docs: improve doc of LockScriptInfo

packages/common-scripts/examples/custom_lock_script_info/custom_lock_script_info.ts

@@ -0,0 +1,279 @@
+import {
+  Cell,
+  CellCollector,
+  CellProvider,
+  QueryOptions,
+  blockchain,
+} from "@ckb-lumos/base";
+import * as apiTypes from "@ckb-lumos/base/lib/api";
+import { BI } from "@ckb-lumos/bi";
+import * as codec from "@ckb-lumos/codec";
+import { getConfig } from "@ckb-lumos/config-manager";
+import { Options, TransactionSkeletonType } from "@ckb-lumos/helpers";
+import { List, Map } from "immutable";
+import * as commons from "../../src";
+import { addCellDep } from "../../src/helper";
+
+// Compare two objects by convert them to molecule buffer to ignore the representation only
+// differences.
+function isSameScript(a: apiTypes.Script, b: apiTypes.Script) {
+  return (
+    codec.bytes.hexify(blockchain.Script.pack(a)) ===
+    codec.bytes.hexify(blockchain.Script.pack(b))
+  );
+}
+
+const MAX_U64_PLUS_ONE = BI.from(1).shl(64);
+function packInt64LE(number: BI) {
+  return codec.number.Uint64LE.pack(
+    number.isNegative() ? MAX_U64_PLUS_ONE.add(number) : number
+  );
+}
+
+// This example demonstrates how to use a custom script [CapacityDiff](https://github.com/doitian/ckb-sdk-examples-capacity-diff).
+//
+// CapacityDiff verifies the witness matches the capacity difference.
+//
+// -   The script loads the witness for the first input in the script group using the WitnessArgs layout.
+// -   The total input capacity is the sum of all the input cells in the script group.
+// -   The total output capacity is the sum of all the output cells having the same lock script as the script group.
+// -   The capacity difference is a 64-bit signed integer which equals to total output capacity minus total input capacity.
+// -   The witness is encoded using two's complement and little endian.
+const capacityDiffLockInfo: commons.LockScriptInfo = {
+  codeHash: "0x",
+  hashType: "type",
+  lockScriptInfo: {
+    CellCollector: class {
+      cellCollector: CellCollector;
+      fromScript = {
+        codeHash: "0x",
+        hashType: "type" as apiTypes.HashType,
+        args: "0x",
+      };
+
+      constructor(
+        fromInfo: commons.FromInfo,
+        cellProvider: CellProvider,
+        { config, queryOptions }: Options & { queryOptions?: QueryOptions }
+      ) {
+        if (!cellProvider) {
+          throw new Error(`Cell provider is missing!`);
+        }
+        config ??= getConfig();
+        const script = commons.parseFromInfo(fromInfo, { config }).fromScript;
+
+        // Please note that the cell collector is called for each specific fromInfo.
+        // Be cautious not to include input cells for accounts that are not locked by this script.
+        const template = config.SCRIPTS.CAPACITY_DIFF!;
+        if (
+          script.codeHash !== template.CODE_HASH ||
+          script.hashType !== template.HASH_TYPE
+        ) {
+          return;
+        }
+
+        // Now we can apply the queryOptions to search the live cells.
+        queryOptions ??= {};
+        queryOptions = {
+          ...queryOptions,
+          lock: script,
+          type: queryOptions.type ?? "empty",
+        };
+
+        this.cellCollector = cellProvider.collector(queryOptions);
+      }
+
+      async *collect() {
+        if (this.cellCollector) {
+          for await (const inputCell of this.cellCollector.collect()) {
+            yield inputCell;
+          }
+        }
+      }
+    },
+
+    // What to do when a inputCell has been found by the cell provider.
+    // - Add input and output cell
+    // - Add cell deps.
+    // - Fill witness to make fee calculation correct.
+    setupInputCell: async (
+      txSkeleton: TransactionSkeletonType,
+      inputCell: Cell,
+      _fromInfo: commons.FromInfo,
+      { config, since, defaultWitness } = {}
+    ) => {
+      // use default config when config is not provided
+      config ??= getConfig();
+      const fromScript = inputCell.cellOutput.lock;
+      const txMutable = txSkeleton.asMutable();
+
+      //===========================
+      // I. Common Skeletons
+      //
+      // There are many steps that setupInputCell must perform carefully, otherwise the whole transaction builder will fail.
+      //===========================
+      // 1.Add inputCell to txSkeleton
+      txMutable.update("inputs", (inputs: List<Cell>) =>
+        inputs.push(inputCell)
+      );
+
+      // 2. Add output. The function `lumos.commons.common.transfer` will scan outputs for available balance for each account.
+      const outputCell = {
+        cellOutput: {
+          ...inputCell.cellOutput,
+        },
+        data: inputCell.data,
+      };
+      txMutable.update("outputs", (outputs: List<Cell>) =>
+        outputs.push(outputCell)
+      );
+
+      // 3. Set Since
+      if (since) {
+        txMutable.setIn(
+          ["inputSinces", txMutable.get("inputs").size - 1],
+          since
+        );
+      }
+
