Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

fs/fserrors/error_test.go

@@ -0,0 +1,119 @@
+package fserrors
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"net/url"
+	"os"
+	"syscall"
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
+)
+
+var errUseOfClosedNetworkConnection = errors.New("use of closed network connection")
+
+// make a plausible network error with the underlying errno
+func makeNetErr(errno syscall.Errno) error {
+	return &net.OpError{
+		Op:     "write",
+		Net:    "tcp",
+		Source: &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 123},
+		Addr:   &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 8080},
+		Err: &os.SyscallError{
+			Syscall: "write",
+			Err:     errno,
+		},
+	}
+}
+
+type myError1 struct {
+	Err error
+}
+
+func (e myError1) Error() string { return e.Err.Error() }
+
+type myError2 struct {
+	Err error
+}
+
+func (e *myError2) Error() string { return e.Err.Error() }
+
+type myError3 struct {
+	Err int
+}
+
+func (e *myError3) Error() string { return "hello" }
+
+type myError4 struct {
+	e error
+}
+
+func (e *myError4) Error() string { return e.e.Error() }
+
+func TestCause(t *testing.T) {
+	e3 := &myError3{3}
+	e4 := &myError4{io.EOF}
+
+	errPotato := errors.New("potato")
+	for i, test := range []struct {
+		err           error
+		wantRetriable bool
+		wantErr       error
+	}{
+		{nil, false, nil},
+		{errPotato, false, errPotato},
+		{errors.Wrap(errPotato, "potato"), false, errPotato},
+		{errors.Wrap(errors.Wrap(errPotato, "potato2"), "potato"), false, errPotato},
+		{errUseOfClosedNetworkConnection, false, errUseOfClosedNetworkConnection},
+		{makeNetErr(syscall.EAGAIN), true, syscall.EAGAIN},
+		{makeNetErr(syscall.Errno(123123123)), false, syscall.Errno(123123123)},
+		{myError1{io.EOF}, false, io.EOF},
+		{&myError2{io.EOF}, false, io.EOF},
+		{e3, false, e3},
+		{e4, false, e4},
+	} {
+		gotRetriable, gotErr := Cause(test.err)
+		what := fmt.Sprintf("test #%d: %v", i, test.err)
+		assert.Equal(t, test.wantErr, gotErr, what)
+		assert.Equal(t, test.wantRetriable, gotRetriable, what)
+	}
+}
+
+func TestShouldRetry(t *testing.T) {
+	for i, test := range []struct {
+		err  error
+		want bool
+	}{
+		{nil, false},
+		{errors.New("potato"), false},
+		{errors.Wrap(errUseOfClosedNetworkConnection, "connection"), true},
+		{io.EOF, true},
+		{io.ErrUnexpectedEOF, true},
+		{makeNetErr(syscall.EAGAIN), true},
+		{makeNetErr(syscall.Errno(123123123)), false},
+		{&url.Error{Op: "post", URL: "/", Err: io.EOF}, true},
+		{&url.Error{Op: "post", URL: "/", Err: errUseOfClosedNetworkConnection}, true},
+		{
+			errors.Wrap(&url.Error{
+				Op:  "post",
+				URL: "http://localhost/",
+				Err: makeNetErr(syscall.EPIPE),
+			}, "potato error"),
+			true,
+		},
+		{
+			errors.Wrap(&url.Error{
+				Op:  "post",
+				URL: "http://localhost/",
+				Err: makeNetErr(syscall.Errno(123123123)),
+			}, "listing error"),
+			false,
+		},
+	} {
+		got := ShouldRetry(test.err)
+		assert.Equal(t, test.want, got, fmt.Sprintf("test #%d: %v", i, test.err))
+	}
+}