Add context propagation to rclone

- Change rclone/fs interfaces to accept context.Context
- Update interface implementations to use context.Context
- Change top level usage to propagate context to lover level functions

Context propagation is needed for stopping transfers and passing other
request-scoped values.

fs/config/rc.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"context"
+
 	"github.com/ncw/rclone/fs"
 	"github.com/ncw/rclone/fs/rc"
 )
@@ -23,7 +25,7 @@ See the [config dump command](/commands/rclone_config_dump/) command for more in
 }
 
 // Return the config file dump
-func rcDump(in rc.Params) (out rc.Params, err error) {
+func rcDump(ctx context.Context, in rc.Params) (out rc.Params, err error) {
 	return DumpRcBlob(), nil
 }
 
@@ -43,7 +45,7 @@ See the [config dump command](/commands/rclone_config_dump/) command for more in
 }
 
 // Return the config file get
-func rcGet(in rc.Params) (out rc.Params, err error) {
+func rcGet(ctx context.Context, in rc.Params) (out rc.Params, err error) {
 	name, err := in.GetString("name")
 	if err != nil {
 		return nil, err
@@ -67,7 +69,7 @@ See the [listremotes command](/commands/rclone_listremotes/) command for more in
 }
 
 // Return the a list of remotes in the config file
-func rcListRemotes(in rc.Params) (out rc.Params, err error) {
+func rcListRemotes(ctx context.Context, in rc.Params) (out rc.Params, err error) {
 	var remotes = []string{}
 	for _, remote := range getConfigData().GetSectionList() {
 		remotes = append(remotes, remote)
@@ -94,7 +96,7 @@ See the [config providers command](/commands/rclone_config_providers/) command f
 }
 
 // Return the config file providers
-func rcProviders(in rc.Params) (out rc.Params, err error) {
+func rcProviders(ctx context.Context, in rc.Params) (out rc.Params, err error) {
 	out = rc.Params{
 		"providers": fs.Registry,
 	}
@@ -111,8 +113,8 @@ func init() {
 		rc.Add(rc.Call{
 			Path:         "config/" + name,
 			AuthRequired: true,
-			Fn: func(in rc.Params) (rc.Params, error) {
-				return rcConfig(in, name)
+			Fn: func(ctx context.Context, in rc.Params) (rc.Params, error) {
+				return rcConfig(ctx, in, name)
 			},
 			Title: name + " the config for a remote.",
 			Help: `This takes the following parameters
@@ -126,7 +128,7 @@ See the [config ` + name + ` command](/commands/rclone_config_` + name + `/) com
 }
 
 // Manipulate the config file
-func rcConfig(in rc.Params, what string) (out rc.Params, err error) {
+func rcConfig(ctx context.Context, in rc.Params, what string) (out rc.Params, err error) {
 	name, err := in.GetString("name")
 	if err != nil {
 		return nil, err
@@ -167,7 +169,7 @@ See the [config delete command](/commands/rclone_config_delete/) command for mor
 }
 
 // Return the config file delete
-func rcDelete(in rc.Params) (out rc.Params, err error) {
+func rcDelete(ctx context.Context, in rc.Params) (out rc.Params, err error) {
 	name, err := in.GetString("name")
 	if err != nil {
 		return nil, err

fs/config/rc_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"context"
 	"testing"
 
 	_ "github.com/ncw/rclone/backend/local"
@@ -24,7 +25,7 @@ func TestRc(t *testing.T) {
 			"test_key": "sausage",
 		},
 	}
-	out, err := call.Fn(in)
+	out, err := call.Fn(context.Background(), in)
 	require.NoError(t, err)
 	require.Nil(t, out)
 	assert.Equal(t, "local", FileGet(testName, "type"))
@@ -37,7 +38,7 @@ func TestRc(t *testing.T) {
 		call := rc.Calls.Get("config/dump")
 		assert.NotNil(t, call)
 		in := rc.Params{}
-		out, err := call.Fn(in)
+		out, err := call.Fn(context.Background(), in)
 		require.NoError(t, err)
 		require.NotNil(t, out)
 
@@ -54,7 +55,7 @@ func TestRc(t *testing.T) {
 		in := rc.Params{
 			"name": testName,
 		}
-		out, err := call.Fn(in)
+		out, err := call.Fn(context.Background(), in)
 		require.NoError(t, err)
 		require.NotNil(t, out)
 
@@ -66,7 +67,7 @@ func TestRc(t *testing.T) {
 		call := rc.Calls.Get("config/listremotes")
 		assert.NotNil(t, call)
 		in := rc.Params{}
-		out, err := call.Fn(in)
+		out, err := call.Fn(context.Background(), in)
 		require.NoError(t, err)
 		require.NotNil(t, out)
 
@@ -87,7 +88,7 @@ func TestRc(t *testing.T) {
 				"test_key2": "cabbage",
 			},
 		}
-		out, err := call.Fn(in)
+		out, err := call.Fn(context.Background(), in)
 		require.NoError(t, err)
 		assert.Nil(t, out)
 
@@ -106,7 +107,7 @@ func TestRc(t *testing.T) {
 				"test_key2": "cabbage",
 			},
 		}
-		out, err := call.Fn(in)
+		out, err := call.Fn(context.Background(), in)
 		require.NoError(t, err)
 		assert.Nil(t, out)
 
@@ -121,7 +122,7 @@ func TestRc(t *testing.T) {
 	in = rc.Params{
 		"name": testName,
 	}
-	out, err = call.Fn(in)
+	out, err = call.Fn(context.Background(), in)
 	require.NoError(t, err)
 	assert.Nil(t, out)
 	assert.Equal(t, "", FileGet(testName, "type"))
@@ -132,7 +133,7 @@ func TestRcProviders(t *testing.T) {
 	call := rc.Calls.Get("config/providers")
 	assert.NotNil(t, call)
 	in := rc.Params{}
-	out, err := call.Fn(in)
+	out, err := call.Fn(context.Background(), in)
 	require.NoError(t, err)
 	require.NotNil(t, out)
 	var registry []*fs.RegInfo