Fix some SonarLint findings

Simple ones:

- Logging statements: use placeholders, not string concatenation
- Abstract classes: use protected, not public, constructors
- Some simplified lambdas
- Some simplified exception catching
- Use StringBuilder instead of StringBuffer
- Use BigInteger.valueOf() instead of new BigInteger()
- Use "byte[] buf" instead of "byte buf[]"

There are still a lot of more findings some of them worrying, such as
throwing exceptions in finally blocks, or catching Error or Throwable
in several places, or others.

sshd-cli/src/main/java/org/apache/sshd/cli/client/SshClientCliSupport.java

@@ -695,10 +695,10 @@ protected synchronized void setOutputStream(OutputStream out) throws SecurityExc
         fh.setLevel(Level.FINEST);
         fh.setFormatter(new Formatter() {
             @Override
-            public String format(LogRecord record) {
-                String message = formatMessage(record);
+            public String format(LogRecord logRecord) {
+                String message = formatMessage(logRecord);
                 String throwable = "";
-                Throwable t = record.getThrown();
+                Throwable t = logRecord.getThrown();
                 if (t != null) {
                     StringWriter sw = new StringWriter();
                     try (PrintWriter pw = new PrintWriter(sw)) {
@@ -708,8 +708,8 @@ public String format(LogRecord record) {
                     throwable = sw.toString();
                 }
                 return String.format("%1$tY-%1$tm-%1$td: %2$-7.7s: %3$-32.32s: %4$s%5$s%n",
-                        new Date(record.getMillis()), record.getLevel().getName(),
-                        record.getLoggerName(), message, throwable);
+                        new Date(logRecord.getMillis()), logRecord.getLevel().getName(),
+                        logRecord.getLoggerName(), message, throwable);
             }
         });
 

sshd-cli/src/main/java/org/apache/sshd/cli/server/SshServerCliSupport.java

@@ -225,8 +225,7 @@ public static List<SubsystemFactory> resolveServerSubsystems(
                 continue;
             }
 
-            factory = registerSubsystemFactoryListeners(
-                    server, level, stdout, stderr, options, factory);
+            registerSubsystemFactoryListeners(server, level, stdout, stderr, options, factory);
             subsystems.add(factory);
         }
 

sshd-cli/src/main/java/org/apache/sshd/cli/server/helper/ServerEventListenerHelper.java

@@ -26,7 +26,7 @@
 public abstract class ServerEventListenerHelper extends AbstractLoggingBean implements NamedResource {
     private final String name;
 
-    public ServerEventListenerHelper(String name, Logger logger) {
+    protected ServerEventListenerHelper(String name, Logger logger) {
         super(logger);
 
         this.name = name;

sshd-cli/src/main/java/org/apache/sshd/cli/server/helper/ServerPortForwardingEventListener.java

@@ -72,10 +72,10 @@ public void establishedDynamicTunnel(
             throws IOException {
         if (reason == null) {
             if (log.isInfoEnabled()) {
-                log.info("Estalibshed dynamic tunnel for session={}: local={},  bound={}", session, local, boundAddress);
+                log.info("Estalibshed dynamic tunnel for session={}: local={} bound={}", session, local, boundAddress);
             }
         } else {
-            log.error("Failed ({}) to establish dynamic tunnel for session={}, bound={}: {}",
+            log.error("Failed ({}) to establish dynamic tunnel for session={}: local={} bound={}: {}",
                     reason.getClass().getSimpleName(), session, local, boundAddress, reason.getMessage());
         }
     }
@@ -86,7 +86,7 @@ public void tornDownDynamicTunnel(
             throws IOException {
         if (reason == null) {
             if (log.isInfoEnabled()) {
-                log.info("Torn down dynamic tunnel for session={}: address={}", session);
+                log.info("Torn down dynamic tunnel for session={}: address={}", session, address);
             }
         } else {
             log.error("Failed ({}) to tear down dynamic tunnel for session={}, address={}: {}",

sshd-common/src/main/java/org/apache/sshd/client/auth/hostbased/HostKeyIdentityProvider.java

@@ -58,7 +58,7 @@ static HostKeyIdentityProvider wrap(KeyPair... pairs) {
         return wrap(GenericUtils.asList(pairs));
     }
 
