Handle HTTP errors when fetching a nonce

The nonce is fetched via HEAD request. Before this fix, if there was a
HTTP error, acme4j expected a Problem JSON body, which was not send
because of the HEAD request, and lead to an AcmeProtocolException.

Now either an AcmeException or AcmeRetryAfterException is thrown.

acme4j-client/src/main/java/org/shredzone/acme4j/AcmeJsonResource.java

@@ -152,6 +152,10 @@ public abstract class AcmeJsonResource extends AcmeResource {
             retryAfterOpt.ifPresent(instant -> LOG.debug("Retry-After: {}", instant));
             setRetryAfter(retryAfterOpt.orElse(null));
             return retryAfterOpt;
+        } catch (AcmeRetryAfterException ex) {
+            LOG.debug("Retry-After while attempting to read the resource", ex);
+            setRetryAfter(ex.getRetryAfter());
+            return Optional.of(ex.getRetryAfter());
         }
     }
 

acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java

@@ -51,6 +51,7 @@ import org.shredzone.acme4j.exception.AcmeException;
 import org.shredzone.acme4j.exception.AcmeNetworkException;
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.exception.AcmeRateLimitedException;
+import org.shredzone.acme4j.exception.AcmeRetryAfterException;
 import org.shredzone.acme4j.exception.AcmeServerException;
 import org.shredzone.acme4j.exception.AcmeUnauthorizedException;
 import org.shredzone.acme4j.exception.AcmeUserActionRequiredException;
@@ -132,7 +133,12 @@ public class DefaultConnection implements Connection {
 
             var rc = getResponse().statusCode();
             if (rc != HTTP_OK && rc != HTTP_NO_CONTENT) {
-                throwAcmeException();
+                var message = "Server responded with HTTP " + rc + " while trying to retrieve a nonce";
+                var retryAfterInstant = getRetryAfter();
+                if (retryAfterInstant.isPresent()) {
+                    throw new AcmeRetryAfterException(message, retryAfterInstant.get());
+                };
+                throw new AcmeException(message);
             }
 
             session.setNonce(getNonce()

acme4j-client/src/test/java/org/shredzone/acme4j/connector/DefaultConnectionTest.java

@@ -52,6 +52,7 @@ import org.shredzone.acme4j.Session;
 import org.shredzone.acme4j.exception.AcmeException;
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.exception.AcmeRateLimitedException;
+import org.shredzone.acme4j.exception.AcmeRetryAfterException;
 import org.shredzone.acme4j.exception.AcmeServerException;
 import org.shredzone.acme4j.exception.AcmeUnauthorizedException;
 import org.shredzone.acme4j.exception.AcmeUserActionRequiredException;
@@ -142,6 +143,57 @@ public class DefaultConnectionTest {
         verify(getRequestedFor(urlEqualTo(REQUEST_PATH)));
     }
 
+    /**
+     * Test that {@link DefaultConnection#getNonce()} handles a retry-after header
+     * correctly.
+     */
+    @Test
+    public void testGetNonceFromHeaderRetryAfter() {
+        var retryAfter = Instant.now().plusSeconds(30L).truncatedTo(SECONDS);
+
+        stubFor(head(urlEqualTo(NEW_NONCE_PATH)).willReturn(aResponse()
+                .withStatus(HttpURLConnection.HTTP_UNAVAILABLE)
+                .withHeader("Content-Type", "application/problem+json")
+                .withHeader("Retry-After", DATE_FORMATTER.format(retryAfter))
+                // do not send a body here because it is a HEAD request!
+        ));
+
+        assertThat(session.getNonce()).isNull();
+
+        var ex = assertThrows(AcmeRetryAfterException.class, () -> {
+            try (var conn = session.connect()) {
+                conn.resetNonce(session);
+            }
+        });
+        assertThat(ex.getMessage()).isEqualTo("Server responded with HTTP 503 while trying to retrieve a nonce");
+        assertThat(ex.getRetryAfter()).isEqualTo(retryAfter);
+
+        verify(headRequestedFor(urlEqualTo(NEW_NONCE_PATH)));
+    }
+
+    /**
+     * Test that {@link DefaultConnection#getNonce()} handles a general HTTP error
+     * correctly.
+     */
+    @Test
+    public void testGetNonceFromHeaderHttpError() {
+        stubFor(head(urlEqualTo(NEW_NONCE_PATH)).willReturn(aResponse()
+                .withStatus(HttpURLConnection.HTTP_INTERNAL_ERROR)
+                // do not send a body here because it is a HEAD request!
+        ));
+
+        assertThat(session.getNonce()).isNull();
+
+        var ex = assertThrows(AcmeException.class, () -> {
+            try (var conn = session.connect()) {
+                conn.resetNonce(session);
+            }
+        });
+        assertThat(ex.getMessage()).isEqualTo("Server responded with HTTP 500 while trying to retrieve a nonce");
+
+        verify(headRequestedFor(urlEqualTo(NEW_NONCE_PATH)));
+    }
+
     /**
      * Test that {@link DefaultConnection#getNonce()} fails on an invalid
      * {@code Replay-Nonce} header.