I'm trying to communicate with a C library from Go using Google Protocol Buffers, but I can't make it work. I'm facing an error trying to send the protobuf into the C library
I'll post the minimum code to reproduce the error I'm facing right now (I've removed most of the C part as it is not relevant for this error):
/*
#cgo CFLAGS: -I@CURRENT_SOURCE_DIR@/../../library/crnd/include -
I@CMAKE_CURRENT_BINARY_DIR@/../../library
#cgo LDFLAGS: -L@CRND_LIBRARY_PATH@ -lcrnd
#include <api_c.h>
#include <stdint.h>
#include <stdio.h>
#include <inttypes.h>
typedef struct SerializedStruct {
void* data;
int64_t size;
} Serialized;
*/
import "C"
func (crnd wrapper) MyFunction() {
// Create a protobuf
sample_request := &messages.SampleRequest { ... add members ...}
fmt.Printf(proto.MarshalTextString(sample_request)); // print the message to check it works
data, err := proto.Marshal(sample_request)
if err != nil {
log.Fatal("marshaling error: ", err)
}
sample_request_serialized := C.Serialized {
data: pointer.Save(data),
size: C.int64_t(len(data)),
}
// Here I would send my protobuf to the C library, but it is not
// working, so I'm trying to reconstruct the protobuf to check
// if something is broken before getting to the C side
// Let's reconstruct the protobuf back
data_req := (*[1 << 30]byte)(sample_request_serialized.data)[:int(sample_request_serialized.size):int(sample_request_serialized.size)]
sample_req := &messages.SampleRequest{}
err := proto.Unmarshal(data_req, sample_req)
if err != nil {
log.Fatal("unmarshaling error: ", err)
}
}
I get the following error:
unmarshaling error: proto: crnd.SampleRequest: illegal tag 0 (wire type 0)
I managed to make it work creating a copy of the buffer (taken from this question):
...
p := C.malloc(C.size_t(len(data)))
defer C.free(p)
cBuf := (*[1 << 30]byte)(p)
copy(cBuf[:], data)
sample_request_serialized := &C.Serialized {
data: p,
size: C.int64_t(len(data)),
}