[Qemu-devel] [PATCH v2 01/10] qdict: implement a qdict_crumple method for un-flattening a dict

["Daniel P. Berrange" <berrange@redhat.com>]

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 nested
used when the same object is defined over QMP.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 include/qapi/qmp/qdict.h |   1 +
 qobject/qdict.c          | 237 +++++++++++++++++++++++++++++++++++++++++++++++
 tests/check-qdict.c      | 114 +++++++++++++++++++++++
 3 files changed, 352 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 9833bd0..b0f3447 100644
--- a/qobject/qdict.c
+++ b/qobject/qdict.c
@@ -682,6 +682,243 @@ void qdict_array_split(QDict *src, QList **dst)
     }
 }
 
+
+/**
+ * qdict_split_flat_key:
+ *
+ * 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.
+ */
+static void qdict_split_flat_key(const char *key, char **prefix, 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 = g_strdup(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] == '.' &&
+            (*prefix)[i + 1] == '.') {
+            i++;
+        }
+        (*prefix)[j] = (*prefix)[i];
+    }
+    (*prefix)[j] = '\0';
+}
+
+
+/**
+ * qdict_crumple:
+ *
+ * Reverses the flattening done by qdict_flatten by
+ * crumpling the dicts into a nested structure. Similar
+ * qdict_array_split, but copes with arbitrary nesting
+ * of dicts & arrays, not meely one level of arrays
+ *
+ * { 'foo.0.bar': 'one', 'foo.0.wizz': '1',
+ *   'foo.1.bar': 'two', 'foo.1.wizz': '2' }
+ *
+ * =>
+ *
+ * {
+ *   'foo' => [
+ *      { 'bar': 'one', 'wizz': '1' }
+ *      { 'bar': 'two', 'wizz': '2' }
+ *   ],
+ * }
+ *
+ */
+QObject *qdict_crumple(QDict *src, bool recursive, Error **errp)
+{
+    const QDictEntry *entry, *next;
+    QDict *two_level, *multi_level = NULL;
+    QObject *dst = NULL, *child;
+    bool isList = false;
+    ssize_t list_max = -1;
+    size_t list_len = 0;
+    size_t i;
+    int64_t val;
+    char *prefix, *suffix;
+
+    two_level = qdict_new();
+    entry = qdict_first(src);
+
+    /* Step 1: split our totally flat dict into a two level dict */
+    while (entry != NULL) {
+        next = qdict_next(src, entry);
+
+        if (qobject_type(entry->value) == QTYPE_QDICT ||
+            qobject_type(entry->value) == QTYPE_QLIST) {
+            error_setg(errp, "Value %s is not a scalar",
+                       entry->key);
+            goto error;
+        }
+
+        qdict_split_flat_key(entry->key, &prefix, &suffix);
+
+        child = qdict_get(two_level, prefix);
+        if (suffix) {
+            if (child) {
+                if (qobject_type(child) != QTYPE_QDICT) {
+                    error_setg(errp, "Key %s prefix is already set as a scalar",
+                               prefix);
+                    goto error;
+                }
+            } else {
+                child = (QObject *)qdict_new();
+                qdict_put_obj(two_level, prefix, child);
+            }
+            qobject_incref(entry->value);
+            qdict_put_obj(qobject_to_qdict(child), suffix, entry->value);
+        } else {
+            if (child) {
+                error_setg(errp, "Key %s prefix is already set as a dict",
+                           prefix);
+                goto error;
+            }
+            qobject_incref(entry->value);
+            qdict_put_obj(two_level, prefix, entry->value);
+        }
+
+        g_free(suffix);
+        g_free(prefix);
+        suffix = prefix = NULL;
+
+        entry = next;
+    }
+
+    /* Step 2: optionally process the two level dict recursively
+     * into a multi-level dict */
+    if (recursive) {
+        multi_level = qdict_new();
+        entry = qdict_first(two_level);
+        while (entry != NULL) {
+            next = qdict_next(two_level, entry);
+
+            if (qobject_type(entry->value) == QTYPE_QDICT) {
+                child = qdict_crumple(qobject_to_qdict(entry->value),
+                                      recursive, errp);
+                if (!child) {
+                    goto error;
+                }
+
+                qdict_put_obj(multi_level, entry->key, child);
+            } else {
+                qobject_incref(entry->value);
+                qdict_put_obj(multi_level, entry->key, entry->value);
+            }
+
+            entry = next;
+        }
+        QDECREF(two_level);
+    } else {
+        multi_level = two_level;
+    }
+    two_level = NULL;
+
+    /* Step 3: detect if we need to turn our dict into list */
+    entry = qdict_first(multi_level);
+    while (entry != NULL) {
+        next = qdict_next(multi_level, entry);
+
+        errno = 0;
+        if (qemu_strtoll(entry->key, NULL, 10, &val) == 0) {
+            if (!dst) {
+                dst = (QObject *)qlist_new();
+                isList = true;
+            } else if (!isList) {
+                error_setg(errp,
+                           "Key '%s' is for a list, but previous key is "
+                           "for a dict", entry->key);
+                goto error;
+            }
+            list_len++;
+            if (val > list_max) {
+                list_max = val;
+            }
+        } else {
+            if (!dst) {
+                dst = (QObject *)multi_level;
+                qobject_incref(dst);
+                isList = false;
+            } else if (isList) {
+                error_setg(errp,
+                           "Key '%s' is for a dict, but previous key is "
+                           "for a list", entry->key);
+                goto error;
+            }
+        }
+
+        entry = next;
+    }
+
+    /* Step 4: Turn the dict into a list */
+    if (isList) {
+        if (list_len != (list_max + 1)) {
+            error_setg(errp, "List indexes are not continuous, "
+                       "saw %zu elements but %zu largest index",
+                       list_len, list_max);
+            goto error;
+        }
+
+        for (i = 0; i < list_len; i++) {
+            char *key = g_strdup_printf("%zu", i);
+
+            child = qdict_get(multi_level, key);
+            g_free(key);
+            if (!child) {
+                error_setg(errp, "Unexpected missing list entry %zu", i);
+                goto error;
+            }
+
+            qobject_incref(child);
+            qlist_append_obj((QList *)dst, child);
+        }
+    }
+    QDECREF(multi_level);
+
+    return dst;
+
+ error:
+    g_free(suffix);
+    g_free(prefix);
+    QDECREF(multi_level);
+    QDECREF(two_level);
+    qobject_decref(dst);
+    return NULL;
+}
+
+
 /**
  * qdict_array_entries(): Returns the number of direct array entries if the
  * sub-QDict of src specified by the prefix in subqdict (or src itself for
diff --git a/tests/check-qdict.c b/tests/check-qdict.c
index a43056c..20aa1af 100644
--- a/tests/check-qdict.c
+++ b/tests/check-qdict.c
@@ -596,6 +596,113 @@ static void qdict_join_test(void)
     QDECREF(dict2);
 }
 
