json_handler.go

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package slog
     6  
     7  import (
     8  	"bytes"
     9  	"context"
    10  	"encoding/json"
    11  	"errors"
    12  	"fmt"
    13  	"io"
    14  	"log/slog/internal/buffer"
    15  	"strconv"
    16  	"sync"
    17  	"time"
    18  	"unicode/utf8"
    19  )
    20  
    21  // JSONHandler is a [Handler] that writes Records to an [io.Writer] as
    22  // line-delimited JSON objects.
    23  type JSONHandler struct {
    24  	*commonHandler
    25  }
    26  
    27  // NewJSONHandler creates a [JSONHandler] that writes to w,
    28  // using the given options.
    29  // If opts is nil, the default options are used.
    30  func NewJSONHandler(w io.Writer, opts *HandlerOptions) *JSONHandler {
    31  	if opts == nil {
    32  		opts = &HandlerOptions{}
    33  	}
    34  	return &JSONHandler{
    35  		&commonHandler{
    36  			json: true,
    37  			w:    w,
    38  			opts: *opts,
    39  			mu:   &sync.Mutex{},
    40  		},
    41  	}
    42  }
    43  
    44  // Enabled reports whether the handler handles records at the given level.
    45  // The handler ignores records whose level is lower.
    46  func (h *JSONHandler) Enabled(_ context.Context, level Level) bool {
    47  	return h.commonHandler.enabled(level)
    48  }
    49  
    50  // WithAttrs returns a new [JSONHandler] whose attributes consists
    51  // of h's attributes followed by attrs.
    52  func (h *JSONHandler) WithAttrs(attrs []Attr) Handler {
    53  	return &JSONHandler{commonHandler: h.commonHandler.withAttrs(attrs)}
    54  }
    55  
    56  func (h *JSONHandler) WithGroup(name string) Handler {
    57  	return &JSONHandler{commonHandler: h.commonHandler.withGroup(name)}
    58  }
    59  
    60  // Handle formats its argument [Record] as a JSON object on a single line.
    61  //
    62  // If the Record's time is zero, the time is omitted.
    63  // Otherwise, the key is "time"
    64  // and the value is output as with json.Marshal.
    65  //
    66  // The level's key is "level" and its value is the result of calling [Level.String].
    67  //
    68  // If the AddSource option is set and source information is available,
    69  // the key is "source", and the value is a record of type [Source].
    70  //
    71  // The message's key is "msg".
    72  //
    73  // To modify these or other attributes, or remove them from the output, use
    74  // [HandlerOptions.ReplaceAttr].
    75  //
    76  // Values are formatted as with an [encoding/json.Encoder] with SetEscapeHTML(false),
    77  // with two exceptions.
    78  //
    79  // First, an Attr whose Value is of type error is formatted as a string, by
    80  // calling its Error method. Only errors in Attrs receive this special treatment,
    81  // not errors embedded in structs, slices, maps or other data structures that
    82  // are processed by the [encoding/json] package.
    83  //
    84  // Second, an encoding failure does not cause Handle to return an error.
    85  // Instead, the error message is formatted as a string.
    86  //
    87  // Each call to Handle results in a single serialized call to io.Writer.Write.
    88  func (h *JSONHandler) Handle(_ context.Context, r Record) error {
    89  	return h.commonHandler.handle(r)
    90  }
    91  
    92  // Adapted from time.Time.MarshalJSON to avoid allocation.
    93  func appendJSONTime(s *handleState, t time.Time) {
    94  	if y := t.Year(); y < 0 || y >= 10000 {
    95  		// RFC 3339 is clear that years are 4 digits exactly.
    96  		// See golang.org/issue/4556#c15 for more discussion.
    97  		s.appendError(errors.New("time.Time year outside of range [0,9999]"))
    98  	}
    99  	s.buf.WriteByte('"')
   100  	*s.buf = t.AppendFormat(*s.buf, time.RFC3339Nano)
   101  	s.buf.WriteByte('"')
   102  }
   103  
   104  func appendJSONValue(s *handleState, v Value) error {
   105  	switch v.Kind() {
   106  	case KindString:
   107  		s.appendString(v.str())
   108  	case KindInt64:
   109  		*s.buf = strconv.AppendInt(*s.buf, v.Int64(), 10)
   110  	case KindUint64:
   111  		*s.buf = strconv.AppendUint(*s.buf, v.Uint64(), 10)
   112  	case KindFloat64:
   113  		// json.Marshal is funny about floats; it doesn't
   114  		// always match strconv.AppendFloat. So just call it.
