# JSON-Patch
`jsonpatch` is a library which provides functionality for both applying
[RFC6902 JSON patches](http://tools.ietf.org/html/rfc6902) against documents, as
well as for calculating & applying [RFC7396 JSON merge patches](https://tools.ietf.org/html/rfc7396).

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# Get It!

**Latest and greatest**: 
```bash
go get -u github.com/evanphx/json-patch/v5
```

If you need version 4, use `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-merge-patch)
* [Create and apply a JSON Patch](#create-and-apply-a-json-patch)
* [Comparing JSON documents](#comparing-json-documents)
* [Combine merge patches](#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.

These global variables control the behavior of `jsonpatch.Apply`.

An alternative to `jsonpatch.Apply` is `jsonpatch.ApplyWithOptions` whose behavior
is controlled by an `options` parameter of type `*jsonpatch.ApplyOptions`.

Structure `jsonpatch.ApplyOptions` includes the configuration options above 
and adds two new options: `AllowMissingPathOnRemove` and `EnsurePathExistsOnAdd`.

When `AllowMissingPathOnRemove` is set to `true`, `jsonpatch.ApplyWithOptions` will ignore
`remove` operations whose `path` points to a non-existent location in the JSON document.
`AllowMissingPathOnRemove` defaults to `false` which will lead to `jsonpatch.ApplyWithOptions`
returning an error when hitting a missing `path` on `remove`.

When `EnsurePathExistsOnAdd` is set to `true`, `jsonpatch.ApplyWithOptions` will make sure
that `add` operations produce all the `path` elements that are missing from the target object.

Use `jsonpatch.NewApplyOptions` to create an instance of `jsonpatch.ApplyOptions`
whose values are populated from the global configuration variables.

## Create and apply a merge patch
Given both an original JSON document and a modified JSON document, you can create
a [Merge Patch](https://tools.ietf.org/html/rfc7396) 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.

```go
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:

```bash
$ go run main.go
patch document:   {"height":null,"name":"Jane"}
updated alternative 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.

```go
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:

```bash
$ 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.

```go
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 "different"`)
	}
}
```

When ran, you get the following output:
```bash
$ go run main.go
"original" is structurally equal to "similar"
"original" is _not_ structurally equal to "different"
```

## 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. 

```go
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:
```bash
$ 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**
```json
[
    {"op": "replace", "path": "/name", "value": "Jane"},
    {"op": "remove", "path": "/height"}
]
```

**patch.2.json**
```json
[
    {"op": "add", "path": "/address", "value": "123 Main St"},
    {"op": "replace", "path": "/age", "value": "21"}
]
```

**document.json**
```json
{
    "name": "John",
    "age": 24,
    "height": 3.21
}
```

You can then run:

```bash
$ 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](https://github.com/evanphx/json-patch/issues)
or [create a PR](https://github.com/evanphx/json-patch/compare).


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:

```bash
go test -cover ./...
```

Builds for pull requests are tested automatically 
using [GitHub Actions](https://github.com/evanphx/json-patch/actions/workflows/go.yml).
