[Bitcoin-development] More precise type information in API reference

[Bitcoin-development] More precise type information in API reference

[Dario Teixeira]

Dear Bitcoin devs,

I am the author of OCaml-bitcoin [1], a library offering an OCaml 
interface
to the official Bitcoin client API.  For those who may be unfamiliar 
with it,
OCaml is one of those functional programming languages with a very rich 
and
expressive type system [2].  Given its emphasis on safety, its 
industrial
users are disproportionally found in the aerospace and financial 
sectors.

Now, OCaml programmers care a lot about types, because experience has
taught them that deep down most programming errors are just type errors.
 From this stems my request: please consider defining more precisely the 
type
information associated with each API call in the JSON-RPC reference [3].

To give you a better idea of what I'm talking about, please take a look 
at
the API offered by OCaml-bitcoin [4], and the associated type 
definitions
[5] (note that these have not been updated for Bitcoin Core 0.10 yet).
I've created the type definitions from information gathered from the 
Bitcoin
wiki and from looking at the Bitcoin Core source-code.  I wouldn't be 
surprised
if it contains errors, because neither the source-code nor the wiki is 
very
precise about the actual types being used.  As an example, consider type
hexspk_t ("hex representation of script public key").  Is this really 
the
same type used in both signrawtransaction and createmultisig?

Improving this situation would pose a minimal burden on bitcoin devs: 
all
that would be required is defining the precise set of types used in the 
RPC
API, and annotating the RPC calls either in the source-code itself or in 
the
API reference documentation.  It would make writing bindings such as 
mine
far easier and less error prone, and it would have the added advantage 
of
better documenting the Bitcoin Core source-code itself.

Also, note that it is not necessary to extend this request to the deep
data structures returned by some API calls.  Consider for instance the
gettransaction function of the OCaml-bitcoin API: it returns the raw 
JSON
object without any attempt to process it.  This is because that's a 
fairly
niche facility, and the bindings would balloon in size if I were to 
process
every single large return object.  Instead, the bindings take the more
pragmatic stance of only processing the parameters and return results 
where
a strong type discipline is imperative.

When I raised this issue on IRC a number of questions were posed.
What follows is my attempt to answer them:

   Q: What does it matter, if JSON only has a tiny set of types?

   A: JSON being the serialisation format is irrelevant.  The client 
bindings
      know that even if a public ECDSA key is serialised as a string, it 
does
      not stop being a public ECDSA key, and should only be used where a 
public
      ECDSA key is expected.

   Q: What does it matter if the types are not even distinguished in the 
C++
      source of Bitcoin Core?

   A: That is unfortunate, because it opens the door to bugs caused by 
type
      errors.  Moreover, even if the C++ source is "stringly-typed" and 
does
      not enforce a strong type discipline, that does not mean that the 
types
      are not there.  Even if a public and private key are both 
represented
      as strings, can you use one where the other is expected?  If not, 
then
      they actually have different types!

   Q: Isn't this a maintenance nightmare, given the changes to Bitcoin 
core?

   A: Actually, the most burdensome part is what motivated this message:
      keeping track of the types used.  If the Bitcoin API reference were
      more precise, keeping the bindings up-to-date would be trivial and
      even mechanical, because the API is now fairly stable.


Thank you very much for your attention, and for all the work you guys 
put
into Bitcoin development.  It is much appreciated and not acknowledged
often enough!

Best regards,
Dario Teixeira

[1] https://github.com/darioteixeira/ocaml-bitcoin
[2] http://ocaml.org/learn/description.html
[3] https://bitcoin.org/en/developer-reference#bitcoin-core-apis
[4] http://ocaml-bitcoin.forge.ocamlcore.org/apidoc/Bitcoin.ENGINE.html
[5] http://ocaml-bitcoin.forge.ocamlcore.org/apidoc/Bitcoin.html

Re: [Bitcoin-development] More precise type information in API reference

[Dario Teixeira]

Hi again,

My excuses: the formatting of the message seems to have been eaten
by a Gremlin.  Here's a second attempt:

=================================================================

Dear Bitcoin devs,

I am the author of OCaml-bitcoin [1], a library offering an OCaml
interface to the official Bitcoin client API.  For those who may
be unfamiliar with it, OCaml is one of those functional programming
languages with a very rich and expressive type system [2].  Given its
emphasis on safety, its industrial users are disproportionally
found in the aerospace and financial sectors.

Now, OCaml programmers care a lot about types, because experience
has taught them that deep down most programming errors are just
type errors.  From this stems my request: please consider defining
more precisely the type information associated with each API call
in the JSON-RPC reference [3].

To give you a better idea of what I'm talking about, please take a
look at the API offered by OCaml-bitcoin [4], and the associated type
definitions [5] (note that these have not been updated for Bitcoin
Core 0.10 yet).  I've created the type definitions from information
gathered from the Bitcoin wiki and from looking at the Bitcoin
Core source-code.  I wouldn't be surprised if it contains errors,
because neither the source-code nor the wiki is very precise about
the actual types being used.  As an example, consider type hexspk_t
("hex representation of script public key").  Is this really the
same type used in both signrawtransaction and createmultisig?

Improving this situation would pose a minimal burden on bitcoin
devs: all that would be required is defining the precise set of
types used in the RPC API, and annotating the RPC calls either
in the source-code itself or in the API reference documentation.
It would make writing bindings such as mine far easier and less error
prone, and it would have the added advantage of better documenting
the Bitcoin Core source-code itself.

