/
impl-serializer.html
1261 lines (755 loc) · 61.9 KB
/
impl-serializer.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE HTML>
<html lang="en" >
<head>
<meta charset="UTF-8">
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>Implementing a Serializer · Serde</title>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="description" content="">
<meta name="generator" content="GitBook 3.2.3">
<link rel="stylesheet" href="gitbook/style.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-codeblock-rust/block.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-checklist/checklist.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-anchors/plugin.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-highlight/website.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-fontsettings/website.css">
<link rel="stylesheet" href="styles/website.css">
<meta name="HandheldFriendly" content="true"/>
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<link rel="apple-touch-icon-precomposed" sizes="152x152" href="gitbook/images/apple-touch-icon-precomposed-152.png">
<link rel="shortcut icon" href="gitbook/images/favicon.ico" type="image/x-icon">
<link rel="next" href="impl-deserializer.html" />
<link rel="prev" href="error-handling.html" />
</head>
<body>
<div class="book with-summary font-size-2">
<div class="book-summary">
<nav role="navigation">
<ul class="summary">
<li class="chapter " data-level="1.1" data-path="./">
<a href="./">
Overview
</a>
</li>
<li class="chapter " data-level="1.2" data-path="help.html">
<a href="help.html">
Help
</a>
</li>
<li class="chapter " data-level="1.3" data-path="data-model.html">
<a href="data-model.html">
Serde data model
</a>
</li>
<li class="chapter " data-level="1.4" data-path="derive.html">
<a href="derive.html">
Using derive
</a>
</li>
<li class="chapter " data-level="1.5" data-path="attributes.html">
<a href="attributes.html">
Attributes
</a>
<ul class="articles">
<li class="chapter " data-level="1.5.1" data-path="container-attrs.html">
<a href="container-attrs.html">
Container attributes
</a>
</li>
<li class="chapter " data-level="1.5.2" data-path="variant-attrs.html">
<a href="variant-attrs.html">
Variant attributes
</a>
</li>
<li class="chapter " data-level="1.5.3" data-path="field-attrs.html">
<a href="field-attrs.html">
Field attributes
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="1.6" data-path="custom-serialization.html">
<a href="custom-serialization.html">
Custom serialization
</a>
<ul class="articles">
<li class="chapter " data-level="1.6.1" data-path="impl-serialize.html">
<a href="impl-serialize.html">
Implementing Serialize
</a>
</li>
<li class="chapter " data-level="1.6.2" data-path="impl-deserialize.html">
<a href="impl-deserialize.html">
Implementing Deserialize
</a>
</li>
<li class="chapter " data-level="1.6.3" data-path="unit-testing.html">
<a href="unit-testing.html">
Unit testing
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="1.7" data-path="data-format.html">
<a href="data-format.html">
Writing a data format
</a>
<ul class="articles">
<li class="chapter " data-level="1.7.1" data-path="conventions.html">
<a href="conventions.html">
Conventions
</a>
</li>
<li class="chapter " data-level="1.7.2" data-path="error-handling.html">
<a href="error-handling.html">
Error handling
</a>
</li>
<li class="chapter active" data-level="1.7.3" data-path="impl-serializer.html">
<a href="impl-serializer.html">
Implementing a Serializer
</a>
</li>
<li class="chapter " data-level="1.7.4" data-path="impl-deserializer.html">
<a href="impl-deserializer.html">
Implementing a Deserializer
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="1.8" data-path="lifetimes.html">
<a href="lifetimes.html">
Deserializer lifetimes
</a>
</li>
<li class="chapter " data-level="1.9" data-path="examples.html">
<a href="examples.html">
Examples
</a>
<ul class="articles">
<li class="chapter " data-level="1.9.1" data-path="json.html">
<a href="json.html">
Structs and enums in JSON
</a>
</li>
<li class="chapter " data-level="1.9.2" data-path="enum-representations.html">
<a href="enum-representations.html">
Enum representations
</a>
</li>
<li class="chapter " data-level="1.9.3" data-path="attr-default.html">
<a href="attr-default.html">
Default value for a field
</a>
</li>
<li class="chapter " data-level="1.9.4" data-path="attr-flatten.html">
<a href="attr-flatten.html">
Struct flattening
</a>
</li>
<li class="chapter " data-level="1.9.5" data-path="attr-bound.html">
<a href="attr-bound.html">
Handwritten generic type bounds
</a>
</li>
<li class="chapter " data-level="1.9.6" data-path="deserialize-map.html">
<a href="deserialize-map.html">
Deserialize for custom map type
</a>
</li>
<li class="chapter " data-level="1.9.7" data-path="stream-array.html">
<a href="stream-array.html">
Array of values without buffering
</a>
</li>
