to_owned();
+        responses.push(resp.json().await?);
+
+        if let Some(path) = parse_rfc5988(headers.get(http::header::LINK))? {
+            uri = path;
+        } else {
+            break;
+        }
+    }
+    Ok(responses)
+}
+
+/// Given an optional header value possibly containing an RFC5988 formatted
+/// URL, parse said URL into a `String`.
+///
+/// If the header_value does not contain a correctly formatted RFC5988 URL,
+/// or if the header_value is not properly formatted containing a URL
+/// surrounded by angle brackets, separated from the link relation by a ';'
+/// character, the `None` variant will be returned.
+///
+/// # Errors:
+///
+/// Returns and `ApiError` if there is a problem parsing contents of the
+/// supplied header value.
+fn parse_rfc5988(header_value: Option<&http::HeaderValue>) -> Result<Option<String>, ApiError> {
+    log::trace!("parse_rfc5988({header_value:?})");
+
+    if let Some(link_value) = header_value {
+        let link_str = link_value.to_str()?;
+        let parts: Vec<&str> = link_str.split(';').collect();
+        if let Some(url_part) = parts.first() {
+            if let Some(path) = url_part
+                .trim()
+                .strip_prefix('<')
+                .and_then(|s| s.strip_suffix('>'))
+            {
+                return Ok(Some(String::from(path)));
+            }
+        }
+    }
+
+    Ok(None)
+}