1 /*
2 * Copyright (c) 2013-2016 Dave Collins <dave@davec.name>
3 *
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
7 *
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 */
16 17 /*
18 Package spew implements a deep pretty printer for Go data structures to aid in
19 debugging.
20 21 A quick overview of the additional features spew provides over the built-in
22 printing facilities for Go data types are as follows:
23 24 * Pointers are dereferenced and followed
25 * Circular data structures are detected and handled properly
26 * Custom Stringer/error interfaces are optionally invoked, including
27 on unexported types
28 * Custom types which only implement the Stringer/error interfaces via
29 a pointer receiver are optionally invoked when passing non-pointer
30 variables
31 * Byte arrays and slices are dumped like the hexdump -C command which
32 includes offsets, byte values in hex, and ASCII output (only when using
33 Dump style)
34 35 There are two different approaches spew allows for dumping Go data structures:
36 37 * Dump style which prints with newlines, customizable indentation,
38 and additional debug information such as types and all pointer addresses
39 used to indirect to the final value
40 * A custom Formatter interface that integrates cleanly with the standard fmt
41 package and replaces %v, %+v, %#v, and %#+v to provide inline printing
42 similar to the default %v while providing the additional functionality
43 outlined above and passing unsupported format verbs such as %x and %q
44 along to fmt
45 46 Quick Start
47 48 This section demonstrates how to quickly get started with spew. See the
49 sections below for further details on formatting and configuration options.
50 51 To dump a variable with full newlines, indentation, type, and pointer
52 information use Dump, Fdump, or Sdump:
53 spew.Dump(myVar1, myVar2, ...)
54 spew.Fdump(someWriter, myVar1, myVar2, ...)
55 str := spew.Sdump(myVar1, myVar2, ...)
56 57 Alternatively, if you would prefer to use format strings with a compacted inline
58 printing style, use the convenience wrappers Printf, Fprintf, etc with
59 %v (most compact), %+v (adds pointer addresses), %#v (adds types), or
60 %#+v (adds types and pointer addresses):
61 spew.Printf("myVar1: %v -- myVar2: %+v", myVar1, myVar2)
62 spew.Printf("myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
63 spew.Fprintf(someWriter, "myVar1: %v -- myVar2: %+v", myVar1, myVar2)
64 spew.Fprintf(someWriter, "myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
65 66 Configuration Options
67 68 Configuration of spew is handled by fields in the ConfigState type. For
69 convenience, all of the top-level functions use a global state available
70 via the spew.Config global.
71 72 It is also possible to create a ConfigState instance that provides methods
73 equivalent to the top-level functions. This allows concurrent configuration
74 options. See the ConfigState documentation for more details.
75 76 The following configuration options are available:
77 * Indent
78 String to use for each indentation level for Dump functions.
79 It is a single space by default. A popular alternative is "\t".
80 81 * MaxDepth
82 Maximum number of levels to descend into nested data structures.
83 There is no limit by default.
84 85 * DisableMethods
86 Disables invocation of error and Stringer interface methods.
87 Method invocation is enabled by default.
88 89 * DisablePointerMethods
90 Disables invocation of error and Stringer interface methods on types
91 which only accept pointer receivers from non-pointer variables.
92 Pointer method invocation is enabled by default.
93 94 * DisablePointerAddresses
95 DisablePointerAddresses specifies whether to disable the printing of
96 pointer addresses. This is useful when diffing data structures in tests.
97 98 * DisableCapacities
99 DisableCapacities specifies whether to disable the printing of
100 capacities for arrays, slices, maps and channels. This is useful when
101 diffing data structures in tests.
102 103 * ContinueOnMethod
104 Enables recursion into types after invoking error and Stringer interface
105 methods. Recursion after method invocation is disabled by default.
106 107 * SortKeys
108 Specifies map keys should be sorted before being printed. Use
109 this to have a more deterministic, diffable output. Note that
110 only native types (bool, int, uint, floats, uintptr and string)
111 and types which implement error or Stringer interfaces are
112 supported with other types sorted according to the
113 reflect.Value.String() output which guarantees display
114 stability. Natural map order is used by default.
