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logs_to_metrics: Support optional value_field for counters #10055

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5c28512
logs_to_metrics: Support optional value_field for counters
databus23 Mar 6, 2025
5b8e260
Use pre-created ctx->value_ra
databus23 Oct 22, 2025
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51 changes: 42 additions & 9 deletions plugins/filter_log_to_metrics/log_to_metrics.c
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Original file line number Diff line number Diff line change
Expand Up @@ -643,13 +643,14 @@ static int cb_log_to_metrics_init(struct flb_filter_instance *f_ins,
snprintf(metric_description, sizeof(metric_description) - 1, "%s",
ctx->metric_description);

/* Value field only needed for modes gauge and histogram */
if (ctx->mode > 0) {
if (ctx->value_field == NULL || strlen(ctx->value_field) == 0) {
flb_plg_error(f_ins, "value_field is not set");
log_to_metrics_destroy(ctx);
return -1;
if (ctx->value_field == NULL || strlen(ctx->value_field) == 0) {
/* require value field for modes gauge and histogram */
if (ctx->mode > 0) {
flb_plg_error(f_ins, "value_field is not set");
log_to_metrics_destroy(ctx);
return -1;
}
} else {
snprintf(value_field, sizeof(value_field) - 1, "%s",
ctx->value_field);

Expand Down Expand Up @@ -836,6 +837,7 @@ static int cb_log_to_metrics_filter(const void *data, size_t bytes,
char **label_values = NULL;
int label_count = 0;
int i;
double counter_value = 0;
double gauge_value = 0;
double histogram_value = 0;
char kubernetes_label_values
Expand Down Expand Up @@ -912,8 +914,39 @@ static int cb_log_to_metrics_filter(const void *data, size_t bytes,
/* Calculating and setting metric depending on the mode */
switch (ctx->mode) {
case FLB_LOG_TO_METRICS_COUNTER:
ret = cmt_counter_inc(ctx->c, ts, label_count,
label_values);

// If value_field is not set, increment counter by 1
if (ctx->value_field == NULL || strlen(ctx->value_field) == 0) {
ret = cmt_counter_inc(ctx->c, ts, label_count,
label_values);
break;
}
// If value_field is set, increment counter by value
rval = flb_ra_get_value_object(ctx->value_ra, map);

if (!rval) {
flb_warn("given value field is empty or not existent");
break;
}
if (rval->type == FLB_RA_STRING) {
sscanf(rval->val.string, "%lf", &counter_value);
Comment on lines +931 to +932
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@coderabbitai coderabbitai bot Oct 22, 2025 •
edited
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⚠️ Potential issue | 🟡 Minor

Check sscanf return value to avoid undefined behavior.

Line 938 uses sscanf but ignores its return value. If the string is not a valid number, counter_value remains uninitialized or retains a stale value, leading to incorrect metrics.

Apply this diff:

                     if (rval->type == FLB_RA_STRING) {
-                        sscanf(rval->val.string, "%lf", &counter_value);
+                        if (sscanf(rval->val.string, "%lf", &counter_value) != 1) {
+                            flb_plg_error(f_ins, "cannot parse value_field as numeric");
+                            flb_ra_key_value_destroy(rval);
+                            break;
+                        }
                     }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
if (rval->type == FLB_RA_STRING) {
sscanf(rval->val.string, "%lf", &counter_value);
if (rval->type == FLB_RA_STRING) {
if (sscanf(rval->val.string, "%lf", &counter_value) != 1) {
flb_plg_error(f_ins, "cannot parse value_field as numeric");
flb_ra_key_value_destroy(rval);
break;
}
}
🤖 Prompt for AI Agents 
In plugins/filter_log_to_metrics/log_to_metrics.c around lines 937-938, the
sscanf call ignores its return value which can leave counter_value uninitialized
if parsing fails; replace or guard the sscanf usage by checking its return
(expecting 1) and only assign counter_value on success, otherwise handle the
error path (e.g., skip processing this metric, set a safe default, and/or log an
error); alternatively use strtod with an endptr to robustly detect invalid input
and validate endptr before using counter_value.

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@databus23 databus23 Oct 22, 2025

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Thanks coderabbitai for the suggestion but if you check the existing uses of sscanf in the file they also don't check the return value as you suggested.

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@databus23 Thanks — you’re right that the other sscanf sites follow the same pattern. To keep things consistent and safer across all modes, here’s a minimal patch that guards all three sscanf calls. On parse failure we log and skip the emission, avoiding a silent add of 0.

diff --git a/plugins/filter_log_to_metrics/log_to_metrics.c b/plugins/filter_log_to_metrics/log_to_metrics.c
--- a/plugins/filter_log_to_metrics/log_to_metrics.c
+++ b/plugins/filter_log_to_metrics/log_to_metrics.c
@@
-                    if (rval->type == FLB_RA_STRING) {
-                        sscanf(rval->val.string, "%lf", &counter_value);
-                    }
+                    if (rval->type == FLB_RA_STRING) {
+                        if (sscanf(rval->val.string, "%lf", &counter_value) != 1) {
+                            flb_plg_error(f_ins, "cannot parse value_field as numeric");
+                            flb_ra_key_value_destroy(rval);
+                            rval = NULL;
+                            break;
+                        }
+                    }
@@
-                    if (rval->type == FLB_RA_STRING) {
-                        sscanf(rval->val.string, "%lf", &gauge_value);
-                    }
+                    if (rval->type == FLB_RA_STRING) {
+                        if (sscanf(rval->val.string, "%lf", &gauge_value) != 1) {
+                            flb_plg_error(f_ins, "cannot parse value_field as numeric");
+                            flb_ra_key_value_destroy(rval);
+                            rval = NULL;
+                            break;
+                        }
+                    }
@@
-                    if (rval->type == FLB_RA_STRING) {
-                        sscanf(rval->val.string, "%lf", &histogram_value);
-                    }
+                    if (rval->type == FLB_RA_STRING) {
+                        if (sscanf(rval->val.string, "%lf", &histogram_value) != 1) {
+                            flb_plg_error(f_ins, "cannot parse value_field as numeric");
+                            flb_ra_key_value_destroy(rval);
+                            rval = NULL;
+                            break;
+                        }
+                    }