<li class="chapter " data-level="1.9.8" data-path="enum-number.html">
<a href="enum-number.html">
Serialize enum as number
</a>
</li>
<li class="chapter " data-level="1.9.9" data-path="attr-rename.html">
<a href="attr-rename.html">
Serialize fields as camelCase
</a>
</li>
<li class="chapter " data-level="1.9.10" data-path="attr-skip-serializing.html">
<a href="attr-skip-serializing.html">
Skip serializing field
</a>
</li>
<li class="chapter " data-level="1.9.11" data-path="remote-derive.html">
<a href="remote-derive.html">
Derive for remote crate
</a>
</li>
<li class="chapter " data-level="1.9.12" data-path="deserialize-struct.html">
<a href="deserialize-struct.html">
Manually deserialize struct
</a>
</li>
<li class="chapter " data-level="1.9.13" data-path="ignored-any.html">
<a href="ignored-any.html">
Discarding data
</a>
</li>
<li class="chapter " data-level="1.9.14" data-path="transcode.html">
<a href="transcode.html">
Transcode into another format
</a>
</li>
<li class="chapter " data-level="1.9.15" data-path="string-or-struct.html">
<a href="string-or-struct.html">
Either string or struct
</a>
</li>
<li class="chapter " data-level="1.9.16" data-path="convert-error.html">
<a href="convert-error.html">
Convert error types
</a>
</li>
<li class="chapter " data-level="1.9.17" data-path="custom-date-format.html">
<a href="custom-date-format.html">
Custom date format
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="1.10" data-path="no-std.html">
<a href="no-std.html">
No-std support
</a>
</li>
<li class="chapter " data-level="1.11" data-path="feature-flags.html">
<a href="feature-flags.html">
Feature flags
</a>
</li>
</ul>
</nav>
</div>
<div class="book-body">
<div class="body-inner">
<div class="book-header" role="navigation">
<!-- Title -->
<h1>
<i class="fa fa-circle-o-notch fa-spin"></i>
<a href="." >Implementing a Serializer</a>
</h1>
</div>
<div class="page-wrapper" tabindex="-1" role="main">
<div class="page-inner">
<section class="normal markdown-section">
<h1 id="implementing-a-serializer"><a name="implementing-a-serializer" class="plugin-anchor" href="#implementing-a-serializer"><i class="fa fa-link" aria-hidden="true"></i></a>Implementing a Serializer</h1>
<p>This page gives a basic but functional implementation of a JSON serializer using
Serde.</p>
<p>The <a href="https://docs.rs/serde/1/serde/trait.Serializer.html" target="_blank"><code>Serializer</code></a> trait has a lot of methods but none of the ones in this
implementation are complicated. Each method corresponds to one of the types of
the <a href="data-model.html">Serde data model</a>. The serializer is responsible for mapping the data model
into the output representation, in this case JSON.</p>
<p>Refer to the rustdoc of the <code>Serializer</code> trait for examples of how each method
is used.</p>
<div><p class="code-filename">src/ser.rs</p></div>
<pre><code class="lang-rust"><span class="hljs-keyword">use</span> serde::{ser, Serialize};
<span class="hljs-keyword">use</span> error::{Error, <span class="hljs-built_in">Result</span>};
<span class="hljs-keyword">pub</span> <span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Serializer</span></span> {
<span class="hljs-comment">// This string starts empty and JSON is appended as values are serialized.</span>
output: <span class="hljs-built_in">String</span>,
}
<span class="hljs-comment">// By convention, the public API of a Serde serializer is one or more `to_abc`</span>
<span class="hljs-comment">// functions such as `to_string`, `to_bytes`, or `to_writer` depending on what</span>
<span class="hljs-comment">// Rust types the serializer is able to produce as output.</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// This basic serializer supports only `to_string`.</span>
<span class="hljs-keyword">pub</span> <span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">to_string</span></span><T>(value: &T) -> <span class="hljs-built_in">Result</span><<span class="hljs-built_in">String</span>>
<span class="hljs-keyword">where</span>
T: Serialize,
{
<span class="hljs-keyword">let</span> <span class="hljs-keyword">mut</span> serializer = Serializer {
output: <span class="hljs-built_in">String</span>::new(),
};
value.serialize(&<span class="hljs-keyword">mut</span> serializer)?;
<span class="hljs-literal">Ok</span>(serializer.output)
}
<span class="hljs-keyword">impl</span><<span class="hljs-symbol">'a</span>> ser::Serializer <span class="hljs-keyword">for</span> &<span class="hljs-symbol">'a</span> <span class="hljs-keyword">mut</span> Serializer {
<span class="hljs-comment">// The output type produced by this `Serializer` during successful</span>
<span class="hljs-comment">// serialization. Most serializers that produce text or binary output should</span>
<span class="hljs-comment">// set `Ok = ()` and serialize into an `io::Write` or buffer contained</span>
