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JSON-Patch

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

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Get It!

Latest and greatest:

go get -u github.com/evanphx/json-patch/v5

Stable Versions:

  • Version 5: go get -u gopkg.in/evanphx/json-patch.v5
  • Version 4: go get -u gopkg.in/evanphx/json-patch.v4

(previous versions below v3 are unavailable)

Use It!

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 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 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.

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 "different"`)
	}
}

When ran, you get the following output:

$ 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.

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.