prometheus/vendor/github.com/evanphx/json-patch/README.md

JSON-Patch

jsonpatch is a library which provides functionallity for both applying RFC6902 JSON patches against documents, as well as for calculating & applying RFC7396 JSON merge patches.

Get It!

Latest and greatest:

go get -u github.com/evanphx/json-patch

Stable Versions:

• Version 4: go get -u gopkg.in/evanphx/json-patch.v4

(previous versions below v3 are unavailable)

Use It!

• Create and apply a merge patch
• Create and apply a JSON Patch
• Comparing JSON documents
• Combine merge patches

Configuration

• There is a global configuration variable jsonpatch.SupportNegativeIndices. This defaults to true and enables the non-standard practice of allowing negative indices to mean indices starting at the end of an array. This functionality can be disabled by setting jsonpatch.SupportNegativeIndices = false.

• There is a global configuration variable jsonpatch.AccumulatedCopySizeLimit, which limits the total size increase in bytes caused by "copy" operations in a patch. It defaults to 0, which means there is no limit.

Create and apply a merge patch

Given both an original JSON document and a modified JSON document, you can create a Merge Patch document.

It can describe the changes needed to convert from the original to the modified JSON document.

Once you have a merge patch, you can apply it to other JSON documents using the jsonpatch.MergePatch(document, patch) function.

package main

import (
	"fmt"

	jsonpatch "github.com/evanphx/json-patch"
)

func main() {
	// Let's create a merge patch from these two documents...
	original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
	target := []byte(`{"name": "Jane", "age": 24}`)

	patch, err := jsonpatch.CreateMergePatch(original, target)
	if err != nil {
		panic(err)
	}

	// Now lets apply the patch against a different JSON document...

	alternative := []byte(`{"name": "Tina", "age": 28, "height": 3.75}`)
	modifiedAlternative, err := jsonpatch.MergePatch(alternative, patch)

	fmt.Printf("patch document:   %s\n", patch)
	fmt.Printf("updated alternative doc: %s\n", modifiedAlternative)
}

When ran, you get the following output:

$ go run main.go
patch document:   {"height":null,"name":"Jane"}
updated tina doc: {"age":28,"name":"Jane"}

Create and apply a JSON Patch

You can create patch objects using DecodePatch([]byte), which can then be applied against JSON documents.

The following is an example of creating a patch from two operations, and applying it against a JSON document.

package main

import (
	"fmt"

	jsonpatch "github.com/evanphx/json-patch"
)

func main() {
	original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
	patchJSON := []byte(`[
		{"op": "replace", "path": "/name", "value": "Jane"},
		{"op": "remove", "path": "/height"}
	]`)

	patch, err := jsonpatch.DecodePatch(patchJSON)
	if err != nil {
		panic(err)
	}

	modified, err := patch.Apply(original)
	if err != nil {
		panic(err)
	}

	fmt.Printf("Original document: %s\n", original)
	fmt.Printf("Modified document: %s\n", modified)
}

When ran, you get the following output:

$ go run main.go
Original document: {"name": "John", "age": 24, "height": 3.21}
Modified document: {"age":24,"name":"Jane"}

Comparing JSON documents

Due to potential whitespace and ordering differences, one cannot simply compare JSON strings or byte-arrays directly.

As such, you can instead use jsonpatch.Equal(document1, document2) to determine if two JSON documents are structurally equal. This ignores whitespace differences, and key-value ordering.

package main

import (
	"fmt"

	jsonpatch "github.com/evanphx/json-patch"
)

func main() {
	original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
	similar := []byte(`
		{
			"age": 24,
			"height": 3.21,
			"name": "John"
		}
	`)
	different := []byte(`{"name": "Jane", "age": 20, "height": 3.37}`)

	if jsonpatch.Equal(original, similar) {
		fmt.Println(`"original" is structurally equal to "similar"`)
	}

	if !jsonpatch.Equal(original, different) {
		fmt.Println(`"original" is _not_ structurally equal to "similar"`)
	}
}

When ran, you get the following output:

$ go run main.go
"original" is structurally equal to "similar"
"original" is _not_ structurally equal to "similar"

Combine merge patches

Given two JSON merge patch documents, it is possible to combine them into a single merge patch which can describe both set of changes.

The resulting merge patch can be used such that applying it results in a document structurally similar as merging each merge patch to the document in succession.

package main

import (
	"fmt"

	jsonpatch "github.com/evanphx/json-patch"
)

func main() {
	original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)

	nameAndHeight := []byte(`{"height":null,"name":"Jane"}`)
	ageAndEyes := []byte(`{"age":4.23,"eyes":"blue"}`)

	// Let's combine these merge patch documents...
	combinedPatch, err := jsonpatch.MergeMergePatches(nameAndHeight, ageAndEyes)
	if err != nil {
		panic(err)
	}

	// Apply each patch individual against the original document
	withoutCombinedPatch, err := jsonpatch.MergePatch(original, nameAndHeight)
	if err != nil {
		panic(err)
	}

	withoutCombinedPatch, err = jsonpatch.MergePatch(withoutCombinedPatch, ageAndEyes)
	if err != nil {
		panic(err)
	}

	// Apply the combined patch against the original document

	withCombinedPatch, err := jsonpatch.MergePatch(original, combinedPatch)
	if err != nil {
		panic(err)
	}

	// Do both result in the same thing? They should!
	if jsonpatch.Equal(withCombinedPatch, withoutCombinedPatch) {
		fmt.Println("Both JSON documents are structurally the same!")
	}

	fmt.Printf("combined merge patch: %s", combinedPatch)
}

When ran, you get the following output:

$ go run main.go
Both JSON documents are structurally the same!
combined merge patch: {"age":4.23,"eyes":"blue","height":null,"name":"Jane"}

CLI for comparing JSON documents

You can install the commandline program json-patch.

This program can take multiple JSON patch documents as arguments, and fed a JSON document from stdin. It will apply the patch(es) against the document and output the modified doc.

patch.1.json

[
    {"op": "replace", "path": "/name", "value": "Jane"},
    {"op": "remove", "path": "/height"}
]

patch.2.json

[
    {"op": "add", "path": "/address", "value": "123 Main St"},
    {"op": "replace", "path": "/age", "value": "21"}
]

document.json

{
    "name": "John",
    "age": 24,
    "height": 3.21
}

You can then run:

$ go install github.com/evanphx/json-patch/cmd/json-patch
$ cat document.json | json-patch -p patch.1.json -p patch.2.json
{"address":"123 Main St","age":"21","name":"Jane"}

Help It!

Contributions are welcomed! Leave an issue or create a PR.

Before creating a pull request, we'd ask that you make sure tests are passing and that you have added new tests when applicable.

Contributors can run tests using:

go test -cover ./...

Builds for pull requests are tested automatically using TravisCI.