Podspec

specific | spɪˈsɪfɪk | adjective

• clearly defined or identified

ORIGIN mid 17th century (originally in the sense 'having a special determining quality'): from late Latin specificus, from Latin species

A library for validating the structure of PODs in TypeScript, providing static types and runtime validation.

Usage

Install the package:

npm install @pcd/podspec

Create a POD spec:

import { p } from "@pcd/podspec";

const spec = p.entries({
  name: { type: "string" },
  email: { type: "string" },
  high_score: { type: "int" }
});

Then use the spec to validate POD entries:

const entries = {
  name: { type: "string", value: "Bob Dugnutt" },
  email: { type: "string", value: "[email protected]" },
  high_score: { type: "int", value: 999999 }
};

const result = spec.parse(entries);
if (result.isValid) {
  // Ready to use the POD
  result.value; // Contains the POD entries
} else {
  // Handle the error
  result.errors; // Contains information about the errors
}

If the entries are valid, result.value will be a PODEntries object, with static types for the entries which are part of the spec. Otherwise, result.errors will contain information about the errors encountered during parsing.

Use cases

Validating PODEntries before signing a POD

When signing a POD, we want to make sure that the POD's entries meet our expectations. This means not just that the POD is well-formed, but that it also has the right structure and types.

For example, if we have a POD that represents a weapon in a game, we might have a spec that looks like this:

const weaponSpec = p.entries({
  name: { type: "string" },
  damage: { type: "int" },
  durability: { type: "int" },
  price: { type: "int" }
});

Now we can use the spec to validate POD entries before signing a POD:

const entries = {
  name: { type: "string", value: "Narsil" },
  damage: { type: "int", value: 10n },
  durability: { type: "int", value: 100n },
  price: { type: "int", value: 100n }
};

const result = weaponSpec.parse(entries);
if (result.isValid) {
  // Ready to sign the POD
} else {
  // Handle the error
  result.errors; // Contains information about the errors
}

Turning JavaScript objects into PODEntries

In the above example, we assumed that already had POD entries to validate. However, we might have a JavaScript object that we want to turn into POD entries. podspec can do some simple transformations to turn JavaScript objects into POD entries.

To coerce JavaScript objects into POD entries, set the coerce option to true:

const javascriptObject = {
  name: "Narsil",
  damage: 10,
  durability: 100,
  price: 100
};

const result = weaponSpec.parse(javascriptObject, { coerce: true });
if (result.isValid) {
  // Ready to sign the POD
} else {
  // Handle the error
  result.errors; // Contains information about the errors
}

Here, regular JavaScript objects are turned into POD entries. In particular, numbers are turned into ints, and strings are turned into strings.

Validating an existing POD

If you have a POD that is already signed, you can use podspec to validate the POD, including both the entries and the signer public key.

const pod = getPodFromSomewhere();
const pubKey = "expected_public_key";
const entriesSpec = p.entries({
  eventId: { type: "string" },
  productId: { type: "string" }
});
const podSpec = p.pod({ 
  entries: entriesSpec.schema,
  signerPublicKey: { isMemberOf: [pubKey] }
});

const result = podSpec.parse(pod);
if (result.isValid) {
  // Ready to use the POD
} else {
  // Handle the error
  result.errors; // Contains information about the errors
}

This will check that the POD has the right structure and types, and that the signer is the expected signer.

Querying a collection of PODs for matches

If you have a collection of PODs, you can use the spec to query the collection for PODs that match the spec:

const pods = [pod1, pod2, pod3];
const entriesSpec = p.entries({
  eventId: p.string(),
  productId: p.string()
});
const podSpec = p.pod({ entries: entriesSpec.schema });
const result = podSpec.query(pods);
result.matches; // Contains the PODs that match the spec
result.matchingIndexes; // Contains the array indexes of the PODs that match the spec

Other constraints

Range checks

As well as ensuring the existence and type of POD entries, podspec also provides some additional constraints, such as range and list checks.

const rangeSpec = p.entries({
  value: { type: "int", inRange: { min: 0n, max: 50n }}
});

const entries = {
  value: { type: "int", value: 50n }
};

const result = rangeSpec.parse(entries);

This will parse successfully. This will not:

const entries = {
  value: { type: "int", value: 200n }
};

const result = rangeSpec.parse(entries);

List checks

Entries can be checked against a list of values:

const listSpec = p.entries({
  value: { type: "int", isMemberOf: [
    { type: "int", value: 1n },
    { type: "int", value: 2n },
    { type: "int", value: 3n },
  ]}
});

const entries = {
  value: { type: "int", value: 2n }
};

const result = listSpec.parse(entries);

This will parse successfully because the value 2n in the list.

Lists can also be used to specify invalid values which should not be allowed:

const listSpec = p.entries({
  value: { type: "int", isNotMemberOf: [
    { type: "int", value: 1n },
    { type: "int", value: 2n },
    { type: "int", value: 3n },
  ]}
});

const entries = {
  value: { type: "int", value: 2n }
};

const result = listSpec.parse(entries);

This will not parse successfully because the value 2n is in the list of excluded values.

Tuple checks

Multiple entries can be checked against a list of valid tuples.

const entriesSpec = p
  .entries({
    foo: { type: "string" },
    bar: { type: "int" }
  });

const podSpec = p.pod({
  entries: entriesSpec.schema,
  tuples: [{
    entries: ["foo", "bar"],
    isMemberOf: [
      [
        { type: "string", value: "test" },
        { type: "int", value: 5n }
      ],
      [
        { type: "string", value: "test2" },
        { type: "int", value: 10n }
      ]
    ]
  }]
});

In this example, we will accept any set of POD entries which has either a foo entry with value "test" and a bar entry with value 5n or a foo entry with value "test2" and a bar entry with value 10n.

const entries = {
  foo: { type: "string", value: "test" },
  bar: { type: "int", value: 5n }
};

const result = tupleSpec.parse(entries);

This matches the first tuple in the list, so the result will be valid.

const entries = {
  foo: { type: "string", value: "test2" },
  bar: { type: "int", value: 10n }
};

const result = tupleSpec.parse(entries);

This matches the second tuple in the list, so the result will be valid.

const entries = {
  foo: { type: "string", value: "test" },
  bar: { type: "int", value: 10n }
};

const result = tupleSpec.parse(entries);

This has a foo entry which matches the first tuple, and a bar entry which matches the second tuple, but does not match either tuple as a whole. Therefore, the result will be invalid.