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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 02:57:58 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 02:57:58 +0000
commitbe1c7e50e1e8809ea56f2c9d472eccd8ffd73a97 (patch)
tree9754ff1ca740f6346cf8483ec915d4054bc5da2d /libnetdata/eval
parentInitial commit. (diff)
downloadnetdata-be1c7e50e1e8809ea56f2c9d472eccd8ffd73a97.tar.xz
netdata-be1c7e50e1e8809ea56f2c9d472eccd8ffd73a97.zip
Adding upstream version 1.44.3.upstream/1.44.3upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'libnetdata/eval')
-rw-r--r--libnetdata/eval/Makefile.am8
-rw-r--r--libnetdata/eval/README.md1
-rw-r--r--libnetdata/eval/eval.c1201
-rw-r--r--libnetdata/eval/eval.h87
4 files changed, 1297 insertions, 0 deletions
diff --git a/libnetdata/eval/Makefile.am b/libnetdata/eval/Makefile.am
new file mode 100644
index 00000000..161784b8
--- /dev/null
+++ b/libnetdata/eval/Makefile.am
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+AUTOMAKE_OPTIONS = subdir-objects
+MAINTAINERCLEANFILES = $(srcdir)/Makefile.in
+
+dist_noinst_DATA = \
+ README.md \
+ $(NULL)
diff --git a/libnetdata/eval/README.md b/libnetdata/eval/README.md
new file mode 100644
index 00000000..8b137891
--- /dev/null
+++ b/libnetdata/eval/README.md
@@ -0,0 +1 @@
+
diff --git a/libnetdata/eval/eval.c b/libnetdata/eval/eval.c
new file mode 100644
index 00000000..a1ac4483
--- /dev/null
+++ b/libnetdata/eval/eval.c
@@ -0,0 +1,1201 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "../libnetdata.h"
+
+// ----------------------------------------------------------------------------
+// data structures for storing the parsed expression in memory
+
+typedef struct eval_value {
+ int type;
+
+ union {
+ NETDATA_DOUBLE number;
+ EVAL_VARIABLE *variable;
+ struct eval_node *expression;
+ };
+} EVAL_VALUE;
+
+typedef struct eval_node {
+ int id;
+ unsigned char operator;
+ int precedence;
+
+ int count;
+ EVAL_VALUE ops[];
+} EVAL_NODE;
+
+// these are used for EVAL_NODE.operator
+// they are used as internal IDs to identify an operator
+// THEY ARE NOT USED FOR PARSING OPERATORS LIKE THAT
+#define EVAL_OPERATOR_NOP '\0'
+#define EVAL_OPERATOR_EXPRESSION_OPEN '('
+#define EVAL_OPERATOR_EXPRESSION_CLOSE ')'
+#define EVAL_OPERATOR_NOT '!'
+#define EVAL_OPERATOR_PLUS '+'
+#define EVAL_OPERATOR_MINUS '-'
+#define EVAL_OPERATOR_AND '&'
+#define EVAL_OPERATOR_OR '|'
+#define EVAL_OPERATOR_GREATER_THAN_OR_EQUAL 'G'
+#define EVAL_OPERATOR_LESS_THAN_OR_EQUAL 'L'
+#define EVAL_OPERATOR_NOT_EQUAL '~'
+#define EVAL_OPERATOR_EQUAL '='
+#define EVAL_OPERATOR_LESS '<'
+#define EVAL_OPERATOR_GREATER '>'
+#define EVAL_OPERATOR_MULTIPLY '*'
+#define EVAL_OPERATOR_DIVIDE '/'
+#define EVAL_OPERATOR_SIGN_PLUS 'P'
+#define EVAL_OPERATOR_SIGN_MINUS 'M'
+#define EVAL_OPERATOR_ABS 'A'
+#define EVAL_OPERATOR_IF_THEN_ELSE '?'
