Publish messages from C++ using gRPC

[Manuel Bergler]

Hi everyone,

I'm trying to publish messages to Google PubSub topic from a C++ application. So far I've been able to get it to work with the emulator, but when trying to send messages to Google's API, the gRPC request always fails with error 14: Endpoint read failed.

I suspect that I'm not authenticating correctly. So far I've created a service account that is allowed to publish, and I've set GOOGLE_APPLICATION_CREDENTIALS to point to the .json file with the credentials.

My code looks like this:

#include <iostream>
#include <memory>

#include <grpc++/grpc++.h>

#include "google/pubsub/v1/pubsub.grpc.pb.h"

auto main() -> int {
    using grpc::ClientContext;
    using google::pubsub::v1::Publisher;
    using google::pubsub::v1::PublishRequest;
    using google::pubsub::v1::PublishResponse;
    using google::pubsub::v1::PubsubMessage;

    auto creds = grpc::GoogleDefaultCredentials();
    auto stub = std::make_unique<Publisher::Stub>(grpc::CreateChannel("pubsub.googleapis.com", creds));

    PublishRequest request;
    auto const topic_string = "projects/pubsub-cpp-api-1504713535863/topics/testing";
    request.set_topic(topic_string);
    PubsubMessage msg;
    msg.set_data("Hello from C++");
    *request.add_messages() = msg;

    PublishResponse response;
    ClientContext ctx;

    auto status = stub->Publish(&ctx, request, &response);
    if (!status.ok()) {
        std::cout << "Publishing message failed with error " + std::to_string(status.error_code()) + ": " + status.error_message() << '\n';
    }
}

What am I missing?

Best regards

Manuel 

[Alex Mordkovich]

Hi Manuel,

Error code 14 is "UNAVAILABLE": https://grpc.io/grpc/cpp/namespacegrpc.html#enum-members, so this is not an auth issue. See also https://www.google.com/search?q=%2214%3A+Endpoint+read+failed%22.

Check your client for connectivity issues, and make sure that it's talking to the https endpoint: https://pubsub.googleapis.com/

Cheers,

Alex

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[Manuel Bergler]

Am Donnerstag, 7. September 2017 16:40:25 UTC+2 schrieb Alex Mordkovich:

Hi Manuel,

Error code 14 is "UNAVAILABLE": https://grpc.io/grpc/cpp/namespacegrpc.html#enum-members, so this is not an auth issue. See also https://www.google.com/search?q=%2214%3A+Endpoint+read+failed%22.

Check your client for connectivity issues, and make sure that it's talking to the https endpoint: https://pubsub.googleapis.com/

Using "https://pubsub.googleapis.com" in the call to `grpc::CreateChannel` doesn't work, as it causes DNS resolution to fail with error message "Servname not supported for ai_socktype".

I've used wireshark now to verify that gRPC uses https, which it does. The same wireshark capture also shows that pubsub.googleapis.com responded, but also revealed an TLS alert (Level: Fatal, Description: Protocol Version). Do I need to add a specific cipher to GRPC_SSL_CIPHER_SUITES?

[Manuel Bergler]

Ok, I'm stupid. I linked against gRPC::grpc++_unsecure as I simply copied and then modified the CMakeLists.txt from one of the examples. Linking against gRPC::grpc++ fixed the problem.