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256 lines
8.4 KiB
Markdown
256 lines
8.4 KiB
Markdown
merry [](https://github.com/ansel1/merry/actions?query=branch%3Amaster+workflow%3ABuild+) [](https://godoc.org/github.com/ansel1/merry) [](https://goreportcard.com/report/github.com/ansel1/merry)
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=====
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Add context to errors, including automatic stack capture, cause chains, HTTP status code, user
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messages, and arbitrary values.
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The package is largely based on http://github.com/go-errors/errors, with additional
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inspiration from https://github.com/go-errgo/errgo and https://github.com/amattn/deeperror.
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V2
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--
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[github.com/ansel1/merry/v2](https://github.com/ansel1/merry/tree/master/v2) now replaces v1. v1 will continue to be supported. v1 has been re-implemented
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in terms of v2, and the two packages can be used together and interchangeably.
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There are some small enhancements and changes to v1 with the introduction of v2:
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- err.Error() now *always* just prints out the basic error message. It no longer prints out details,
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user message, or cause. VerboseDefault() and SetVerboseDefault() no longer have any effect. To
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print more detailed error information, you must use fmt:
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// print err message and cause chain
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fmt.Printf("%v", err) // %s works too
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// print details, same as Details(err)
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fmt.Printf("%v+", err)
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- MaxStackDepth is no longer supported. Setting it has no effect. It has been replaced with
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GetMaxStackDepth() and SetMaxStackDepth(), which delegate to corresponding v2 functions.
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- New, Errorf, Wrap, and WrapSkipping now accept v2.Wrapper arguments, allowing a mixture of
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v1's fluent API style and v2's option-func API style.
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- Compatibility with other error wrapping libraries is improved. All functions which extract
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a value from an error will now search the entire chain of errors, even if errors created by
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other libraries are inserted in the middle of the chain, so long as those errors implement
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Unwrap().
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Installation
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------------
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go get github.com/ansel1/merry
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Features
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--------
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Merry errors work a lot like google's golang.org/x/net/context package.
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Merry errors wrap normal errors with a context of key/value pairs.
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Like contexts, merry errors are immutable: adding a key/value to an error
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always creates a new error which wraps the original.
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`merry` comes with built-in support for adding information to errors:
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* stacktraces
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* overriding the error message
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* HTTP status codes
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* End user error messages
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You can also add your own additional information.
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The stack capturing feature can be turned off for better performance, though it's pretty fast. Benchmarks
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on an 2017 MacBook Pro, with go 1.10:
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BenchmarkNew_withStackCapture-8 2000000 749 ns/op
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BenchmarkNew_withoutStackCapture-8 20000000 64.1 ns/op
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Details
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-------
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* Support for go 2's errors.Is and errors.As functions
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* New errors have a stacktrace captured where they are created
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* Add a stacktrace to existing errors (captured where they are wrapped)
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```go
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err := lib.Read()
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return merry.Wrap(err) // no-op if err is already merry
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```
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* Add a stacktrace to a sentinel error
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```go
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var ParseError = merry.New("parse error")
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func Parse() error {
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// ...
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return ParseError.Here() // captures a stacktrace here
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}
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```
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* The golang idiom for testing errors against sentinel values or type checking them
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doesn't work with merry errors, since they are wrapped. Use Is() for sentinel value
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checks, or the new go 2 errors.As() function for testing error types.
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```go
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err := Parse()
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// sentinel value check
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if merry.Is(err, ParseError) {
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// ...
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}
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// type check
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if serr, ok := merry.Unwrap(err).(*SyntaxError); ok {
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// ...
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}
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// these only work in go1.13
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// sentinel value check
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if errors.Is(err, ParseError) {}
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// type check
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var serr *SyntaxError
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if errors.As(err, &serr) {}
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```
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* Add to the message on an error.
