Add back support for getXIfChanged(Y, tag)

pgp-certificate-store/src/main/java/pgp/certificate_store/PGPCertificateStore.java

@@ -32,6 +32,23 @@ public interface PGPCertificateStore {
     Certificate getCertificate(String identifier)
             throws IOException, BadNameException, BadDataException;
 
+    /**
+     * Return the certificate that matches the given identifier, but only if it has been changed.
+     * Whether it has been changed is determined by calculating the tag in the directory
+     * (e.g. by looking at the inode and last modification date) and comparing the result with the tag provided by
+     * the caller.
+     *
+     * @param identifier certificate identifier
+     * @param tag tag by the caller
+     * @return certificate if it has been changed, null otherwise
+     *
+     * @throws IOException in case of an IO-error
+     * @throws BadNameException if the identifier is invalid
+     * @throws BadDataException if the certificate file contains invalid data
+     */
+    Certificate getCertificateIfChanged(String identifier, Long tag)
+            throws IOException, BadNameException, BadDataException;
+
     /**
      * Return an {@link Iterator} over all certificates in the store that contain a subkey with the given
      * subkey id.
@@ -42,7 +59,7 @@ public interface PGPCertificateStore {
      * @throws BadDataException if any of the certificate files contains invalid data
      */
     Iterator<Certificate> getCertificatesBySubkeyId(long subkeyId)
-        throws IOException, BadDataException;
+            throws IOException, BadDataException;
 
     /**
      * Insert a certificate into the store.

pgp-certificate-store/src/main/java/pgp/certificate_store/certificate/Certificate.java

@@ -4,13 +4,67 @@
 
 package pgp.certificate_store.certificate;
 
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+import java.util.List;
+
 /**
  * OpenPGP certificate (public key).
  */
-public abstract class Certificate implements KeyMaterial {
+public class Certificate implements KeyMaterial {
+
+    private final byte[] bytes;
+    private final String fingerprint;
+    private final List<Long> subkeyIds;
+    private final Long tag;
+
+    /**
+     * Certificate constructor.
+     *
+     * @param bytes encoding of the certificate
+     * @param fingerprint fingerprint (lowercase hex characters)
+     * @param subkeyIds list of subkey ids
+     * @param tag tag
+     */
+    public Certificate(byte[] bytes, String fingerprint, List<Long> subkeyIds, Long tag) {
+        this.bytes = bytes;
+        this.fingerprint = fingerprint;
+        this.subkeyIds = subkeyIds;
+        this.tag = tag;
+    }
+
+    /**
+     * Copy constructor to assign a new tag to the {@link Certificate}.
+     *
+     * @param cert certificate
+     * @param tag tag
+     */
+    public Certificate(Certificate cert, Long tag) {
+        this(cert.bytes, cert.fingerprint, cert.subkeyIds, tag);
+    }
+
+    @Override
+    public String getFingerprint() {
+        return fingerprint;
+    }
 
     @Override
     public Certificate asCertificate() {
         return this;
     }
+
+    @Override
+    public InputStream getInputStream() {
+        return new ByteArrayInputStream(bytes);
+    }
+
+    @Override
+    public Long getTag() {
+        return tag;
+    }
+
+    @Override
+    public List<Long> getSubkeyIds() {
+        return subkeyIds;
+    }
 }

pgp-certificate-store/src/main/java/pgp/certificate_store/certificate/Key.java

@@ -4,21 +4,74 @@
 
 package pgp.certificate_store.certificate;
 
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+import java.util.List;
+
 /**
  * OpenPGP key (secret key).
  */
-public abstract class Key implements KeyMaterial {
+public class Key implements KeyMaterial {
+
+    private final byte[] bytes;
+    private final Certificate certificate;
+    private final Long tag;
+
+    /**
+     * Key constructor.
+     *
+     * @param bytes encoding of the key
+     * @param certificate associated certificate
+     * @param tag tag
+     */
+    public Key(byte[] bytes, Certificate certificate, Long tag) {
+        this.bytes = bytes;
+        this.certificate = certificate;
+        this.tag = tag;
+    }
+
+    /**
+     * Copy constructor to change the tag of both the {@link Key} and its {@link Certificate}.
+     *
+     * @param key key
+     * @param tag tag
+     */
+    public Key(Key key, Long tag) {
+        this(key.bytes, new Certificate(key.certificate, tag), tag);
+    }
 
     /**
      * Return the certificate part of this OpenPGP key.
      *
      * @return OpenPGP certificate
      */
-    public abstract Certificate getCertificate();
+    public Certificate getCertificate() {
+        return new Certificate(certificate, getTag());
+    }
+
+    @Override
+    public String getFingerprint() {
+        return certificate.getFingerprint();
+    }
 
     @Override
     public Certificate asCertificate() {
         return getCertificate();
     }
 
+    @Override
+    public InputStream getInputStream() {
+        return new ByteArrayInputStream(bytes);
+    }
+
+    @Override
+    public Long getTag() {
+        return tag;
+    }
+
+    @Override
+    public List<Long> getSubkeyIds() {
+        return certificate.getSubkeyIds();
+    }
+
 }

pgp-certificate-store/src/main/java/pgp/certificate_store/certificate/KeyMaterial.java

@@ -4,7 +4,6 @@
 
 package pgp.certificate_store.certificate;
 
-import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;
 import java.util.Set;
@@ -19,23 +18,34 @@ public interface KeyMaterial {
      */
     String getFingerprint();
 
+    /**
+     * Return the {@link Certificate} belonging to this key material.
+     * If this is already a {@link Certificate}, return this.
+     * If this is a {@link Key}, extract the {@link Certificate} and return it.
+     *
+     * @return certificate
+     */
     Certificate asCertificate();
 
     /**
      * Return an {@link InputStream} of the binary representation of the secret key.
      *
      * @return input stream
-     * @throws IOException in case of an IO error
      */
-    InputStream getInputStream() throws IOException;
+    InputStream getInputStream();
 
-    String getTag() throws IOException;
+    /**
+     * Return the tag belonging to this key material.
+     * The tag can be used to keep an application cache in sync with what is in the directory.
+     *
+     * @return tag
+     */
+    Long getTag();
 
     /**
      * Return a {@link Set} containing key-ids of subkeys.
      *
      * @return subkeys
-     * @throws IOException in case of an IO error
      */
-    List<Long> getSubkeyIds() throws IOException;
+    List<Long> getSubkeyIds();
 }

pgp-certificate-store/src/main/java/pgp/certificate_store/certificate/KeyMaterialReaderBackend.java

@@ -20,5 +20,5 @@ public interface KeyMaterialReaderBackend {
      * @throws IOException in case of an IO error
      * @throws BadDataException in case that the data stream does not contain a valid OpenPGP key/certificate
      */
-    KeyMaterial read(InputStream data) throws IOException, BadDataException;
+    KeyMaterial read(InputStream data, Long tag) throws IOException, BadDataException;
 }