-    static HostKeyIdentityProvider wrap(Iterable<? extends KeyPair> pairs) {
+    static HostKeyIdentityProvider wrap(Iterable<KeyPair> pairs) {
         return session -> GenericUtils.wrapIterable(pairs,
                 kp -> new SimpleImmutableEntry<>(kp, Collections.<X509Certificate> emptyList()));
     }

sshd-common/src/main/java/org/apache/sshd/client/config/hosts/KnownHostHashValue.java

@@ -96,10 +96,9 @@ public boolean isHostMatch(String host, int port) {
             byte[] expected = getDigestValue();
             byte[] actual = calculateHashValue(host, port, getDigester(), getSaltValue());
             return Arrays.equals(expected, actual);
+        } catch (RuntimeException e) {
+            throw e;
         } catch (Throwable t) {
-            if (t instanceof RuntimeException) {
-                throw (RuntimeException) t;
-            }
             throw new RuntimeSshException(
                     "Failed (" + t.getClass().getSimpleName() + ")" + " to calculate hash value: " + t.getMessage(), t);
         }

sshd-common/src/main/java/org/apache/sshd/client/config/keys/ClientIdentitiesWatcher.java

@@ -74,7 +74,7 @@ public Iterable<KeyPair> loadKeys(SessionContext session) {
         return loadKeys(session, null);
     }
 
-    protected Iterable<KeyPair> loadKeys(SessionContext session, Predicate<? super KeyPair> filter) {
+    protected Iterable<KeyPair> loadKeys(SessionContext session, Predicate<KeyPair> filter) {
         return ClientIdentityProvider.lazyKeysLoader(providers, p -> doGetKeyPairs(session, p), filter);
     }
 

sshd-common/src/main/java/org/apache/sshd/client/config/keys/ClientIdentityFileWatcher.java

@@ -94,13 +94,13 @@ public Iterable<KeyPair> getClientIdentities(SessionContext session)
             return identitiesHolder.get();
         }
 
-        Iterable<KeyPair> kp = identitiesHolder.getAndSet(null); // start fresh
+        identitiesHolder.set(null); // start fresh
         Path path = getPath();
         if (!exists()) {
             return identitiesHolder.get();
         }
 
-        kp = reloadClientIdentities(session, path);
+        Iterable<KeyPair> kp = reloadClientIdentities(session, path);
         updateReloadAttributes();
         identitiesHolder.set(kp);
         return kp;

sshd-common/src/main/java/org/apache/sshd/client/config/keys/ClientIdentityProvider.java

@@ -79,8 +79,7 @@ static ClientIdentityProvider of(KeyPair kp) {
      */
     static Iterable<KeyPair> lazyKeysLoader(
             Iterable<? extends ClientIdentityProvider> providers,
-            Function<? super ClientIdentityProvider, ? extends Iterable<? extends KeyPair>> kpExtractor,
-            Predicate<? super KeyPair> filter) {
+            Function<? super ClientIdentityProvider, ? extends Iterable<KeyPair>> kpExtractor, Predicate<KeyPair> filter) {
         Objects.requireNonNull(kpExtractor, "No key pair extractor provided");
         if (providers == null) {
             return Collections.emptyList();
@@ -114,8 +113,7 @@ public String toString() {
      */
     static Iterator<KeyPair> lazyKeysIterator(
             Iterator<? extends ClientIdentityProvider> providers,
-            Function<? super ClientIdentityProvider, ? extends Iterable<? extends KeyPair>> kpExtractor,
-            Predicate<? super KeyPair> filter) {
+            Function<? super ClientIdentityProvider, ? extends Iterable<KeyPair>> kpExtractor, Predicate<KeyPair> filter) {
         Objects.requireNonNull(kpExtractor, "No key pair extractor provided");
         return (providers == null)
                 ? Collections.emptyIterator()

sshd-common/src/main/java/org/apache/sshd/client/config/keys/LazyClientIdentityIterator.java

@@ -37,12 +37,12 @@
  */
 public class LazyClientIdentityIterator implements Iterator<KeyPair> {
     protected boolean finished;
-    protected Iterator<? extends KeyPair> currentIdentities;
+    protected Iterator<KeyPair> currentIdentities;
     protected KeyPair currentPair;
 
     private final Iterator<? extends ClientIdentityProvider> providers;
-    private final Function<? super ClientIdentityProvider, ? extends Iterable<? extends KeyPair>> kpExtractor;
-    private final Predicate<? super KeyPair> filter;
+    private final Function<? super ClientIdentityProvider, ? extends Iterable<KeyPair>> kpExtractor;
+    private final Predicate<KeyPair> filter;
 
