Add a stacktrace-inducing template token

[ribasushi]

Having err objects respond to %+v is quite widespread within the golang ecosystem. Add a logger template unit supporting this behavior.

[aldas]

This change is missing tests. Is it tested? Is the goal to use error structs that have custom String method or what the goal is? I do not understand without examples because %v when used for error will call Error() method.

See these examples - is there any difference in output?

This is using ${error_stacktrace} as template

type customError string

func (c customError) Error() string {
	return "err_" + string(c)
}
func (c customError) String() string {
	return "string_" + string(c)
}

func TestXXX(t *testing.T) {
	var testCases = []struct {
		name        string
		when        error
		whenNoError bool
		expect      string
	}{
		{
			name:   "plain errors",
			when:   errors.New("my error"),
			expect: `{"method":"GET","error":"my error"}`,
		},
		{
			name:   "echo errors",
			when:   echo.ErrBadGateway,
			expect: `{"method":"GET","error":"code=502, message=Bad Gateway"}`,
		},
		{
			name:   "custom stringer error",
			when:   customError("my stringer"),
			expect: `{"method":"GET","error":"err_my stringer"}`, // %+v does not call String()
		},
	}
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			e := echo.New()
			buf := new(bytes.Buffer)
			e.Use(LoggerWithConfig(LoggerConfig{
				Format: `{"method":"${method}","error":"${error_stacktrace}"}` + "\n",
				Output: buf,
			}))

			e.GET("/", func(c echo.Context) error {
				if tc.whenNoError {
					return c.String(http.StatusOK, "OK")
				}
				return tc.when
			})

			req := httptest.NewRequest(http.MethodGet, "/", nil)
			rec := httptest.NewRecorder()
			e.ServeHTTP(rec, req)

			assert.Equal(t, tc.expect+"\n", buf.String())
		})
	}
}

This is using ${error} as template

type customError string

func (c customError) Error() string {
	return "err_" + string(c)
}
func (c customError) String() string {
	return "string_" + string(c)
}

func TestXXX2(t *testing.T) {
	var testCases = []struct {
		name        string
		when        error
		whenNoError bool
		expect      string
	}{
		{
			name:   "plain errors",
			when:   errors.New("my error"),
			expect: `{"method":"GET","error":"my error"}`,
		},
		{
			name:   "echo errors",
			when:   echo.ErrBadGateway,
			expect: `{"method":"GET","error":"code=502, message=Bad Gateway"}`,
		},
		{
			name:   "custom stringer error",
			when:   customError("my stringer"),
			expect: `{"method":"GET","error":"err_my stringer"}`, // %+v does not call String()
		},
	}
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			e := echo.New()
			buf := new(bytes.Buffer)
			e.Use(LoggerWithConfig(LoggerConfig{
				Format: `{"method":"${method}","error":"${error}"}` + "\n",
				Output: buf,
			}))

			e.GET("/", func(c echo.Context) error {
				if tc.whenNoError {
					return c.String(http.StatusOK, "OK")
				}
				return tc.when
			})

			req := httptest.NewRequest(http.MethodGet, "/", nil)
			rec := httptest.NewRecorder()
			e.ServeHTTP(rec, req)

			assert.Equal(t, tc.expect+"\n", buf.String())
		})
	}
}

[zubairalam]

Hi @aldas . Can I pick this if it needs to cleaned?

[ribasushi]

@aldas apologies for the radio silence. Was not tested originally as it wasn't clear what would substitute a reasonable test. Please observe this playground for the real-world-use motivation behind this change.

Would you accept a test using stacked xerrors.Errorf(... %w) ?