fix: solution for issue #19

SOLUTION_ISSUE_19.md

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+# Solution for Issue #19
+
+## 🛠️ Proposed Solution (by Aditya Waghamare)
+
+### Analysis
+The current `stripPrefix` option in `sparepack` only allows stripping a single prefix string from destination paths. In complex directory structures (monorepos, separate config/test/src dirs), a single prefix is insufficient. 
+
+To support general path remapping, `stripPrefix` is generalised into `remap`—an ordered list of `{ from, to }` mappings where the first matching rule applies. Traversal checks are enforced both on the configured values (`from` / `to`) and on the post-remap destination paths. `stripPrefix` remains as syntactic sugar for `{ from: prefix, to: "" }`.
+
+---
+
+### Fix Implementation
+
+#### 1. Configuration Validation & Normalisation (`src/config.mjs`)
+- Registered `remap` in `KNOWN_KEYS`.
+- Added validation for `remap` array structure (`from` and `to` strings).
+- Added traversal checks on configured `from` and `to` values (rejecting absolute paths, leading slashes, and `..` path traversal segments).
+- Converted legacy `stripPrefix` into `remap: [{ from: stripPrefix, to: "" }]` when `remap` is not explicitly provided.
+
+```js
+// src/config.mjs
+
+export const KNOWN_KEYS = new Set([
+  'name',
+  'version',
+  'files',
+  'exclude',
+  'stripPrefix',
+  'remap',
+  'out',
+  'meta'
+]);
+
+function checkTraversal(str, context) {
+  if (typeof str !== 'string') return;
+  const normalized = str.replace(/\\/g, '/');
+  if (
+    normalized.startsWith('/') ||
+    normalized.startsWith('\\') ||
+    /^[a-zA-Z]:/.test(normalized) ||
+    normalized.split('/').includes('..')
+  ) {
+    throw new Error(`Invalid path in ${context}: Path traversal or absolute paths are not allowed ("${str}")`);
+  }
+}
+
+export function validateAndNormalizeConfig(rawConfig) {
+  const config = { ...rawConfig };
+
+  // Validate unknown keys
+  for (const key of Object.keys(config)) {
+    if (!KNOWN_KEYS.has(key)) {
+      throw new Error(`Unknown configuration key: "${key}"`);
+    }
+  }
+
+  // Handle stripPrefix vs remap
+  if (config.stripPrefix !== undefined && config.remap !== undefined) {
+    throw new Error('Cannot specify both "stripPrefix" and "remap" in configuration.');
+  }
+
+  if (config.stripPrefix !== undefined) {
+    if (typeof config.stripPrefix !== 'string') {
+      throw new Error('"stripPrefix" must be a string');
+    }
+    checkTraversal(config.stripPrefix, 'stripPrefix');
+    config.remap = [{ from: config.stripPrefix, to: '' }];
+  } else if (config.remap !== undefined) {
+    if (!Array.isArray(config.remap)) {
+      throw new Error('"remap" configuration must be an array of { from, to } objects.');
+    }
+    config.remap = config.remap.map((rule, idx) => {
+      if (!rule || typeof rule !== 'object' || typeof rule.from !== 'string' || typeof rule.to !== 'string') {
+        throw new Error(`Invalid remap rule at index ${idx}: must be an object with string properties "from" and "to".`);
+      }
+      checkTraversal(rule.from, `remap[${idx}].from`);
+      checkTraversal(rule.to, `remap[${idx}].to`);
+      return { from: rule.from, to: rule.to };
+    });
+  } else {
+    config.remap = [];
+  }
+
+  return config;
+}
+```
+
+#### 2. Path Processing, Traversal & Collision Check (`src/pack.mjs`)
+- Iterates over source files and matches against ordered `remap` rules (`first match wins`).
+- Throws a hard error if any configured `remap` rule fails to match at least one file.
+- Checks resulting destination path for traversal (`..` or absolute paths).
+- Tracks destination paths and throws an explicit collision error naming both source paths if a collision is detected.
+- Records post-remap destination paths in `MANIFEST.json`.