115 116 * SpewKeys
117 Specifies that, as a last resort attempt, map keys should be
118 spewed to strings and sorted by those strings. This is only
119 considered if SortKeys is true.
120 121 Dump Usage
122 123 Simply call spew.Dump with a list of variables you want to dump:
124 125 spew.Dump(myVar1, myVar2, ...)
126 127 You may also call spew.Fdump if you would prefer to output to an arbitrary
128 io.Writer. For example, to dump to standard error:
129 130 spew.Fdump(os.Stderr, myVar1, myVar2, ...)
131 132 A third option is to call spew.Sdump to get the formatted output as a string:
133 134 str := spew.Sdump(myVar1, myVar2, ...)
135 136 Sample Dump Output
137 138 See the Dump example for details on the setup of the types and variables being
139 shown here.
140 141 (main.Foo) {
142 unexportedField: (*main.Bar)(0xf84002e210)({
143 flag: (main.Flag) flagTwo,
144 data: (uintptr) <nil>
145 }),
146 ExportedField: (map[interface {}]interface {}) (len=1) {
147 (string) (len=3) "one": (bool) true
148 }
149 }
150 151 Byte (and uint8) arrays and slices are displayed uniquely like the hexdump -C
152 command as shown.
153 ([]uint8) (len=32 cap=32) {
154 00000000 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 |............... |
155 00000010 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 |!"#$%&'()*+,-./0|
156 00000020 31 32 |12|
157 }
158 159 Custom Formatter
160 161 Spew provides a custom formatter that implements the fmt.Formatter interface
162 so that it integrates cleanly with standard fmt package printing functions. The
163 formatter is useful for inline printing of smaller data types similar to the
164 standard %v format specifier.
165 166 The custom formatter only responds to the %v (most compact), %+v (adds pointer
167 addresses), %#v (adds types), or %#+v (adds types and pointer addresses) verb
168 combinations. Any other verbs such as %x and %q will be sent to the the
169 standard fmt package for formatting. In addition, the custom formatter ignores
170 the width and precision arguments (however they will still work on the format
171 specifiers not handled by the custom formatter).
172 173 Custom Formatter Usage
174 175 The simplest way to make use of the spew custom formatter is to call one of the
176 convenience functions such as spew.Printf, spew.Println, or spew.Printf. The
177 functions have syntax you are most likely already familiar with:
178 179 spew.Printf("myVar1: %v -- myVar2: %+v", myVar1, myVar2)
180 spew.Printf("myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
181 spew.Println(myVar, myVar2)
182 spew.Fprintf(os.Stderr, "myVar1: %v -- myVar2: %+v", myVar1, myVar2)
183 spew.Fprintf(os.Stderr, "myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
184 185 See the Index for the full list convenience functions.
186 187 Sample Formatter Output
188 189 Double pointer to a uint8:
190 %v: <**>5
191 %+v: <**>(0xf8400420d0->0xf8400420c8)5
192 %#v: (**uint8)5
193 %#+v: (**uint8)(0xf8400420d0->0xf8400420c8)5
194 195 Pointer to circular struct with a uint8 field and a pointer to itself:
196 %v: <*>{1 <*><shown>}
197 %+v: <*>(0xf84003e260){ui8:1 c:<*>(0xf84003e260)<shown>}
198 %#v: (*main.circular){ui8:(uint8)1 c:(*main.circular)<shown>}
199 %#+v: (*main.circular)(0xf84003e260){ui8:(uint8)1 c:(*main.circular)(0xf84003e260)<shown>}
200 201 See the Printf example for details on the setup of variables being shown
202 here.
203 204 Errors
205 206 Since it is possible for custom Stringer/error interfaces to panic, spew
207 detects them and handles them internally by printing the panic information
208 inline with the output. Since spew is intended to provide deep pretty printing
209 capabilities on structures, it intentionally does not return any errors.
210 */
211 package spew
212