mongo_client() fail with error MONGO_CONN_ADDR_FAIL - c

Question

I want to use mongodb c driver in my project, I'm on Windows 7 so built it with command :
scons --m32 --c99
My problem is I can't make the Connecting example work :
#include <stdio.h>
#define MONGO_HAVE_STDINT
#include "mongo.h"
int main() {
mongo conn[1];
int status = mongo_client( conn, "127.0.0.1", 27017 );
printf("status %d, err %d", status, conn->err);
mongo_destroy( conn );
return 0;
}
Whether mongod is running on my machine or not, the output of executing the exe is :
$ ./mongodb_example.exe
status -1, err 3
Error 3 corresponds to MONGO_CONN_ADDR_FAIL error code (An error occured while calling getaddrinfo()).
Any suggestion about how to connect successfully ?
Updates:
version is mongodb-mongo-c-driver-v0.8.1-0-g8f27c0f

Answer 1

So there are two things you need to do to make this work:
When building with scons, you need to make sure you that you enable the "standard-env" target like so:
scons --m32 --standard-env
Secondly in your code and in addition to the MONGO_HAVE_STDINT that you already have, make sure you call mongo_init_sockets() before establishing a connection. This is required on windows.
#include <stdio.h>
#define MONGO_HAVE_STDINT
#include "mongo.h"
int main() {
mongo_init_sockets();
mongo conn[1];
int status = mongo_client( conn, "192.168.2.7", 27017 );
printf("status %d, err %d", status, conn->err);
mongo_destroy( conn );
return 0;
}
So the first part resolves the issue with getaddrinfo() there is an implementation included in the "standard environment". And the second part is a necessary "winsock" initialization that is required on Windows platforms. In the test files this is implemented with a defined macro.
Also make sure you are using a Python 2.7 32bit (not 64bit) as well. Not too sure how valid that is on a current scons release, but it doesn't hurt to be sure.
Some of this is in the documentation you may have missed here, as is the fairly apt description of the mongo_init_sockets() function in the API documentation. Of course, looking at the test files in the distribution did not hurt.
And a little pain for me, as I don't normally build C programs on Windows.

Answer 2

You can get the exact reason of the mongo failure if you print
conn->errcode
conn->errstr
The errcode is the equivalent of errno in linux or GetLastError in Windows.
The errstr will contain the same as a string. So you shall see something like getaddrinfo failed with error <the return status of getaddrinfo>
There could be multiple reasons why getaddrinfo might fail in your system. You can get these values from the man page man gai_strerror (errstr should report this)
EAI_AGAIN temporary failure in name resolution
EAI_BADFLAGS invalid value for ai_flags
EAI_BADHINTS invalid value for hints
EAI_FAIL non-recoverable failure in name resolution
EAI_FAMILY ai_family not supported
EAI_MEMORY memory allocation failure
EAI_NONAME hostname or servname not provided, or not known
EAI_OVERFLOW argument buffer overflow
EAI_PROTOCOL resolved protocol is unknown
EAI_SERVICE servname not supported for ai_socktype
EAI_SOCKTYPE ai_socktype not supported
EAI_SYSTEM system error returned in errno

Answer 3

I haven't used the mongodb c driver, so this is just a guess. From the tutorial, it looks like you skipped the initialization step:
http://api.mongodb.org/c/current/tutorial.html
mongo conn[1];
mongo_init( conn );
...
mongo_client( conn, "127.0.0.1", 27017 );