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I noticed that we're using a homegrown package for assertions. The functions are extremely similar to testify, but with enough slight differences to be confusing (for example, Equal takes its arguments in a different order). We already vendor testify, and it's used in a few places by tests. I also found some problems with pkg/testutil/assert. For example, the NotNil function seems to be broken. It checks the argument against "nil", which only works for an interface. If you pass in a nil map or slice, the equality check will fail. In the interest of avoiding NIH, I'm proposing replacing pkg/testutil/assert with testify. The test code looks almost the same, but we avoid the confusion of having two similar but slightly different assertion packages, and having to maintain our own package instead of using a commonly-used one. In the process, I found a few places where the tests should halt if an assertion fails, so I've made those cases (that I noticed) use "require" instead of "assert", and I've vendored the "require" package from testify alongside the already-present "assert" package. Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
205 lines
7 KiB
Markdown
205 lines
7 KiB
Markdown
go-spew
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=======
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[]
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(https://travis-ci.org/davecgh/go-spew) [![ISC License]
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(http://img.shields.io/badge/license-ISC-blue.svg)](http://copyfree.org) [![Coverage Status]
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(https://img.shields.io/coveralls/davecgh/go-spew.svg)]
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(https://coveralls.io/r/davecgh/go-spew?branch=master)
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Go-spew implements a deep pretty printer for Go data structures to aid in
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debugging. A comprehensive suite of tests with 100% test coverage is provided
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to ensure proper functionality. See `test_coverage.txt` for the gocov coverage
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report. Go-spew is licensed under the liberal ISC license, so it may be used in
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open source or commercial projects.
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If you're interested in reading about how this package came to life and some
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of the challenges involved in providing a deep pretty printer, there is a blog
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post about it
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[here](https://web.archive.org/web/20160304013555/https://blog.cyphertite.com/go-spew-a-journey-into-dumping-go-data-structures/).
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## Documentation
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[]
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(http://godoc.org/github.com/davecgh/go-spew/spew)
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Full `go doc` style documentation for the project can be viewed online without
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installing this package by using the excellent GoDoc site here:
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http://godoc.org/github.com/davecgh/go-spew/spew
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You can also view the documentation locally once the package is installed with
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the `godoc` tool by running `godoc -http=":6060"` and pointing your browser to
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http://localhost:6060/pkg/github.com/davecgh/go-spew/spew
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## Installation
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```bash
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$ go get -u github.com/davecgh/go-spew/spew
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```
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## Quick Start
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Add this import line to the file you're working in:
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```Go
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import "github.com/davecgh/go-spew/spew"
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```
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To dump a variable with full newlines, indentation, type, and pointer
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information use Dump, Fdump, or Sdump:
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```Go
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spew.Dump(myVar1, myVar2, ...)
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spew.Fdump(someWriter, myVar1, myVar2, ...)
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str := spew.Sdump(myVar1, myVar2, ...)
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```
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Alternatively, if you would prefer to use format strings with a compacted inline
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printing style, use the convenience wrappers Printf, Fprintf, etc with %v (most
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compact), %+v (adds pointer addresses), %#v (adds types), or %#+v (adds types
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and pointer addresses):
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```Go
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spew.Printf("myVar1: %v -- myVar2: %+v", myVar1, myVar2)
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spew.Printf("myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
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spew.Fprintf(someWriter, "myVar1: %v -- myVar2: %+v", myVar1, myVar2)
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spew.Fprintf(someWriter, "myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
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```
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## Debugging a Web Application Example
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Here is an example of how you can use `spew.Sdump()` to help debug a web application. Please be sure to wrap your output using the `html.EscapeString()` function for safety reasons. You should also only use this debugging technique in a development environment, never in production.
