Raise an exception when the specified cipher suite is not available

Motivation:

SSL_set_cipher_list() in OpenSSL does not fail as long as at least one
cipher suite is available.  It is different from the semantics of
SSLEngine.setEnabledCipherSuites(), which raises an exception when the
list contains an unavailable cipher suite.

Modifications:

- Add OpenSsl.isCipherSuiteAvailable(String) which checks the
  availability of a cipher suite
- Raise an IllegalArgumentException when the specified cipher suite is
  not available

Result:

Fixed compatibility

handler/src/main/java/io/netty/handler/ssl/OpenSsl.java

@@ -24,9 +24,9 @@ import org.apache.tomcat.jni.Pool;
 import org.apache.tomcat.jni.SSL;
 import org.apache.tomcat.jni.SSLContext;
 
-import java.util.ArrayList;
 import java.util.Collections;
-import java.util.List;
+import java.util.LinkedHashSet;
+import java.util.Set;
 
 /**
  * Tells if <a href="http://netty.io/wiki/forked-tomcat-native.html">{@code netty-tcnative}</a> and its OpenSSL support
@@ -37,7 +37,7 @@ public final class OpenSsl {
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(OpenSsl.class);
     private static final Throwable UNAVAILABILITY_CAUSE;
 
-    private static final List<String> AVAILABLE_CIPHER_SUITES;
+    private static final Set<String> AVAILABLE_CIPHER_SUITES;
 
     static {
         Throwable cause = null;
@@ -54,7 +54,7 @@ public final class OpenSsl {
         UNAVAILABILITY_CAUSE = cause;
 
         if (cause == null) {
-            final List<String> availableCipherSuites = new ArrayList<String>(128);
+            final Set<String> availableCipherSuites = new LinkedHashSet<String>(128);
             final long aprPool = Pool.create(0);
             try {
                 final long sslCtx = SSLContext.make(aprPool, SSL.SSL_PROTOCOL_ALL, SSL.SSL_MODE_SERVER);
@@ -82,9 +82,9 @@ public final class OpenSsl {
                 Pool.destroy(aprPool);
             }
 
-            AVAILABLE_CIPHER_SUITES = Collections.unmodifiableList(availableCipherSuites);
+            AVAILABLE_CIPHER_SUITES = Collections.unmodifiableSet(availableCipherSuites);
         } else {
-            AVAILABLE_CIPHER_SUITES = Collections.emptyList();
+            AVAILABLE_CIPHER_SUITES = Collections.emptySet();
         }
     }
 
@@ -124,8 +124,20 @@ public final class OpenSsl {
      * Returns all the available OpenSSL cipher suites.
      * Please note that the returned array may include the cipher suites that are insecure or non-functional.
      */
-    public static String[] availableCipherSuites() {
-        return AVAILABLE_CIPHER_SUITES.toArray(new String[AVAILABLE_CIPHER_SUITES.size()]);
+    public static Set<String> availableCipherSuites() {
+        return AVAILABLE_CIPHER_SUITES;
+    }
+
+    /**
+     * Returns {@code true} if and only if the specified cipher suite is available in OpenSSL.
+     * Both Java-style cipher suite and OpenSSL-style cipher suite are accepted.
+     */
+    public static boolean isCipherSuiteAvailable(String cipherSuite) {
+        String converted = CipherSuiteConverter.toOpenSsl(cipherSuite);
+        if (converted != null) {
+            cipherSuite = converted;
+        }
+        return AVAILABLE_CIPHER_SUITES.contains(cipherSuite);
     }
 
     static boolean isError(long errorCode) {

handler/src/main/java/io/netty/handler/ssl/OpenSslEngine.java

@@ -650,7 +650,8 @@ public final class OpenSslEngine extends SSLEngine {
 
     @Override
     public String[] getSupportedCipherSuites() {
-        return OpenSsl.availableCipherSuites();
+        Set<String> availableCipherSuites = OpenSsl.availableCipherSuites();
+        return availableCipherSuites.toArray(new String[availableCipherSuites.size()]);
     }
 
     @Override
@@ -677,11 +678,35 @@ public final class OpenSslEngine extends SSLEngine {
             throw new NullPointerException("cipherSuites");
         }
 
-        final String converted = CipherSuiteConverter.toOpenSsl(Arrays.asList(cipherSuites));
+        final StringBuilder buf = new StringBuilder();
+        for (String c: cipherSuites) {
+            if (c == null) {
+                break;
+            }
+
+            String converted = CipherSuiteConverter.toOpenSsl(c);
+            if (converted == null) {
+                converted = c;
+            }
+
+            if (!OpenSsl.isCipherSuiteAvailable(converted)) {
+                throw new IllegalArgumentException("unsupported cipher suite: " + c + '(' + converted + ')');
+            }
+
+            buf.append(converted);
+            buf.append(':');
+        }
+
+        if (buf.length() == 0) {
+            throw new IllegalArgumentException("empty cipher suites");
+        }
+        buf.setLength(buf.length() - 1);
+
+        final String cipherSuiteSpec = buf.toString();
         try {
-            SSL.setCipherSuites(ssl, converted);
+            SSL.setCipherSuites(ssl, cipherSuiteSpec);
         } catch (Exception e) {
-            throw new IllegalStateException("failed to enable cipher suites: " + converted, e);
+            throw new IllegalStateException("failed to enable cipher suites: " + cipherSuiteSpec, e);
         }
     }