fix: mask file mode (#39)

Only expose documented bits to calling code but respect them when
turning the entry into a protobuf.

Author: achingbrain

src/index.js

@@ -80,7 +80,8 @@ class Data {
     this.fanout = fanout
     this.blockSizes = blockSizes || []
     this.mtime = mtime || new Date(0)
-    this.mode = mode
+    this.mode = mode || mode === 0 ? (mode & 0xFFF) : undefined
+    this._originalMode = mode
 
     if (this.mode === undefined && type === 'file') {
       this.mode = DEFAULT_FILE_MODE
@@ -151,8 +152,8 @@ class Data {
 
     let mode
 
-    if (!isNaN(parseInt(this.mode))) {
-      mode = this.mode
+    if (this.mode || this.mode === 0) {
+      mode = (this._originalMode & 0xFFFFF000) | (this.mode & 0xFFF)
 
       if (mode === DEFAULT_FILE_MODE && this.type === 'file') {
         mode = undefined

test/unixfs-format.spec.js

@@ -13,6 +13,8 @@ const directory = loadFixture('test/fixtures/directory.unixfs')
 const file = loadFixture('test/fixtures/file.txt.unixfs')
 const symlink = loadFixture('test/fixtures/symlink.txt.unixfs')
 const { Buffer } = require('buffer')
+const protons = require('protons')
+const unixfsData = protons(require('../src/unixfs.proto')).Data
 
 describe('unixfs-format', () => {
   it('defaults to file', () => {
@@ -145,6 +147,20 @@ describe('unixfs-format', () => {
     expect(UnixFS.unmarshal(data.marshal())).to.have.deep.property('mtime', new Date(Math.round(mtime.getTime() / 1000) * 1000))
   })
 
+  it('does not overwrite unknown mode bits', () => {
+    const mode = 0xFFFFFFF // larger than currently defined mode bits
+    const buf = unixfsData.encode({
+      Type: 0,
+      mode
+    })
+
+    const unmarshaled = UnixFS.unmarshal(buf)
+    const marshaled = unmarshaled.marshal()
+
+    const entry = unixfsData.decode(marshaled)
+    expect(entry).to.have.property('mode', mode)
+  })
+
   // figuring out what is this metadata for https://github.com/ipfs/js-ipfs-data-importing/issues/3#issuecomment-182336526
   it.skip('metadata', () => {})