+      // 4. Insert a witness to ensure they are aligned to the location of the corresponding input cells.
+      txMutable.update("witnesses", (witnesses: List<string>) =>
+        witnesses.push(defaultWitness ?? "0x")
+      );
+      //=> Common Skeletons End Here
+
+      //===========================
+      // II. CellDeps
+      //===========================
+      // Assume that script onchain infos are stored as CAPACITY_DIFF
+      const template = config.SCRIPTS.CAPACITY_DIFF;
+      if (!template) {
+        throw new Error(
+          "Provided config does not have CAPACITY_DIFF script setup!"
+        );
+      }
+      const scriptOutPoint = {
+        txHash: template.TX_HASH,
+        index: template.INDEX,
+      };
+      // The helper method addCellDep avoids adding duplicated cell deps.
+      addCellDep(txMutable, {
+        outPoint: scriptOutPoint,
+        depType: template.DEP_TYPE,
+      });
+
+      //===========================
+      // II. Witness Placeholder
+      //===========================
+      // Fill witness. These code are copied from
+      // https://github.com/ckb-js/lumos/blob/1cb43fe72dc95c4b3283acccb5120b7bcaeb9346/packages/common-scripts/src/secp256k1_blake160.ts#L90
+      //
+      // It takes a lot of code to set the witness for the first input cell in
+      // the script group to 8 bytes of zeros.
+      const firstIndex = txMutable
+        .get("inputs")
+        .findIndex((input: Cell) =>
+          isSameScript(input.cellOutput.lock, fromScript)
+        );
+
+      if (firstIndex !== -1) {
+        // Ensure witnesses are aligned to inputs
+        const toFillWitnessesCount =
+          firstIndex + 1 - txMutable.get("witnesses").size;
+        if (toFillWitnessesCount > 0) {
+          txMutable.update("witnesses", (witnesses: List<string>) =>
+            witnesses.concat(Array(toFillWitnessesCount).fill("0x"))
+          );
+        }
+        txMutable.updateIn(["witnesses", firstIndex], (witness: any) => {
+          const witnessArgs = {
+            ...(witness === "0x"
+              ? {}
+              : blockchain.WitnessArgs.unpack(codec.bytes.bytify(witness))),
+            lock: "0x0000000000000000",
+          };
+          return codec.bytes.hexify(blockchain.WitnessArgs.pack(witnessArgs));
+        });
+      }
+
+      return txMutable.asImmutable();
+    },
+
+    // Create entries in txSkeleton.signingEntries
+    prepareSigningEntries: (
+      txSkeleton: TransactionSkeletonType,
+      { config }
+    ) => {
+      // use default config when config is not provided
+      config ??= getConfig();
+      const template = config.SCRIPTS.CAPACITY_DIFF;
+      if (!template) {
+        throw new Error(
+          `Provided config does not have CAPACITY_DIFF script setup!`
+        );
+      }
+
+      const balances = Map<
+        string,
+        { index: number; capacity: BI }
+      >().asMutable();
+      // Group inputs by args and tally the total capacity as negative values.
+      txSkeleton.get("inputs").forEach((input: Cell, index: number) => {
+        const {
+          capacity,
+          lock: { codeHash, hashType, args },
+        } = input.cellOutput;
+        if (
+          template.CODE_HASH === codeHash &&
+          template.HASH_TYPE === hashType
+        ) {
+          if (balances.has(args)) {
+            balances.updateIn([args, "capacity"], (total: any) =>
+              total.sub(capacity)
+            );
+          } else {
+            balances.set(args, { index, capacity: BI.from(0).sub(capacity) });
+          }
+        }
+      });
+      // Add capacity of output cells to the tally.
+      txSkeleton.get("outputs").forEach((output: Cell) => {
+        const {
+          capacity,
+          lock: { codeHash, hashType, args },
+        } = output.cellOutput;
+        if (
+          template.CODE_HASH === codeHash &&
+          template.HASH_TYPE === hashType &&
+          balances.has(args)
+        ) {
+          balances.updateIn([args, "capacity"], (total: any) =>
+            total.add(capacity)
+          );
+        }
+      });
+      // Create signing entries. Indeed, for this simple script, we could set
+      // the witness directly. However, for serious lock script, it often
+      // requires sining by the private
+      // key.
+      return txSkeleton.update(
+        "signingEntries",
+        (entries: List<{ index: number; type: string; message: string }>) =>
+          entries.concat(
+            balances
+              .asImmutable()
+              .valueSeq()
+              .map(({ index, capacity }: any) => ({
+                index,
+                // This is the only supported type, which indicate the signature
+                // follows the WitnewsArgs layout.
+                type: "witness_args_lock",
+                message: codec.bytes.hexify(packInt64LE(capacity)),
+              }))
+          )
+      );
+    },
+  },
+};
+
+commons.common.registerCustomLockScriptInfos([capacityDiffLockInfo]);