<span class="hljs-comment">// within the `Serializer` instance, as happens here. Serializers that build</span>
<span class="hljs-comment">// in-memory data structures may be simplified by using `Ok` to propagate</span>
<span class="hljs-comment">// the data structure around.</span>
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Ok</span></span> = ();
<span class="hljs-comment">// The error type when some error occurs during serialization.</span>
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Error</span></span> = Error;
<span class="hljs-comment">// Associated types for keeping track of additional state while serializing</span>
<span class="hljs-comment">// compound data structures like sequences and maps. In this case no</span>
<span class="hljs-comment">// additional state is required beyond what is already stored in the</span>
<span class="hljs-comment">// Serializer struct.</span>
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeSeq</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeTuple</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeTupleStruct</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeTupleVariant</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeMap</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeStruct</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">SerializeStructVariant</span></span> = <span class="hljs-keyword">Self</span>;
<span class="hljs-comment">// Here we go with the simple methods. The following 12 methods receive one</span>
<span class="hljs-comment">// of the primitive types of the data model and map it to JSON by appending</span>
<span class="hljs-comment">// into the output string.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_bool</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">bool</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-keyword">if</span> v { <span class="hljs-string">"true"</span> } <span class="hljs-keyword">else</span> { <span class="hljs-string">"false"</span> };
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-comment">// JSON does not distinguish between different sizes of integers, so all</span>
<span class="hljs-comment">// signed integers will be serialized the same and all unsigned integers</span>
<span class="hljs-comment">// will be serialized the same. Other formats, especially compact binary</span>
<span class="hljs-comment">// formats, may need independent logic for the different sizes.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_i8</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">i8</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_i64(i64::from(v))
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_i16</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">i16</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_i64(i64::from(v))
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_i32</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">i32</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_i64(i64::from(v))
}
<span class="hljs-comment">// Not particularly efficient but this is example code anyway. A more</span>
<span class="hljs-comment">// performant approach would be to use the `itoa` crate.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_i64</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">i64</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += &v.to_string();
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_u8</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">u8</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_u64(u64::from(v))
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_u16</span></span>(<span class="hljs-keyword">self</span>, v: u16) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_u64(u64::from(v))
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_u32</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">u32</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_u64(u64::from(v))
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_u64</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">u64</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += &v.to_string();
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_f32</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">f32</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_f64(f64::from(v))
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_f64</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">f64</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += &v.to_string();
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-comment">// Serialize a char as a single-character string. Other formats may</span>
