qc: Add qc_get_field_info

This function returns more detailed information about the fields
of a statement. Supersedes qc_get_affected_fields() that will
be deprecated and removed.

Note that this function now introduced new kind of behaviour; the
returned data belongs to the GWBUF and remains valid for as long as
the GWBUF is alive. That means that unnecessary copying need not
be done.

include/maxscale/query_classifier.h

@@ -87,6 +87,18 @@ typedef enum qc_parse_result
 } qc_parse_result_t;
 
 
+/**
+ * QC_FIELD_INFO contains information about a field used in a statement.
+ */
+typedef struct qc_field_info
+{
+    char* database;  /** Present if the field is of the form "a.b.c", NULL otherwise. */
+    char* table;     /** Present if the field is of the form "a.b", NULL otherwise. */
+    char* column;    /** Always present. */
+    // TODO: Possibly add bits telling where the field is used; e.g. in the select
+    // TODO: part or the where part, or both.
+} QC_FIELD_INFO;
+
 /**
  * QUERY_CLASSIFIER defines the object a query classifier plugin must
  * implement and return.
@@ -117,6 +129,7 @@ typedef struct query_classifier
     char** (*qc_get_database_names)(GWBUF* stmt, int* size);
     char* (*qc_get_prepare_name)(GWBUF* stmt);
     qc_query_op_t (*qc_get_prepare_operation)(GWBUF* stmt);
+    void (*qc_get_field_info)(GWBUF* stmt, const QC_FIELD_INFO** infos, size_t* n_infos);
 } QUERY_CLASSIFIER;
 
 /**
@@ -223,6 +236,21 @@ qc_parse_result_t qc_parse(GWBUF* stmt);
  */
 char* qc_get_affected_fields(GWBUF* stmt);
 
+/**
+ * Returns information about affected fields.
+ *
+ * @param stmt     A buffer containing a COM_QUERY packet.
+ * @param infos    Pointer to pointer that after the call will point to an
+ *                 array of QC_FIELD_INFO:s.
+ * @param n_infos  Pointer to size_t variable where the number of items
+ *                 in @c infos will be returned.
+ *
+ * @note The returned array belongs to the GWBUF and remains valid for as
+ *       long as the GWBUF is valid. If the data is needed for longer than
+ *       that, it must be copied.
+ */
+void qc_get_field_info(GWBUF* stmt, const QC_FIELD_INFO** infos, size_t* n_infos);
+
 /**
  * Returns the statement, with literals replaced with question marks.
  *

query_classifier/qc_mysqlembedded/qc_mysqlembedded.cc

@@ -2010,6 +2010,14 @@ qc_query_op_t qc_get_prepare_operation(GWBUF* stmt)
     return operation;
 }
 
+void qc_get_field_info(GWBUF* stmt, const QC_FIELD_INFO** infos, size_t* n_infos)
+{
+    MXS_ERROR("qc_get_field_info not implemented yet.");
+
+    *infos = NULL;
+    *n_infos = 0;
+}
+
 namespace
 {
 
@@ -2156,6 +2164,7 @@ static QUERY_CLASSIFIER qc =
     qc_get_database_names,
     qc_get_prepare_name,
     qc_get_prepare_operation,
+    qc_get_field_info,
 };
 
  /* @see function load_module in load_utils.c for explanation of the following

query_classifier/qc_sqlite/qc_sqlite.c

@@ -248,6 +248,21 @@ static bool ensure_query_is_parsed(GWBUF* query)
     return parsed;
 }
 
+void free_field_infos(QC_FIELD_INFO* infos, size_t n_infos)
+{
+    if (infos)
+    {
+        for (int i = 0; i < n_infos; ++i)
+        {
+            MXS_FREE(infos[i].database);
+            MXS_FREE(infos[i].table);
+            MXS_FREE(infos[i].column);
+        }
+
+        MXS_FREE(infos);
+    }
+}
+
 static void free_string_array(char** sa)
 {
     if (sa)
@@ -2954,6 +2969,18 @@ static qc_query_op_t qc_sqlite_get_prepare_operation(GWBUF* query)
     return op;
 }
 
+void qc_sqlite_get_field_info(GWBUF* stmt, const QC_FIELD_INFO** infos, size_t* n_infos)
+{
+    QC_TRACE();
+    ss_dassert(this_unit.initialized);
+    ss_dassert(this_thread.initialized);
+
+    MXS_ERROR("qc_get_field_info not implemented yet.");
+
+    *infos = NULL;
+    *n_infos = 0;
+}
+
 /**
  * EXPORTS
  */
@@ -2979,6 +3006,7 @@ static QUERY_CLASSIFIER qc =
     qc_sqlite_get_database_names,
     qc_sqlite_get_prepare_name,
     qc_sqlite_get_prepare_operation,
+    qc_sqlite_get_field_info,
 };
 
 

server/core/query_classifier.c

@@ -197,6 +197,14 @@ char* qc_get_affected_fields(GWBUF* query)
     return classifier->qc_get_affected_fields(query);
 }
 
+void qc_get_field_info(GWBUF* query, const QC_FIELD_INFO** infos, size_t* n_infos)
+{
+    QC_TRACE();
+    ss_dassert(classifier);
+
+    classifier->qc_get_field_info(query, infos, n_infos);
+}
+
 char** qc_get_database_names(GWBUF* query, int* sizep)
 {
     QC_TRACE();