mirror of https://github.com/prometheus/prometheus
293 lines
7.6 KiB
Markdown
293 lines
7.6 KiB
Markdown
# JSON-Patch
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`jsonpatch` is a library which provides functionallity for both applying
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[RFC6902 JSON patches](http://tools.ietf.org/html/rfc6902) against documents, as
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well as for calculating & applying [RFC7396 JSON merge patches](https://tools.ietf.org/html/rfc7396).
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[](http://godoc.org/github.com/evanphx/json-patch)
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[](https://travis-ci.org/evanphx/json-patch)
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[](https://goreportcard.com/report/github.com/evanphx/json-patch)
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# Get It!
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**Latest and greatest**:
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```bash
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go get -u github.com/evanphx/json-patch
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```
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**Stable Versions**:
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* Version 4: `go get -u gopkg.in/evanphx/json-patch.v4`
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(previous versions below `v3` are unavailable)
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# Use It!
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* [Create and apply a merge patch](#create-and-apply-a-merge-patch)
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* [Create and apply a JSON Patch](#create-and-apply-a-json-patch)
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* [Comparing JSON documents](#comparing-json-documents)
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* [Combine merge patches](#combine-merge-patches)
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# Configuration
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There is a single global configuration variable `jsonpatch.SupportNegativeIndices'. This
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defaults to `true` and enables the non-standard practice of allowing negative indices
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to mean indices starting at the end of an array. This functionality can be disabled
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by setting `jsonpatch.SupportNegativeIndices = false`.
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## Create and apply a merge patch
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Given both an original JSON document and a modified JSON document, you can create
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a [Merge Patch](https://tools.ietf.org/html/rfc7396) document.
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It can describe the changes needed to convert from the original to the
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modified JSON document.
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Once you have a merge patch, you can apply it to other JSON documents using the
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`jsonpatch.MergePatch(document, patch)` function.
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```go
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package main
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import (
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"fmt"
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jsonpatch "github.com/evanphx/json-patch"
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)
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func main() {
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// Let's create a merge patch from these two documents...
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original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
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target := []byte(`{"name": "Jane", "age": 24}`)
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patch, err := jsonpatch.CreateMergePatch(original, target)
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if err != nil {
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panic(err)
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}
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// Now lets apply the patch against a different JSON document...
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alternative := []byte(`{"name": "Tina", "age": 28, "height": 3.75}`)
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modifiedAlternative, err := jsonpatch.MergePatch(alternative, patch)
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fmt.Printf("patch document: %s\n", patch)
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fmt.Printf("updated alternative doc: %s\n", modifiedAlternative)
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}
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```
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When ran, you get the following output:
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```bash
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$ go run main.go
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patch document: {"height":null,"name":"Jane"}
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updated tina doc: {"age":28,"name":"Jane"}
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```
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## Create and apply a JSON Patch
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You can create patch objects using `DecodePatch([]byte)`, which can then
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be applied against JSON documents.
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The following is an example of creating a patch from two operations, and
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applying it against a JSON document.
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```go
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package main
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import (
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"fmt"
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jsonpatch "github.com/evanphx/json-patch"
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)
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func main() {
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original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
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patchJSON := []byte(`[
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{"op": "replace", "path": "/name", "value": "Jane"},
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{"op": "remove", "path": "/height"}
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]`)
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patch, err := jsonpatch.DecodePatch(patchJSON)
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if err != nil {
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panic(err)
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}
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modified, err := patch.Apply(original)
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if err != nil {
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panic(err)
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}
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fmt.Printf("Original document: %s\n", original)
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fmt.Printf("Modified document: %s\n", modified)
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}
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```
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When ran, you get the following output:
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```bash
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$ go run main.go
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Original document: {"name": "John", "age": 24, "height": 3.21}
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Modified document: {"age":24,"name":"Jane"}
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```
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## Comparing JSON documents
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Due to potential whitespace and ordering differences, one cannot simply compare
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JSON strings or byte-arrays directly.
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As such, you can instead use `jsonpatch.Equal(document1, document2)` to
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determine if two JSON documents are _structurally_ equal. This ignores
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whitespace differences, and key-value ordering.