     /**
      * @param providers   The providers - ignored if {@code null}
@@ -52,10 +52,9 @@ public class LazyClientIdentityIterator implements Iterator<KeyPair> {
      * @param filter      Any further filter to apply on (non-{@code null}) key pairs before returning it as the
      *                    {@link Iterator#next()} result.
      */
-    public LazyClientIdentityIterator(
-                                      Iterator<? extends ClientIdentityProvider> providers,
-                                      Function<? super ClientIdentityProvider, ? extends Iterable<? extends KeyPair>> kpExtractor,
-                                      Predicate<? super KeyPair> filter) {
+    public LazyClientIdentityIterator(Iterator<? extends ClientIdentityProvider> providers,
+                                      Function<? super ClientIdentityProvider, ? extends Iterable<KeyPair>> kpExtractor,
+                                      Predicate<KeyPair> filter) {
         this.providers = providers;
         this.kpExtractor = Objects.requireNonNull(kpExtractor, "No key pair extractor provided");
         this.filter = filter;
@@ -65,11 +64,11 @@ public Iterator<? extends ClientIdentityProvider> getProviders() {
         return providers;
     }
 
-    public Function<? super ClientIdentityProvider, ? extends Iterable<? extends KeyPair>> getIdentitiesExtractor() {
+    public Function<? super ClientIdentityProvider, ? extends Iterable<KeyPair>> getIdentitiesExtractor() {
         return kpExtractor;
     }
 
-    public Predicate<? super KeyPair> getFilter() {
+    public Predicate<KeyPair> getFilter() {
         return filter;
     }
 
@@ -90,15 +89,15 @@ public boolean hasNext() {
             return true;
         }
 
-        Function<? super ClientIdentityProvider, ? extends Iterable<? extends KeyPair>> x = getIdentitiesExtractor();
-        Predicate<? super KeyPair> f = getFilter();
+        Function<? super ClientIdentityProvider, ? extends Iterable<KeyPair>> x = getIdentitiesExtractor();
+        Predicate<KeyPair> f = getFilter();
         while (provs.hasNext()) {
             ClientIdentityProvider p = provs.next();
             if (p == null) {
                 continue;
             }
 
-            Iterable<? extends KeyPair> ids = x.apply(p);
+            Iterable<KeyPair> ids = x.apply(p);
             currentIdentities = (ids == null) ? null : ids.iterator();
             currentPair = KeyIdentityProvider.exhaustCurrentIdentities(currentIdentities);
             if (currentPair == null) {

sshd-common/src/main/java/org/apache/sshd/common/channel/PtyMode.java

@@ -301,20 +301,17 @@ public enum PtyMode {
      * A {@code null}-safe {@link ToIntFunction} that returns the {@link PtyMode#toInt()} value and (-1) for
      * {@code null}
      */
-    public static final ToIntFunction<PtyMode> OPCODE_EXTRACTOR = v -> (v == null) ? -1 : v.toInt();
+    public static final ToIntFunction<PtyMode> OPCODE_EXTRACTOR = op -> (op == null) ? -1 : op.toInt();
 
     /**
      * A {@code null}-safe {@link Comparator} of {@link PtyMode} values according to their {@link PtyMode#toInt()} value
      *
      * @see #OPCODE_EXTRACTOR
      */
-    public static final Comparator<PtyMode> BY_OPCODE = new Comparator<PtyMode>() {
-        @Override
-        public int compare(PtyMode o1, PtyMode o2) {
-            int v1 = OPCODE_EXTRACTOR.applyAsInt(o1);
-            int v2 = OPCODE_EXTRACTOR.applyAsInt(o2);
-            return Integer.compare(v1, v2);
-        }
+    public static final Comparator<PtyMode> BY_OPCODE = (o1, o2) -> {
+        int v1 = OPCODE_EXTRACTOR.applyAsInt(o1);
+        int v2 = OPCODE_EXTRACTOR.applyAsInt(o2);
+        return Integer.compare(v1, v2);
     };
 
     private final int v;

