pt_json.c

/*-------------------------------------------------------------------------
 *
 * pt_json.c
 *      For building the required json structure for telemetry.
 *
 * IDENTIFICATION
 *    contrib/percona_pg_telemetry/pt_json.c
 *
 *-------------------------------------------------------------------------
 */

#include "pt_json.h"
#include "percona_pg_telemetry.h"

#include <sys/stat.h>

/* Local functions */
static char *json_fix_value(char *str);

/*
 * Fixes a JSON string to avoid malformation of a json value. Returns
 * a palloced string that caller must pfree.
 */
char *
json_fix_value(char *str)
{
	int			i;
	int			len;
	int			maxlen;
	char	   *str_escaped;
	char	   *s;

	if (str == NULL)
		return NULL;

	len = strlen(str);
	maxlen = (len > 0) ? len * 2 : 1;

	/* Max we'd need twice the space. */
	str_escaped = (char *) palloc(maxlen);
	s = str_escaped;

	for (i = 0; i < len; i++)
	{
		if (str[i] == '"' || str[i] == '\\')
		{
			*s++ = '\\';
			*s++ = str[i];

			continue;
		}

		*s++ = str[i];
	}

	/* Ensure that we always end up with a string value. */
	*s = '\0';

	return str_escaped;
}

/*
 * Construct a JSON block for writing.
 *
 * NOTE: We are not escape any quote characters in key or value strings, as
 * we don't expect to encounter that in extension names.
 */
char *
construct_json_block(char *msg_block, size_t msg_block_sz, char *key, char *raw_value, int flags, int *json_file_indent)
{
	char	   *value = NULL;
	char		msg[2048] = {0};
	char		msg_json[2048] = {0};

	/* Make the string empty so that we can always concat. */
	msg_block[0] = '\0';

	if (raw_value)
		value = json_fix_value(raw_value);

	if (flags & PT_JSON_BLOCK_START)
	{
		PT_FORMAT_JSON(msg_json, sizeof(msg_json), "{", (*json_file_indent));
		strlcpy(msg_block, msg_json, msg_block_sz);

		(*json_file_indent)++;
	}

	if (flags & PT_JSON_KEY_VALUE_PAIR)
	{
		snprintf(msg, sizeof(msg), "\"%s\": \"%s\",", key, value);
		PT_FORMAT_JSON(msg_json, sizeof(msg_json), msg, (*json_file_indent));
		strlcat(msg_block, msg_json, msg_block_sz);
	}

	if (flags & PT_JSON_BLOCK_KEY)
	{
		snprintf(msg, sizeof(msg), "\"key\": \"%s\",", key);
		PT_FORMAT_JSON(msg_json, sizeof(msg_json), msg, (*json_file_indent));
		strlcat(msg_block, msg_json, msg_block_sz);
	}

	if (flags & PT_JSON_BLOCK_VALUE)
	{
		snprintf(msg, sizeof(msg), "\"value\": \"%s\"", value);
		PT_FORMAT_JSON(msg_json, sizeof(msg_json), msg, (*json_file_indent));
		strlcat(msg_block, msg_json, msg_block_sz);
	}

	if (flags & PT_JSON_ARRAY_START)
	{
		if (value && value[0] != '\0')
			snprintf(msg, sizeof(msg), "\"%s\": [", value);
		else
			snprintf(msg, sizeof(msg), "\"value\": [");

		PT_FORMAT_JSON(msg_json, sizeof(msg_json), msg, (*json_file_indent));
		strlcat(msg_block, msg_json, msg_block_sz);

		(*json_file_indent)++;
	}

	/* Value is not an array so we can close the block. */
	if (flags & PT_JSON_ARRAY_END)
	{
		char		closing[3] = {']', ',', '\0'};

		if (flags & PT_JSON_BLOCK_LAST)
		{
			/* Let's remove the comma in case this is the last block. */
			closing[1] = '\0';
		}

		(*json_file_indent)--;

		PT_FORMAT_JSON(msg_json, sizeof(msg_json), closing, (*json_file_indent));
		strlcat(msg_block, msg_json, msg_block_sz);
	}

	/* Value is not an array so we can close the block. */
	if (flags & PT_JSON_BLOCK_END)
	{
		char		closing[3] = {'}', ',', '\0'};

		if (flags & PT_JSON_BLOCK_LAST)
		{
			/* Let's remove the comma in case this is the last block. */
			closing[1] = '\0';
		}

		(*json_file_indent)--;

		PT_FORMAT_JSON(msg_json, sizeof(msg_json), closing, (*json_file_indent));
		strlcat(msg_block, msg_json, msg_block_sz);
	}

	if (value)
		pfree(value);

	return msg_block;
}

/*
 * Open a file in the given mode.
 */
FILE *
json_file_open(char *pathname, char *mode)
{
	FILE	   *fp;

	fp = fopen(pathname, mode);
	if (fp == NULL)
	{
		ereport(LOG,
				(errcode_for_file_access(),
				 errmsg("Could not open file %s for writing.", pathname)));
		PT_WORKER_EXIT(PT_FILE_ERROR);
	}

	return fp;
}

/*
 * Write JSON to file.
 */
void
write_json_to_file(FILE *fp, char *json_str)
{
	int			len;
	int			bytes_written;

	len = strlen(json_str);
	bytes_written = fwrite(json_str, 1, len, fp);

	if (len != bytes_written)
	{
		ereport(LOG,
				(errcode_for_file_access(),
				 errmsg("Could not write to json file.")));

		fclose(fp);
		PT_WORKER_EXIT(PT_FILE_ERROR);
	}
}