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```go
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err := merry.Prepend(ParseError, "reading config").Append("bad input")
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fmt.Println(err.Error()) // reading config: parse error: bad input
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```
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* Hierarchies of errors
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```go
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var ParseError = merry.New("Parse error")
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var InvalidCharSet = merry.WithMessage(ParseError, "Invalid char set")
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var InvalidSyntax = merry.WithMessage(ParseError, "Invalid syntax")
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func Parse(s string) error {
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// use chainable methods to add context
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return InvalidCharSet.Here().WithMessagef("Invalid char set: %s", "UTF-8")
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// or functions
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// return merry.WithMessagef(merry.Here(InvalidCharSet), "Invalid char set: %s", "UTF-8")
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}
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func Check() {
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err := Parse("fields")
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merry.Is(err, ParseError) // yup
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merry.Is(err, InvalidCharSet) // yup
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merry.Is(err, InvalidSyntax) // nope
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}
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```
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* Add an HTTP status code
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```go
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merry.HTTPCode(errors.New("regular error")) // 500
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merry.HTTPCode(merry.New("merry error").WithHTTPCode(404)) // 404
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```
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* Set an alternate error message for end users
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```go
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e := merry.New("crash").WithUserMessage("nothing to see here")
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merry.UserMessage(e) // returns "nothing to see here"
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```
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* Functions for printing error details
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```go
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err := merry.New("boom")
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m := merry.Stacktrace(err) // just the stacktrace
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m = merry.Details(err) // error message and stacktrace
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fmt.Sprintf("%+v", err) == merry.Details(err) // errors implement fmt.Formatter
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```
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* Add your own context info
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```go
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err := merry.New("boom").WithValue("explosive", "black powder")
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```
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Basic Usage
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-----------
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The package contains functions for creating new errors with stacks, or adding a stack to `error`
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instances. Functions with add context (e.g. `WithValue()`) work on any `error`, and will
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automatically convert them to merry errors (with a stack) if necessary.
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Capturing the stack can be globally disabled with `SetStackCaptureEnabled(false)`
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Functions which get context values from errors also accept `error`, and will return default
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values if the error is not merry, or doesn't have that key attached.
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All the functions which create or attach context return concrete instances of `*Error`. `*Error`
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implements methods to add context to the error (they mirror the functions and do
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the same thing). They allow for a chainable syntax for adding context.
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Example:
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```go
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package main
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import (
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"github.com/ansel1/merry"
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"errors"
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)
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var InvalidInputs = errors.New("Input is invalid")
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func main() {
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// create a new error, with a stacktrace attached
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err := merry.New("bad stuff happened")
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// create a new error with format string, like fmt.Errorf
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err = merry.Errorf("bad input: %v", os.Args)
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// capture a fresh stacktrace from this callsite
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err = merry.Here(InvalidInputs)
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// Make err merry if it wasn't already. The stacktrace will be captured here if the
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// error didn't already have one. Also useful to cast to *Error
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err = merry.Wrap(err, 0)
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// override the original error's message
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err.WithMessagef("Input is invalid: %v", os.Args)
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// Use Is to compare errors against values, which is a common golang idiom
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merry.Is(err, InvalidInputs) // will be true
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// associated an http code
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err.WithHTTPCode(400)
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perr := parser.Parse("blah")
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err = Wrap(perr, 0)
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// Get the original error back
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merry.Unwrap(err) == perr // will be true
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// Print the error to a string, with the stacktrace, if it has one
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s := merry.Details(err)
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// Just print the stacktrace (empty string if err is not a RichError)
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s := merry.Stacktrace(err)
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// Get the location of the error (the first line in the stacktrace)
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file, line := merry.Location(err)
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// Get an HTTP status code for an error. Defaults to 500 for non-nil errors, and 200 if err is nil.
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code := merry.HTTPCode(err)
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}
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```
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See inline docs for more details.
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Plugs
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-----
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- Check out my HTTP client library: [github.com/gemalto/requester](https://github.com/gemalto/requester)
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- Check out my log library: [github.com/gemalto/flume](https://github.com/gemalto/flume)
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License
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-------
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This package is licensed under the MIT license, see LICENSE.MIT for details.
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