tidy-up: example, tests continued

- fix skip auth if `userauthlist` is NULL.
  Closes #836 (Reported-by: @sudipm-mukherjee on github)
- fix most silenced `checksrc` warnings.
- sync examples/tests code between each other.
  (output messages, error handling, declaration order, comments)
- stop including unnecessary headers.
- always deinitialize in case of error.
- drop some redundant variables.
- add error handling where missing.
- show more error codes.
- switch `perror()` to `fprintf()`.
- fix some `printf()`s to be `fprintf()`.
- formatting.

Closes #960

example/scp_write.c

@@ -17,9 +17,6 @@
 #ifdef HAVE_ARPA_INET_H
 #include <arpa/inet.h>
 #endif
-#ifdef HAVE_SYS_TIME_H
-#include <sys/time.h>
-#endif
 
 #include <sys/types.h>
 #include <fcntl.h>
@@ -27,6 +24,13 @@
 #include <stdio.h>
 #include <ctype.h>
 
+static const char *pubkey = "/home/username/.ssh/id_rsa.pub";
+static const char *privkey = "/home/username/.ssh/id_rsa";
+static const char *username = "username";
+static const char *password = "password";
+static const char *loclfile = "scp_write.c";
+static const char *scppath = "/tmp/TEST";
+
 int main(int argc, char *argv[])
 {
     uint32_t hostaddr;
@@ -34,28 +38,21 @@ int main(int argc, char *argv[])
     int i, auth_pw = 1;
     struct sockaddr_in sin;
     const char *fingerprint;
+    int rc;
     LIBSSH2_SESSION *session = NULL;
     LIBSSH2_CHANNEL *channel;
-    const char *pubkey = "/home/username/.ssh/id_rsa.pub";
-    const char *privkey = "/home/username/.ssh/id_rsa";
-    const char *username = "username";
-    const char *password = "password";
-    const char *loclfile = "scp_write.c";
-    const char *scppath = "/tmp/TEST";
     FILE *local;
-    int rc;
     char mem[1024];
     size_t nread;
     char *ptr;
     struct stat fileinfo;
-    int err;
 
 #ifdef WIN32
     WSADATA wsadata;
 
-    err = WSAStartup(MAKEWORD(2, 0), &wsadata);
-    if(err != 0) {
-        fprintf(stderr, "WSAStartup failed with error: %d\n", err);
+    rc = WSAStartup(MAKEWORD(2, 0), &wsadata);
+    if(rc) {
+        fprintf(stderr, "WSAStartup failed with error: %d\n", rc);
         return 1;
     }
 #endif
@@ -80,7 +77,7 @@ int main(int argc, char *argv[])
     }
 
     rc = libssh2_init(0);
-    if(rc != 0) {
+    if(rc) {
         fprintf(stderr, "libssh2 initialization failed (%d)\n", rc);
         return 1;
     }
@@ -88,19 +85,18 @@ int main(int argc, char *argv[])
     local = fopen(loclfile, "rb");
     if(!local) {
         fprintf(stderr, "Can't open local file %s\n", loclfile);
-        return -1;
+        return 1;
     }
 
     stat(loclfile, &fileinfo);
 
-    /* Ultra basic "connect to port 22 on localhost"
-     * Your code is responsible for creating the socket establishing the
-     * connection
+    /* Ultra basic "connect to port 22 on localhost".  Your code is
+     * responsible for creating the socket establishing the connection
      */
     sock = socket(AF_INET, SOCK_STREAM, 0);
     if(sock == LIBSSH2_INVALID_SOCKET) {
         fprintf(stderr, "failed to create socket!\n");
-        return -1;
+        goto shutdown;
     }
 
     sin.sin_family = AF_INET;
@@ -108,14 +104,15 @@ int main(int argc, char *argv[])
     sin.sin_addr.s_addr = hostaddr;
     if(connect(sock, (struct sockaddr*)(&sin), sizeof(struct sockaddr_in))) {
         fprintf(stderr, "failed to connect!\n");
-        return -1;
+        goto shutdown;
     }
 
-    /* Create a session instance
-     */
+    /* Create a session instance */
     session = libssh2_session_init();
-    if(!session)
-        return -1;
+    if(!session) {
+        fprintf(stderr, "Could not initialize SSH session!\n");
+        goto shutdown;
+    }
 
     /* ... start it up. This will trade welcome banners, exchange keys,
      * and setup crypto, compression, and MAC layers
@@ -123,7 +120,7 @@ int main(int argc, char *argv[])
     rc = libssh2_session_handshake(session, sock);
     if(rc) {
         fprintf(stderr, "Failure establishing SSH session: %d\n", rc);
-        return -1;
+        goto shutdown;
     }
 
     /* At this point we have not yet authenticated.  The first thing to do
@@ -141,7 +138,7 @@ int main(int argc, char *argv[])
     if(auth_pw) {
         /* We could authenticate via password */
         if(libssh2_userauth_password(session, username, password)) {
-            fprintf(stderr, "Authentication by password failed.\n");
+            fprintf(stderr, "Authentication by password failed!\n");
             goto shutdown;
         }
     }
@@ -150,7 +147,7 @@ int main(int argc, char *argv[])
         if(libssh2_userauth_publickey_fromfile(session, username,
                                                pubkey, privkey,
                                                password)) {
-            fprintf(stderr, "\tAuthentication by public key failed\n");
+            fprintf(stderr, "Authentication by public key failed!\n");
             goto shutdown;
         }
     }
@@ -162,6 +159,7 @@ int main(int argc, char *argv[])
     if(!channel) {
         char *errmsg;
         int errlen;
+        int err;
         err = libssh2_session_last_error(session, &errmsg, &errlen, 0);
         fprintf(stderr, "Unable to open a session: (%d) %s\n", err, errmsg);
         goto shutdown;
@@ -211,13 +209,18 @@ shutdown:
         libssh2_session_disconnect(session, "Normal Shutdown");
         libssh2_session_free(session);
     }
+
+    if(sock != LIBSSH2_INVALID_SOCKET) {
 #ifdef WIN32
-    closesocket(sock);
+        closesocket(sock);
 #else
-    close(sock);
+        close(sock);
 #endif
+    }
+
     if(local)
         fclose(local);
+
     fprintf(stderr, "all done\n");
 
     libssh2_exit();