+
+// ----------------------------------------------------------------------------
+// forward function definitions
+
+static inline void eval_node_free(EVAL_NODE *op);
+static inline EVAL_NODE *parse_full_expression(const char **string, int *error);
+static inline EVAL_NODE *parse_one_full_operand(const char **string, int *error);
+static inline NETDATA_DOUBLE eval_node(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error);
+static inline void print_parsed_as_node(BUFFER *out, EVAL_NODE *op, int *error);
+static inline void print_parsed_as_constant(BUFFER *out, NETDATA_DOUBLE n);
+
+// ----------------------------------------------------------------------------
+// evaluation of expressions
+
+static inline NETDATA_DOUBLE eval_variable(EVAL_EXPRESSION *exp, EVAL_VARIABLE *v, int *error) {
+ static STRING
+ *this_string = NULL,
+ *now_string = NULL,
+ *after_string = NULL,
+ *before_string = NULL,
+ *status_string = NULL,
+ *removed_string = NULL,
+ *uninitialized_string = NULL,
+ *undefined_string = NULL,
+ *clear_string = NULL,
+ *warning_string = NULL,
+ *critical_string = NULL;
+
+ NETDATA_DOUBLE n;
+
+ if(unlikely(this_string == NULL)) {
+ this_string = string_strdupz("this");
+ now_string = string_strdupz("now");
+ after_string = string_strdupz("after");
+ before_string = string_strdupz("before");
+ status_string = string_strdupz("status");
+ removed_string = string_strdupz("REMOVED");
+ uninitialized_string = string_strdupz("UNINITIALIZED");
+ undefined_string = string_strdupz("UNDEFINED");
+ clear_string = string_strdupz("CLEAR");
+ warning_string = string_strdupz("WARNING");
+ critical_string = string_strdupz("CRITICAL");
+ }
+
+ if(unlikely(v->name == this_string)) {
+ n = (exp->myself)?*exp->myself:NAN;
+ buffer_strcat(exp->error_msg, "[ $this = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == after_string)) {
+ n = (exp->after && *exp->after)?*exp->after:NAN;
+ buffer_strcat(exp->error_msg, "[ $after = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == before_string)) {
+ n = (exp->before && *exp->before)?*exp->before:NAN;
+ buffer_strcat(exp->error_msg, "[ $before = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == now_string)) {
+ n = (NETDATA_DOUBLE)now_realtime_sec();
+ buffer_strcat(exp->error_msg, "[ $now = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == status_string)) {
+ n = (exp->status)?*exp->status:RRDCALC_STATUS_UNINITIALIZED;
+ buffer_strcat(exp->error_msg, "[ $status = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == removed_string)) {
+ n = RRDCALC_STATUS_REMOVED;
+ buffer_strcat(exp->error_msg, "[ $REMOVED = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == uninitialized_string)) {
+ n = RRDCALC_STATUS_UNINITIALIZED;
+ buffer_strcat(exp->error_msg, "[ $UNINITIALIZED = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == undefined_string)) {
+ n = RRDCALC_STATUS_UNDEFINED;
+ buffer_strcat(exp->error_msg, "[ $UNDEFINED = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == clear_string)) {
+ n = RRDCALC_STATUS_CLEAR;
+ buffer_strcat(exp->error_msg, "[ $CLEAR = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == warning_string)) {
+ n = RRDCALC_STATUS_WARNING;
+ buffer_strcat(exp->error_msg, "[ $WARNING = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(unlikely(v->name == critical_string)) {
+ n = RRDCALC_STATUS_CRITICAL;
+ buffer_strcat(exp->error_msg, "[ $CRITICAL = ");
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ if(exp->rrdcalc && health_variable_lookup(v->name, exp->rrdcalc, &n)) {
+ buffer_sprintf(exp->error_msg, "[ ${%s} = ", string2str(v->name));
+ print_parsed_as_constant(exp->error_msg, n);
+ buffer_strcat(exp->error_msg, " ] ");
+ return n;
+ }
+
+ *error = EVAL_ERROR_UNKNOWN_VARIABLE;
+ buffer_sprintf(exp->error_msg, "[ undefined variable '%s' ] ", string2str(v->name));
+ return NAN;
+}
+
+static inline NETDATA_DOUBLE eval_value(EVAL_EXPRESSION *exp, EVAL_VALUE *v, int *error) {
+ NETDATA_DOUBLE n;
+
+ switch(v->type) {
+ case EVAL_VALUE_EXPRESSION:
+ n = eval_node(exp, v->expression, error);
+ break;
+
+ case EVAL_VALUE_NUMBER:
+ n = v->number;
+ break;
+
+ case EVAL_VALUE_VARIABLE:
+ n = eval_variable(exp, v->variable, error);
+ break;
+
+ default:
+ *error = EVAL_ERROR_INVALID_VALUE;
+ n = 0;
+ break;
+ }
+
+ return n;
+}
+
+static inline int is_true(NETDATA_DOUBLE n) {
+ if(isnan(n)) return 0;
+ if(isinf(n)) return 1;
+ if(n == 0) return 0;
+ return 1;
+}
+
+NETDATA_DOUBLE eval_and(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ return is_true(eval_value(exp, &op->ops[0], error)) && is_true(eval_value(exp, &op->ops[1], error));
+}
+NETDATA_DOUBLE eval_or(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ return is_true(eval_value(exp, &op->ops[0], error)) || is_true(eval_value(exp, &op->ops[1], error));
+}
+NETDATA_DOUBLE eval_greater_than_or_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ return isgreaterequal(n1, n2);
+}
+NETDATA_DOUBLE eval_less_than_or_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ return islessequal(n1, n2);
+}