+
+static void qdict_crumple_test_nonrecursive(void)
+{
+    QDict *src, *dst, *rules;
+    QObject *child;
+
+    src = qdict_new();
+    qdict_put(src, "rule.0.match", qstring_from_str("fred"));
+    qdict_put(src, "rule.0.policy", qstring_from_str("allow"));
+    qdict_put(src, "rule.1.match", qstring_from_str("bob"));
+    qdict_put(src, "rule.1.policy", qstring_from_str("deny"));
+
+    dst = (QDict *)qdict_crumple(src, false, &error_abort);
+
+    g_assert_cmpint(qdict_size(dst), ==, 1);
+
+    child = qdict_get(dst, "rule");
+    g_assert_cmpint(qobject_type(child), ==, QTYPE_QDICT);
+
+    rules = qdict_get_qdict(dst, "rule");
+
+    g_assert_cmpstr("fred", ==, qdict_get_str(rules, "0.match"));
+    g_assert_cmpstr("allow", ==, qdict_get_str(rules, "0.policy"));
+    g_assert_cmpstr("bob", ==, qdict_get_str(rules, "1.match"));
+    g_assert_cmpstr("deny", ==, qdict_get_str(rules, "1.policy"));
+
+    QDECREF(src);
+    QDECREF(dst);
+}
+
+
+static void qdict_crumple_test_recursive(void)
+{
+    QDict *src, *dst, *rule;
+    QObject *child;
+    QList *rules;
+
+    src = qdict_new();
+    qdict_put(src, "rule.0.match", qstring_from_str("fred"));
+    qdict_put(src, "rule.0.policy", qstring_from_str("allow"));
+    qdict_put(src, "rule.1.match", qstring_from_str("bob"));
+    qdict_put(src, "rule.1.policy", qstring_from_str("deny"));
+
+    dst = (QDict *)qdict_crumple(src, true, &error_abort);
+
+    g_assert_cmpint(qdict_size(dst), ==, 1);
+
+    child = qdict_get(dst, "rule");
+    g_assert_cmpint(qobject_type(child), ==, QTYPE_QLIST);
+
+    rules = qdict_get_qlist(dst, "rule");
+    g_assert_cmpint(qlist_size(rules), ==, 2);
+
+    rule = qobject_to_qdict(qlist_pop(rules));
+    g_assert_cmpstr("fred", ==, qdict_get_str(rule, "match"));
+    g_assert_cmpstr("allow", ==, qdict_get_str(rule, "policy"));
+    QDECREF(rule);
+
+    rule = qobject_to_qdict(qlist_pop(rules));
+    g_assert_cmpstr("bob", ==, qdict_get_str(rule, "match"));
+    g_assert_cmpstr("deny", ==, qdict_get_str(rule, "policy"));
+    QDECREF(rule);
+
+    QDECREF(src);
+    QDECREF(dst);
+}
+
+
+static void qdict_crumple_test_bad_inputs(void)
+{
+    QDict *src;
+    Error *error = NULL;
+
+    src = qdict_new();
+    /* rule.0 can't be both a string and a dict */
+    qdict_put(src, "rule.0", qstring_from_str("fred"));
+    qdict_put(src, "rule.0.policy", qstring_from_str("allow"));
+
+    g_assert(qdict_crumple(src, true, &error) == NULL);
+    g_assert(error != NULL);
+    error_free(error);
+    error = NULL;
+    QDECREF(src);
+
+    src = qdict_new();
+    /* rule can't be both a list and a dict */
+    qdict_put(src, "rule.0", qstring_from_str("fred"));
+    qdict_put(src, "rule.a", qstring_from_str("allow"));
+
+    g_assert(qdict_crumple(src, true, &error) == NULL);
+    g_assert(error != NULL);
+    error_free(error);
+    error = NULL;
+    QDECREF(src);
+
+    src = qdict_new();
+    /* The input should be flat, ie no dicts or lists */
+    qdict_put(src, "rule.0", qdict_new());
+    qdict_put(src, "rule.a", qstring_from_str("allow"));
+
+    g_assert(qdict_crumple(src, true, &error) == NULL);
+    g_assert(error != NULL);
+    error_free(error);
+    error = NULL;
+    QDECREF(src);
+}
+
 /*
  * Errors test-cases
  */
@@ -743,6 +850,13 @@ int main(int argc, char **argv)
     g_test_add_func("/errors/put_exists", qdict_put_exists_test);
     g_test_add_func("/errors/get_not_exists", qdict_get_not_exists_test);
 
+    g_test_add_func("/public/crumple/nonrecursive",
+                    qdict_crumple_test_nonrecursive);
+    g_test_add_func("/public/crumple/recursive",
+                    qdict_crumple_test_recursive);
+    g_test_add_func("/public/crumple/bad_inputs",
+                    qdict_crumple_test_bad_inputs);
+
     /* The Big one */
     if (g_test_slow()) {
         g_test_add_func("/stress/test", qdict_stress_test);
-- 
2.5.0