add: cache downloading

src/lib.rs

@@ -168,4 +168,83 @@ impl Client {
 
         Ok(())
     }
+
+    pub fn load_cache(&self, key: &CacheKey) -> Result<Option<Box<[u8]>>> {
+        let Some(cache_location) = self.get_cache_entry(key).context("getting cache entry")? else {
+            // cache miss
+            return Ok(None);
+        };
+
+        let cache = self
+            .download_cache(cache_location)
+            .context("downloading the cache")?;
+
+        Ok(Some(cache))
+    }
+
+    fn get_cache_entry(&self, key: &CacheKey) -> Result<Option<String>> {
+        let uri = format!("{}_apis/artifactcache/cache/{}", self.base_url, key.0);
+        let request = Request::builder()
+            .uri(uri)
+            .method(Method::GET)
+            .body(())
+            .context("building the request")?;
+        let mut response = self
+            .http_client
+            .send(request)
+            .context("sending the request")?;
+        let status = response.status();
+        if status == StatusCode::NO_CONTENT {
+            // cache miss
+            return Ok(None);
+        }
+        let mut body = Vec::with_capacity(100);
+        response
+            .body_mut()
+            .read_to_end(&mut body)
+            .context("reading response body")?;
+        if status != StatusCode::OK {
+            bail!(
+                "Failed reading a cache entry (status {status}): {:?}",
+                str::from_utf8(&body)
+            );
+        }
+
+        let body_val =
+            serde_json::from_slice::<serde_json::Value>(&body).context("parsing response body")?;
+
+        let location = body_val
+            .get("archiveLocation")
+            .context("not cache location field")?
+            .as_str()
+            .context("archiveLocation is not a string")?;
+
+        Ok(Some(location.to_string()))
+    }
+
+    fn download_cache(&self, location: String) -> Result<Box<[u8]>> {
+        let request = Request::builder()
+            .uri(location)
+            .method(Method::GET)
+            .body(())
+            .context("building the request")?;
+        let mut response = self
+            .http_client
+            .send(request)
+            .context("sending the request")?;
+        let status = response.status();
+        let mut body = Vec::with_capacity(100);
+        response
+            .body_mut()
+            .read_to_end(&mut body)
+            .context("reading response body")?;
+        if status == StatusCode::OK {
+            bail!(
+                "Failed downloading the cache (status {status}): {:?}",
+                str::from_utf8(&body)
+            );
+        }
+
+        Ok(body.into_boxed_slice())
+    }
 }