+NETDATA_DOUBLE eval_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ if(isnan(n1) && isnan(n2)) return 1;
+ if(isinf(n1) && isinf(n2)) return 1;
+ if(isnan(n1) || isnan(n2)) return 0;
+ if(isinf(n1) || isinf(n2)) return 0;
+ return considered_equal_ndd(n1, n2);
+}
+NETDATA_DOUBLE eval_not_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ return !eval_equal(exp, op, error);
+}
+NETDATA_DOUBLE eval_less(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ return isless(n1, n2);
+}
+NETDATA_DOUBLE eval_greater(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ return isgreater(n1, n2);
+}
+NETDATA_DOUBLE eval_plus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ if(isnan(n1) || isnan(n2)) return NAN;
+ if(isinf(n1) || isinf(n2)) return INFINITY;
+ return n1 + n2;
+}
+NETDATA_DOUBLE eval_minus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ if(isnan(n1) || isnan(n2)) return NAN;
+ if(isinf(n1) || isinf(n2)) return INFINITY;
+ return n1 - n2;
+}
+NETDATA_DOUBLE eval_multiply(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ if(isnan(n1) || isnan(n2)) return NAN;
+ if(isinf(n1) || isinf(n2)) return INFINITY;
+ return n1 * n2;
+}
+NETDATA_DOUBLE eval_divide(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ NETDATA_DOUBLE n2 = eval_value(exp, &op->ops[1], error);
+ if(isnan(n1) || isnan(n2)) return NAN;
+ if(isinf(n1) || isinf(n2)) return INFINITY;
+ return n1 / n2;
+}
+NETDATA_DOUBLE eval_nop(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ return eval_value(exp, &op->ops[0], error);
+}
+NETDATA_DOUBLE eval_not(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ return !is_true(eval_value(exp, &op->ops[0], error));
+}
+NETDATA_DOUBLE eval_sign_plus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ return eval_value(exp, &op->ops[0], error);
+}
+NETDATA_DOUBLE eval_sign_minus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ if(isnan(n1)) return NAN;
+ if(isinf(n1)) return INFINITY;
+ return -n1;
+}
+NETDATA_DOUBLE eval_abs(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ NETDATA_DOUBLE n1 = eval_value(exp, &op->ops[0], error);
+ if(isnan(n1)) return NAN;
+ if(isinf(n1)) return INFINITY;
+ return ABS(n1);
+}
+NETDATA_DOUBLE eval_if_then_else(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ if(is_true(eval_value(exp, &op->ops[0], error)))
+ return eval_value(exp, &op->ops[1], error);
+ else
+ return eval_value(exp, &op->ops[2], error);
+}
+
+static struct operator {
+ const char *print_as;
+ char precedence;
+ char parameters;
+ char isfunction;
+ NETDATA_DOUBLE (*eval)(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error);
+} operators[256] = {
+ // this is a random access array
+ // we always access it with a known EVAL_OPERATOR_X
+
+ [EVAL_OPERATOR_AND] = { "&&", 2, 2, 0, eval_and },
+ [EVAL_OPERATOR_OR] = { "||", 2, 2, 0, eval_or },
+ [EVAL_OPERATOR_GREATER_THAN_OR_EQUAL] = { ">=", 3, 2, 0, eval_greater_than_or_equal },
+ [EVAL_OPERATOR_LESS_THAN_OR_EQUAL] = { "<=", 3, 2, 0, eval_less_than_or_equal },
+ [EVAL_OPERATOR_NOT_EQUAL] = { "!=", 3, 2, 0, eval_not_equal },
+ [EVAL_OPERATOR_EQUAL] = { "==", 3, 2, 0, eval_equal },
+ [EVAL_OPERATOR_LESS] = { "<", 3, 2, 0, eval_less },
+ [EVAL_OPERATOR_GREATER] = { ">", 3, 2, 0, eval_greater },
+ [EVAL_OPERATOR_PLUS] = { "+", 4, 2, 0, eval_plus },
+ [EVAL_OPERATOR_MINUS] = { "-", 4, 2, 0, eval_minus },
+ [EVAL_OPERATOR_MULTIPLY] = { "*", 5, 2, 0, eval_multiply },
+ [EVAL_OPERATOR_DIVIDE] = { "/", 5, 2, 0, eval_divide },
+ [EVAL_OPERATOR_NOT] = { "!", 6, 1, 0, eval_not },
+ [EVAL_OPERATOR_SIGN_PLUS] = { "+", 6, 1, 0, eval_sign_plus },
+ [EVAL_OPERATOR_SIGN_MINUS] = { "-", 6, 1, 0, eval_sign_minus },
+ [EVAL_OPERATOR_ABS] = { "abs(",6,1, 1, eval_abs },
+ [EVAL_OPERATOR_IF_THEN_ELSE] = { "?", 7, 3, 0, eval_if_then_else },
+ [EVAL_OPERATOR_NOP] = { NULL, 8, 1, 0, eval_nop },
+ [EVAL_OPERATOR_EXPRESSION_OPEN] = { NULL, 8, 1, 0, eval_nop },
+
+ // this should exist in our evaluation list
+ [EVAL_OPERATOR_EXPRESSION_CLOSE] = { NULL, 99, 1, 0, eval_nop }
+};
+
+#define eval_precedence(operator) (operators[(unsigned char)(operator)].precedence)
+
+static inline NETDATA_DOUBLE eval_node(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+ if(unlikely(op->count != operators[op->operator].parameters)) {
+ *error = EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS;
+ return 0;
+ }
+
+ NETDATA_DOUBLE n = operators[op->operator].eval(exp, op, error);
+
+ return n;
+}
+
+// ----------------------------------------------------------------------------
+// parsed-as generation
+
+static inline void print_parsed_as_variable(BUFFER *out, EVAL_VARIABLE *v, int *error) {
+ (void)error;
+ buffer_sprintf(out, "${%s}", string2str(v->name));
+}
+
+static inline void print_parsed_as_constant(BUFFER *out, NETDATA_DOUBLE n) {
+ if(unlikely(isnan(n))) {
+ buffer_strcat(out, "nan");
+ return;
+ }
+
+ if(unlikely(isinf(n))) {
+ buffer_strcat(out, "inf");
+ return;
+ }
+
+ char b[100+1], *s;
+ snprintfz(b, sizeof(b) - 1, NETDATA_DOUBLE_FORMAT, n);
+
+ s = &b[strlen(b) - 1];
+ while(s > b && *s == '0') {
+ *s ='\0';
+ s--;
+ }
+
+ if(s > b && *s == '.')
