# 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).
[](http://godoc.org/github.com/evanphx/json-patch)
[](https://travis-ci.org/evanphx/json-patch)
[](https://goreportcard.com/report/github.com/evanphx/json-patch)
# Get It!
**Latest and greatest**:
```bash
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!
* [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 [TravisCI](https://travis-ci.org/evanphx/json-patch).
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