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Backport Bug#28949700: SUBOPTIMAL USE OF STRING::RESERVE() IN WRAPPER_TO_STRING() to 5.7 #336

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Backport Bug#28949700: SUBOPTIMAL USE OF STRING::RESERVE() IN WRAPPER_TO_STRING() to 5.7 #336

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47 changes: 34 additions & 13 deletions sql/json_dom.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1570,6 +1570,16 @@ void Json_array::clear()
delete_container_pointers(m_v);
}

/**
Reserve space in a string buffer. If reallocation is needed,
increase the size of the buffer exponentially.
@param buffer the string buffer
@param needed the number of bytes needed
@return true on error, false on success
*/
static bool reserve(String *buffer, size_t needed) {
return buffer->reserve(needed, buffer->length());
}

/**
Perform quoting on a JSON string to make an external representation
Expand Down Expand Up @@ -1605,8 +1615,8 @@ void Json_array::clear()
*/
bool double_quote(const char *cptr, size_t length, String *buf)
{
if (buf->append('"'))
return true; /* purecov: inspected */
if (reserve(buf, length + 2) || buf->append('"'))
return true; /* purecov: inspected */

for (size_t i= 0; i < length; i++)
{
Expand Down Expand Up @@ -2004,6 +2014,18 @@ static bool newline_and_indent(String *buffer, size_t level)
buffer->fill(buffer->length() + level * 2, ' ');
}

/**
Append a comma to separate elements in JSON arrays and objects.
@param buffer the string buffer
@param pretty true if pretty printing is enabled
@return true on error, false on success
*/
static bool append_comma(String *buffer, bool pretty) {
// Append a comma followed by a blank space. If pretty printing is
// enabled, a newline will be added in front of the next element, so
// the blank space can be omitted.
return buffer->append(',') || (!pretty && buffer->append(' '));
}

/**
Helper function which does all the heavy lifting for
Expand Down Expand Up @@ -2037,7 +2059,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
case Json_dom::J_TIMESTAMP:
{
// Make sure the buffer has space for the datetime and the quotes.
if (buffer->reserve(MAX_DATE_STRING_REP_LENGTH + 2))
if (reserve(buffer, MAX_DATE_STRING_REP_LENGTH + 2))
return true; /* purecov: inspected */
MYSQL_TIME t;
wr.get_datetime(&t);
Expand All @@ -2058,7 +2080,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
size_t array_len= wr.length();
for (uint32 i= 0; i < array_len; ++i)
{
if (i > 0 && buffer->append(pretty ? "," : ", "))
if (i > 0 && append_comma(buffer, pretty))
return true; /* purecov: inspected */

if (pretty && newline_and_indent(buffer, depth))
Expand All @@ -2077,14 +2099,14 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
break;
}
case Json_dom::J_BOOLEAN:
if (buffer->append(wr.get_boolean() ? "true" : "false"))
if (wr.get_boolean() ? buffer->append(STRING_WITH_LEN("true"))
: buffer->append(STRING_WITH_LEN("false")))
return true; /* purecov: inspected */
break;
case Json_dom::J_DECIMAL:
{
int length= DECIMAL_MAX_STR_LENGTH + 1;
if (buffer->reserve(length))
return true; /* purecov: inspected */
if (reserve(buffer, length)) return true;
char *ptr= const_cast<char *>(buffer->ptr()) + buffer->length();
my_decimal m;
if (wr.get_decimal_data(&m) ||
Expand All @@ -2095,7 +2117,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
}
case Json_dom::J_DOUBLE:
{
if (buffer->reserve(MY_GCVT_MAX_FIELD_WIDTH + 1))
if (reserve(buffer, MY_GCVT_MAX_FIELD_WIDTH + 1))
return true; /* purecov: inspected */
double d= wr.get_double();
size_t len= my_gcvt(d, MY_GCVT_ARG_DOUBLE, MY_GCVT_MAX_FIELD_WIDTH,
Expand All @@ -2111,7 +2133,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
break;
}
case Json_dom::J_NULL:
if (buffer->append("null"))
if (buffer->append(STRING_WITH_LEN("null")))
return true; /* purecov: inspected */
break;
case Json_dom::J_OBJECT:
Expand All @@ -2123,7 +2145,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
for (Json_wrapper_object_iterator iter= wr.object_iterator();
!iter.empty(); iter.next())
{
if (!first && buffer->append(pretty ? "," : ", "))
if (!first && append_comma(buffer, pretty))
return true; /* purecov: inspected */

first= false;
Expand All @@ -2135,7 +2157,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
const char *key_data= key.c_str();
size_t key_length= key.length();
if (print_string(buffer, true, key_data, key_length) ||
buffer->append(": ") ||
buffer->append(':') || buffer->append(' ') ||
wrapper_to_string(iter.elt().second, buffer, true, pretty,
func_name, depth))
return true; /* purecov: inspected */
Expand All @@ -2154,7 +2176,6 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,
if (wr.get_data_length() > base64_encode_max_arg_length())
{
/* purecov: begin inspected */
buffer->append("\"<data too long to decode - unexpected error>\"");
my_error(ER_INTERNAL_ERROR, MYF(0),
"JSON: could not decode opaque data");
return true;
Expand All @@ -2172,7 +2193,7 @@ static bool wrapper_to_string(const Json_wrapper &wr, String *buffer,

// "base64:typeXX:<binary data>"
size_t pos= buffer->length();
if (buffer->reserve(needed) ||
if (reserve(buffer, needed) ||
base64_encode(wr.get_data(), wr.get_data_length(),
const_cast<char*>(buffer->ptr() + pos)))
return true; /* purecov: inspected */
Expand Down