bytes.NewBuffer(make([]byte, 0, <some size >)) allocates 4096 bytes buffer

[Gautam Saha]

Trying to allocate an in-memory  buff of small size (few bytes) using 

bytes.NewBuffer(make([]byte, 0, <some size >))

The allocated buffer has size 4096 bytes i.e. > than what I requested for. Why is this so?

[Brian Candler]

Can you show how you came to that conclusion?  It seems to work as expected for me:

https://play.golang.org/p/wPBC1VBvkde

4096 bytes is typically a page, so maybe something is going on to do with allocation on page boundaries, but need to see your code.

[Jan Mercl]

Nowhere the docs say one can control the buffer size. Instead, the
passed []byte is documented to be used "as its initial contents", not
"as its initial buffer".

[Brian Candler]

However, it does say "The new Buffer takes ownership of buf" - why would it do that if it were allocating a new buffer and taking a copy of the original?

The code has the answer, it's just a single line:

https://golang.org/src/bytes/buffer.go?s=14279:14313#L440

func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }

ISTM that the Buffer object is simply using the buf you provided.  I don't understand where the claim comes from that (a) it allocates a buffer, and (b) the allocated buffer is of size 4096 bytes.

[Gautam Saha]

Probably I was doing something wrong. @Brian your snippet works as I would have expected.