sshd-common/src/main/java/org/apache/sshd/common/config/VersionProperties.java

@@ -69,7 +69,7 @@ private static NavigableMap<String, String> loadVersionProperties(
                     log.warn("Failed ({}) to load version properties from {}: {}",
                             e.getClass().getSimpleName(), cl, e.getMessage());
                     if (log.isDebugEnabled()) {
-                        log.debug("Version property failure details for loader=" + cl, e);
+                        log.debug("Version property failure details for loader={}", cl, e);
                     }
                     continue;
                 }
@@ -85,7 +85,7 @@ private static NavigableMap<String, String> loadVersionProperties(
                     String prev = result.put(key, value);
                     if (prev != null) {
                         Logger log = LoggerFactory.getLogger(anchor);
-                        log.warn("Multiple values for key=" + key + ": current=" + value + ", previous=" + prev);
+                        log.warn("Multiple values for key={}: current={}, previous={}", key, value, prev);
                     }
                 }
 

sshd-common/src/main/java/org/apache/sshd/common/config/keys/KeyUtils.java

@@ -103,7 +103,7 @@ public final class KeyUtils {
     /**
      * The most commonly used RSA public key exponent
      */
-    public static final BigInteger DEFAULT_RSA_PUBLIC_EXPONENT = new BigInteger("65537");
+    public static final BigInteger DEFAULT_RSA_PUBLIC_EXPONENT = BigInteger.valueOf(65537);
 
     /**
      * Name of algorithm for DSS keys to be used when calling security provider

sshd-common/src/main/java/org/apache/sshd/common/config/keys/impl/AbstractPublicKeyEntryDecoder.java

@@ -51,7 +51,7 @@ protected final boolean parseBooleanHeader(Map<String, String> headers, String p
         try {
             boolVal = PropertyResolverUtils.parseBoolean(stringVal);
         } catch (IllegalArgumentException e) {
-            log.warn("Ignoring non-boolean property value for \"" + propertyKey + "\": " + stringVal);
+            log.warn("Ignoring non-boolean property value for \"{}\": {}", propertyKey, stringVal);
             boolVal = null;
         }
         if (boolVal == null) {

sshd-common/src/main/java/org/apache/sshd/common/config/keys/loader/openssh/OpenSSHDSSPrivateKeyEntryDecoder.java

@@ -70,16 +70,7 @@ public DSAPrivateKey decodePrivateKey(
         Objects.requireNonNull(y, "No public key data"); // TODO run some validation on it
         BigInteger x = KeyEntryResolver.decodeBigInt(keyData);
 
-        try {
-            return generatePrivateKey(new DSAPrivateKeySpec(x, p, q, g));
-        } finally {
-            // get rid of sensitive data a.s.a.p
-            p = null;
-            q = null;
-            g = null;
-            y = null;
-            x = null;
-        }
+        return generatePrivateKey(new DSAPrivateKeySpec(x, p, q, g));
     }
 
     @Override

sshd-common/src/main/java/org/apache/sshd/common/config/keys/loader/openssh/OpenSSHECDSAPrivateKeyEntryDecoder.java

@@ -81,12 +81,7 @@ public ECPrivateKey decodePrivateKey(
         Objects.requireNonNull(pubKey, "No public point"); // TODO validate it is a valid ECPoint
         BigInteger s = KeyEntryResolver.decodeBigInt(keyData);
         ECParameterSpec params = curve.getParameters();
-        try {
-            return generatePrivateKey(new ECPrivateKeySpec(s, params));
-        } finally {
-            // get rid of sensitive data a.s.a.p
-            s = null;
-        }
+        return generatePrivateKey(new ECPrivateKeySpec(s, params));
     }
 
     @Override

sshd-common/src/main/java/org/apache/sshd/common/config/keys/loader/openssh/OpenSSHRSAPrivateKeyDecoder.java

@@ -48,7 +48,7 @@
  * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
  */
 public class OpenSSHRSAPrivateKeyDecoder extends AbstractPrivateKeyEntryDecoder<RSAPublicKey, RSAPrivateKey> {
-    public static final BigInteger DEFAULT_PUBLIC_EXPONENT = new BigInteger("65537");
+    public static final BigInteger DEFAULT_PUBLIC_EXPONENT = KeyUtils.DEFAULT_RSA_PUBLIC_EXPONENT;
     public static final OpenSSHRSAPrivateKeyDecoder INSTANCE = new OpenSSHRSAPrivateKeyDecoder();
 