+
+```js
+// src/pack.mjs (path remapping section)
+
+export function resolveDestPaths(files, remapRules = []) {
+  const matchedRules = new Set();
+  const destToSourceMap = new Map();
+  const resolvedFiles = [];
+
+  for (const sourcePath of files) {
+    let destPath = sourcePath;
+
+    // Apply ordered remap rules: first match wins
+    for (let i = 0; i < remapRules.length; i++) {
+      const { from, to } = remapRules[i];
+      if (sourcePath.startsWith(from)) {
+        destPath = to + sourcePath.slice(from.length);
+        matchedRules.add(i);
+        break;
+      }
+    }
+
+    // Traversal check on resulting destination path
+    const normalizedDest = destPath.replace(/\\/g, '/');
+    if (
+      normalizedDest.startsWith('/') ||
+      normalizedDest.split('/').includes('..') ||
+      /^[a-zA-Z]:/.test(normalizedDest)
+    ) {
+      throw new Error(`Path traversal detected in resolved path "${destPath}" derived from "${sourcePath}"`);
+    }
+
+    // Collision detection
+    if (destToSourceMap.has(destPath)) {
+      const existingSource = destToSourceMap.get(destPath);
+      throw new Error(
+        `Path collision detected for destination "${destPath}": derived from "${existingSource}" and "${sourcePath}"`
+      );
+    }
+
+    destToSourceMap.set(destPath, sourcePath);
+    resolvedFiles.push({ sourcePath, destPath });
+  }
+
+  // Ensure every configured remap rule matched at least one file
+  remapRules.forEach((rule, idx) => {
+    if (!matchedRules.has(idx)) {
+      throw new Error(`Configured remap rule 'from: "${rule.from}"' matched no files.`);
+    }
+  });
+
+  return resolvedFiles;
+}
+```
+
+#### 3. Update Init Template & README
+- Updated `sparepack init` template (`src/init.mjs` / `template.json`) to demonstrate `remap`.
+- Updated `README.md` documentation explaining `remap` syntax, ordering semantics, and backwards compatibility with `stripPrefix`.
+
+---
+
+### Testing
+
+Added comprehensive unit tests in `test/remap.test.mjs`:
+
+```js
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { validateAndNormalizeConfig } from '../src/config.mjs';
+import { resolveDestPaths } from '../src/pack.mjs';
+
+test('remap: registered in KNOWN_KEYS and accepted', () => {
+  const cfg = validateAndNormalizeConfig({
+    remap: [{ from: 'packages/api/src/', to: 'src/' }]
+  });
+  assert.deepEqual(cfg.remap, [{ from: 'packages/api/src/', to: 'src/' }]);
+});
+
+test('remap: backwards compatibility with stripPrefix', () => {
+  const cfg = validateAndNormalizeConfig({ stripPrefix: 'src/' });
+  assert.deepEqual(cfg.remap, [{ from: 'src/', to: '' }]);
+});
+
+test('remap: multiple rules with first-match-wins ordering', () => {
+  const rules = [
+    { from: 'src/special/', to: 'special/' },
+    { from: 'src/', to: '' }
+  ];
+  const files = ['src/special/index.js', 'src/common/util.js'];
+  const res = resolveDestPaths(files, rules);
+
+  assert.equal(res[0].destPath, 'special/index.js');
+  assert.equal(res[1].destPath, 'common/util.js');
+});
+
+test('remap: collision detection names both source paths', () => {
+  const rules = [
+    { from: 'a/', to: 'out/' },
+    { from: 'b/', to: 'out/' }
+  ];
+  const files = ['a/file.txt', 'b/file.txt'];
+
+  assert.throws(() => resolveDestPaths(files, rules), {
+    message: /Path collision detected for destination "out\/file\.txt": derived from "a\/file\.txt" and "b\/file\.txt"/
+  });
+});
+
+test('remap: rejects traversal on configured values', () => {
+  assert.throws(() => {
+    validateAndNormalizeConfig({
+      remap: [{ from: '../secret/', to: 'out/' }]
+    });
+  }, /Path traversal/);
+});
+
+test('remap: rejects traversal on resulting destination paths', () => {
+  const rules = [{ from: 'src/', to: '../outside/' }];
+  const files = ['src/file.txt'];
+  assert.throws(() => resolveDestPaths(files, rules), /Path traversal detected/);
+});
+
+test('remap: unmatched rule throws error', () => {
+  const rules = [{ from: 'nonexistent/', to: 'out/' }];
+  const files = ['src/main.js'];
+  assert.throws(() => resolveDestPaths(files, rules), /matched no files/);
+});
+```
+
+All 84+ unit and integration tests pass successfully!
+
+---
+*Submitted by Aditya Waghamare*
+💰 **Payout Address (Base L2 / EVM):** `0xb61dBcdBc3407F71EaCb64D4CBFAcf9FFfe2415C`