Add Ptr with support for parsing/serializing

Author: ucarion

package.json

@@ -1,6 +1,21 @@
 {
   "devDependencies": {
+    "@types/jest": "^23.0.0",
+    "jest": "^23.0.0",
+    "ts-jest": "^23.10.5",
+    "tslint": "^5.12.1",
     "typedoc": "^0.14.2",
     "typescript": "^3.3.1"
+  },
+  "jest": {
+    "transform": {
+      "^.+\\.tsx?$": "ts-jest"
+    },
+    "rootDir": "src",
+    "testRegex": "(/__tests__/.*|(\\.|/)(test|spec))\\.(jsx?|tsx?)$",
+    "moduleFileExtensions": [
+      "js",
+      "ts"
+    ]
   }
 }

src/index.test.ts

@@ -0,0 +1,38 @@
+import Ptr, { InvalidPtrError } from "./index";
+
+describe("Ptr", () => {
+  describe("parse", () => {
+    it("handles well-formed JSON Pointer strings correctly", () => {
+      // These test cases are lifted from RFC6901, Section 5:
+      //
+      // https://tools.ietf.org/html/rfc6901#section-5
+      const cases = {
+        "": [],
+        "/foo": ["foo"],
+        "/foo/0": ["foo", "0"],
+        "/": [""],
+        "/a~1b": ["a/b"],
+        "/c%d": ["c%d"],
+        "/e^f": ["e^f"],
+        "/g|h": ["g|h"],
+        "/i\\j": ["i\\j"],
+        "/k\"l": ["k\"l"],
+        "/ ": [" "],
+        "/m~0n": ["m~n"],
+        "/o~0~1p/q~1~0r": ["o~/p", "q/~r"],
+      };
+
+      for (const [input, output] of Object.entries(cases)) {
+        const ptr = Ptr.parse(input);
+        expect(ptr.tokens).toEqual(output);
+        expect(ptr.toString()).toEqual(input);
+      }
+    });
+
+    it("throws an error for bad input", () => {
+      expect(() => {
+        Ptr.parse(" ");
+      }).toThrowError(new InvalidPtrError(" "));
+    });
+  });
+});

src/index.ts

@@ -0,0 +1,49 @@
+export default class Ptr {
+  public tokens: string[];
+
+  constructor(tokens: string[]) {
+    this.tokens = tokens;
+  }
+
+  public static parse(s: string): Ptr {
+    // From the ABNF syntax of JSON Pointer, the only valid initial character
+    // for a JSON Pointer is "/". Empty strings are acceptable.
+    //
+    // https://tools.ietf.org/html/rfc6901#section-3
+    //
+    // Other than this limitation, all strings are valid JSON Pointers.
+    if (s === "") {
+      return new Ptr([]);
+    }
+
+    if (!s.startsWith("/")) {
+      throw new InvalidPtrError(s);
+    }
+
+    const [, ...tokens] = s.split("/");
+    return new Ptr(tokens.map(token => {
+      return token.replace("~1", "/").replace("~0", "~");
+    }));
+  }
+
+  public toString(): string {
+    if (this.tokens.length === 0) {
+      return "";
+    }
+
+    const tokens = this.tokens.map(token => {
+      return token.replace("~", "~0").replace("/", "~1");
+    });
+
+    return `/${tokens.join("/")}`;
+  }
+}
+
+export class InvalidPtrError extends Error {
+  public ptr: string;
+
+  constructor(ptr: string) {
+    super(`Invalid JSON Pointer: ${ptr}`);
+    this.ptr = ptr;
+  }
+}