apps/net: add http connectivity check API

[zs39]

Summary

Add netlib_check_httpconnectivity() to verify HTTP service connectivity by sending GET request and validating status code.

Impact

The new features have no impact.

Testing

Use the demo below for testing. Test passed.

/****************************************************************************
 * apps/examples/hello/hello_main.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

#include <netutils/netlib.h>

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * hello_main
 ****************************************************************************/

int main(int argc, FAR char *argv[])
{
  const char *host = "www.example.com";
  const char *path = "";
  int port = 80;
  int expect_code = 200;
  int ret;

  printf("Hello, World!!\n");
  printf("\n");
  printf("========================================\n");
  printf("HTTP Connectivity Test\n");
  printf("========================================\n");
  printf("\n");

  printf("Testing: http://%s:%d/%s\n", host, port, path);
  printf("Expected HTTP status code: %d\n", expect_code);
  printf("\n");

  printf("Checking HTTP connectivity...\n");
  ret = netlib_check_httpconnectivity(host, path, port, expect_code);

  printf("\n");
  printf("========================================\n");
  if (ret == 0)
    {
      printf("SUCCESS: HTTP connectivity check passed!\n");
      printf("Server returned expected status code: %d\n", expect_code);
    }
  else
    {
      printf("FAILED: HTTP connectivity check failed!\n");
      if (ret < 0)
        {
          if (ret > -1000)
            {
              printf("HTTP Status Code: %d (expected %d)\n",
                     -ret, expect_code);
            }
          else
            {
              printf("Error: %s\n", strerror(-ret));
            }
        }
    }
  printf("========================================\n");

  return (ret == 0) ? 0 : 1;
}

The results are as follows

nsh> hello
Hello, World!!

========================================
HTTP Connectivity Test
========================================

Testing: http://www.example.com:80/
Expected HTTP status code: 200

Checking HTTP connectivity...

========================================
SUCCESS: HTTP connectivity check passed!
Server returned expected status code: 200
========================================

[zs39]

Documentation supplement here
apache/nuttx#17812

[acassis]

@zs39 please fix the typo: nagtive -> negative

[cederom]

Thank you @zs39 :-)

• Are you sure use or return -errno; is always valid? Please take a look at code comments. I think there are functions that does not set global errno and thus return value may be undefined?
• Would it be possible to add example code from the PR to apps/examples please? :-)

[cederom]

Where is errno defined and what sets its value?

Looking at https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/include/errno.h#L43 there is no set_errno(e) in the https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/libs/libc/netdb/lib_getaddrinfo.c#L133.

If getaddrinfo() returns error code by return then why not this?

int ret = getaddrinfo(hostname, NULL, &hint, &info);
id ( ret != OK ) return ret;

[xiaoxiang781216]

@cederom the usage is right, please read https://man7.org/linux/man-pages/man3/errno.3.html, to understand when errno get set.

[cederom]

Similar as above why not return ret ?

[cederom]

@cederom: Where is errno defined and what sets its value?

Looking at https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/include/errno.h#L43 there is no set_errno(e) in the https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/libs/libc/netdb/lib_getaddrinfo.c#L133.

If getaddrinfo() returns error code by return then why not this?

int ret = getaddrinfo(hostname, NULL, &hint, &info);
id ( ret != OK ) return ret;

@xiaoxiang781216: @cederom the usage is right, please read https://man7.org/linux/man-pages/man3/errno.3.html, to understand when errno get set.

I am putting this discussion here so it does not disappear after code comments are closed ;-)

@zs39 please answer my questions about errno handling:

1. Where is errno defined and what sets its value? There are places in getaddrinfo() that will return an error code but does not set errno with set_errno() that is required to use errno as valid error code that you may reference in the caller function.
2. If getaddrinfo() returns error code by return then why not return ret instead return -errno?

Lets take a looks at your proposition netutils/netlib/netlib_checkhttpconnectivity.c line 76:

 if (getaddrinfo(hostname, NULL, &hint, &info) != OK)
    {
      return -errno;
    }

You are not getting and returning code of getaddrinfo(). Instead when getaddrinfo() fails you return -errno that does not reflect error code returned.

Let's go to that function (https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/libs/libc/netdb/lib_getaddrinfo.c#L133) and see first check (https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/libs/libc/netdb/lib_getaddrinfo.c#L151):

  if (hostname == NULL && servname == NULL)
    {
      return EAI_NONAME;
    }

I cannot see set_errno() here (https://github.com/apache/nuttx/blob/fac76746eae2afe91a5cb9948e3843596c9f941f/include/errno.h#L44) thus in the call above you will not forward EAI_NONAME but some random errno that was probably set before by something else.

If you look at existing code use of getaddrinfo() in the apps (https://github.com/search?q=repo%3Aapache%2Fnuttx-apps%20getaddrinfo&type=code) there are use cases like:

1. Return ERROR=-1 when getaddrinfo() fails, see:

   nuttx-apps/netutils/ping/icmpv6_ping.c

   Line 119 in 63f61d0

   if (getaddrinfo(hostname, NULL, &hint, &info) != OK)

2. Convert ret = getaddrinfo() to get string error, see:

   nuttx-apps/examples/ftpc/ftpc_main.c

   Line 444 in 63f61d0

   ret = getaddrinfo(host, port, &hints, &info);

3. Both (1) and (2) above ret is used to get error strting and ERROR=-1 is returned, see:

   nuttx-apps/nshlib/nsh_netcmds.c

   Line 1172 in 63f61d0

   ret = getaddrinfo(argv[1], NULL, NULL, &info);

Once again, your implementation is prone to returning errno set somewhere else instead valid return code from getaddrinfo().

I would advise update to something like existing examples (1,2,3) above use:

int ret = getaddrinfo(hostname, NULL, &hint, &info);
if ( ret != OK ) return ret;

The only valid use of errno may be for socket() [1] as it known to set it explicitly. But it's not for getaddrinfo() [2].

[1] https://man.freebsd.org/cgi/man.cgi?query=socket&apropos=0&sektion=0
[2] https://man.freebsd.org/cgi/man.cgi?query=getaddrinfo&apropos=0&sektion=3