internal: don't cancel http contexts until the body has been read

Contexts for HTTP requests should not be cancelled until after the HTTP
body has been successfully read, or errors can be encountered.

internal/resource/http.go

@@ -194,13 +194,14 @@ func (f *Fetcher) newHttpClient() {
 	}
 }
 
-// getReaderWithHeader performs an HTTP GET on the provided URL with the provided request header
-// and returns the response body Reader, HTTP status code, and error (if any). By
+// getReaderWithHeader performs an HTTP GET on the provided URL with the
+// provided request header and returns the response body Reader, HTTP status
+// code, a cancel function for the result's context, and error (if any). By
 // default, User-Agent is added to the header but this can be overridden.
-func (c HttpClient) getReaderWithHeader(ctx context.Context, url string, header http.Header) (io.ReadCloser, int, error) {
+func (c HttpClient) getReaderWithHeader(url string, header http.Header) (io.ReadCloser, int, context.CancelFunc, error) {
 	req, err := http.NewRequest("GET", url, nil)
 	if err != nil {
-		return nil, 0, err
+		return nil, 0, nil, err
 	}
 
 	req.Header.Set("User-Agent", "Ignition/"+version.Raw)
@@ -212,10 +213,10 @@ func (c HttpClient) getReaderWithHeader(ctx context.Context, url string, header
 		}
 	}
 
+	ctx, cancelFn := context.WithCancel(context.Background())
 	if c.timeout != 0 {
-		ctxTo, cancel := context.WithTimeout(ctx, c.timeout)
-		ctx = ctxTo
-		defer cancel()
+		cancelFn()
+		ctx, cancelFn = context.WithTimeout(context.Background(), c.timeout)
 	}
 
 	duration := initialBackoff
@@ -226,7 +227,7 @@ func (c HttpClient) getReaderWithHeader(ctx context.Context, url string, header
 		if err == nil {
 			c.logger.Info("GET result: %s", http.StatusText(resp.StatusCode))
 			if resp.StatusCode < 500 {
-				return resp.Body, resp.StatusCode, nil
+				return resp.Body, resp.StatusCode, cancelFn, nil
 			}
 			resp.Body.Close()
 		} else {
@@ -242,7 +243,7 @@ func (c HttpClient) getReaderWithHeader(ctx context.Context, url string, header
 		select {
 		case <-time.After(duration):
 		case <-ctx.Done():
-			return nil, 0, ErrTimeout
+			return nil, 0, cancelFn, ErrTimeout
 		}
 	}
 }

internal/resource/url.go

@@ -218,11 +218,15 @@ func (f *Fetcher) FetchFromTFTP(u url.URL, dest *os.File, opts FetchOptions) err
 // FetchFromHTTP fetches a resource from u via HTTP(S) into dest, returning an
 // error if one is encountered.
 func (f *Fetcher) FetchFromHTTP(u url.URL, dest *os.File, opts FetchOptions) error {
-	ctx := context.Background()
 	if f.client == nil {
 		f.newHttpClient()
 	}
-	dataReader, status, err := f.client.getReaderWithHeader(ctx, u.String(), opts.Headers)
+	dataReader, status, ctxCancel, err := f.client.getReaderWithHeader(u.String(), opts.Headers)
+	if ctxCancel != nil {
+		// whatever context getReaderWithHeader created for the request should
+		// be cancelled once we're done reading the response
+		defer ctxCancel()
+	}
 	if err != nil {
 		return err
 	}