Re: [Qemu-devel] [Qemu-block] storing machine data in qcow images?

[Michael S. Tsirkin]

On Tue, Jun 05, 2018 at 03:09:17PM -0500, Eric Blake wrote:
> On 06/05/2018 02:58 PM, Richard W.M. Jones wrote:
> > > Binary blobs can always be base64 encoded for representation within
> > > a valid JSON UTF-8 string (and we already have several QMP
> > > interfaces that utilize base64 encoding to pass through what is
> > > otherwise invalid UTF-8).  It does inflate things slightly compared
> > > to a format that allows a raw length coupled with raw data, but that
> > > is not necessarily a problem.
> > 
> > Of course how we represent them externally and/or while
> > using QMP / qemu-img to store and retrieve them is up for grabs.
> > Doesn't JSON allow binary to be encoded?  (Knowing how poorly
> > done JSON is, I wouldn't be surprised if not)
> 
> JSON itself does not have a binary primitive; to pass arbitrary data through
> JSON you have to first encode that data into something like base64 that can
> then be represented as a UTF-8 string.  For reference, look at
> qapi/crypto.json and the definition of QCryptoSecretFormat.

But there isn't a way to figure out that a string is base64, which
means each application needs to know whether it's a string or
a binary.

How about specifying the encoding in the value?

string value:
[A-Za-z][^=\0]=S[^\0]*

base64 value:
[A-Za-z][^=\0]=B[A-Za-z0-9+/]*

or the key:
S[A-Za-z][^=\0]=[^\0]*

base64 value:
B[A-Za-z][^=\0]=[A-Za-z0-9+/]*

?

-- 
MST