Add vks-java-cli Command Line Frontend

vks-java-cli/src/main/java/pgp/vks/client/cli/GetCmd.java

@@ -0,0 +1,74 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package pgp.vks.client.cli;
+
+import pgp.vks.client.Get;
+import pgp.vks.client.VKS;
+import picocli.CommandLine;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.MalformedURLException;
+
+@CommandLine.Command(name = "get", description = "Retrieve an OpenPGP certificate from the key server")
+public class GetCmd implements Runnable {
+
+    @CommandLine.Mixin
+    VKSCLI.KeyServerMixin keyServerMixin;
+
+    @CommandLine.ArgGroup(exclusive = true, multiplicity = "1")
+    Exclusive by;
+
+    static class Exclusive {
+        @CommandLine.Option(names = {"-f", "--by-fingerprint"}, description = "Retrieve a key by its fingerprint (NOT prefixed with '0x')")
+        String fingerprint;
+
+        @CommandLine.Option(names = {"-i", "--by-keyid"}, description = "Retrieve a key by its decimal key ID or that of one of its subkeys.")
+        Long keyId;
+
+        @CommandLine.Option(names = {"-e", "--by-email"}, description = "Retrieve a key by email address.")
+        String email;
+    }
+
+    public void run() {
+        VKS vks;
+        try {
+            vks = keyServerMixin.parent.getApi();
+        } catch (MalformedURLException e) {
+            throw new AssertionError(e);
+        }
+
+        Get get = vks.get();
+        InputStream inputStream = null;
+        try {
+            if (by.fingerprint != null) {
+                inputStream = get.byFingerprint(by.fingerprint);
+            } else if (by.keyId != null) {
+                inputStream = get.byKeyId(by.keyId);
+            } else if (by.email != null) {
+                inputStream = get.byEmail(by.email);
+            } else {
+                throw new IllegalArgumentException("Missing --by-* option.");
+            }
+
+            int read;
+            byte[] buf = new byte[4096];
+            while ((read = inputStream.read(buf)) != -1) {
+                System.out.write(buf, 0, read);
+            }
+
+        } catch (IOException e) {
+            throw new AssertionError(e);
+        } finally {
+            if (inputStream != null) {
+                try {
+                    inputStream.close();
+                } catch (IOException e) {
+                    throw new AssertionError(e);
+                }
+            }
+        }
+    }
+}