<span class="hljs-comment">// represent this differently.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_char</span></span>(<span class="hljs-keyword">self</span>, v: <span class="hljs-keyword">char</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_str(&v.to_string())
}
<span class="hljs-comment">// This only works for strings that don't require escape sequences but you</span>
<span class="hljs-comment">// get the idea. For example it would emit invalid JSON if the input string</span>
<span class="hljs-comment">// contains a '"' character.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_str</span></span>(<span class="hljs-keyword">self</span>, v: &<span class="hljs-keyword">str</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"\""</span>;
<span class="hljs-keyword">self</span>.output += v;
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"\""</span>;
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-comment">// Serialize a byte array as an array of bytes. Could also use a base64</span>
<span class="hljs-comment">// string here. Binary formats will typically represent byte arrays more</span>
<span class="hljs-comment">// compactly.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_bytes</span></span>(<span class="hljs-keyword">self</span>, v: &[<span class="hljs-keyword">u8</span>]) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">use</span> serde::ser::SerializeSeq;
<span class="hljs-keyword">let</span> <span class="hljs-keyword">mut</span> seq = <span class="hljs-keyword">self</span>.serialize_seq(<span class="hljs-literal">Some</span>(v.len()))?;
<span class="hljs-keyword">for</span> byte <span class="hljs-keyword">in</span> v {
seq.serialize_element(byte)?;
}
seq.end()
}
<span class="hljs-comment">// An absent optional is represented as the JSON `null`.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_none</span></span>(<span class="hljs-keyword">self</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_unit()
}
<span class="hljs-comment">// A present optional is represented as just the contained value. Note that</span>
<span class="hljs-comment">// this is a lossy representation. For example the values `Some(())` and</span>
<span class="hljs-comment">// `None` both serialize as just `null`. Unfortunately this is typically</span>
<span class="hljs-comment">// what people expect when working with JSON. Other formats are encouraged</span>
<span class="hljs-comment">// to behave more intelligently if possible.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_some</span></span><T>(<span class="hljs-keyword">self</span>, value: &T) -> <span class="hljs-built_in">Result</span><()>
<span class="hljs-keyword">where</span>
T: ?<span class="hljs-built_in">Sized</span> + Serialize,
{
value.serialize(<span class="hljs-keyword">self</span>)
}
<span class="hljs-comment">// In Serde, unit means an anonymous value containing no data. Map this to</span>
<span class="hljs-comment">// JSON as `null`.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_unit</span></span>(<span class="hljs-keyword">self</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"null"</span>;
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-comment">// Unit struct means a named value containing no data. Again, since there is</span>
<span class="hljs-comment">// no data, map this to JSON as `null`. There is no need to serialize the</span>
<span class="hljs-comment">// name in most formats.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_unit_struct</span></span>(<span class="hljs-keyword">self</span>, _name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_unit()
}
<span class="hljs-comment">// When serializing a unit variant (or any other kind of variant), formats</span>
<span class="hljs-comment">// can choose whether to keep track of it by index or by name. Binary</span>
<span class="hljs-comment">// formats typically use the index of the variant and human-readable formats</span>
<span class="hljs-comment">// typically use the name.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_unit_variant</span></span>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
_variant_index: <span class="hljs-keyword">u32</span>,
variant: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.serialize_str(variant)
}
<span class="hljs-comment">// As is done here, serializers are encouraged to treat newtype structs as</span>
<span class="hljs-comment">// insignificant wrappers around the data they contain.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_newtype_struct</span></span><T>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
value: &T,
) -> <span class="hljs-built_in">Result</span><()>
<span class="hljs-keyword">where</span>
T: ?<span class="hljs-built_in">Sized</span> + Serialize,
{
value.serialize(<span class="hljs-keyword">self</span>)
}
<span class="hljs-comment">// Note that newtype variant (and all of the other variant serialization</span>