Also, note that it is not necessary to extend this request to the
deep data structures returned by some API calls.  Consider for
instance the gettransaction function of the OCaml-bitcoin API:
it returns the raw JSON object without any attempt to process it.
This is because that's a fairly niche facility, and the bindings
would balloon in size if I were to process every single large return
object.  Instead, the bindings take the more pragmatic stance of
only processing the parameters and return results where a strong
type discipline is imperative.

When I raised this issue on IRC a number of questions were posed.
What follows is my attempt to answer them:

   Q: What does it matter, if JSON only has a tiny set of types?

   A: JSON being the serialisation format is irrelevant.  The client
      bindings know that even if a public ECDSA key is serialised as
      a string, it does not stop being a public ECDSA key, and should
      only be used where a public ECDSA key is expected.

   Q: What does it matter if the types are not even distinguished in
      the C++ source of Bitcoin Core?

   A: That is unfortunate, because it opens the door to bugs caused by
      type errors.  Moreover, even if the C++ source is "stringly-typed"
      and does not enforce a strong type discipline, that does not mean
      that the types are not there.  Even if a public and private key
      are both represented as strings, can you use one where the other
      is expected?  If not, then they actually have different types!

   Q: Isn't this a maintenance nightmare, given the changes to Bitcoin
      core?

   A: Actually, the most burdensome part is what motivated this message:
      keeping track of the types used.  If the Bitcoin API reference were
      more precise, keeping the bindings up-to-date would be trivial and
      even mechanical, because the API is now fairly stable.


Thank you very much for your attention, and for all the work you
guys put into Bitcoin development.  It is much appreciated and not
acknowledged often enough!

Best regards,
Dario Teixeira

[1] https://github.com/darioteixeira/ocaml-bitcoin
[2] http://ocaml.org/learn/description.html
[3] https://bitcoin.org/en/developer-reference#bitcoin-core-apis
[4] http://ocaml-bitcoin.forge.ocamlcore.org/apidoc/Bitcoin.ENGINE.html
[5] http://ocaml-bitcoin.forge.ocamlcore.org/apidoc/Bitcoin.html

Re: [Bitcoin-development] More precise type information in API reference

[David A. Harding]

On Tue, Feb 17, 2015 at 01:33:28PM +0000, Dario Teixeira wrote:
> From this stems my request: please consider defining
> more precisely the type information associated with each API call
> in the JSON-RPC reference [3].

Hi Dario,

I'm the primary author of the Bitcoin.org JSON-RPC reference, and I'd
be happy to help.

Do you think it would be possible for you to submit a minimal pull
request against the docs adding the type information you need to just
one RPC call?  From there we can see how much work it would take to
generalize that across all 100+ printed pages worth of RPC docs.

I've tried to make this as easy as possible: if you hover your mouse
over the title of an RPC[1], an "Edit" link will appear that will take you
to a page on GitHub to edit the file describing that RPC call.  Or you
can checkout[2] the website repository and edit the file locally; the
individual RPCs are in _includes/ref/bitcoin-core/rpcs/rpcs/

    [1] For example, https://bitcoin.org/en/developer-reference#addmultisigaddress
    [2] https://github.com/bitcoin/bitcoin.org

If you have any questions about the editing process, or anything else,
please feel free to email me at this address or PM harding on Freenode.

Thanks!,

-Dave
-- 
David A. Harding

Re: [Bitcoin-development] More precise type information in API reference

[Dario Teixeira]

Hi Dave,

> I'm the primary author of the Bitcoin.org JSON-RPC reference, and I'd
> be happy to help.

Thanks -- it is much appreciated!


> Do you think it would be possible for you to submit a minimal pull
> request against the docs adding the type information you need to just
> one RPC call?  From there we can see how much work it would take to
> generalize that across all 100+ printed pages worth of RPC docs.

Sure, I would be glad to help.  In fact, most of grunt work has
already been done for the OCaml-bitcoin API [1,2], which could be
used as a guide even if you don't use OCaml (beware that it may
contain errors, though).

Besides tweaking each RPC call, we would need to add a new section
to the docs, to be placed before the RPC calls.  This List of
Types section would list all the custom types defined in the API,
providing a brief description for each and indicating the JSON type
used for serialisation (almost invariantly "string", I reckon).

But before I submit a pull request, allow me to exemplify with
AddMultiSigAddress:

Parameter #1: (no changes)

Parameter #2: I would keep "array" as the type of "Keys or
Addresses".  If we follow the convention of using a pipe character to
represent unions, then the type for "Key or Address" is not "string",
but "public_key | p2pkh_address".  This would also require adding
two entries to the List of Types section, describing public_key and
p2pkh_address, and letting the users know that they are serialised
as JSON strings.  (Note that the precise type of "Keys or Addresses"
is actually "Array [public_key | p2pkh_address]".  However, since
the type of each element is also listed, this info is redundant
and we can safely state it's just an array.)

Parameter #3: The type should be "account", obviously.

Result: a p2sh_address.  If there is only one type of such P2SH
addresses and they can be used interchangeably, then this would
suffice.  If however, there are actually several incompatible kinds
of P2SH address, then we'd need to be more precise about which one
we mean.

Thanks again for your time!
Kind regards,
Dario Teixeira

[1] http://ocaml-bitcoin.forge.ocamlcore.org/apidoc/Bitcoin.ENGINE.html
[2] http://ocaml-bitcoin.forge.ocamlcore.org/apidoc/Bitcoin.html