Storing data in a TypeBuffer and then retrieving it from a file can lead to surprising outcomes

Question

Storing data in a TypeBuffer and then retrieving it from a file can lead to surprising outcomes

Upon executing the following code:

var list = new Uint32Array(16);
for (var i=0; i<16; ++i) list[i] = i;
fs.writeFileSync("list", new Uint8Array(list).buffer);
console.log([].slice.call(new Uint32Array(fs.readFileSync("list"))));

We anticipate the output to be:

[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ]

However, what is actually generated is:

[ 91, 111, 98, 106, 101, 99, 116, 32, 65, 114, 114, 97, 121, 66, 117, 102, 102, 101, 114, 93 ]

A detailed view of the list file exhibits this:

0000000 5b 6f 62 6a 65 63 74 20 41 72 72 61 79 42 75 66
0000010 66 65 72 5d

What could be causing the disparity between the expected and actual results?

javascript node.js file io

Answer 1

Answer №1

The property known as buffer within a TypedArray (specifically Uint8Array) refers to an ArrayBuffer, which differs from the node.js Buffer. If attempting to manipulate data between an ArrayBuffer and a file using the fs module that expects a node.js Buffer, it will not function properly.

To address this issue, various methods are available for converting between the two types. The most straightforward solution to ensure the expected functionality is to create a new Buffer object using the original arr array instead of relying on the .buffer property:

var arr = new Uint32Array(16);
for (var i=0; i<16; ++i) arr[i] = i;
fs.writeFileSync("arr", new Buffer(arr)); // <-- HERE
console.log([].slice.call(new Uint32Array(fs.readFileSync("arr"))));

Output:

[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ]

Additionally, a hexadecimal representation of the contents in the resulting file named arr appears as follows:

0000000 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f

Answer 2

The property known as buffer within a TypedArray (specifically Uint8Array) refers to an ArrayBuffer, which differs from the node.js Buffer. If attempting to manipulate data between an ArrayBuffer and a file using the fs module that expects a node.js Buffer, it will not function properly.

To address this issue, various methods are available for converting between the two types. The most straightforward solution to ensure the expected functionality is to create a new Buffer object using the original arr array instead of relying on the .buffer property:

var arr = new Uint32Array(16);
for (var i=0; i<16; ++i) arr[i] = i;
fs.writeFileSync("arr", new Buffer(arr)); // <-- HERE
console.log([].slice.call(new Uint32Array(fs.readFileSync("arr"))));

Output:

[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ]

Additionally, a hexadecimal representation of the contents in the resulting file named arr appears as follows:

0000000 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f

Storing data in a TypeBuffer and then retrieving it from a file can lead to surprising outcomes

Answer №1

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