   115  		// That's expensive, but floats are rare.
   116  		if err := appendJSONMarshal(s.buf, v.Float64()); err != nil {
   117  			return err
   118  		}
   119  	case KindBool:
   120  		*s.buf = strconv.AppendBool(*s.buf, v.Bool())
   121  	case KindDuration:
   122  		// Do what json.Marshal does.
   123  		*s.buf = strconv.AppendInt(*s.buf, int64(v.Duration()), 10)
   124  	case KindTime:
   125  		s.appendTime(v.Time())
   126  	case KindAny:
   127  		a := v.Any()
   128  		_, jm := a.(json.Marshaler)
   129  		if err, ok := a.(error); ok && !jm {
   130  			s.appendString(err.Error())
   131  		} else {
   132  			return appendJSONMarshal(s.buf, a)
   133  		}
   134  	default:
   135  		panic(fmt.Sprintf("bad kind: %s", v.Kind()))
   136  	}
   137  	return nil
   138  }
   139  
   140  type jsonEncoder struct {
   141  	buf *bytes.Buffer
   142  	// Use a json.Encoder to avoid escaping HTML.
   143  	json *json.Encoder
   144  }
   145  
   146  var jsonEncoderPool = &sync.Pool{
   147  	New: func() any {
   148  		enc := &jsonEncoder{
   149  			buf: new(bytes.Buffer),
   150  		}
   151  		enc.json = json.NewEncoder(enc.buf)
   152  		enc.json.SetEscapeHTML(false)
   153  		return enc
   154  	},
   155  }
   156  
   157  func appendJSONMarshal(buf *buffer.Buffer, v any) error {
   158  	j := jsonEncoderPool.Get().(*jsonEncoder)
   159  	defer func() {
   160  		// To reduce peak allocation, return only smaller buffers to the pool.
   161  		const maxBufferSize = 16 << 10
   162  		if j.buf.Cap() > maxBufferSize {
   163  			return
   164  		}
   165  		j.buf.Reset()
   166  		jsonEncoderPool.Put(j)
   167  	}()
   168  
   169  	if err := j.json.Encode(v); err != nil {
   170  		return err
   171  	}
   172  
   173  	bs := j.buf.Bytes()
   174  	buf.Write(bs[:len(bs)-1]) // remove final newline
   175  	return nil
   176  }
   177  
   178  // appendEscapedJSONString escapes s for JSON and appends it to buf.
   179  // It does not surround the string in quotation marks.
   180  //
   181  // Modified from encoding/json/encode.go:encodeState.string,
   182  // with escapeHTML set to false.
   183  func appendEscapedJSONString(buf []byte, s string) []byte {
   184  	char := func(b byte) { buf = append(buf, b) }
   185  	str := func(s string) { buf = append(buf, s...) }
   186  
   187  	start := 0
   188  	for i := 0; i < len(s); {
   189  		if b := s[i]; b < utf8.RuneSelf {
   190  			if safeSet[b] {
   191  				i++
   192  				continue
   193  			}
   194  			if start < i {
   195  				str(s[start:i])
   196  			}
   197  			char('\\')
   198  			switch b {
   199  			case '\\', '"':
   200  				char(b)
   201  			case '\n':
   202  				char('n')
   203  			case '\r':
   204  				char('r')
   205  			case '\t':
   206  				char('t')
   207  			default:
   208  				// This encodes bytes < 0x20 except for \t, \n and \r.
   209  				str(`u00`)
   210  				char(hex[b>>4])
   211  				char(hex[b&0xF])
   212  			}
   213  			i++
   214  			start = i
   215  			continue
   216  		}
   217  		c, size := utf8.DecodeRuneInString(s[i:])
   218  		if c == utf8.RuneError && size == 1 {
   219  			if start < i {
   220  				str(s[start:i])
   221  			}
   222  			str(`\ufffd`)
   223  			i += size
   224  			start = i
   225  			continue
   226  		}
   227  		// U+2028 is LINE SEPARATOR.
