Refactoring of the repo module

Refactor out several smaller single-responsibility methods from the
current `handle_list` method, including: `fetch_all` and `parse_rfc5988`.
Also provide some better documentation around that module.

src/commands/repo.rs

@@ -1,10 +1,19 @@
+//! Command module responsible for handling the "repo" command.
+//!
+//! The "repo" command works with the Docker Registry API's "repository"
+//! entitity available at /v2/_catalog.
+//!
 use crate::cli::{RepoArgs, RepoCommands};
 use crate::config::Config;
 use crate::error::ApiError;
 use serde::Deserialize;
 
-const BASE_CATALOG_URI: &str = "/v2/_catalog";
+/// Path to the Docker Registry API's "repository" entity.
+const BASE_CATALOG_URI: &str = "/v2/_catalog?n=1000";
 
+/// Main handler function for the "repo" command.
+///
+/// Responsible for dispatching the various subcommands.
 pub async fn handler(config: &Config, args: &RepoArgs) -> Result<(), ApiError> {
     log::trace!("handler()");
 
@@ -15,42 +24,19 @@ pub async fn handler(config: &Config, args: &RepoArgs) -> Result<(), ApiError> {
     Ok(())
 }
 
+/// Handle the repository list command.
+///
+/// Fetch the list of repository names from the Docker Registry API, and
+/// simply print the resulting names to stdout.
+async fn handle_list(config: &Config, _args: &RepoArgs) -> Result<(), ApiError> {
     #[derive(Deserialize)]
-struct CatalogResponse {
+    struct Response {
         repositories: Vec<String>,
     }
 
-async fn handle_list(config: &Config, _args: &RepoArgs) -> Result<(), ApiError> {
     log::trace!("handle_list()");
 
-    let mut url = config.registry_url.join(BASE_CATALOG_URI)?;
-    let mut responses = Vec::new();
-
-    loop {
-        log::debug!("Using url {url}");
-        let response = reqwest::get(url.clone()).await?;
-        let headers = response.headers().to_owned();
-        let body: CatalogResponse = response.json().await?;
-
-        responses.push(body);
-
-        if let Some(link_value) = headers.get(http::header::LINK) {
-            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(uri) = url_part
-                    .trim()
-                    .strip_prefix('<')
-                    .and_then(|s| s.strip_suffix('>'))
-                {
-                    url = config.registry_url.join(uri)?;
-                }
-            }
-        } else {
-            break;
-        }
-    }
-
+    let responses: Vec<Response> = fetch_all(config, BASE_CATALOG_URI).await?;
     let repo_list: Vec<&str> = responses
         .iter()
         .flat_map(|r| r.repositories.iter().map(String::as_str))
@@ -62,3 +48,70 @@ async fn handle_list(config: &Config, _args: &RepoArgs) -> Result<(), ApiError>
 
     Ok(())
 }
+
+/// 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>.
+async fn fetch_all<T: for<'de> serde::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)
+}