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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package slog
import (
"bytes"
"context"
"encoding/json"
"errors"
"fmt"
"io"
"log/slog/internal/buffer"
"strconv"
"sync"
"time"
"unicode/utf8"
)
// JSONHandler is a [Handler] that writes Records to an [io.Writer] as
// line-delimited JSON objects.
type JSONHandler struct {
*commonHandler
}
// NewJSONHandler creates a [JSONHandler] that writes to w,
// using the given options.
// If opts is nil, the default options are used.
func NewJSONHandler(w io.Writer, opts *HandlerOptions) *JSONHandler {
if opts == nil {
opts = &HandlerOptions{}
}
return &JSONHandler{
&commonHandler{
json: true,
w: w,
opts: *opts,
mu: &sync.Mutex{},
},
}
}
// Enabled reports whether the handler handles records at the given level.
// The handler ignores records whose level is lower.
func (h *JSONHandler) Enabled(_ context.Context, level Level) bool {
return h.commonHandler.enabled(level)
}
// WithAttrs returns a new [JSONHandler] whose attributes consists
// of h's attributes followed by attrs.
func (h *JSONHandler) WithAttrs(attrs []Attr) Handler {
return &JSONHandler{commonHandler: h.commonHandler.withAttrs(attrs)}
}
func (h *JSONHandler) WithGroup(name string) Handler {
return &JSONHandler{commonHandler: h.commonHandler.withGroup(name)}
}
// Handle formats its argument [Record] as a JSON object on a single line.
//
// If the Record's time is zero, the time is omitted.
// Otherwise, the key is "time"
// and the value is output as with json.Marshal.
//
// If the Record's level is zero, the level is omitted.
// Otherwise, the key is "level"
// and the value of [Level.String] is output.
//
// If the AddSource option is set and source information is available,
// the key is "source", and the value is a record of type [Source].
//
// The message's key is "msg".
//
// To modify these or other attributes, or remove them from the output, use
// [HandlerOptions.ReplaceAttr].
//
// Values are formatted as with an [encoding/json.Encoder] with SetEscapeHTML(false),
// with two exceptions.
//
// First, an Attr whose Value is of type error is formatted as a string, by
// calling its Error method. Only errors in Attrs receive this special treatment,
// not errors embedded in structs, slices, maps or other data structures that
// are processed by the [encoding/json] package.
//
// Second, an encoding failure does not cause Handle to return an error.
// Instead, the error message is formatted as a string.
//
// Each call to Handle results in a single serialized call to io.Writer.Write.
func (h *JSONHandler) Handle(_ context.Context, r Record) error {
return h.commonHandler.handle(r)
}
// Adapted from time.Time.MarshalJSON to avoid allocation.
func appendJSONTime(s *handleState, t time.Time) {
if y := t.Year(); y < 0 || y >= 10000 {
// RFC 3339 is clear that years are 4 digits exactly.
// See golang.org/issue/4556#c15 for more discussion.
s.appendError(errors.New("time.Time year outside of range [0,9999]"))
}
s.buf.WriteByte('"')
*s.buf = t.AppendFormat(*s.buf, time.RFC3339Nano)
s.buf.WriteByte('"')
}
func appendJSONValue(s *handleState, v Value) error {
switch v.Kind() {
case KindString:
s.appendString(v.str())
case KindInt64:
*s.buf = strconv.AppendInt(*s.buf, v.Int64(), 10)
case KindUint64:
*s.buf = strconv.AppendUint(*s.buf, v.Uint64(), 10)
case KindFloat64:
// json.Marshal is funny about floats; it doesn't
// always match strconv.AppendFloat. So just call it.
// That's expensive, but floats are rare.
if err := appendJSONMarshal(s.buf, v.Float64()); err != nil {
return err
}
case KindBool:
*s.buf = strconv.AppendBool(*s.buf, v.Bool())
case KindDuration:
// Do what json.Marshal does.
