Adding expand-path@openssh.com extension for client

Signed-off-by: anshul agrawal <anshulagrawal2902@gmail.com>
Reviewed-by: Sahana Prasad <sahana@redhat.com>
Reviewed-by: Eshan Kelkar <eshankelkar@galorithm.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

src/sftp.c

@@ -3744,4 +3744,98 @@ sftp_attributes sftp_fstat(sftp_file file)
     return NULL;
 }
 
+char *sftp_expand_path(sftp_session sftp, const char *path)
+{
+    sftp_status_message status = NULL;
+    sftp_message msg = NULL;
+    ssh_buffer buffer = NULL;
+    uint32_t id;
+    int rc;
+
+    if (sftp == NULL) {
+        return NULL;
+    }
+
+    if (path == NULL) {
+        ssh_set_error(sftp->session,
+                      SSH_FATAL,
+                      "NULL received as an argument instead of the path to expand");
+        sftp_set_error(sftp, SSH_FX_FAILURE);
+        return NULL;
+    }
+
+    buffer = ssh_buffer_new();
+    if (buffer == NULL) {
+        ssh_set_error_oom(sftp->session);
+        sftp_set_error(sftp, SSH_FX_FAILURE);
+        return NULL;
+    }
+
+    id = sftp_get_new_id(sftp);
+
+    rc = ssh_buffer_pack(buffer,
+                         "dss",
+                         id,
+                         "expand-path@openssh.com",
+                         path);
+    if (rc != SSH_OK) {
+        ssh_set_error_oom(sftp->session);
+        SSH_BUFFER_FREE(buffer);
+        sftp_set_error(sftp, SSH_FX_FAILURE);
+        return NULL;
+    }
+
+    rc = sftp_packet_write(sftp, SSH_FXP_EXTENDED, buffer);
+    SSH_BUFFER_FREE(buffer);
+    if (rc < 0) {
+        return NULL;
+    }
+
+    while (msg == NULL) {
+        rc = sftp_read_and_dispatch(sftp);
+        if (rc < 0) {
+            return NULL;
+        }
+        msg = sftp_dequeue(sftp, id);
+    }
+
+    if (msg->packet_type == SSH_FXP_NAME) {
+        uint32_t ignored = 0;
+        char *cname = NULL;
+
+        rc = ssh_buffer_unpack(msg->payload,
+                               "ds",
+                               &ignored,
+                               &cname);
+        sftp_message_free(msg);
+        if (rc != SSH_OK) {
+            ssh_set_error(sftp->session,
+                          SSH_ERROR,
+                          "Failed to parse expanded path");
+            sftp_set_error(sftp, SSH_FX_FAILURE);
+            return NULL;
+        }
+
+        return cname;
+    } else if (msg->packet_type == SSH_FXP_STATUS) {
+        status = parse_status_msg(msg);
+        sftp_message_free(msg);
+        if (status == NULL) {
+            return NULL;
+        }
+        sftp_set_error(sftp, status->status);
+        ssh_set_error(sftp->session, SSH_REQUEST_DENIED,
+                      "SFTP server: %s", status->errormsg);
+        status_msg_free(status);
+    } else {
+        ssh_set_error(sftp->session, SSH_FATAL,
+                      "Received message %d when attempting to expand path",
+                      msg->packet_type);
+        sftp_message_free(msg);
+        sftp_set_error(sftp, SSH_FX_BAD_MESSAGE);
+    }
+
+    return NULL;
+}
+
 #endif /* WITH_SFTP */