Skip blank lines when detecting key formats

Some private keys found in the wild start with a blank line, which
breaks SSHJ. OpenSSH utilities worked as expected with these key files.

Also add some basic tests for key formats.

src/main/java/net/schmizz/sshj/userauth/keyprovider/KeyProviderUtil.java

@@ -51,8 +51,7 @@ public class KeyProviderUtil {
      * @return name of the key file format
      * @throws java.io.IOException
      */
-    public static KeyFormat detectKeyFileFormat(String privateKey,
-                                                             boolean separatePubKey)
+    public static KeyFormat detectKeyFileFormat(String privateKey, boolean separatePubKey)
             throws IOException {
         return detectKeyFileFormat(new StringReader(privateKey), separatePubKey);
     }
@@ -67,35 +66,44 @@ public class KeyProviderUtil {
      * @return name of the key file format
      * @throws java.io.IOException
      */
-    public static KeyFormat detectKeyFileFormat(Reader privateKey,
-                                                             boolean separatePubKey)
+    public static KeyFormat detectKeyFileFormat(Reader privateKey, boolean separatePubKey)
             throws IOException {
-        BufferedReader br = new BufferedReader(privateKey);
-        final String firstLine;
-        try {
-            firstLine = br.readLine();
-        }
-        finally {
-            IOUtils.closeQuietly(br);
-        }
-        if(firstLine == null) {
+        String header = readHeader(privateKey);
+        if (header == null) {
             throw new IOException("Empty file");
         }
-        if(firstLine.startsWith("-----BEGIN") && firstLine.endsWith("PRIVATE KEY-----")) {
-            if(separatePubKey)
-            // Can delay asking for password since have unencrypted pubkey
-            {
-                return KeyFormat.OpenSSH;
+        return keyFormatFromHeader(header, separatePubKey);
+    }
+
+    private static String readHeader(Reader privateKey) throws IOException {
+        BufferedReader br = new BufferedReader(privateKey);
+        try {
+            String header;
+            while ((header = br.readLine()) != null) {
+                header = header.trim();
+                if (!header.isEmpty()) {
+                    break;
+                }
             }
-            else
-            // More general
-            {
+            return header;
+        } finally {
+            IOUtils.closeQuietly(br);
+        }
+    }
+
+    private static KeyFormat keyFormatFromHeader(String header, boolean separatePubKey) {
+        if (header.startsWith("-----BEGIN") && header.endsWith("PRIVATE KEY-----")) {
+            if (separatePubKey) {
+                // Can delay asking for password since have unencrypted pubkey
+                return KeyFormat.OpenSSH;
+            } else {
+                // More general
                 return KeyFormat.PKCS8;
             }
-        }
-        if(firstLine.startsWith("PuTTY-User-Key-File-")) {
+        } else if (header.startsWith("PuTTY-User-Key-File-")) {
             return KeyFormat.PuTTY;
+        } else {
+            return KeyFormat.Unknown;
         }
-        return KeyFormat.Unknown;
     }
 }

src/test/java/net/schmizz/sshj/keyprovider/KeyProviderUtilTest.java

@@ -0,0 +1,40 @@
+package net.schmizz.sshj.keyprovider;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.junit.Test;
+
+import net.schmizz.sshj.userauth.keyprovider.KeyFormat;
+import net.schmizz.sshj.userauth.keyprovider.KeyProviderUtil;
+
+public class KeyProviderUtilTest {
+
+    private static final File ROOT = new File("src/test/resources/keyformats");
+
+    @Test
+    public void testOpenSsh() throws IOException {
+        KeyFormat format = KeyProviderUtil.detectKeyFileFormat(new File(ROOT, "openssh"));
+        assertEquals(KeyFormat.OpenSSH, format);
+    }
+
+    @Test
+    public void testPkcs8() throws IOException {
+        KeyFormat format = KeyProviderUtil.detectKeyFileFormat(new File(ROOT, "pkcs8"));
+        assertEquals(KeyFormat.PKCS8, format);
+    }
+
+    @Test
+    public void testPutty() throws IOException {
+        KeyFormat format = KeyProviderUtil.detectKeyFileFormat(new File(ROOT, "putty"));
+        assertEquals(KeyFormat.PuTTY, format);
+    }
+
+    @Test
+    public void testSkipsBlankLines() throws IOException {
+        KeyFormat format = KeyProviderUtil.detectKeyFileFormat(new File(ROOT, "pkcs8-blanks"));
+        assertEquals(KeyFormat.PKCS8, format);
+    }
+}

src/test/resources/keyformats/openssh

@@ -0,0 +1,15 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----

src/test/resources/keyformats/openssh.pub

@@ -0,0 +1 @@
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQCm2IJ9gWDkPTlQ37NNUB0za5mCsQ8bi++8fyEqw7wl8ZNBh3qtTcnL+m+NZfQjUC0BXic7PcMLVm4A3ID2IAZQM+axfq9aL4huWerm4ua6tvdt4gQKoL1+8JFmdFvFw5pWW/NZHtkIprbVf7KtYrU27WmMhXruN071UzqLsw08cw==

src/test/resources/keyformats/pkcs8

@@ -0,0 +1,15 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----

src/test/resources/keyformats/pkcs8-blanks

@@ -0,0 +1,18 @@
+
+
+
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----

src/test/resources/keyformats/putty

@@ -0,0 +1,19 @@
+PuTTY-User-Key-File-2: ssh-rsa
+Encryption: none
+Comment: rsa-key-20150817
+Public-Lines: 4
+AAAAB3NzaC1yc2EAAAABJQAAAIEAhoCAakZdrCNrHNpJHRIED4movsposAlk4ZPz
+n/IFGkiIZOWRF/p4Sq+CaLigamwpe3f2/vYxCwtF3oCcJMQdn6CLYytHgrC2pRWa
+bNBBClSO4jzWMlBRBZnzXBHKJ04kviqIybEvrN2weg5ArSOK7297DU2id+kDxSJz
+QleZ+9c=
+Private-Lines: 8
+AAAAgBItCm858PuWFWTDjVb0mMPUVRLdFRDerMSJnXZ6pr5c1ClPdHjcqHjLnABQ
+TQd2Znh3/siCIk2ZvVVrU17qEdcZyivntbi8NuehqcVQr2ny8pc+sXvxXv2inoA3
+4mIVqjhIoljYf1VWgDXUxUsGU6QZdMfkDCEuoxL9QM7RdFXNAAAAQQDk01miHj3M
+LozpMovCU2oKDFLsmOrXe7jroff2sM4BX5Iwym4N197O7ZIs5E52K0bWIDH9SouX
+RTseqiHsPxexAAAAQQCWeZFwG7qm8cyAGSzsDsN35cmzgkvlFl4uIuJ9jh0S2Yt5
+2couD/AoQVmHqGaxwYPc+q24yvbFbjCxtlkqMTYHAAAAQQCcpItltKrhNW2svG2P
+NuOi0TQmMZQigMOYQx4wd/8G2n+nr0Qsi4wuq/qccgKViVRyobB7nxQqoJdGAI90
+ECNG
+Private-MAC: 4f200e5f5b766351b996d92f3b733b671b9ff957
+