keep MEMFS files as typed arrays until we need them to be flexible

1 files changed, 28 insertions, 4 deletions

diff --git a/src/library_memfs.js b/src/library_memfs.js
index 0fa6cdfb..0ed0a61a 100644
--- a/src/library_memfs.js
+++ b/src/library_memfs.js
@@ -1,6 +1,16 @@
 mergeInto(LibraryManager.library, {
   $MEMFS__deps: ['$FS'],
   $MEMFS: {
+    // content modes
+    CONTENT_ORIGINAL: 1, // contains the original content written into it (in a typed array most likely)
+    CONTENT_FLEXIBLE: 2, // has been modified or never set to anything, and is a flexible js array that can grow/shrink
+    ensureFlexible: function(node) {
+      if (node.contentMode !== MEMFS.CONTENT_FLEXIBLE) {
+        node.contents = Array.prototype.slice.call(node.contents);
+        node.contentMode = MEMFS.CONTENT_FLEXIBLE;
+      }
+    },
+
     mount: function(mount) {
       return MEMFS.create_node(null, '/', {{{ cDefine('S_IFDIR') }}} | 0777, 0);
     },
@@ -40,6 +50,7 @@ mergeInto(LibraryManager.library, {
           mmap: MEMFS.stream_ops.mmap
         };
         node.contents = [];
+        node.contentMode = MEMFS.CONTENT_FLEXIBLE;
       } else if (FS.isLink(node.mode)) {
         node.node_ops = {
           getattr: MEMFS.node_ops.getattr,
@@ -98,6 +109,7 @@ mergeInto(LibraryManager.library, {
           node.timestamp = attr.timestamp;
         }
         if (attr.size !== undefined) {
+          MEMFS.ensureFlexible(node);
           var contents = node.contents;
           if (attr.size < contents.length) contents.length = attr.size;
           else while (attr.size > contents.length) contents.push(0);
@@ -165,7 +177,7 @@ mergeInto(LibraryManager.library, {
         var contents = stream.node.contents;
         var size = Math.min(contents.length - position, length);
 #if USE_TYPED_ARRAYS == 2
-        if (contents.subarray) { // typed array
+        if (size > 8 && contents.subarray) { // non-trivial, and typed array
           buffer.set(contents.subarray(position, position + size), offset);
         } else
 #endif
@@ -177,12 +189,22 @@ mergeInto(LibraryManager.library, {
         return size;
       },
       write: function(stream, buffer, offset, length, position) {
-        var contents = stream.node.contents;
+        var node = stream.node;
+        node.timestamp = Date.now();
+        var contents = node.contents;
+        if (length && contents.length === 0 && position === 0 && buffer.subarray) {
+          // just replace it with the new data
+          assert(buffer.length);
+          node.contents = new Uint8Array(buffer.subarray(offset, offset+length)); // TODO: do not copy when unnecessary
+          node.contentMode = MEMFS.CONTENT_ORIGINAL;
+          return length;
+        }
+        MEMFS.ensureFlexible(node);
+        var contents = node.contents;
         while (contents.length < position) contents.push(0);
         for (var i = 0; i < length; i++) {
           contents[position + i] = buffer[offset + i];
         }
-        stream.node.timestamp = Date.now();
         return length;
       },
       llseek: function(stream, offset, whence) {
@@ -202,6 +224,7 @@ mergeInto(LibraryManager.library, {
         return position;
       },
       allocate: function(stream, offset, length) {
+        MEMFS.ensureFlexible(stream.node);
         var contents = stream.node.contents;
         var limit = offset + length;
         while (limit > contents.length) contents.push(0);
@@ -240,4 +263,5 @@ mergeInto(LibraryManager.library, {
       },
     }
   }
-});
\ No newline at end of file
+});
+