Re: [Qemu-devel] [PATCH v8 1/7] qdict: implement a qdict_crumple method for un-flattening a dict

[Markus Armbruster <armbru@redhat.com>]

"Daniel P. Berrange" <berrange@redhat.com> 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: Marc-André Lureau <marcandre.lureau@redhat.com>
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  include/qapi/qmp/qdict.h |   1 +
>  qobject/qdict.c          | 283 +++++++++++++++++++++++++++++++++++++++++++++++
>  tests/check-qdict.c      | 241 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 525 insertions(+)
>
> diff --git a/include/qapi/qmp/qdict.h b/include/qapi/qmp/qdict.h
> index 71b8eb0..8a3ac13 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(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..fd2d0e3 100644
> --- a/qobject/qdict.c
> +++ b/qobject/qdict.c
> @@ -17,6 +17,7 @@
>  #include "qapi/qmp/qbool.h"
>  #include "qapi/qmp/qstring.h"
>  #include "qapi/qmp/qobject.h"
> +#include "qapi/error.h"
>  #include "qemu/queue.h"
>  #include "qemu-common.h"
>  #include "qemu/cutils.h"
> @@ -683,6 +684,288 @@ void qdict_array_split(QDict *src, QList **dst)
>      }
>  }
>  
> +
> +/**
> + * qdict_split_flat_key:
> + * @key: the key string to split
> + * @prefix: non-NULL pointer to hold extracted prefix
> + * @suffix: non-NULL pointer to remaining suffix
> + *
> + * Given a flattened key such as 'foo.0.bar', split it into two parts
> + * at the first '.' separator. Allows double dot ('..') to escape the
> + * normal separator.
> + *
> + * eg
> + *    'foo.0.bar' -> prefix='foo' and suffix='0.bar'
> + *    'foo..0.bar' -> prefix='foo.0' and suffix='bar'
> + *
> + * The '..' sequence will be unescaped in the returned 'prefix'
> + * string. The 'suffix' string will be left in escaped format, so it
> + * can be fed back into the qdict_split_flat_key() key as the input
> + * later.
> + *
> + * The caller is responsible for freeing the string returned in @prefix
> + * using g_free().
> + */
> +static void qdict_split_flat_key(const char *key, char **prefix,
> +                                 const char **suffix)
> +{
> +    const char *separator;
> +    size_t i, j;
> +
> +    /* Find first '.' separator, but if there is a pair '..'
> +     * that acts as an escape, so skip over '..' */
> +    separator = NULL;
> +    do {
> +        if (separator) {
> +            separator += 2;
> +        } else {
> +            separator = key;
> +        }
> +        separator = strchr(separator, '.');
> +    } while (separator && separator[1] == '.');
> +
> +    if (separator) {
> +        *prefix = g_strndup(key,
> +                            separator - key);
> +        *suffix = separator + 1;
> +    } else {
> +        *prefix = g_strdup(key);
> +        *suffix = NULL;
> +    }
> +
> +    /* Unescape the '..' sequence into '.' */
> +    for (i = 0, j = 0; (*prefix)[i] != '\0'; i++, j++) {
> +        if ((*prefix)[i] == '.') {
> +            assert((*prefix)[i + 1] == '.');
> +            i++;
> +        }
> +        (*prefix)[j] = (*prefix)[i];
> +    }
> +    (*prefix)[j] = '\0';
> +}
> +
> +
> +/**
> + * qdict_is_list:
> + * @maybe_list: dict to check if keys represent list elements.
> + *
> + * Determine whether all keys in @maybe_list are valid list elements.
> + * If @maybe_list is non-zero in length and all the keys look like
> + * valid list indexes, this will return 1. If @maybe_list is zero
> + * length or all keys are non-numeric then it will return 0 to indicate
> + * it is a normal qdict. If there is a mix of numeric and non-numeric
> + * keys, or the list indexes are non-contiguous, an error is reported.
> + *
> + * Returns: 1 if a valid list, 0 if a dict, -1 on error
> + */
> +static int qdict_is_list(QDict *maybe_list, Error **errp)
> +{
> +    const QDictEntry *ent;
> +    ssize_t len = 0;
> +    ssize_t max = -1;
> +    int is_list = -1;
> +    int64_t val;
> +
> +    for (ent = qdict_first(maybe_list); ent != NULL;
> +         ent = qdict_next(maybe_list, ent)) {
> +
> +        if (qemu_strtoll(ent->key, NULL, 10, &val) == 0) {
> +            if (is_list == -1) {
> +                is_list = 1;
> +            } else if (!is_list) {
> +                error_setg(errp,
> +                           "Cannot crumple a dictionary with a mix of list "
> +                           "and non-list keys");
> +                return -1;
> +            }
> +            len++;
> +            if (val > max) {
> +                max = val;
> +            }
> +        } else {
> +            if (is_list == -1) {
> +                is_list = 0;
> +            } else if (is_list) {
> +                error_setg(errp,
> +                           "Cannot crumple a dictionary with a mix of list "
> +                           "and non-list keys");
> +                return -1;
> +            }
> +        }
> +    }
> +
> +    if (is_list == -1) {
> +        assert(!qdict_size(maybe_list));
> +        is_list = 0;
> +    }
> +
> +    if (len != (max + 1)) {
> +        error_setg(errp, "List indexes are not contigous, "

contiguous

> +                   "saw %zd elements but %zd largest index",
> +                   len, max);
> +        return -1;
> +    }
> +
> +    return is_list ? 1 : 0;

Why not simply return is_list?

> +}
[...]