+ *s = '\0';
+
+ buffer_strcat(out, b);
+}
+
+static inline void print_parsed_as_value(BUFFER *out, EVAL_VALUE *v, int *error) {
+ switch(v->type) {
+ case EVAL_VALUE_EXPRESSION:
+ print_parsed_as_node(out, v->expression, error);
+ break;
+
+ case EVAL_VALUE_NUMBER:
+ print_parsed_as_constant(out, v->number);
+ break;
+
+ case EVAL_VALUE_VARIABLE:
+ print_parsed_as_variable(out, v->variable, error);
+ break;
+
+ default:
+ *error = EVAL_ERROR_INVALID_VALUE;
+ break;
+ }
+}
+
+static inline void print_parsed_as_node(BUFFER *out, EVAL_NODE *op, int *error) {
+ if(unlikely(op->count != operators[op->operator].parameters)) {
+ *error = EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS;
+ return;
+ }
+
+ if(operators[op->operator].parameters == 1) {
+
+ if(operators[op->operator].print_as)
+ buffer_sprintf(out, "%s", operators[op->operator].print_as);
+
+ //if(op->operator == EVAL_OPERATOR_EXPRESSION_OPEN)
+ // buffer_strcat(out, "(");
+
+ print_parsed_as_value(out, &op->ops[0], error);
+
+ //if(op->operator == EVAL_OPERATOR_EXPRESSION_OPEN)
+ // buffer_strcat(out, ")");
+ }
+
+ else if(operators[op->operator].parameters == 2) {
+ buffer_strcat(out, "(");
+ print_parsed_as_value(out, &op->ops[0], error);
+
+ if(operators[op->operator].print_as)
+ buffer_sprintf(out, " %s ", operators[op->operator].print_as);
+
+ print_parsed_as_value(out, &op->ops[1], error);
+ buffer_strcat(out, ")");
+ }
+ else if(op->operator == EVAL_OPERATOR_IF_THEN_ELSE && operators[op->operator].parameters == 3) {
+ buffer_strcat(out, "(");
+ print_parsed_as_value(out, &op->ops[0], error);
+
+ if(operators[op->operator].print_as)
+ buffer_sprintf(out, " %s ", operators[op->operator].print_as);
+
+ print_parsed_as_value(out, &op->ops[1], error);
+ buffer_strcat(out, " : ");
+ print_parsed_as_value(out, &op->ops[2], error);
+ buffer_strcat(out, ")");
+ }
+
+ if(operators[op->operator].isfunction)
+ buffer_strcat(out, ")");
+}
+
+// ----------------------------------------------------------------------------
+// parsing expressions
+
+// skip spaces
+static inline void skip_spaces(const char **string) {
+ const char *s = *string;
+ while(isspace(*s)) s++;
+ *string = s;
+}
+
+// what character can appear just after an operator keyword
+// like NOT AND OR ?
+static inline int isoperatorterm_word(const char s) {
+ if(isspace(s) || s == '(' || s == '$' || s == '!' || s == '-' || s == '+' || isdigit(s) || !s)
+ return 1;
+
+ return 0;
+}
+
+// what character can appear just after an operator symbol?
+static inline int isoperatorterm_symbol(const char s) {
+ if(isoperatorterm_word(s) || isalpha(s))
+ return 1;
+
+ return 0;
+}
+
+// return 1 if the character should never appear in a variable
+static inline int isvariableterm(const char s) {
+ if(isalnum(s) || s == '.' || s == '_')
+ return 0;
+
+ return 1;
+}
+
+// ----------------------------------------------------------------------------
+// parse operators
+
+static inline int parse_and(const char **string) {
+ const char *s = *string;
+
+ // AND
+ if((s[0] == 'A' || s[0] == 'a') && (s[1] == 'N' || s[1] == 'n') && (s[2] == 'D' || s[2] == 'd') && isoperatorterm_word(s[3])) {
+ *string = &s[4];
+ return 1;
+ }
+
+ // &&
+ if(s[0] == '&' && s[1] == '&' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_or(const char **string) {
+ const char *s = *string;
+
+ // OR
+ if((s[0] == 'O' || s[0] == 'o') && (s[1] == 'R' || s[1] == 'r') && isoperatorterm_word(s[2])) {
+ *string = &s[3];
+ return 1;
+ }
+
+ // ||
+ if(s[0] == '|' && s[1] == '|' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_greater_than_or_equal(const char **string) {
+ const char *s = *string;
+
+ // >=
+ if(s[0] == '>' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_less_than_or_equal(const char **string) {
+ const char *s = *string;
+
+ // <=
+ if (s[0] == '<' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_greater(const char **string) {
+ const char *s = *string;
+
+ // >
+ if(s[0] == '>' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_less(const char **string) {
+ const char *s = *string;
+
+ // <
+ if(s[0] == '<' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_equal(const char **string) {
+ const char *s = *string;
+
+ // ==
+ if(s[0] == '=' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ return 1;
+ }
+
+ // =
+ if(s[0] == '=' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_not_equal(const char **string) {
+ const char *s = *string;
+
+ // !=
+ if(s[0] == '!' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ return 1;
+ }
+
+ // <>
+ if(s[0] == '<' && s[1] == '>' && isoperatorterm_symbol(s[2])) {
+ *string = &s[2];
+ }
+
+ return 0;
+}
+
+static inline int parse_not(const char **string) {
+ const char *s = *string;
+
+ // NOT
+ if((s[0] == 'N' || s[0] == 'n') && (s[1] == 'O' || s[1] == 'o') && (s[2] == 'T' || s[2] == 't') && isoperatorterm_word(s[3])) {