<span class="hljs-comment">// methods) refer exclusively to the "externally tagged" enum</span>
<span class="hljs-comment">// representation.</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// Serialize this to JSON in externally tagged form as `{ NAME: VALUE }`.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_newtype_variant</span></span><T>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
_variant_index: <span class="hljs-keyword">u32</span>,
variant: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
value: &T,
) -> <span class="hljs-built_in">Result</span><()>
<span class="hljs-keyword">where</span>
T: ?<span class="hljs-built_in">Sized</span> + Serialize,
{
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"{"</span>;
variant.serialize(&<span class="hljs-keyword">mut</span> *<span class="hljs-keyword">self</span>)?;
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">":"</span>;
value.serialize(&<span class="hljs-keyword">mut</span> *<span class="hljs-keyword">self</span>)?;
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"}"</span>;
<span class="hljs-literal">Ok</span>(())
}
<span class="hljs-comment">// Now we get to the serialization of compound types.</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// The start of the sequence, each value, and the end are three separate</span>
<span class="hljs-comment">// method calls. This one is responsible only for serializing the start,</span>
<span class="hljs-comment">// which in JSON is `[`.</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// The length of the sequence may or may not be known ahead of time. This</span>
<span class="hljs-comment">// doesn't make a difference in JSON because the length is not represented</span>
<span class="hljs-comment">// explicitly in the serialized form. Some serializers may only be able to</span>
<span class="hljs-comment">// support sequences for which the length is known up front.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_seq</span></span>(<span class="hljs-keyword">self</span>, _len: <span class="hljs-built_in">Option</span><usize>) -> <span class="hljs-built_in">Result</span><Self::SerializeSeq> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"["</span>;
<span class="hljs-literal">Ok</span>(<span class="hljs-keyword">self</span>)
}
<span class="hljs-comment">// Tuples look just like sequences in JSON. Some formats may be able to</span>
<span class="hljs-comment">// represent tuples more efficiently by omitting the length, since tuple</span>
<span class="hljs-comment">// means that the corresponding `Deserialize implementation will know the</span>
<span class="hljs-comment">// length without needing to look at the serialized data.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_tuple</span></span>(<span class="hljs-keyword">self</span>, len: usize) -> <span class="hljs-built_in">Result</span><Self::SerializeTuple> {
<span class="hljs-keyword">self</span>.serialize_seq(<span class="hljs-literal">Some</span>(len))
}
<span class="hljs-comment">// Tuple structs look just like sequences in JSON.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_tuple_struct</span></span>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
len: usize,
) -> <span class="hljs-built_in">Result</span><Self::SerializeTupleStruct> {
<span class="hljs-keyword">self</span>.serialize_seq(<span class="hljs-literal">Some</span>(len))
}
<span class="hljs-comment">// Tuple variants are represented in JSON as `{ NAME: [DATA...] }`. Again</span>
<span class="hljs-comment">// this method is only responsible for the externally tagged representation.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_tuple_variant</span></span>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
_variant_index: <span class="hljs-keyword">u32</span>,
variant: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
_len: usize,
) -> <span class="hljs-built_in">Result</span><Self::SerializeTupleVariant> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"{"</span>;
variant.serialize(&<span class="hljs-keyword">mut</span> *<span class="hljs-keyword">self</span>)?;
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">":["</span>;
<span class="hljs-literal">Ok</span>(<span class="hljs-keyword">self</span>)
}
<span class="hljs-comment">// Maps are represented in JSON as `{ K: V, K: V, ... }`.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_map</span></span>(<span class="hljs-keyword">self</span>, _len: <span class="hljs-built_in">Option</span><usize>) -> <span class="hljs-built_in">Result</span><Self::SerializeMap> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"{"</span>;
<span class="hljs-literal">Ok</span>(<span class="hljs-keyword">self</span>)
}
<span class="hljs-comment">// Structs look just like maps in JSON. In particular, JSON requires that we</span>