packages/common-scripts/src/common.ts

@@ -31,22 +31,61 @@ const { ScriptValue } = values;
 import { Set } from "immutable";
 import { isAcpScript } from "./helper";
 import { BI, BIish } from "@ckb-lumos/bi";
-import { CellCollectorConstructor } from "./type";
+import { CellCollectorConstructor, CellCollectorType } from "./type";
 import omnilock from "./omnilock";
 
 function defaultLogger(level: string, message: string) {
   console.log(`[${level}] ${message}`);
 }
+
+export type { CellCollectorConstructor, CellCollectorType };
+
 /**
- * CellCollector should be a class which implement CellCollectorInterface.
- * If you want to work well with `transfer`, `injectCapacity`, `payFee`, `payFeeByFeeRate`,
- *  please add the `output` at the end of `txSkeleton.get("outputs")`
+ * LockScriptInfo describes how to integrate a lock script in transaction building.
+ *
+ * Custom lock scripts must register their LockScriptInfo before using
+ * `transfer`, `injectCapacity`, `payFee`, `payFeeByFeeRate` via
+ * `registerCustomLockScriptInfos`.
+ *
+ * See an example in
+ * [custom_lock_script_info.ts](https://github.com/ckb-js/lumos/blob/develop/packages/common-scripts/examples/custom_lock_script_info/custom_lock_script_info.ts).
  */
 export interface LockScriptInfo {
   codeHash: Hash;
   hashType: HashType;
+  /**
+   * @interface
+   */
   lockScriptInfo: {
+    /**
+     * Collects input cell candidates for the lock script.
+     *
+     * It's a constructor that initializes objects implementing function
+     * `collect()` to provide input cells. Attention that transaction builders
+     * will not match `fromInfo` and lock script. It's the responsibility of
+     * `CellCollector` to filter based on `fromInfo`. For example, when
+     * `fromInfo` does not match, the function `collect()` should not return
+     * any cell.
+     */
     CellCollector: CellCollectorConstructor;
+
+    /**
+     * Called when a candidate input cell is found.
+     *
+     * What this function should do:
+     *
+     * 1. Frist double-check the cell and decide whether continue the following steps or skip.
+     * 2. Add the cell as an input in the `txSkeleton` and an output cell with
+     *    the same fields since functions like `transfer`, `injectCapacity`,
+     *    `payFee`, and `payFeeByFeeRate` collects account balance in outputs.
+     * 3. Add `cellDeps`
+     * 4. Prefill witnesses to ensure the transaction size will not increase after signing.
+     *
+     * @param txSkeleton transaction skeleton built so far
+     * @param inputCell the new input cell candidate
+     * @param fromInfo which account the inputCell belongs to
+     * @return the updated transaction skeleton
+     */
     setupInputCell(
       txSkeleton: TransactionSkeletonType,
       inputCell: Cell,
@@ -57,10 +96,16 @@ export interface LockScriptInfo {
         since?: PackedSince;
       }
     ): Promise<TransactionSkeletonType>;
+
+    /**
+     * Scans the transaction and add signing entries into `txSkeleton.signingEnties`.
+     * @return the updated txSkeleton
+     */
     prepareSigningEntries(
       txSkeleton: TransactionSkeletonType,
       options: Options
     ): TransactionSkeletonType;
+
     setupOutputCell?: (
       txSkeleton: TransactionSkeletonType,
       outputCell: Cell,
@@ -96,6 +141,7 @@ function getLockScriptInfos(): LockScriptInfosType {
   return lockScriptInfos;
 }
 
+/** Registers LockScriptInfo for custom scripts. */
 export function registerCustomLockScriptInfos(infos: LockScriptInfo[]): void {
   lockScriptInfos._customInfos = infos;
 }

packages/common-scripts/src/index.ts

@@ -3,7 +3,11 @@ import secp256k1Blake160Multisig from "./secp256k1_blake160_multisig";
 import { MultisigScript, FromInfo, parseFromInfo } from "./from_info";
 import dao from "./dao";
 import locktimePool, { LocktimeCell } from "./locktime_pool";
-import common, { LockScriptInfo } from "./common";
+import common, {
+  LockScriptInfo,
+  CellCollectorConstructor,
+  CellCollectorType,
+} from "./common";
 import sudt from "./sudt";
 import anyoneCanPay from "./anyone_can_pay";
 import { createP2PKHMessageGroup } from "./p2pkh";
@@ -34,4 +38,11 @@ export default {
   anyoneCanPay,
 };
 
-export type { LocktimeCell, MultisigScript, FromInfo, LockScriptInfo };
+export type {
+  LocktimeCell,
+  MultisigScript,
+  FromInfo,
+  LockScriptInfo,
+  CellCollectorConstructor,
+  CellCollectorType,
+};