*s.buf = strconv.AppendInt(*s.buf, int64(v.Duration()), 10)
case KindTime:
s.appendTime(v.Time())
case KindAny:
a := v.Any()
_, jm := a.(json.Marshaler)
if err, ok := a.(error); ok && !jm {
s.appendString(err.Error())
} else {
return appendJSONMarshal(s.buf, a)
}
default:
panic(fmt.Sprintf("bad kind: %s", v.Kind()))
}
return nil
}
func appendJSONMarshal(buf *buffer.Buffer, v any) error {
// Use a json.Encoder to avoid escaping HTML.
var bb bytes.Buffer
enc := json.NewEncoder(&bb)
enc.SetEscapeHTML(false)
if err := enc.Encode(v); err != nil {
return err
}
bs := bb.Bytes()
buf.Write(bs[:len(bs)-1]) // remove final newline
return nil
}
// appendEscapedJSONString escapes s for JSON and appends it to buf.
// It does not surround the string in quotation marks.
//
// Modified from encoding/json/encode.go:encodeState.string,
// with escapeHTML set to false.
func appendEscapedJSONString(buf []byte, s string) []byte {
char := func(b byte) { buf = append(buf, b) }
str := func(s string) { buf = append(buf, s...) }
start := 0
for i := 0; i < len(s); {
if b := s[i]; b < utf8.RuneSelf {
if safeSet[b] {
i++
continue
}
if start < i {
str(s[start:i])
}
char('\\')
switch b {
case '\\', '"':
char(b)
case '\n':
char('n')
case '\r':
char('r')
case '\t':
char('t')
default:
// This encodes bytes < 0x20 except for \t, \n and \r.
str(`u00`)
char(hex[b>>4])
char(hex[b&0xF])
}
i++
start = i
continue
}
c, size := utf8.DecodeRuneInString(s[i:])
if c == utf8.RuneError && size == 1 {
if start < i {
str(s[start:i])
}
str(`\ufffd`)
i += size
start = i
continue
}
// U+2028 is LINE SEPARATOR.
// U+2029 is PARAGRAPH SEPARATOR.
// They are both technically valid characters in JSON strings,
// but don't work in JSONP, which has to be evaluated as JavaScript,
// and can lead to security holes there. It is valid JSON to
// escape them, so we do so unconditionally.
// See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion.
if c == '\u2028' || c == '\u2029' {
if start < i {
str(s[start:i])
}
str(`\u202`)
char(hex[c&0xF])
i += size
start = i
continue
}
i += size
}
if start < len(s) {
str(s[start:])
}
return buf
}
const hex = "0123456789abcdef"
// Copied from encoding/json/tables.go.
//
// safeSet holds the value true if the ASCII character with the given array
// position can be represented inside a JSON string without any further
// escaping.
//
// All values are true except for the ASCII control characters (0-31), the
// double quote ("), and the backslash character ("\").
var safeSet = [utf8.RuneSelf]bool{
' ': true,
'!': true,
'"': false,
'#': true,
'$': true,
'%': true,
'&': true,
'\'': true,
'(': true,
')': true,
'*': true,
'+': true,
',': true,
'-': true,
'.': true,
'/': true,
'0': true,
'1': true,
'2': true,
'3': true,
'4': true,
'5': true,
'6': true,
'7': true,
'8': true,
'9': true,
':': true,
';': true,
'<': true,
'=': true,
'>': true,
'?': true,
'@': true,
'A': true,
'B': true,
'C': true,
'D': true,
'E': true,
'F': true,
'G': true,
'H': true,
'I': true,
'J': true,
'K': true,
'L': true,
'M': true,
'N': true,
'O': true,
'P': true,
'Q': true,
'R': true,
'S': true,
'T': true,
'U': true,
'V': true,
'W': true,
'X': true,
'Y': true,
'Z': true,
'[': true,
'\\': false,
']': true,
'^': true,
'_': true,
'`': true,
'a': true,
'b': true,
'c': true,
'd': true,
'e': true,
'f': true,
'g': true,
'h': true,
'i': true,
'j': true,
'k': true,
'l': true,
'm': true,
'n': true,
'o': true,
'p': true,
'q': true,
'r': true,
's': true,
't': true,
'u': true,
'v': true,
'w': true,
'x': true,
'y': true,
'z': true,
'{': true,
'|': true,
'}': true,
'~': true,
'\u007f': true,
}