If you’d prefer to align with how buckets are parsed, we can switch these three sites to a strtod-based helper (or reuse convert_double) instead; happy to provide that variant too.

}
else if (rval->type == FLB_RA_FLOAT) {
counter_value = rval->val.f64;
}
else if (rval->type == FLB_RA_INT) {
counter_value = (double)rval->val.i64;
}
else {
flb_plg_error(f_ins,
"cannot convert given value to metric");
flb_ra_key_value_destroy(rval);
break;
}
ret = cmt_counter_add(ctx->c, ts, counter_value,
label_count, label_values);
flb_ra_key_value_destroy(rval);
rval = NULL;
break;

case FLB_LOG_TO_METRICS_GAUGE:
Expand Down Expand Up @@ -1057,7 +1090,7 @@ static struct flb_config_map config_map[] = {
{
FLB_CONFIG_MAP_STR, "value_field", NULL,
0, FLB_TRUE, offsetof(struct log_to_metrics_ctx, value_field),
"Numeric field to use for gauge or histogram"
"Numeric field to use for gauge, histogram or counter"
},
{
FLB_CONFIG_MAP_STR, "metric_name", "a",
Expand Down
70 changes: 70 additions & 0 deletions tests/runtime/filter_log_to_metrics.c
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@
/* Test functions */
void flb_test_log_to_metrics_counter_k8s(void);
void flb_test_log_to_metrics_counter(void);
void flb_test_log_to_metrics_counter_value_field(void);
void flb_test_log_to_metrics_counter_k8s_two_tuples(void);
void flb_test_log_to_metrics_gauge(void);
void flb_test_log_to_metrics_histogram(void);
Expand Down Expand Up @@ -118,6 +119,7 @@ void flb_test_log_to_metrics_label(void);
TEST_LIST = {
{"counter_k8s", flb_test_log_to_metrics_counter_k8s },
{"counter", flb_test_log_to_metrics_counter },
{"counter_value_field", flb_test_log_to_metrics_counter_value_field },
{"counter_k8s_two_tuples", flb_test_log_to_metrics_counter_k8s_two_tuples },
{"gauge", flb_test_log_to_metrics_gauge },
{"histogram", flb_test_log_to_metrics_histogram },
Expand Down Expand Up @@ -321,6 +323,74 @@ void flb_test_log_to_metrics_counter(void)

}

void flb_test_log_to_metrics_counter_value_field(void)
{
int ret;
int i;
flb_ctx_t *ctx;
int in_ffd;
int filter_ffd;
int out_ffd;
char *result = NULL;
struct flb_lib_out_cb cb_data;
char *input = JSON_MSG1;
char finalString[32768] = "";
const char *expected = "\"value\":100.0,\"labels\":[\"red\",\"right\"]";
const char *expected2 = "{\"ns\":\"myns\",\"ss\":\"subsystem\","
"\"name\":\"test\",\"desc\":\"Counts durations\"}";

ctx = flb_create();
flb_service_set(ctx, "Flush", "0.200000000", "Grace", "1", "Log_Level",
"error", NULL);

cb_data.cb = callback_test;
cb_data.data = NULL;

in_ffd = flb_input(ctx, (char *) "lib", NULL);
TEST_CHECK(in_ffd >= 0);
flb_input_set(ctx, in_ffd, "tag", "test", NULL);

filter_ffd = flb_filter(ctx, (char *) "log_to_metrics", NULL);
TEST_CHECK(filter_ffd >= 0);
ret = flb_filter_set(ctx, filter_ffd,
"Match", "*",
"Tag", "test_metric",
"metric_mode", "counter",
"metric_name", "test",
"metric_description", "Counts durations",
"metric_subsystem", "subsystem",
"metric_namespace", "myns",
"kubernetes_mode", "off",
"label_field", "color",
"label_field", "direction",
"value_field", "duration",
NULL);

out_ffd = flb_output(ctx, (char *) "lib", (void *)&cb_data);
TEST_CHECK(out_ffd >= 0);
flb_output_set(ctx, out_ffd,
"match", "*",
"format", "json",
NULL);
ret = flb_start(ctx);
TEST_CHECK(ret == 0);

for (i = 0; i < 5; i++){
flb_lib_push(ctx, in_ffd, input, strlen(input));
}
wait_with_timeout(2000, finalString);
result = strstr(finalString, expected);
if (!TEST_CHECK(result != NULL)) {
TEST_MSG("expected substring:\n%s\ngot:\n%s\n", expected, finalString);
}
result = strstr(finalString, expected2);
if (!TEST_CHECK(result != NULL)) {
TEST_MSG("expected substring:\n%s\ngot:\n%s\n", expected, finalString);
}
filter_test_destroy(ctx);

}

void flb_test_log_to_metrics_counter_k8s_two_tuples(void)
{
int ret;
Expand Down
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