+ *string = &s[3];
+ return 1;
+ }
+
+ if(s[0] == '!') {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_multiply(const char **string) {
+ const char *s = *string;
+
+ // *
+ if(s[0] == '*' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_divide(const char **string) {
+ const char *s = *string;
+
+ // /
+ if(s[0] == '/' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_minus(const char **string) {
+ const char *s = *string;
+
+ // -
+ if(s[0] == '-' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_plus(const char **string) {
+ const char *s = *string;
+
+ // +
+ if(s[0] == '+' && isoperatorterm_symbol(s[1])) {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_open_subexpression(const char **string) {
+ const char *s = *string;
+
+ // (
+ if(s[0] == '(') {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+#define parse_close_function(x) parse_close_subexpression(x)
+
+static inline int parse_close_subexpression(const char **string) {
+ const char *s = *string;
+
+ // )
+ if(s[0] == ')') {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_variable(const char **string, char *buffer, size_t len) {
+ const char *s = *string;
+
+ // $
+ if(*s == '$') {
+ size_t i = 0;
+ s++;
+
+ if(*s == '{') {
+ // ${variable_name}
+
+ s++;
+ while (*s && *s != '}' && i < len)
+ buffer[i++] = *s++;
+
+ if(*s == '}')
+ s++;
+ }
+ else {
+ // $variable_name
+
+ while (*s && !isvariableterm(*s) && i < len)
+ buffer[i++] = *s++;
+ }
+
+ buffer[i] = '\0';
+
+ if (buffer[0]) {
+ *string = s;
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
+static inline int parse_constant(const char **string, NETDATA_DOUBLE *number) {
+ char *end = NULL;
+ NETDATA_DOUBLE n = str2ndd(*string, &end);
+ if(unlikely(!end || *string == end)) {
+ *number = 0;
+ return 0;
+ }
+ *number = n;
+ *string = end;
+ return 1;
+}
+
+static inline int parse_abs(const char **string) {
+ const char *s = *string;
+
+ // ABS
+ if((s[0] == 'A' || s[0] == 'a') && (s[1] == 'B' || s[1] == 'b') && (s[2] == 'S' || s[2] == 's') && s[3] == '(') {
+ *string = &s[3];
+ return 1;
+ }
+
+ return 0;
+}
+
+static inline int parse_if_then_else(const char **string) {
+ const char *s = *string;
+
+ // ?
+ if(s[0] == '?') {
+ *string = &s[1];
+ return 1;
+ }
+
+ return 0;
+}
+
+static struct operator_parser {
+ unsigned char id;
+ int (*parse)(const char **);
+} operator_parsers[] = {
+ // the order in this list is important!
+ // the first matching will be used
+ // so place the longer of overlapping ones
+ // at the top
+
+ { EVAL_OPERATOR_AND, parse_and },
+ { EVAL_OPERATOR_OR, parse_or },
+ { EVAL_OPERATOR_GREATER_THAN_OR_EQUAL, parse_greater_than_or_equal },
+ { EVAL_OPERATOR_LESS_THAN_OR_EQUAL, parse_less_than_or_equal },
+ { EVAL_OPERATOR_NOT_EQUAL, parse_not_equal },
+ { EVAL_OPERATOR_EQUAL, parse_equal },
+ { EVAL_OPERATOR_LESS, parse_less },
+ { EVAL_OPERATOR_GREATER, parse_greater },
+ { EVAL_OPERATOR_PLUS, parse_plus },
+ { EVAL_OPERATOR_MINUS, parse_minus },
+ { EVAL_OPERATOR_MULTIPLY, parse_multiply },
+ { EVAL_OPERATOR_DIVIDE, parse_divide },
+ { EVAL_OPERATOR_IF_THEN_ELSE, parse_if_then_else },
+
+ /* we should not put in this list the following:
+ *
+ * - NOT
+ * - (
+ * - )
+ *
+ * these are handled in code
+ */
+
+ // termination
+ { EVAL_OPERATOR_NOP, NULL }
+};
+
+static inline unsigned char parse_operator(const char **string, int *precedence) {
+ skip_spaces(string);
+
+ int i;
+ for(i = 0 ; operator_parsers[i].parse != NULL ; i++)
+ if(operator_parsers[i].parse(string)) {
+ if(precedence) *precedence = eval_precedence(operator_parsers[i].id);
+ return operator_parsers[i].id;
+ }
+
+ return EVAL_OPERATOR_NOP;
+}
+
+// ----------------------------------------------------------------------------
+// memory management
+
+static inline EVAL_NODE *eval_node_alloc(int count) {
+ static int id = 1;
+
+ EVAL_NODE *op = callocz(1, sizeof(EVAL_NODE) + (sizeof(EVAL_VALUE) * count));
+
+ op->id = id++;
+ op->operator = EVAL_OPERATOR_NOP;
+ op->precedence = eval_precedence(EVAL_OPERATOR_NOP);
+ op->count = count;
+ return op;
+}
+
+static inline void eval_node_set_value_to_node(EVAL_NODE *op, int pos, EVAL_NODE *value) {
+ if(pos >= op->count)
+ fatal("Invalid request to set position %d of OPERAND that has only %d values", pos + 1, op->count + 1);
+
+ op->ops[pos].type = EVAL_VALUE_EXPRESSION;
+ op->ops[pos].expression = value;
+}
+
+static inline void eval_node_set_value_to_constant(EVAL_NODE *op, int pos, NETDATA_DOUBLE value) {
+ if(pos >= op->count)
+ fatal("Invalid request to set position %d of OPERAND that has only %d values", pos + 1, op->count + 1);
+
+ op->ops[pos].type = EVAL_VALUE_NUMBER;
+ op->ops[pos].number = value;
+}
+
+static inline void eval_node_set_value_to_variable(EVAL_NODE *op, int pos, const char *variable) {