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```go
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package main
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import (
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"fmt"
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jsonpatch "github.com/evanphx/json-patch"
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)
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func main() {
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original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
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similar := []byte(`
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{
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"age": 24,
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"height": 3.21,
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"name": "John"
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}
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`)
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different := []byte(`{"name": "Jane", "age": 20, "height": 3.37}`)
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if jsonpatch.Equal(original, similar) {
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fmt.Println(`"original" is structurally equal to "similar"`)
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}
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if !jsonpatch.Equal(original, different) {
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fmt.Println(`"original" is _not_ structurally equal to "similar"`)
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}
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}
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```
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When ran, you get the following output:
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```bash
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$ go run main.go
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"original" is structurally equal to "similar"
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"original" is _not_ structurally equal to "similar"
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```
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## Combine merge patches
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Given two JSON merge patch documents, it is possible to combine them into a
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single merge patch which can describe both set of changes.
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The resulting merge patch can be used such that applying it results in a
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document structurally similar as merging each merge patch to the document
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in succession.
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```go
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package main
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import (
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"fmt"
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jsonpatch "github.com/evanphx/json-patch"
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)
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func main() {
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original := []byte(`{"name": "John", "age": 24, "height": 3.21}`)
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nameAndHeight := []byte(`{"height":null,"name":"Jane"}`)
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ageAndEyes := []byte(`{"age":4.23,"eyes":"blue"}`)
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// Let's combine these merge patch documents...
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combinedPatch, err := jsonpatch.MergeMergePatches(nameAndHeight, ageAndEyes)
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if err != nil {
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panic(err)
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}
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// Apply each patch individual against the original document
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withoutCombinedPatch, err := jsonpatch.MergePatch(original, nameAndHeight)
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if err != nil {
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panic(err)
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}
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withoutCombinedPatch, err = jsonpatch.MergePatch(withoutCombinedPatch, ageAndEyes)
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if err != nil {
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panic(err)
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}
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// Apply the combined patch against the original document
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withCombinedPatch, err := jsonpatch.MergePatch(original, combinedPatch)
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if err != nil {
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panic(err)
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}
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// Do both result in the same thing? They should!
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if jsonpatch.Equal(withCombinedPatch, withoutCombinedPatch) {
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fmt.Println("Both JSON documents are structurally the same!")
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}
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fmt.Printf("combined merge patch: %s", combinedPatch)
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}
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```
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When ran, you get the following output:
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```bash
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$ go run main.go
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Both JSON documents are structurally the same!
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combined merge patch: {"age":4.23,"eyes":"blue","height":null,"name":"Jane"}
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```
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# CLI for comparing JSON documents
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You can install the commandline program `json-patch`.
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This program can take multiple JSON patch documents as arguments,
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and fed a JSON document from `stdin`. It will apply the patch(es) against
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the document and output the modified doc.
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**patch.1.json**
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```json
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[
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{"op": "replace", "path": "/name", "value": "Jane"},
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{"op": "remove", "path": "/height"}
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]
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```
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**patch.2.json**
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```json
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[
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{"op": "add", "path": "/address", "value": "123 Main St"},
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{"op": "replace", "path": "/age", "value": "21"}
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]
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```
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**document.json**
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```json
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{
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"name": "John",
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"age": 24,
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"height": 3.21
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}
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```
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You can then run:
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```bash
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$ go install github.com/evanphx/json-patch/cmd/json-patch
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$ cat document.json | json-patch -p patch.1.json -p patch.2.json
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{"address":"123 Main St","age":"21","name":"Jane"}
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```
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# Help It!
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Contributions are welcomed! Leave [an issue](https://github.com/evanphx/json-patch/issues)
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or [create a PR](https://github.com/evanphx/json-patch/compare).
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Before creating a pull request, we'd ask that you make sure tests are passing
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and that you have added new tests when applicable.
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Contributors can run tests using:
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```bash
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go test -cover ./...
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```
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Builds for pull requests are tested automatically
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using [TravisCI](https://travis-ci.org/evanphx/json-patch).
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