capi: fix sample Golang client (#1956)

Fix the init settings in our Go sample code using the C API library and improve error handling.

cmd/capi/sample-go-client/main.go

@@ -4,21 +4,51 @@ package main
 // #cgo LDFLAGS: -L${SRCDIR}/../../../build/silkworm/capi
 // #cgo LDFLAGS: -Wl,-rpath ${SRCDIR}/../../../build/silkworm/capi
 // #cgo CFLAGS: -I${SRCDIR}/../../../silkworm/capi
-// #include "silkworm.h"
+/*
+#include "silkworm.h"
+#include <stdlib.h>
+#include <string.h>
+
+static bool go_string_copy(_GoString_ s, char *dest, size_t size) {
+	size_t len = _GoStringLen(s);
+	if (len >= size) return false;
+	const char *src = _GoStringPtr(s);
+	strncpy(dest, src, len);
+	dest[len] = '\0';
+	return true;
+}
+*/
 import "C"
 
 import "fmt"
 import "os"
 
 func main() {
+	dataDirPath := os.Getenv("HOME")
+	libMdbxVersion := C.GoString(C.silkworm_libmdbx_version())
+
 	var handle C.SilkwormHandle
 	settings := &C.struct_SilkwormSettings{}
-	if C.silkworm_init(&handle, settings) != C.SILKWORM_OK {
-		fmt.Fprintln(os.Stderr, "silkworm_init failed")
-		return
+	if !C.go_string_copy(dataDirPath, &settings.data_dir_path[0], C.SILKWORM_PATH_SIZE) {
+		fmt.Fprintln(os.Stderr, "silkworm.New failed to copy dataDirPath")
+		os.Exit(1)
+	}
+	if !C.go_string_copy(libMdbxVersion, &settings.libmdbx_version[0], C.SILKWORM_GIT_VERSION_SIZE) {
+		fmt.Fprintln(os.Stderr, "silkworm.New failed to copy libMdbxVersion")
+		os.Exit(2)
 	}
-	if C.silkworm_fini(handle) != C.SILKWORM_OK {
-		fmt.Fprintln(os.Stderr, "silkworm_fini failed")
-		return
+
+	initResult := C.silkworm_init(&handle, settings)
+	if initResult != C.SILKWORM_OK {
+		fmt.Fprintln(os.Stderr, "silkworm_init failed:", initResult)
+		os.Exit(int(initResult))
+	}
+
+	finiResult := C.silkworm_fini(handle)
+	if finiResult != C.SILKWORM_OK {
+		fmt.Fprintln(os.Stderr, "silkworm_fini failed:", finiResult)
+		os.Exit(int(finiResult))
 	}
+
+	os.Exit(0)
 }