+ if(pos >= op->count)
+ fatal("Invalid request to set position %d of OPERAND that has only %d values", pos + 1, op->count + 1);
+
+ op->ops[pos].type = EVAL_VALUE_VARIABLE;
+ op->ops[pos].variable = callocz(1, sizeof(EVAL_VARIABLE));
+ op->ops[pos].variable->name = string_strdupz(variable);
+}
+
+static inline void eval_variable_free(EVAL_VARIABLE *v) {
+ string_freez(v->name);
+ freez(v);
+}
+
+static inline void eval_value_free(EVAL_VALUE *v) {
+ switch(v->type) {
+ case EVAL_VALUE_EXPRESSION:
+ eval_node_free(v->expression);
+ break;
+
+ case EVAL_VALUE_VARIABLE:
+ eval_variable_free(v->variable);
+ break;
+
+ default:
+ break;
+ }
+}
+
+static inline void eval_node_free(EVAL_NODE *op) {
+ if(op->count) {
+ int i;
+ for(i = op->count - 1; i >= 0 ;i--)
+ eval_value_free(&op->ops[i]);
+ }
+
+ freez(op);
+}
+
+// ----------------------------------------------------------------------------
+// the parsing logic
+
+// helper function to avoid allocations all over the place
+static inline EVAL_NODE *parse_next_operand_given_its_operator(const char **string, unsigned char operator_type, int *error) {
+ EVAL_NODE *sub = parse_one_full_operand(string, error);
+ if(!sub) return NULL;
+
+ EVAL_NODE *op = eval_node_alloc(1);
+ op->operator = operator_type;
+ eval_node_set_value_to_node(op, 0, sub);
+ return op;
+}
+
+// parse a full operand, including its sign or other associative operator (e.g. NOT)
+static inline EVAL_NODE *parse_one_full_operand(const char **string, int *error) {
+ char variable_buffer[EVAL_MAX_VARIABLE_NAME_LENGTH + 1];
+ EVAL_NODE *op1 = NULL;
+ NETDATA_DOUBLE number;
+
+ *error = EVAL_ERROR_OK;
+
+ skip_spaces(string);
+ if(!(**string)) {
+ *error = EVAL_ERROR_MISSING_OPERAND;
+ return NULL;
+ }
+
+ if(parse_not(string)) {
+ op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_NOT, error);
+ op1->precedence = eval_precedence(EVAL_OPERATOR_NOT);
+ }
+ else if(parse_plus(string)) {
+ op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_SIGN_PLUS, error);
+ op1->precedence = eval_precedence(EVAL_OPERATOR_SIGN_PLUS);
+ }
+ else if(parse_minus(string)) {
+ op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_SIGN_MINUS, error);
+ op1->precedence = eval_precedence(EVAL_OPERATOR_SIGN_MINUS);
+ }
+ else if(parse_abs(string)) {
+ op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_ABS, error);
+ op1->precedence = eval_precedence(EVAL_OPERATOR_ABS);
+ }
+ else if(parse_open_subexpression(string)) {
+ EVAL_NODE *sub = parse_full_expression(string, error);
+ if(sub) {
+ op1 = eval_node_alloc(1);
+ op1->operator = EVAL_OPERATOR_EXPRESSION_OPEN;
+ op1->precedence = eval_precedence(EVAL_OPERATOR_EXPRESSION_OPEN);
+ eval_node_set_value_to_node(op1, 0, sub);
+ if(!parse_close_subexpression(string)) {
+ *error = EVAL_ERROR_MISSING_CLOSE_SUBEXPRESSION;
+ eval_node_free(op1);
+ return NULL;
+ }
+ }
+ }
+ else if(parse_variable(string, variable_buffer, EVAL_MAX_VARIABLE_NAME_LENGTH)) {
+ op1 = eval_node_alloc(1);
+ op1->operator = EVAL_OPERATOR_NOP;
+ eval_node_set_value_to_variable(op1, 0, variable_buffer);
+ }
+ else if(parse_constant(string, &number)) {
+ op1 = eval_node_alloc(1);
+ op1->operator = EVAL_OPERATOR_NOP;
+ eval_node_set_value_to_constant(op1, 0, number);
+ }
+ else if(**string)
+ *error = EVAL_ERROR_UNKNOWN_OPERAND;
+ else
+ *error = EVAL_ERROR_MISSING_OPERAND;
+
+ return op1;
+}
+
+// parse an operator and the rest of the expression
+// precedence processing is handled here
+static inline EVAL_NODE *parse_rest_of_expression(const char **string, int *error, EVAL_NODE *op1) {
+ EVAL_NODE *op2 = NULL;
+ unsigned char operator;
+ int precedence;
+
+ operator = parse_operator(string, &precedence);
+ skip_spaces(string);
+
+ if(operator != EVAL_OPERATOR_NOP) {
+ op2 = parse_one_full_operand(string, error);
+ if(!op2) {
+ // error is already reported
+ eval_node_free(op1);
+ return NULL;
+ }
+
+ EVAL_NODE *op = eval_node_alloc(operators[operator].parameters);
+ op->operator = operator;
+ op->precedence = precedence;
+
+ if(operator == EVAL_OPERATOR_IF_THEN_ELSE && op->count == 3) {
+ skip_spaces(string);
+
+ if(**string != ':') {
+ eval_node_free(op);
+ eval_node_free(op1);
+ eval_node_free(op2);
+ *error = EVAL_ERROR_IF_THEN_ELSE_MISSING_ELSE;
+ return NULL;
+ }
+ (*string)++;
+
+ skip_spaces(string);
+
+ EVAL_NODE *op3 = parse_one_full_operand(string, error);
+ if(!op3) {
+ eval_node_free(op);
+ eval_node_free(op1);
+ eval_node_free(op2);
+ // error is already reported
+ return NULL;
+ }
+
+ eval_node_set_value_to_node(op, 2, op3);
+ }
+
+ eval_node_set_value_to_node(op, 1, op2);
+
+ // precedence processing
+ // if this operator has a higher precedence compared to its next
+ // put the next operator on top of us (top = evaluated later)
+ // function recursion does the rest...
