Http client request within a RESTful server

[f4r4]

• My goal is: To understand mongoose http client requests
• My question is: I have a Restful server built using mongoose and I want to send a client http request to another server,
  I am using a new event manager (mgr) to do the request, I got the code from this example but still I have the issue of operation in progress could anyone please advice

0 3 mongoose.c:4219:write_conn          1 0x5 113:0 113 err 115 (Operation now in progress)
0 3 mongoose.c:4208:read_conn           1 0x5 0:0 211 err 115 (Operation now in progress)

my server code

• main calls fn
• fn calls client call client_request
• client_request calls fnpost

// The very first web page in history. You can replace it from command line
static const char *s_url = "127.0.0.1:3000";
static const char *s_post_data = NULL;      // POST data
static const uint64_t s_timeout_ms = 1500;  // Connect timeout in milliseconds

// Print HTTP response and signal that we're done
void fnpost(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  if (ev == MG_EV_OPEN) {
    // Connection created. Store connect expiration time in c->label
    *(uint64_t *) c->label = mg_millis() + s_timeout_ms;
  } else if (ev == MG_EV_POLL) {
    if (mg_millis() > *(uint64_t *) c->label &&
        (c->is_connecting || c->is_resolving)) {
      mg_error(c, "Connect timeout");
    }
  } else if (ev == MG_EV_CONNECT) {
    // Connected to server. Extract host name from URL
    struct mg_str host = mg_url_host(s_url);

    mjson_printf(&mjson_print_dynamic_buf, &s_post_data, "{\"result\": \"%s\"}\n", "new_data");

    // Send request
    int content_length = s_post_data ? strlen(s_post_data) : 0;
    mg_printf(c,
              "%s %s HTTP/1.0\r\n"
              "Host: %.*s\r\n"
              "Content-Type: application/json\r\n"
              "Content-Length: %d\r\n"
              "\r\n",
              s_post_data ? "POST" : "GET", mg_url_uri(s_url), (int) host.len,
              host.ptr, content_length);
    mg_send(c, s_post_data, content_length);
    //free(s_post_data);
  } else if (ev == MG_EV_HTTP_MSG) {
    // Response is received. Print it
    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
    printf("%.*s\n", (int) hm->message.len, hm->message.ptr);
    c->is_closing = 1;         // Tell mongoose to close this connection
    *(bool *) fn_data = true;  // Tell event loop to stop
  } else if (ev == MG_EV_ERROR) {
    *(bool *) fn_data = true;  // Error, tell event loop to stop
  }
}

void client_request(){
  mg_log_set("3");          // Set to 0 to disable debug
  mg_mgr_init(&mgr);              // Initialise event manager
  mg_http_connect(&mgr, s_url, fnpost, &done);  // Create client connection
  while (!done) mg_mgr_poll(&mgr, 50);      // Event manager loops until 'done'
  mg_mgr_free(&mgr);                        // Free resources
}


static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
   (void)fn_data;
   if (ev == MG_EV_HTTP_MSG) {
      struct mg_http_message *hm = (struct mg_http_message *) ev_data;
      if(mg_http_match_uri(hm, "/api/version")){
        //some other code and I execute
        char *s = NULL;
        mjson_printf(&mjson_print_dynamic_buf, &s, "{\"result\": \"%s\"}\n", "1.0.0-beta");
        mg_http_reply(c, 200, "Content-Type: application/json\r\n", s);
        free(s);

        client_request();
      }
 }

int main(void) {
  struct mg_mgr mgr;
  mg_log_set("3");
  mg_mgr_init(&mgr);                                        // Init manager
  mg_http_listen(&mgr, "http://0.0.0.0:8010", fn, &mgr);  // Setup listener
  for (;;) mg_mgr_poll(&mgr, 1000);                         // Event loop
  mg_mgr_free(&mgr);                                        // Cleanup
  return 0;
}

Please advice

Environment

• mongoose version: 7.7
• Compiler/IDE and SDK: GCC 4.9.2
• Target hardware/board: x86

[scaprile]

No example uses more than one event manager
Check how the reverse proxy example solves it, tutorial here

[f4r4]

Used one event manager and came up with this script still I have the issue of Operation in progress but getting the desired result
the question I have is whats the best practice ? using one event manager and two connections ?

