examples: Use safer names for stdin, stdout, stderr

BUG: https://red.libssh.org/issues/168

On some platforms, like OpenBSD, stdin and friends are macros which break
compilation of this struct. I've fixed these names such that it compiles and
runs cleanly on OpenBSD

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

examples/ssh_server_fork.c

@@ -221,10 +221,10 @@ struct channel_data_struct {
     socket_t pty_master;
     socket_t pty_slave;
     /* For communication with the child process. */
-    socket_t stdin;
-    socket_t stdout;
+    socket_t child_stdin;
+    socket_t child_stdout;
     /* Only used for subsystem and exec requests. */
-    socket_t stderr;
+    socket_t child_stderr;
     /* Event which is used to poll the above descriptors. */
     ssh_event event;
     /* Terminal size struct. */
@@ -251,7 +251,7 @@ static int data_function(ssh_session session, ssh_channel channel, void *data,
         return 0;
     }
 
-    return write(cdata->stdin, (char *) data, len);
+    return write(cdata->child_stdin, (char *) data, len);
 }
 
 static int pty_request(ssh_session session, ssh_channel channel,
@@ -313,7 +313,7 @@ static int exec_pty(const char *mode, const char *command,
         default:
             close(cdata->pty_slave);
             /* pty fd is bi-directional */
-            cdata->stdout = cdata->stdin = cdata->pty_master;
+            cdata->child_stdout = cdata->child_stdin = cdata->pty_master;
     }
     return SSH_OK;
 }
@@ -355,9 +355,9 @@ static int exec_nopty(const char *command, struct channel_data_struct *cdata) {
     close(out[1]);
     close(err[1]);
 
-    cdata->stdin = in[1];
-    cdata->stdout = out[0];
-    cdata->stderr = err[0];
+    cdata->child_stdin = in[1];
+    cdata->child_stdout = out[0];
+    cdata->child_stderr = err[0];
 
     return SSH_OK;
 
@@ -487,9 +487,9 @@ static void handle_session(ssh_event event, ssh_session session) {
         .pid = 0,
         .pty_master = -1,
         .pty_slave = -1,
-        .stdin = -1,
-        .stdout = -1,
-        .stderr = -1,
+        .child_stdin = -1,
+        .child_stdout = -1,
+        .child_stderr = -1,
         .event = NULL,
         .winsize = &wsize
     };
@@ -562,8 +562,8 @@ static void handle_session(ssh_event event, ssh_session session) {
         /* Executed only once, once the child process starts. */
         cdata.event = event;
         /* If stdout valid, add stdout to be monitored by the poll event. */
-        if (cdata.stdout != -1) {
-            if (ssh_event_add_fd(event, cdata.stdout, POLLIN, process_stdout,
+        if (cdata.child_stdout != -1) {
+            if (ssh_event_add_fd(event, cdata.child_stdout, POLLIN, process_stdout,
                                  sdata.channel) != SSH_OK) {
                 fprintf(stderr, "Failed to register stdout to poll context\n");
                 ssh_channel_close(sdata.channel);
@@ -571,8 +571,8 @@ static void handle_session(ssh_event event, ssh_session session) {
         }
 
         /* If stderr valid, add stderr to be monitored by the poll event. */
-        if (cdata.stderr != -1){
-            if (ssh_event_add_fd(event, cdata.stderr, POLLIN, process_stderr,
+        if (cdata.child_stderr != -1){
+            if (ssh_event_add_fd(event, cdata.child_stderr, POLLIN, process_stderr,
                                  sdata.channel) != SSH_OK) {
                 fprintf(stderr, "Failed to register stderr to poll context\n");
                 ssh_channel_close(sdata.channel);
@@ -582,14 +582,14 @@ static void handle_session(ssh_event event, ssh_session session) {
             (cdata.pid == 0 || waitpid(cdata.pid, &rc, WNOHANG) == 0));
 
     close(cdata.pty_master);
-    close(cdata.stdin);
-    close(cdata.stdout);
-    close(cdata.stderr);
+    close(cdata.child_stdin);
+    close(cdata.child_stdout);
+    close(cdata.child_stderr);
 
     /* Remove the descriptors from the polling context, since they are now
      * closed, they will always trigger during the poll calls. */
-    ssh_event_remove_fd(event, cdata.stdout);
-    ssh_event_remove_fd(event, cdata.stderr);
+    ssh_event_remove_fd(event, cdata.child_stdout);
+    ssh_event_remove_fd(event, cdata.child_stderr);
 
     /* If the child process exited. */
     if (kill(cdata.pid, 0) < 0 && WIFEXITED(rc)) {