+ if(op->precedence > op1->precedence && op1->count == 2 && op1->operator != '(' && op1->ops[1].type == EVAL_VALUE_EXPRESSION) {
+ eval_node_set_value_to_node(op, 0, op1->ops[1].expression);
+ op1->ops[1].expression = op;
+ op = op1;
+ }
+ else
+ eval_node_set_value_to_node(op, 0, op1);
+
+ return parse_rest_of_expression(string, error, op);
+ }
+ else if(**string == ')') {
+ ;
+ }
+ else if(**string) {
+ eval_node_free(op1);
+ op1 = NULL;
+ *error = EVAL_ERROR_MISSING_OPERATOR;
+ }
+
+ return op1;
+}
+
+// high level function to parse an expression or a sub-expression
+static inline EVAL_NODE *parse_full_expression(const char **string, int *error) {
+ EVAL_NODE *op1 = parse_one_full_operand(string, error);
+ if(!op1) {
+ *error = EVAL_ERROR_MISSING_OPERAND;
+ return NULL;
+ }
+
+ return parse_rest_of_expression(string, error, op1);
+}
+
+// ----------------------------------------------------------------------------
+// public API
+
+int expression_evaluate(EVAL_EXPRESSION *expression) {
+ expression->error = EVAL_ERROR_OK;
+
+ buffer_reset(expression->error_msg);
+ expression->result = eval_node(expression, (EVAL_NODE *)expression->nodes, &expression->error);
+
+ if(unlikely(isnan(expression->result))) {
+ if(expression->error == EVAL_ERROR_OK)
+ expression->error = EVAL_ERROR_VALUE_IS_NAN;
+ }
+ else if(unlikely(isinf(expression->result))) {
+ if(expression->error == EVAL_ERROR_OK)
+ expression->error = EVAL_ERROR_VALUE_IS_INFINITE;
+ }
+ else if(unlikely(expression->error == EVAL_ERROR_UNKNOWN_VARIABLE)) {
+ // although there is an unknown variable
+ // the expression was evaluated successfully
+ expression->error = EVAL_ERROR_OK;
+ }
+
+ if(expression->error != EVAL_ERROR_OK) {
+ expression->result = NAN;
+
+ if(buffer_strlen(expression->error_msg))
+ buffer_strcat(expression->error_msg, "; ");
+
+ buffer_sprintf(expression->error_msg, "failed to evaluate expression with error %d (%s)", expression->error, expression_strerror(expression->error));
+ return 0;
+ }
+
+ return 1;
+}
+
+EVAL_EXPRESSION *expression_parse(const char *string, const char **failed_at, int *error) {
+ const char *s = string;
+ int err = EVAL_ERROR_OK;
+
+ EVAL_NODE *op = parse_full_expression(&s, &err);
+
+ if(*s) {
+ if(op) {
+ eval_node_free(op);
+ op = NULL;
+ }
+ err = EVAL_ERROR_REMAINING_GARBAGE;
+ }
+
+ if (failed_at) *failed_at = s;
+ if (error) *error = err;
+
+ if(!op) {
+ unsigned long pos = s - string + 1;
+ netdata_log_error("failed to parse expression '%s': %s at character %lu (i.e.: '%s').", string, expression_strerror(err), pos, s);
+ return NULL;
+ }
+
+ BUFFER *out = buffer_create(1024, NULL);
+ print_parsed_as_node(out, op, &err);
+ if(err != EVAL_ERROR_OK) {
+ netdata_log_error("failed to re-generate expression '%s' with reason: %s", string, expression_strerror(err));
+ eval_node_free(op);
+ buffer_free(out);
+ return NULL;
+ }
+
+ EVAL_EXPRESSION *exp = callocz(1, sizeof(EVAL_EXPRESSION));
+
+ exp->source = strdupz(string);
+ exp->parsed_as = strdupz(buffer_tostring(out));
+ buffer_free(out);
+
+ exp->error_msg = buffer_create(100, NULL);
+ exp->nodes = (void *)op;
+
+ return exp;
+}
+
+void expression_free(EVAL_EXPRESSION *expression) {
+ if(!expression) return;
+
+ if(expression->nodes) eval_node_free((EVAL_NODE *)expression->nodes);
+ freez((void *)expression->source);
+ freez((void *)expression->parsed_as);
+ buffer_free(expression->error_msg);
+ freez(expression);
+}
+
+const char *expression_strerror(int error) {
+ switch(error) {
+ case EVAL_ERROR_OK:
+ return "success";
+
+ case EVAL_ERROR_MISSING_CLOSE_SUBEXPRESSION:
