Re: [Qemu-devel] [PATCH v3 07/18] qapi: Add json output visitor

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> We have several places that want to go from qapi to JSON; right now,
> they have to create an intermediate QObject to do the work.  That
> also has the drawback that the JSON formatting of a QDict will
> rearrange keys (according to a deterministic, but unpredictable,
> hash), when humans have an easier time if dicts are produced in
> the same order as the qapi type.
>
> For these reasons, it is time to add a new JSON output visitor.
> This patch just adds the basic visitor and tests that it works;
> later patches will add pretty-printing, and convert clients to
> use the visitor.
>
> Design choices: Unlike the QMP output visitor, the JSON visitor
> refuses to visit a required string with a NULL value (abort), as
> well as a non-finite number (raises an error message).  Reusing
> QString to grow the contents means that we easily share code with
> both qobject-json.c and qjson.c; although it might be nice to
> enhance things to take an optional output callback function so
> that the output can truly be streamed instead of collected in
> memory.
>
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> v3: retitle, rebase to master, minor cleanups
> v2: rebase to qapi subset E v8; add test of error outputting
> infinity; use unsigned depth
> ---
>  include/qapi/visitor.h             |  20 +-
>  include/qapi/json-output-visitor.h |  29 +++
>  qapi/json-output-visitor.c         | 202 ++++++++++++++++++
>  tests/test-json-output-visitor.c   | 418 
> +++++++++++++++++++++++++++++++++++++
>  qapi/Makefile.objs                 |   2 +-
>  tests/.gitignore                   |   1 +
>  tests/Makefile                     |   4 +
>  7 files changed, 665 insertions(+), 11 deletions(-)
>  create mode 100644 include/qapi/json-output-visitor.h
>  create mode 100644 qapi/json-output-visitor.c
>  create mode 100644 tests/test-json-output-visitor.c
>
> diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
> index a430c19..e8a4403 100644
> --- a/include/qapi/visitor.h
> +++ b/include/qapi/visitor.h
> @@ -26,16 +26,16 @@
>   *
>   * There are three kinds of visitor classes: input visitors (QMP,
>   * string, and QemuOpts) parse an external representation and build
> - * the corresponding QAPI graph, output visitors (QMP and string) take
> - * a completed QAPI graph and generate an external representation, and
> - * the dealloc visitor can take a QAPI graph (possibly partially
> - * constructed) and recursively free its resources.  While the dealloc
> - * and QMP input/output visitors are general, the string and QemuOpts
> - * visitors have some implementation limitations; see the
> - * documentation for each visitor for more details on what it
> - * supports.  Also, see visitor-impl.h for the callback contracts
> - * implemented by each visitor, and docs/qapi-code-gen.txt for more
> - * about the QAPI code generator.
> + * the corresponding QAPI graph, output visitors (QMP, string, and
> + * JSON) take a completed QAPI graph and generate an external
> + * representation, and the dealloc visitor can take a QAPI graph
> + * (possibly partially constructed) and recursively free its
> + * resources.  While the dealloc and QMP input/output visitors are

and the JSON output visitor?

> + * general, the string and QemuOpts visitors have some implementation
> + * limitations; see the documentation for each visitor for more
> + * details on what it supports.  Also, see visitor-impl.h for the
> + * callback contracts implemented by each visitor, and
> + * docs/qapi-code-gen.txt for more about the QAPI code generator.
>   *
>   * All QAPI types have a corresponding function with a signature
>   * roughly compatible with this:
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