   228  		// U+2029 is PARAGRAPH SEPARATOR.
   229  		// They are both technically valid characters in JSON strings,
   230  		// but don't work in JSONP, which has to be evaluated as JavaScript,
   231  		// and can lead to security holes there. It is valid JSON to
   232  		// escape them, so we do so unconditionally.
   233  		// See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion.
   234  		if c == '\u2028' || c == '\u2029' {
   235  			if start < i {
   236  				str(s[start:i])
   237  			}
   238  			str(`\u202`)
   239  			char(hex[c&0xF])
   240  			i += size
   241  			start = i
   242  			continue
   243  		}
   244  		i += size
   245  	}
   246  	if start < len(s) {
   247  		str(s[start:])
   248  	}
   249  	return buf
   250  }
   251  
   252  const hex = "0123456789abcdef"
   253  
   254  // Copied from encoding/json/tables.go.
   255  //
   256  // safeSet holds the value true if the ASCII character with the given array
   257  // position can be represented inside a JSON string without any further
   258  // escaping.
   259  //
   260  // All values are true except for the ASCII control characters (0-31), the
   261  // double quote ("), and the backslash character ("\").
   262  var safeSet = [utf8.RuneSelf]bool{
   263  	' ':      true,
   264  	'!':      true,
   265  	'"':      false,
   266  	'#':      true,
   267  	'$':      true,
   268  	'%':      true,
   269  	'&':      true,
   270  	'\'':     true,
   271  	'(':      true,
   272  	')':      true,
   273  	'*':      true,
   274  	'+':      true,
   275  	',':      true,
   276  	'-':      true,
   277  	'.':      true,
   278  	'/':      true,
   279  	'0':      true,
   280  	'1':      true,
   281  	'2':      true,
   282  	'3':      true,
   283  	'4':      true,
   284  	'5':      true,
   285  	'6':      true,
   286  	'7':      true,
   287  	'8':      true,
   288  	'9':      true,
   289  	':':      true,
   290  	';':      true,
   291  	'<':      true,
   292  	'=':      true,
   293  	'>':      true,
   294  	'?':      true,
   295  	'@':      true,
   296  	'A':      true,
   297  	'B':      true,
   298  	'C':      true,
   299  	'D':      true,
   300  	'E':      true,
   301  	'F':      true,
   302  	'G':      true,
   303  	'H':      true,
   304  	'I':      true,
   305  	'J':      true,
   306  	'K':      true,
   307  	'L':      true,
   308  	'M':      true,
   309  	'N':      true,
   310  	'O':      true,
   311  	'P':      true,
   312  	'Q':      true,
   313  	'R':      true,
   314  	'S':      true,
   315  	'T':      true,
   316  	'U':      true,
   317  	'V':      true,
   318  	'W':      true,
   319  	'X':      true,
   320  	'Y':      true,
   321  	'Z':      true,
   322  	'[':      true,
   323  	'\\':     false,
   324  	']':      true,
   325  	'^':      true,
   326  	'_':      true,
   327  	'`':      true,
   328  	'a':      true,
   329  	'b':      true,
   330  	'c':      true,
   331  	'd':      true,
   332  	'e':      true,
   333  	'f':      true,
   334  	'g':      true,
   335  	'h':      true,
   336  	'i':      true,
   337  	'j':      true,
   338  	'k':      true,
   339  	'l':      true,
   340  	'm':      true,
   341  	'n':      true,
   342  	'o':      true,
   343  	'p':      true,
   344  	'q':      true,
   345  	'r':      true,
   346  	's':      true,
   347  	't':      true,
   348  	'u':      true,
   349  	'v':      true,
   350  	'w':      true,
   351  	'x':      true,
   352  	'y':      true,
   353  	'z':      true,
   354  	'{':      true,
   355  	'|':      true,
   356  	'}':      true,
   357  	'~':      true,
   358  	'\u007f': true,
   359  }
   360
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