+ return "missing closing parenthesis";
+
+ case EVAL_ERROR_UNKNOWN_OPERAND:
+ return "unknown operand";
+
+ case EVAL_ERROR_MISSING_OPERAND:
+ return "expected operand";
+
+ case EVAL_ERROR_MISSING_OPERATOR:
+ return "expected operator";
+
+ case EVAL_ERROR_REMAINING_GARBAGE:
+ return "remaining characters after expression";
+
+ case EVAL_ERROR_INVALID_VALUE:
+ return "invalid value structure - internal error";
+
+ case EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS:
+ return "wrong number of operands for operation - internal error";
+
+ case EVAL_ERROR_VALUE_IS_NAN:
+ return "value is unset";
+
+ case EVAL_ERROR_VALUE_IS_INFINITE:
+ return "computed value is infinite";
+
+ case EVAL_ERROR_UNKNOWN_VARIABLE:
+ return "undefined variable";
+
+ case EVAL_ERROR_IF_THEN_ELSE_MISSING_ELSE:
+ return "missing second sub-expression of inline conditional";
+
+ default:
+ return "unknown error";
+ }
+}
diff --git a/libnetdata/eval/eval.h b/libnetdata/eval/eval.h
new file mode 100644
index 00000000..05a26936
--- /dev/null
+++ b/libnetdata/eval/eval.h
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_EVAL_H
+#define NETDATA_EVAL_H 1
+
+#include "../libnetdata.h"
+
+#define EVAL_MAX_VARIABLE_NAME_LENGTH 300
+
+typedef enum rrdcalc_status {
+ RRDCALC_STATUS_REMOVED = -2,
+ RRDCALC_STATUS_UNDEFINED = -1,
+ RRDCALC_STATUS_UNINITIALIZED = 0,
+ RRDCALC_STATUS_CLEAR = 1,
+ RRDCALC_STATUS_RAISED = 2, // DO NOT CHANGE THESE NUMBERS
+ RRDCALC_STATUS_WARNING = 3, // DO NOT CHANGE THESE NUMBERS
+ RRDCALC_STATUS_CRITICAL = 4, // DO NOT CHANGE THESE NUMBERS
+} RRDCALC_STATUS;
+
+typedef struct eval_variable {
+ STRING *name;
+ struct eval_variable *next;
+} EVAL_VARIABLE;
+
+typedef struct eval_expression {
+ const char *source;
+ const char *parsed_as;
+
+ RRDCALC_STATUS *status;
+ NETDATA_DOUBLE *myself;
+ time_t *after;
+ time_t *before;
+
+ NETDATA_DOUBLE result;
+
+ int error;
+ BUFFER *error_msg;
+
+ // hidden EVAL_NODE *
+ void *nodes;
+
+ // custom data to be used for looking up variables
+ struct rrdcalc *rrdcalc;
+} EVAL_EXPRESSION;
+
+#define EVAL_VALUE_INVALID 0
+#define EVAL_VALUE_NUMBER 1
+#define EVAL_VALUE_VARIABLE 2
+#define EVAL_VALUE_EXPRESSION 3
+
+// parsing and evaluation
+#define EVAL_ERROR_OK 0
+
+// parsing errors
+#define EVAL_ERROR_MISSING_CLOSE_SUBEXPRESSION 1
+#define EVAL_ERROR_UNKNOWN_OPERAND 2
+#define EVAL_ERROR_MISSING_OPERAND 3
+#define EVAL_ERROR_MISSING_OPERATOR 4
+#define EVAL_ERROR_REMAINING_GARBAGE 5
+#define EVAL_ERROR_IF_THEN_ELSE_MISSING_ELSE 6
+
+// evaluation errors
+#define EVAL_ERROR_INVALID_VALUE 101
+#define EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS 102
+#define EVAL_ERROR_VALUE_IS_NAN 103
+#define EVAL_ERROR_VALUE_IS_INFINITE 104
+#define EVAL_ERROR_UNKNOWN_VARIABLE 105
+
+// parse the given string as an expression and return:
+// a pointer to an expression if it parsed OK
+// NULL in which case the pointer to error has the error code
+EVAL_EXPRESSION *expression_parse(const char *string, const char **failed_at, int *error);
+
+// free all resources allocated for an expression
+void expression_free(EVAL_EXPRESSION *expression);
+
+// convert an error code to a message
+const char *expression_strerror(int error);
+
+// evaluate an expression and return
+// 1 = OK, the result is in: expression->result
+// 2 = FAILED, the error message is in: buffer_tostring(expression->error_msg)
+int expression_evaluate(EVAL_EXPRESSION *expression);
+
+int health_variable_lookup(STRING *variable, struct rrdcalc *rc, NETDATA_DOUBLE *result);
+
+#endif //NETDATA_EVAL_H