<span class="hljs-comment">// serialize the field names of the struct. Other formats may be able to</span>
<span class="hljs-comment">// omit the field names when serializing structs because the corresponding</span>
<span class="hljs-comment">// Deserialize implementation is required to know what the keys are without</span>
<span class="hljs-comment">// looking at the serialized data.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_struct</span></span>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
len: usize,
) -> <span class="hljs-built_in">Result</span><Self::SerializeStruct> {
<span class="hljs-keyword">self</span>.serialize_map(<span class="hljs-literal">Some</span>(len))
}
<span class="hljs-comment">// Struct variants are represented in JSON as `{ NAME: { K: V, ... } }`.</span>
<span class="hljs-comment">// This is the externally tagged representation.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_struct_variant</span></span>(
<span class="hljs-keyword">self</span>,
_name: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
_variant_index: <span class="hljs-keyword">u32</span>,
variant: &<span class="hljs-symbol">'static</span> <span class="hljs-keyword">str</span>,
_len: usize,
) -> <span class="hljs-built_in">Result</span><Self::SerializeStructVariant> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"{"</span>;
variant.serialize(&<span class="hljs-keyword">mut</span> *<span class="hljs-keyword">self</span>)?;
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">":{"</span>;
<span class="hljs-literal">Ok</span>(<span class="hljs-keyword">self</span>)
}
}
<span class="hljs-comment">// The following 7 impls deal with the serialization of compound types like</span>
<span class="hljs-comment">// sequences and maps. Serialization of such types is begun by a Serializer</span>
<span class="hljs-comment">// method and followed by zero or more calls to serialize individual elements of</span>
<span class="hljs-comment">// the compound type and one call to end the compound type.</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// This impl is SerializeSeq so these methods are called after `serialize_seq`</span>
<span class="hljs-comment">// is called on the Serializer.</span>
<span class="hljs-keyword">impl</span><<span class="hljs-symbol">'a</span>> ser::SerializeSeq <span class="hljs-keyword">for</span> &<span class="hljs-symbol">'a</span> <span class="hljs-keyword">mut</span> Serializer {
<span class="hljs-comment">// Must match the `Ok` type of the serializer.</span>
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Ok</span></span> = ();
<span class="hljs-comment">// Must match the `Error` type of the serializer.</span>
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Error</span></span> = Error;
<span class="hljs-comment">// Serialize a single element of the sequence.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_element</span></span><T>(&<span class="hljs-keyword">mut</span> <span class="hljs-keyword">self</span>, value: &T) -> <span class="hljs-built_in">Result</span><()>
<span class="hljs-keyword">where</span>
T: ?<span class="hljs-built_in">Sized</span> + Serialize,
{
<span class="hljs-keyword">if</span> !<span class="hljs-keyword">self</span>.output.ends_with(<span class="hljs-string">'['</span>) {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">","</span>;
}
value.serialize(&<span class="hljs-keyword">mut</span> **<span class="hljs-keyword">self</span>)
}
<span class="hljs-comment">// Close the sequence.</span>
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">end</span></span>(<span class="hljs-keyword">self</span>) -> <span class="hljs-built_in">Result</span><()> {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">"]"</span>;
<span class="hljs-literal">Ok</span>(())
}
}
<span class="hljs-comment">// Same thing but for tuples.</span>
<span class="hljs-keyword">impl</span><<span class="hljs-symbol">'a</span>> ser::SerializeTuple <span class="hljs-keyword">for</span> &<span class="hljs-symbol">'a</span> <span class="hljs-keyword">mut</span> Serializer {
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Ok</span></span> = ();
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Error</span></span> = Error;
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize_element</span></span><T>(&<span class="hljs-keyword">mut</span> <span class="hljs-keyword">self</span>, value: &T) -> <span class="hljs-built_in">Result</span><()>
<span class="hljs-keyword">where</span>
T: ?<span class="hljs-built_in">Sized</span> + Serialize,
{
<span class="hljs-keyword">if</span> !<span class="hljs-keyword">self</span>.output.ends_with(<span class="hljs-string">'['</span>) {
<span class="hljs-keyword">self</span>.output += <span class="hljs-string">","</span>;
}
value.serialize(&<span class="hljs-keyword">mut</span> **<span class="hljs-keyword">self</span>)
}