please advice

#include "mongoose.h"

static const char *s_listen_url = "http://localhost:8000";
static const char *s_req_url = "http://127.0.0.1:3000";
static const uint64_t s_timeout_ms = 1500;  // Connect timeout in milliseconds

static void fn2(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  const char *s_post_data = "{\"hi\":\"hix\"}";      // POST data

  if (ev == MG_EV_OPEN) {
    // Connection created. Store connect expiration time in c->label
    *(uint64_t *) c->label = mg_millis() + s_timeout_ms;
  } else if (ev == MG_EV_POLL) {
    if (mg_millis() > *(uint64_t *) c->label &&
        (c->is_connecting || c->is_resolving)) {
      mg_error(c, "Connect timeout");
    }
  } else if (ev == MG_EV_CONNECT) {
    // Connected to server. Extract host name from URL
    struct mg_str host = mg_url_host(s_req_url);

    // Send request
    int content_length = s_post_data ? strlen(s_post_data) : 0;
    mg_printf(c,
              "%s %s HTTP/1.0\r\n"
              "Host: %.*s\r\n"
              "Content-Type: application/json\r\n"
              "Content-Length: %d\r\n"
              "\r\n",
              s_post_data ? "POST" : "GET", mg_url_uri(s_url), (int) host.len,
              host.ptr, content_length);
    mg_send(c, s_post_data, content_length);
  } else if (ev == MG_EV_HTTP_MSG) {
    // Response is received. Print it
    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
    printf("%.*s", (int) hm->message.len, hm->message.ptr);
    c->is_closing = 1;         // Tell mongoose to close this connection
    *(bool *) fn_data = true;  // Tell event loop to stop
  } else if (ev == MG_EV_ERROR) {
    *(bool *) fn_data = true;  // Error, tell event loop to stop
  }
}

static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  struct mg_connection *c2 = fn_data;
  if (ev == MG_EV_HTTP_MSG) {
    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
    if (mg_http_match_uri(hm, "/")) {
      
      //-------------------------------------------------------------------------------------------- SUB REQUEST
      bool done = false;              // Event handler flips it to true
      mg_http_connect(c->mgr, s_req_url, fn2, &done);
      while (!done) mg_mgr_poll(c->mgr, 50);      // Event manager loops until 'done'
      //--------------------------------------------------------------------------------------------

      mg_http_reply(c, 200, "Content-Type: application/json\r\n", "{\"res\":\"res\"}\n");
    }

  } else if (ev == MG_EV_CLOSE) {
    if (c2 != NULL) c2->is_closing = 1;
    if (c2 != NULL) c2->fn_data = NULL;
  }
}

int main(void) {
  struct mg_mgr mgr;

  mg_log_set("3");                       // Set log level
  mg_mgr_init(&mgr);                             // Initialise event manager
  mg_http_listen(&mgr, s_listen_url, fn, NULL);  // Start proxy
  for (;;) mg_mgr_poll(&mgr, 1000);              // Event loop
  mg_mgr_free(&mgr);

  return 0;
}

0 3 mongoose.c:3570:mg_listen           1 0x3 http://localhost:8000
0 3 mongoose.c:4321:accept_conn         2 accepted 127.0.0.1:47666
0 3 mongoose.c:4213:read_conn           2 0x4 0:0 586 err 0 (Success)
0 3 mongoose.c:3548:mg_connect          3 -1 127.0.0.1:3000
0 3 mongoose.c:4278:mg_connect_resolved 3 0x5 connect in progress...
0 3 mongoose.c:4224:write_conn          3 0x5 100:0 100 err 115 (Operation now in progress)
0 3 mongoose.c:4213:read_conn           3 0x5 0:0 212 err 115 (Operation now in progress)
HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 13
ETag: W/"d-oLZZOWcLwsAQ9NXWoLPk5FkPuSs"
Date: Wed, 03 Aug 2022 16:32:59 GMT
Connection: close

Hello World!(response from the server)
0 3 mongoose.c:3525:mg_close_conn       3 closed
0 3 mongoose.c:4224:write_conn          2 0x4 85:0 85 err 115 (Operation now in progress)

[scaprile]

I see a loop calling the event manager from within an event handler. No example does that. Please follow the guidelines in the documentation and the tutorial linked above.

If you need to wait for a client response to generate your server response, and for some reason that has to be done from within the server event handler, then implement a finite state machine in your server handler and use the MG_EV_POLL event (read the documentation) to check if the response is ready. The easiest way is to follow the tutorial and example and send the response from within the client event handler, as the linked example does.

If there is something that you can't do, please describe it with the smallest piece of code possible.

If you think an example can be useful, please describe what you want to achieve that is not covered in any of the examples and tutorials available.

[f4r4]

Thanks for the answer, I will go through the docs again to understand more
I have one could you please advice on the best method to pass data to the event handler