C API

init_dora_context_from_env

init_dora_context_from_env initiate a node from environment variables set by dora-coordinator

void *dora_context = init_dora_context_from_env();

dora_next_event

dora_next_event waits for the next event (e.g. an input). Use read_dora_event_type to read the event's type. Inputs are of type DoraEventType_Input. To extract the ID and data of an input event, use read_dora_input_id and read_dora_input_data on the returned pointer. It is safe to ignore any events and handle only the events that are relevant to the node.

void *input = dora_next_input(dora_context);

// read out the ID as a UTF8-encoded string
char *id;
size_t id_len;
read_dora_input_id(input, &id, &id_len);

// read out the data as a byte array
char *data;
size_t data_len;
read_dora_input_data(input, &data, &data_len);

dora_send_output

dora_send_output send data from the node.

char out_id[] = "tick";
char out_data[50];
dora_send_output(dora_context, out_id, strlen(out_id), out_data, out_data_len);

Try it out!

• Create an node.c file:

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "../../apis/c/node/node_api.h"

// sleep
#ifdef _WIN32
#include <Windows.h>
#else
#include <unistd.h>
#endif

int main()
{
    printf("[c node] Hello World\n");

    void *dora_context = init_dora_context_from_env();
    if (dora_context == NULL)
    {
        fprintf(stderr, "failed to init dora context\n");
        return -1;
    }

    printf("[c node] dora context initialized\n");

    for (char i = 0; i < 100; i++)
    {
        void *event = dora_next_event(dora_context);
        if (event == NULL)
        {
            printf("[c node] ERROR: unexpected end of event\n");
            return -1;
        }

        enum DoraEventType ty = read_dora_event_type(event);

        if (ty == DoraEventType_Input)
        {
            char *data;
            size_t data_len;
            read_dora_input_data(event, &data, &data_len);

            assert(data_len == 0);

            char out_id[] = "message";
            char out_data[50];
            int out_data_len = sprintf(out_data, "loop iteration %d", i);

            dora_send_output(dora_context, out_id, strlen(out_id), out_data, out_data_len);
        }
        else if (ty == DoraEventType_Stop)
        {
            printf("[c node] received stop event\n");
        }
        else
        {
            printf("[c node] received unexpected event: %d\n", ty);
        }

        free_dora_event(event);
    }

    printf("[c node] received 10 events\n");

    free_dora_context(dora_context);

    printf("[c node] finished successfully\n");

    return 0;
}

Build the custom nodes:

• Create a build folder in this directory (i.e., next to the node.c file)
• Compile the dora-node-api-c crate into a static library.
  • Run cargo build -p dora-node-api-c --release
  • The resulting staticlib is then available under ../../target/release/libdora-node-api-c.a.
• Compile the node.c (e.g. using clang) and link the staticlib
  • For example, use the following command:

    clang node.c <FLAGS> -ldora_node_api_c -L ../../target/release --output build/c_node

  • The <FLAGS> depend on the operating system and the libraries that the C node uses. The following flags are required for each OS:
    • Linux: -lm -lrt -ldl -pthread
    • macOS: -framework CoreServices -framework Security -l System -l resolv -l pthread -l c -l m
    • Windows:

      -ladvapi32 -luserenv -lkernel32 -lws2_32 -lbcrypt -lncrypt -lschannel -lntdll -liphlpapi
      -lcfgmgr32 -lcredui -lcrypt32 -lcryptnet -lfwpuclnt -lgdi32 -lmsimg32 -lmswsock -lole32
      -lopengl32 -lsecur32 -lshell32 -lsynchronization -luser32 -lwinspool
      -Wl,-nodefaultlib:libcmt -D_DLL -lmsvcrt

      Also: On Windows, the output file should have an .exe extension: --output build/c_node.exe
• Repeat the previous step for the sink.c executable