MDEV-6109: EXPLAIN JSON

Add pretty-printing of possible_keys column.

1 files changed, 73 insertions, 4 deletions

diff --git a/sql/my_json_writer.h b/sql/my_json_writer.h
index 101df7c3215..d92f98f20d8 100644
--- a/sql/my_json_writer.h
+++ b/sql/my_json_writer.h
@@ -1,5 +1,64 @@
 /* Todo: SkySQL copyrights */
 
+class Json_writer;
+
+/*
+  The idea is to catch arrays that can be printed on one line:
+
+    arrayName : [ "boo", 123, 456 ] 
+
+  and actually print them on one line. Arrrays that occupy too much space on
+  the line, or have nested members cannot be printed on one line.
+  
+  We hook into JSON printing functions and try to detect the pattern. While
+  detecting the pattern, we will accumulate "boo", 123, 456 as strings.
+
+  Then, 
+   - either the pattern is broken, and we print the elements out, 
+   - or the pattern lasts till the end of the array, and we print the 
+     array on one line.
+
+  TODO: 
+    fix the quoting. If we start to accumulate an array and but then it grows
+    too large to be printed on one line, the elements will be printed as
+    strings (even if some of them could be initially numbers).
+*/
+
+class Single_line_formatting_helper
+{
+  enum enum_state
+  {
+    INACTIVE,
+    ADD_MEMBER,
+    IN_ARRAY,
+    DISABLED
+  };
+
+  enum enum_state state;
+  enum { MAX_LINE_LEN= 80 };
+  char buffer[80];
+  char *buf_ptr;
+  uint line_len;
+
+  Json_writer *owner;
+public:
+  Single_line_formatting_helper() : state(INACTIVE), buf_ptr(buffer) {}
+
+  void init(Json_writer *owner_arg) { owner= owner_arg; }
+
+  bool on_add_member(const char *name);
+
+  bool on_start_array();
+  bool on_end_array();
+  void on_start_object();
+  // on_end_object() is not needed.
+   
+  bool on_add_str(const char *str);
+
+  void flush_on_one_line();
+  void disable_and_flush();
+};
+
 
 /*
   A class to write well-formed JSON documents. The documents are also formatted
@@ -13,12 +72,16 @@ public:
   Json_writer& add_member(const char *name);
   
   /* Add atomic values */
-  void add_ll(longlong val);
   void add_str(const char* val);
   void add_str(const String &str);
+
+  void add_ll(longlong val);
   void add_double(double val);
   void add_bool(bool val);
-  
+
+private:
+  void add_unquoted_str(const char* val);
+public:
   /* Start a child object */
   void start_object();
   void start_array();
@@ -29,18 +92,24 @@ public:
   Json_writer() : 
     indent_level(0), document_start(true), element_started(false), 
     first_child(true)
-  {}
+  {
+    fmt_helper.init(this);
+  }
 private:
   // TODO: a stack of (name, bool is_object_or_array) elements.
   int indent_level;
   enum { INDENT_SIZE = 2 };
-  
+ 
+  friend class Single_line_formatting_helper;
   bool document_start;
   bool element_started;
   bool first_child;
 
+  Single_line_formatting_helper fmt_helper;
+
   void append_indent();
   void start_element();
+  void start_sub_element();
 
   //const char *new_member_name;
 public: