Support problem title. Enhance returned problem message.

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

@@ -62,7 +62,20 @@ public class Problem implements Serializable {
     }
 
     /**
-     * Returns a human-readable description of the problem.
+     * Returns a short, human-readable summary of the problem. The text may be localized
+     * if supported by the server. {@code null} if the server did not provide a title.
+     *
+     * @see #toString()
+     */
+    public String getTitle() {
+        return problemJson.get("title").asString();
+    }
+
+    /**
+     * Returns a detailed and specific human-readable explanation of the problem. The
+     * text may be localized if supported by the server.
+     *
+     * @see #toString()
      */
     public String getDetail() {
         return problemJson.get("detail").asString();
@@ -120,11 +133,42 @@ public class Problem implements Serializable {
     }
 
     /**
-     * Returns the problem as JSON string.
+     * Returns a human-readable description of the problem, that is as specific as
+     * possible. The description may be localized if supported by the server.
+     * <p>
+     * If {@link #getSubProblems()} exist, they will be appended.
+     * <p>
+     * Technically, it returns {@link #getDetail()}. If not set, {@link #getTitle()} is
+     * returned instead. As a last resort, {@link #getType()} is returned.
      */
     @Override
     public String toString() {
-        return problemJson.toString();
+        StringBuilder sb = new StringBuilder();
+
+        if (getDetail() != null) {
+            sb.append(getDetail());
+        } else if (getTitle() != null) {
+            sb.append(getTitle());
+        } else {
+            sb.append(getType());
+        }
+
+        List<Problem> subproblems = getSubProblems();
+
+        if (!subproblems.isEmpty()) {
+            sb.append(" (");
+            boolean first = true;
+            for (Problem sub : subproblems) {
+                if (!first) {
+                    sb.append(" ‒ ");
+                }
+                sb.append(sub.toString());
+                first = false;
+            }
+            sb.append(')');
+        }
+
+        return sb.toString();
     }
 
 }

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeServerException.java

@@ -34,7 +34,7 @@ public class AcmeServerException extends AcmeException {
      *            {@link Problem} that caused the exception
      */
     public AcmeServerException(Problem problem) {
-        super(Objects.requireNonNull(problem).getDetail());
+        super(Objects.requireNonNull(problem).toString());
         this.problem = problem;
     }
 

acme4j-client/src/test/java/org/shredzone/acme4j/ProblemTest.java

@@ -25,6 +25,7 @@ import java.util.List;
 
 import org.junit.Test;
 import org.shredzone.acme4j.toolbox.JSON;
+import org.shredzone.acme4j.toolbox.JSONBuilder;
 import org.shredzone.acme4j.toolbox.TestUtils;
 
 /**
@@ -40,11 +41,15 @@ public class ProblemTest {
         Problem problem = new Problem(original, baseUrl);
 
         assertThat(problem.getType(), is(URI.create("urn:ietf:params:acme:error:malformed")));
-        assertThat(problem.getDetail(), is("Some of the identifiers requested were rejected"));
+        assertThat(problem.getTitle(), is("Some of the identifiers requested were rejected"));
+        assertThat(problem.getDetail(), is("Identifier \"abc12_\" is malformed"));
         assertThat(problem.getInstance(), is(URI.create("https://example.com/documents/error.html")));
         assertThat(problem.getDomain(), is(nullValue()));
         assertThat(problem.asJSON().toString(), is(sameJSONAs(original.toString())));
-        assertThat(problem.toString(), is(sameJSONAs(original.toString())));
+        assertThat(problem.toString(), is(
+                "Identifier \"abc12_\" is malformed ("
+                + "Invalid underscore in DNS name \"_example.com\" ‒ "
+                + "This CA will not issue for \"example.net\")"));
 
         List<Problem> subs = problem.getSubProblems();
         assertThat(subs, not(nullValue()));
@@ -52,13 +57,40 @@ public class ProblemTest {
 
         Problem p1 = subs.get(0);
         assertThat(p1.getType(), is(URI.create("urn:ietf:params:acme:error:malformed")));
+        assertThat(p1.getTitle(), is(nullValue()));
         assertThat(p1.getDetail(), is("Invalid underscore in DNS name \"_example.com\""));
         assertThat(p1.getDomain(), is("_example.com"));
+        assertThat(p1.toString(), is("Invalid underscore in DNS name \"_example.com\""));
 
         Problem p2 = subs.get(1);
         assertThat(p2.getType(), is(URI.create("urn:ietf:params:acme:error:rejectedIdentifier")));
+        assertThat(p2.getTitle(), is(nullValue()));
         assertThat(p2.getDetail(), is("This CA will not issue for \"example.net\""));
         assertThat(p2.getDomain(), is("example.net"));
+        assertThat(p2.toString(), is("This CA will not issue for \"example.net\""));
+    }
+
+    /**
+     * Test that {@link Problem#toString()} always returns the most specific message.
+     */
+    @Test
+    public void testToString() {
+        URL baseUrl = url("https://example.com/acme/1");
+        URI typeUri = URI.create("urn:ietf:params:acme:error:malformed");
+
+        JSONBuilder jb = new JSONBuilder();
+
+        jb.put("type", typeUri);
+        Problem p1 = new Problem(jb.toJSON(), baseUrl);
+        assertThat(p1.toString(), is(typeUri.toString()));
+
+        jb.put("title", "Some of the identifiers requested were rejected");
+        Problem p2 = new Problem(jb.toJSON(), baseUrl);
+        assertThat(p2.toString(), is("Some of the identifiers requested were rejected"));
+
+        jb.put("detail", "Identifier \"abc12_\" is malformed");
+        Problem p3 = new Problem(jb.toJSON(), baseUrl);
+        assertThat(p3.toString(), is("Identifier \"abc12_\" is malformed"));
     }
 
 }

acme4j-client/src/test/resources/json/problem.json

@@ -1,6 +1,7 @@
 {
   "type": "urn:ietf:params:acme:error:malformed",
-  "detail": "Some of the identifiers requested were rejected",
+  "title": "Some of the identifiers requested were rejected",
+  "detail": "Identifier \"abc12_\" is malformed",
   "instance": "/documents/error.html",
   "subproblems": [
     {