Re: [Qemu-devel] [PATCH v14 02/21] qdict: implement a qdict_crumple method for un-flattening a dict

[Markus Armbruster]

"Daniel P. Berrange" <address@hidden> writes:

> The qdict_flatten() method will take a dict whose elements are
> further nested dicts/lists and flatten them by concatenating
> keys.
>
> The qdict_crumple() method aims to do the reverse, taking a flat
> qdict, and turning it into a set of nested dicts/lists. It will
> apply nesting based on the key name, with a '.' indicating a
> new level in the hierarchy. If the keys in the nested structure
> are all numeric, it will create a list, otherwise it will create
> a dict.
>
> If the keys are a mixture of numeric and non-numeric, or the
> numeric keys are not in strictly ascending order, an error will
> be reported.
>
> As an example, a flat dict containing
>
>  {
>    'foo.0.bar': 'one',
>    'foo.0.wizz': '1',
>    'foo.1.bar': 'two',
>    'foo.1.wizz': '2'
>  }
>
> will get turned into a dict with one element 'foo' whose
> value is a list. The list elements will each in turn be
> dicts.
>
>  {
>    'foo': [
>      { 'bar': 'one', 'wizz': '1' },
>      { 'bar': 'two', 'wizz': '2' }
>    ],
>  }
>
> If the key is intended to contain a literal '.', then it must
> be escaped as '..'. ie a flat dict
>
>   {
>      'foo..bar': 'wizz',
>      'bar.foo..bar': 'eek',
>      'bar.hello': 'world'
>   }
>
> Will end up as
>
>   {
>      'foo.bar': 'wizz',
>      'bar': {
>         'foo.bar': 'eek',
>         'hello': 'world'
>      }
>   }
>
> The intent of this function is that it allows a set of QemuOpts
> to be turned into a nested data structure that mirrors the nesting
> used when the same object is defined over QMP.
>
> Reviewed-by: Eric Blake <address@hidden>
> Reviewed-by: Kevin Wolf <address@hidden>
> Reviewed-by: Marc-André Lureau <address@hidden>
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>  include/qapi/qmp/qdict.h |   1 +
>  qobject/qdict.c          | 289 
> +++++++++++++++++++++++++++++++++++++++++++++++
>  tests/check-qdict.c      | 261 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 551 insertions(+)
>
> diff --git a/include/qapi/qmp/qdict.h b/include/qapi/qmp/qdict.h
> index 71b8eb0..e0d24e1 100644
> --- a/include/qapi/qmp/qdict.h
> +++ b/include/qapi/qmp/qdict.h
> @@ -73,6 +73,7 @@ void qdict_flatten(QDict *qdict);
>  void qdict_extract_subqdict(QDict *src, QDict **dst, const char *start);
>  void qdict_array_split(QDict *src, QList **dst);
>  int qdict_array_entries(QDict *src, const char *subqdict);
> +QObject *qdict_crumple(const QDict *src, bool recursive, Error **errp);
>  
>  void qdict_join(QDict *dest, QDict *src, bool overwrite);
>  
> diff --git a/qobject/qdict.c b/qobject/qdict.c
> index 60f158c..c38e90e 100644
> --- a/qobject/qdict.c
> +++ b/qobject/qdict.c
[...]
> +/**
> + * qdict_crumple:
> + * @src: the original flat dictionary (only scalar values) to crumple
> + * @recursive: true to recursively crumple nested dictionaries

Is recursive=false used outside tests in this series?

> + *
> + * Takes a flat dictionary whose keys use '.' separator to indicate
> + * nesting, and values are scalars, and crumples it into a nested
> + * structure. If the @recursive parameter is false, then only the
> + * first level of structure implied by the keys will be crumpled. If
> + * @recursive is true, then the input will be recursively crumpled to
> + * expand all levels of structure in the keys.
> + *
> + * To include a literal '.' in a key name, it must be escaped as '..'
> + *
> + * For example, an input of:
> + *
> + * { 'foo.0.bar': 'one', 'foo.0.wizz': '1',
> + *   'foo.1.bar': 'two', 'foo.1.wizz': '2' }
> + *
> + * will result in an output of:
> + *
> + * {
> + *   'foo': [
> + *      { 'bar': 'one', 'wizz': '1' },
> + *      { 'bar': 'two', 'wizz': '2' }
> + *   ],
> + * }
> + *
> + * The following scenarios in the input dict will result in an
> + * error being returned:
> + *
> + *  - Any values in @src are non-scalar types
> + *  - If keys in @src imply that a particular level is both a
> + *    list and a dict. e.g., "foo.0.bar" and "foo.eek.bar".
> + *  - If keys in @src imply that a particular level is a list,
> + *    but the indices are non-contiguous. e.g. "foo.0.bar" and
> + *    "foo.2.bar" without any "foo.1.bar" present.
> + *  - If keys in @src represent list indexes, but are not in
> + *    the "%zu" format. e.g. "foo.+0.bar"
> + *
> + * Returns: either a QDict or QList for the nested data structure, or NULL
> + * on error
> + */
> +QObject *qdict_crumple(const QDict *src, bool recursive, Error **errp)
[...]