gleamson/patch

JSON Patch (RFC 6902): describe and apply changes to a gleamson.Json document, and compute the difference between two documents.

A patch is a list of Operations applied in order and atomically — if any operation fails, apply returns an error and the original document is left untouched. Paths are JSON Pointers (RFC 6901).

import gleamson
import gleamson/patch.{Add, Replace}

let assert Ok(doc) = gleamson.parse("{\"a\":1,\"b\":[10]}")
let assert Ok(out) =
  patch.apply(doc, [Replace("/a", gleamson.Int(2)), Add("/b/-", gleamson.Int(20))])
// out == {"a":2,"b":[10,20]}

Types

Operation

</>

A single JSON Patch operation. Paths and from are JSON Pointer strings.

pub type Operation {
  Add(path: String, value: gleamson.Json)
  Remove(path: String)
  Replace(path: String, value: gleamson.Json)
  Move(from: String, path: String)
  Copy(from: String, path: String)
  Test(path: String, value: gleamson.Json)
}

Constructors

```
Add(path: String, value: gleamson.Json)
```
```
Remove(path: String)
```

Replace(path: String, value: gleamson.Json)

```
Move(from: String, path: String)
```
```
Copy(from: String, path: String)
```

Test(path: String, value: gleamson.Json)

PatchError

</>

Why applying a patch failed.

pub type PatchError {
  PathNotFound(path: String)
  InvalidPath(path: String)
  TestFailed(
    path: String,
    expected: gleamson.Json,
    actual: gleamson.Json,
  )
}

Constructors

```
PathNotFound(path: String)
```
A path referred to a location that does not exist.
```
InvalidPath(path: String)
```
A path was not a valid JSON Pointer for the target.

TestFailed(
  path: String,
  expected: gleamson.Json,
  actual: gleamson.Json,
)

A Test operation did not match.

Values

apply

</>

pub fn apply(
  json: gleamson.Json,
  operations: List(Operation),
) -> Result(gleamson.Json, PatchError)

Apply a patch to a document. All operations succeed, or none are applied.

decoder

</>

pub fn decoder() -> fn(gleamson.Json) -> #(
  List(Operation),
  List(decode.DecodeError),
)

A decoder for a JSON Patch document (an array of operations). Pair it with gleamson.parse / decode.from_string to read a patch off the wire.

diff

</>

pub fn diff(
  from from: gleamson.Json,
  to to: gleamson.Json,
) -> List(Operation)

Compute a patch that turns from into to. The result is correct but not guaranteed minimal: array changes are emitted positionally rather than by detecting moves.

to_json

</>

pub fn to_json(operations: List(Operation)) -> gleamson.Json

Encode a patch as a JSON value (an array of operation objects).