librclone: change interface for C code and add Mobile interface #4891

This changes the interface for the C code to return a struct on the
stack that is defined in the code rather than one which is defined by
the cgo compiler. This is more future proof and inline with the
gomobile interface.

This also adds a gomobile interface RcloneMobileRPC which uses generic
go types conforming to the gobind restrictions.

It also fixes up initialisation errors.

librclone/ctest/ctest.c

@@ -5,10 +5,10 @@
 #include "librclone.h"
 
 void testRPC(char *method, char *in) {
-    struct RcloneRPC_return out = RcloneRPC(method, in);
-    printf("status: %d\n", out.r1);
-    printf("output: %s\n", out.r0);
-    free(out.r0);
+    struct RcloneRPCResult out = RcloneRPC(method, in);
+    printf("status: %d\n", out.Status);
+    printf("output: %s\n", out.Output);
+    free(out.Output);
 }
 
 // noop command

librclone/librclone.go

@@ -19,9 +19,15 @@
 // The library will depend on `libdl` and `libpthread`.
 package main
 
-import (
-	"C"
+/*
+struct RcloneRPCResult {
+	char*	Output;
+	int	Status;
+};
+*/
+import "C"
 
+import (
 	"context"
 	"encoding/json"
 	"fmt"
@@ -31,6 +37,9 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/accounting"
+	"github.com/rclone/rclone/fs/config/configfile"
+	"github.com/rclone/rclone/fs/log"
 	"github.com/rclone/rclone/fs/rc"
 	"github.com/rclone/rclone/fs/rc/jobs"
 
@@ -42,7 +51,19 @@ import (
 //
 //export RcloneInitialize
 func RcloneInitialize() {
-	// TODO: what need to be initialized manually?
+	// A subset of initialisation copied from cmd.go
+	// Note that we don't want to pull in anything which depends on pflags
+
+	ctx := context.Background()
+
+	// Start the logger
+	log.InitLogging()
+
+	// Load the config - this may need to be configurable
+	configfile.Install()
+
+	// Start accounting
+	accounting.Start(ctx)
 }
 
 // RcloneFinalize finalizes the library
@@ -54,50 +75,73 @@ func RcloneFinalize() {
 	runtime.GC()
 }
 
+// RcloneRPCResult is returned from RcloneRPC
+//
+//   Output will be returned as a serialized JSON object
+//   Status is a HTTP status return (200=OK anything else fail)
+type RcloneRPCResult struct {
+	Output *C.char
+	Status C.int
+}
+
 // RcloneRPC does a single RPC call. The inputs are (method, input)
 // and the output is (output, status). This is an exported interface
 // to the rclone API as described in https://rclone.org/rc/
 //
 //   method is a string, eg "operations/list"
 //   input should be a serialized JSON object
-//   output will be returned as a serialized JSON object
-//   status is a HTTP status return (200=OK anything else fail)
+//   result.Output will be returned as a serialized JSON object
+//   result.Status is a HTTP status return (200=OK anything else fail)
 //
-// Caller is responsible for freeing the memory for output
-//
-// Note that when calling from C output and status are returned in an
-// RcloneRPC_return which has two members r0 which is output and r1
-// which is status.
+// Caller is responsible for freeing the memory for result.Output,
+// result itself is passed on the stack.
 //
 //export RcloneRPC
-func RcloneRPC(method *C.char, input *C.char) (output *C.char, status C.int) { //nolint:golint
-	res, s := callFunctionJSON(C.GoString(method), C.GoString(input))
-	return C.CString(res), C.int(s)
+func RcloneRPC(method *C.char, input *C.char) (result C.struct_RcloneRPCResult) { //nolint:golint
+	output, status := callFunctionJSON(C.GoString(method), C.GoString(input))
+	result.Output = C.CString(output)
+	result.Status = C.int(status)
+	return result
+}
+
+// RcloneMobileRPCResult is returned from RcloneMobileRPC
+//
+//   Output will be returned as a serialized JSON object
+//   Status is a HTTP status return (200=OK anything else fail)
+type RcloneMobileRPCResult struct {
+	Output string
+	Status int
+}
+
+// RcloneMobileRPCRPC this works the same as RcloneRPC but has an interface
+// optimised for gomobile, in particular the function signature is
+// valid under gobind rules.
+//
+// https://pkg.go.dev/golang.org/x/mobile/cmd/gobind#hdr-Type_restrictions
+func RcloneMobileRPCRPC(method string, input string) (result RcloneMobileRPCResult) {
+	output, status := callFunctionJSON(method, input)
+	result.Output = output
+	result.Status = status
+	return result
 }
 
 // writeError returns a formatted error string and the status passed in
 func writeError(path string, in rc.Params, err error, status int) (string, int) {
 	fs.Errorf(nil, "rc: %q: error: %v", path, err)
+	params, status := rc.Error(path, in, err, status)
 	var w strings.Builder
-	// FIXME should factor this
-	// Adjust the error return for some well known errors
-	errOrig := errors.Cause(err)
-	switch {
-	case errOrig == fs.ErrorDirNotFound || errOrig == fs.ErrorObjectNotFound:
-		status = http.StatusNotFound
-	case rc.IsErrParamInvalid(err) || rc.IsErrParamNotFound(err):
-		status = http.StatusBadRequest
-	}
-	// w.WriteHeader(status)
-	err = rc.WriteJSON(&w, rc.Params{
-		"status": status,
-		"error":  err.Error(),
-		"input":  in,
-		"path":   path,
-	})
+	err = rc.WriteJSON(&w, params)
 	if err != nil {
-		// can't return the error at this point
-		return fmt.Sprintf(`{"error": "rc: failed to write JSON output: %v"}`, err), status
+		// ultimate fallback error
+		fs.Errorf(nil, "writeError: failed to write JSON output from %#v: %v", in, err)
+		status = http.StatusInternalServerError
+		w.Reset()
+		fmt.Fprintf(&w, `{
+	"error": %q,
+	"path": %q,
+	"status": %d
+}`, err, path, status)
+
 	}
 	return w.String(), status
 }
@@ -110,7 +154,6 @@ func callFunctionJSON(method string, input string) (output string, status int) {
 	in := make(rc.Params)
 	err := json.NewDecoder(strings.NewReader(input)).Decode(&in)
 	if err != nil {
-		// TODO: handle error
 		return writeError(method, in, errors.Wrap(err, "failed to read input JSON"), http.StatusBadRequest)
 	}
 
@@ -132,10 +175,9 @@ func callFunctionJSON(method string, input string) (output string, status int) {
 	}
 
 	fs.Debugf(nil, "rc: %q: with parameters %+v", method, in)
-	// TODO: what is r.Context()? use Background() for the moment
+
 	_, out, err := jobs.NewJob(context.Background(), call.Fn, in)
 	if err != nil {
-		// handle error
 		return writeError(method, in, err, http.StatusInternalServerError)
 	}
 	if out == nil {
@@ -150,6 +192,7 @@ func callFunctionJSON(method string, input string) (output string, status int) {
 		fs.Errorf(nil, "rc: failed to write JSON output: %v", err)
 		return writeError(method, in, err, http.StatusInternalServerError)
 	}
+
 	return w.String(), http.StatusOK
 }