     public OpenSSHRSAPrivateKeyDecoder() {
@@ -79,16 +79,8 @@ public RSAPrivateKey decodePrivateKey(
         if (!Objects.equals(n, modulus)) {
             log.warn("decodePrivateKey({}) mismatched modulus values: encoded={}, calculated={}", keyType, n, modulus);
         }
-        try {
-            return generatePrivateKey(new RSAPrivateCrtKeySpec(
-                    n, e, d, p, q, d.mod(p.subtract(BigInteger.ONE)), d.mod(q.subtract(BigInteger.ONE)), inverseQmodP));
-        } finally {
-            // get rid of sensitive data a.s.a.p
-            d = null;
-            inverseQmodP = null;
-            p = null;
-            q = null;
-        }
+        return generatePrivateKey(new RSAPrivateCrtKeySpec(n, e, d, p, q, d.mod(p.subtract(BigInteger.ONE)),
+                d.mod(q.subtract(BigInteger.ONE)), inverseQmodP));
     }
 
     @Override

sshd-common/src/main/java/org/apache/sshd/common/file/util/BaseFileSystem.java

@@ -41,7 +41,7 @@ public abstract class BaseFileSystem<T extends Path> extends FileSystem {
     protected final Logger log;
     private final FileSystemProvider fileSystemProvider;
 
-    public BaseFileSystem(FileSystemProvider fileSystemProvider) {
+    protected BaseFileSystem(FileSystemProvider fileSystemProvider) {
         this.log = LoggerFactory.getLogger(getClass());
         this.fileSystemProvider = Objects.requireNonNull(fileSystemProvider, "No file system provider");
     }

sshd-common/src/main/java/org/apache/sshd/common/file/util/BasePath.java

@@ -47,7 +47,7 @@ public abstract class BasePath<T extends BasePath<T, FS>, FS extends BaseFileSys
     private String strValue;
     private int hashValue;
 
-    public BasePath(FS fileSystem, String root, List<String> names) {
+    protected BasePath(FS fileSystem, String root, List<String> names) {
         this.fileSystem = Objects.requireNonNull(fileSystem, "No file system provided");
         this.root = root;
         this.names = names;

sshd-common/src/main/java/org/apache/sshd/common/io/AbstractIoWriteFuture.java

@@ -20,6 +20,7 @@
 package org.apache.sshd.common.io;
 
 import java.io.IOException;
+import java.util.Objects;
 
 import org.apache.sshd.common.SshException;
 import org.apache.sshd.common.future.DefaultVerifiableSshFuture;
@@ -62,4 +63,11 @@ public Throwable getException() {
             return null;
         }
     }
+
+    public static IoWriteFuture fulfilled(Object id, Object value) {
+        AbstractIoWriteFuture result = new AbstractIoWriteFuture(id, null) {
+        };
+        result.setValue(Objects.requireNonNull(value));
+        return result;
+    }
 }

sshd-common/src/main/java/org/apache/sshd/common/keyprovider/AbstractResourceKeyPairProvider.java

@@ -105,7 +105,7 @@ protected void resetCacheMap(Collection<?> resources) {
         }
 
         if (log.isDebugEnabled()) {
-            log.debug("resetCacheMap(" + resources + ") removed previous cached keys for " + toDelete);
+            log.debug("resetCacheMap({}) removed previous cached keys for {}", resources, toDelete);
         }
     }
 
@@ -208,10 +208,8 @@ public boolean hasNext() {
 
         @Override
         public KeyPair next() {
-            if (!nextKeyPairSet) {
-                if (!setNextObject()) {
-                    throw new NoSuchElementException("Out of files to try");
-                }
+            if (!nextKeyPairSet && !setNextObject()) {
+                throw new NoSuchElementException("Out of files to try");
             }
             nextKeyPairSet = false;
             return nextKeyPair;

sshd-common/src/main/java/org/apache/sshd/common/keyprovider/KeyIdentityProvider.java

@@ -192,7 +192,7 @@ static KeyIdentityProvider wrapKeyPairs(Iterable<KeyPair> pairs) {
      * @return     The first non-{@code null} key pair found in the iterator - {@code null} if all elements exhausted
      *             without such an entry
      */
-    static KeyPair exhaustCurrentIdentities(Iterator<? extends KeyPair> ids) {
+    static KeyPair exhaustCurrentIdentities(Iterator<KeyPair> ids) {
         while ((ids != null) && ids.hasNext()) {
             KeyPair kp = ids.next();
             if (kp != null) {