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```Go
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package main
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import (
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"fmt"
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"html"
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"net/http"
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"github.com/davecgh/go-spew/spew"
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)
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func handler(w http.ResponseWriter, r *http.Request) {
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w.Header().Set("Content-Type", "text/html")
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fmt.Fprintf(w, "Hi there, %s!", r.URL.Path[1:])
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fmt.Fprintf(w, "<!--\n" + html.EscapeString(spew.Sdump(w)) + "\n-->")
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}
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func main() {
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http.HandleFunc("/", handler)
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http.ListenAndServe(":8080", nil)
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}
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```
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## Sample Dump Output
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```
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(main.Foo) {
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unexportedField: (*main.Bar)(0xf84002e210)({
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flag: (main.Flag) flagTwo,
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data: (uintptr) <nil>
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}),
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ExportedField: (map[interface {}]interface {}) {
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(string) "one": (bool) true
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}
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}
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([]uint8) {
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00000000 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 |............... |
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00000010 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 |!"#$%&'()*+,-./0|
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00000020 31 32 |12|
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}
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```
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## Sample Formatter Output
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Double pointer to a uint8:
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```
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%v: <**>5
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%+v: <**>(0xf8400420d0->0xf8400420c8)5
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%#v: (**uint8)5
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%#+v: (**uint8)(0xf8400420d0->0xf8400420c8)5
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```
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Pointer to circular struct with a uint8 field and a pointer to itself:
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```
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%v: <*>{1 <*><shown>}
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%+v: <*>(0xf84003e260){ui8:1 c:<*>(0xf84003e260)<shown>}
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%#v: (*main.circular){ui8:(uint8)1 c:(*main.circular)<shown>}
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%#+v: (*main.circular)(0xf84003e260){ui8:(uint8)1 c:(*main.circular)(0xf84003e260)<shown>}
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```
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## Configuration Options
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Configuration of spew is handled by fields in the ConfigState type. For
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convenience, all of the top-level functions use a global state available via the
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spew.Config global.
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It is also possible to create a ConfigState instance that provides methods
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equivalent to the top-level functions. This allows concurrent configuration
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options. See the ConfigState documentation for more details.
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```
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* Indent
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String to use for each indentation level for Dump functions.
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It is a single space by default. A popular alternative is "\t".
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* MaxDepth
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Maximum number of levels to descend into nested data structures.
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There is no limit by default.
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* DisableMethods
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Disables invocation of error and Stringer interface methods.
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Method invocation is enabled by default.
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* DisablePointerMethods
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Disables invocation of error and Stringer interface methods on types
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which only accept pointer receivers from non-pointer variables. This option
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relies on access to the unsafe package, so it will not have any effect when
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running in environments without access to the unsafe package such as Google
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App Engine or with the "safe" build tag specified.
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Pointer method invocation is enabled by default.
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* DisablePointerAddresses
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DisablePointerAddresses specifies whether to disable the printing of
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pointer addresses. This is useful when diffing data structures in tests.
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* DisableCapacities
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DisableCapacities specifies whether to disable the printing of capacities
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for arrays, slices, maps and channels. This is useful when diffing data
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structures in tests.
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* ContinueOnMethod
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Enables recursion into types after invoking error and Stringer interface
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methods. Recursion after method invocation is disabled by default.
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* SortKeys
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Specifies map keys should be sorted before being printed. Use
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this to have a more deterministic, diffable output. Note that
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only native types (bool, int, uint, floats, uintptr and string)
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and types which implement error or Stringer interfaces are supported,
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with other types sorted according to the reflect.Value.String() output
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which guarantees display stability. Natural map order is used by
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default.
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* SpewKeys
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SpewKeys specifies that, as a last resort attempt, map keys should be
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spewed to strings and sorted by those strings. This is only considered
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if SortKeys is true.
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```
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## Unsafe Package Dependency
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This package relies on the unsafe package to perform some of the more advanced
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features, however it also supports a "limited" mode which allows it to work in
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environments where the unsafe package is not available. By default, it will
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operate in this mode on Google App Engine and when compiled with GopherJS. The
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"safe" build tag may also be specified to force the package to build without
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using the unsafe package.
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## License
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Go-spew is licensed under the [copyfree](http://copyfree.org) ISC License.
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