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in_tail: drop multiline records whose reassembled content is empty (fixes #6703) #12262

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in_tail: drop multiline records whose reassembled content is empty (fixes #6703) #12262

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be73b92
multiline: add drop_empty_content option to parser instance
allxm4 Aug 11, 2026
76ac34b
in_tail: wire Skip_Empty_Lines to multiline drop_empty_content
allxm4 Aug 11, 2026
daa157c
tests: add multiline drop_empty_content coverage for issue 6703
allxm4 Aug 11, 2026
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3 changes: 3 additions & 0 deletions include/fluent-bit/multiline/flb_ml.h
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Original file line number Diff line number Diff line change
Expand Up @@ -254,6 +254,9 @@ struct flb_ml_parser_ins {

/* Link to struct flb_ml_group->parsers */
struct mk_list _head;

/* drop a flush whose key_content is an empty string (off) */
int drop_empty_content;
};

struct flb_ml_group {
Expand Down
2 changes: 2 additions & 0 deletions plugins/in_tail/tail_config.c
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,8 @@ static int multiline_load_parsers(struct flb_tail_config *ctx)
if (!parser_i) {
return -1;
}

parser_i->drop_empty_content = ctx->skip_empty_lines;
}
}

Expand Down
14 changes: 12 additions & 2 deletions src/multiline/flb_ml.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1596,6 +1596,7 @@ int flb_ml_flush_stream_group(struct flb_ml_parser *ml_parser,
int ret;
int size;
int len;
int key_id;
size_t off = 0;
msgpack_object map;
msgpack_object k;
Expand Down Expand Up @@ -1682,8 +1683,17 @@ int flb_ml_flush_stream_group(struct flb_ml_parser *ml_parser,
}
}
else {
/* The buffer is empty, so just pack the original map from the context */
msgpack_pack_object(&mp_pck, map);
key_id = -1;
if (parser_i->drop_empty_content) {
key_id = get_key_id(&map, parser_i->key_content);
}
Comment on lines +1687 to +1689

@coderabbitai coderabbitai Bot Aug 11, 2026

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📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win

Use the required control-block brace style.

Move each control-block opening brace to the next line.

  • src/multiline/flb_ml.c#L1687-L1689: move the if opening brace to the next line.
  • tests/internal/multiline.c#L650-L655: move the for opening brace to the next line.
  • tests/internal/multiline.c#L659-L661: move the if opening brace to the next line.
  • tests/internal/multiline.c#L697-L702: move the for opening brace to the next line.
  • tests/internal/multiline.c#L706-L708: move the if opening brace to the next line.
  • tests/internal/multiline.c#L744-L749: move the for opening brace to the next line.
  • tests/internal/multiline.c#L753-L755: move the if opening brace to the next line.

As per coding guidelines, C control blocks must place the opening brace on the next line.

📍 Affects 2 files
  • src/multiline/flb_ml.c#L1687-L1689 (this comment)
  • tests/internal/multiline.c#L650-L655
  • tests/internal/multiline.c#L659-L661
  • tests/internal/multiline.c#L697-L702
  • tests/internal/multiline.c#L706-L708
  • tests/internal/multiline.c#L744-L749
  • tests/internal/multiline.c#L753-L755
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/multiline/flb_ml.c` around lines 1687 - 1689, Apply the project’s C brace
style by moving each control-block opening brace onto its own following line:
the if block in src/multiline/flb_ml.c (1687-1689), and the for/if blocks in
tests/internal/multiline.c (650-655, 659-661, 697-702, 706-708, 744-749, and
753-755). Preserve all existing control-flow behavior.

Source: Coding guidelines


if (key_id == -1 ||
map.via.map.ptr[key_id].val.type != MSGPACK_OBJECT_STR ||
map.via.map.ptr[key_id].val.via.str.size > 0) {
/* The buffer is empty, so just pack the original map from the context */
msgpack_pack_object(&mp_pck, map);
}
}

msgpack_unpacked_destroy(&result);
Expand Down
178 changes: 178 additions & 0 deletions tests/internal/multiline.c
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Expand Up @@ -82,6 +82,37 @@ struct record_check cri_output[] = {
{"4b. non multiline 2"}
};

/* CRI, empty payload dropped via drop_empty_content */
struct record_check issue_6703_input[] = {
{"2025-01-01T00:00:00.000000000Z stdout F hello world"},
{"2025-01-01T00:00:00.000000001Z stdout F "},
{"2025-01-01T00:00:00.000000002Z stdout F goodbye world"}
};

struct record_check issue_6703_output[] = {
{"hello world"},
{"goodbye world"}
};

/* Same input, drop_empty_content left off (default): behavior is unchanged */
struct record_check issue_6703_disabled_output[] = {
{"hello world"},
{""},
{"goodbye world"}
};

/* CRI, every line in isolation is an empty payload */
struct record_check issue_6703_all_empty_input[] = {
{"2025-01-01T00:00:00.000000000Z stdout F "},
{"2025-01-01T00:00:00.000000001Z stdout F "},
{"2025-01-01T00:00:00.000000002Z stdout F "}
};

/* Sink for issue_6703_all_empty: only read if the fix regresses */
struct record_check issue_6703_all_empty_output[] = {
{""}, {""}, {""}
};
Comment on lines +85 to +114

@coderabbitai coderabbitai Bot Aug 11, 2026

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📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win

Use four-space indentation in the new fixtures.

Lines 87-113 use two-space indentation for initializer entries. Use four spaces.

As per coding guidelines, **/*.{c,h,cc,cpp,cxx} requires four-space indentation.

🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@tests/internal/multiline.c` around lines 85 - 114, Update the initializer
entries in the new issue_6703 fixtures to use four-space indentation instead of
two spaces, including issue_6703_input, issue_6703_output,
issue_6703_disabled_output, issue_6703_all_empty_input, and
issue_6703_all_empty_output.

Source: Coding guidelines


/* ENDSWITH */
struct record_check endswith_input[] = {
{"1a. some multiline log \\"},
Expand Down Expand Up @@ -585,6 +616,150 @@ static void test_parser_cri()
flb_config_exit(config);
}

static void test_issue_6703()
{
int i;
int len;
int ret;
int entries;
uint64_t stream_id;
struct record_check *r;
struct flb_config *config;
struct flb_time tm;
struct flb_ml *ml;
struct flb_ml_parser_ins *mlp_i;
struct expected_result res = {0};

res.key = "log";
res.out_records = issue_6703_output;

config = flb_config_init();

ml = flb_ml_create(config, "cri-drop-empty-test");
TEST_CHECK(ml != NULL);

mlp_i = flb_ml_parser_instance_create(ml, "cri");
TEST_CHECK(mlp_i != NULL);
mlp_i->drop_empty_content = FLB_TRUE;

ret = flb_ml_stream_create(ml, "cri-drop-empty", -1, flush_callback,
(void *) &res, &stream_id);
TEST_CHECK(ret == 0);

entries = sizeof(issue_6703_input) / sizeof(struct record_check);
for (i = 0; i < entries; i++) {
r = &issue_6703_input[i];
len = strlen(r->buf);
flb_time_get(&tm);
ret = flb_ml_append_text(ml, stream_id, &tm, r->buf, len);
TEST_CHECK(ret == FLB_MULTILINE_OK);
}
Comment on lines +649 to +656

@coderabbitai coderabbitai Bot Aug 11, 2026

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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Check every flb_ml_append_text() result.

The tests discard the append result. In test_issue_6703 and test_issue_6703_all_empty, failure to process empty input can still satisfy the expected flush count. Assign the result to ret and check ret >= 0 in each loop.

  • tests/internal/multiline.c#L649-L655: check each append result in the enabled test.
  • tests/internal/multiline.c#L696-L702: check each append result in the disabled test.
  • tests/internal/multiline.c#L743-L749: check each append result in the all-empty test.

As per coding guidelines, validate both success and failure paths.

📍 Affects 1 file
  • tests/internal/multiline.c#L649-L655 (this comment)
  • tests/internal/multiline.c#L696-L702
  • tests/internal/multiline.c#L743-L749
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@tests/internal/multiline.c` around lines 649 - 655, In
tests/internal/multiline.c at lines 649-655, 696-702, and 743-749, update the
append loops in test_issue_6703 and test_issue_6703_all_empty to assign each
flb_ml_append_text() result to ret and assert ret >= 0, covering both success
and failure paths.

Source: Coding guidelines


TEST_CHECK(res.current_record == 2);

if (ml) {
flb_ml_destroy(ml);
}

flb_config_exit(config);
}

static void test_issue_6703_disabled()
{
int i;
int len;
int ret;
int entries;
uint64_t stream_id;
struct record_check *r;
struct flb_config *config;
struct flb_time tm;
struct flb_ml *ml;
struct flb_ml_parser_ins *mlp_i;
struct expected_result res = {0};

res.key = "log";
res.out_records = issue_6703_disabled_output;

config = flb_config_init();

ml = flb_ml_create(config, "cri-drop-empty-disabled-test");
TEST_CHECK(ml != NULL);

mlp_i = flb_ml_parser_instance_create(ml, "cri");
TEST_CHECK(mlp_i != NULL);
TEST_CHECK(mlp_i->drop_empty_content == FLB_FALSE);

ret = flb_ml_stream_create(ml, "cri-drop-empty-disabled", -1, flush_callback,
(void *) &res, &stream_id);
TEST_CHECK(ret == 0);

entries = sizeof(issue_6703_input) / sizeof(struct record_check);
for (i = 0; i < entries; i++) {
r = &issue_6703_input[i];
len = strlen(r->buf);
flb_time_get(&tm);
ret = flb_ml_append_text(ml, stream_id, &tm, r->buf, len);
TEST_CHECK(ret == FLB_MULTILINE_OK);
}

TEST_CHECK(res.current_record == 3);

if (ml) {
flb_ml_destroy(ml);
}

flb_config_exit(config);
}

static void test_issue_6703_all_empty()
{
int i;
int len;
int ret;
int entries;
uint64_t stream_id;
struct record_check *r;
struct flb_config *config;
struct flb_time tm;
struct flb_ml *ml;
struct flb_ml_parser_ins *mlp_i;
struct expected_result res = {0};

res.key = "log";
res.out_records = issue_6703_all_empty_output;

config = flb_config_init();

ml = flb_ml_create(config, "cri-drop-empty-all-empty-test");
TEST_CHECK(ml != NULL);

mlp_i = flb_ml_parser_instance_create(ml, "cri");
TEST_CHECK(mlp_i != NULL);
mlp_i->drop_empty_content = FLB_TRUE;

ret = flb_ml_stream_create(ml, "cri-drop-empty-all-empty", -1, flush_callback,
(void *) &res, &stream_id);
TEST_CHECK(ret == 0);

entries = sizeof(issue_6703_all_empty_input) / sizeof(struct record_check);
for (i = 0; i < entries; i++) {
r = &issue_6703_all_empty_input[i];
len = strlen(r->buf);
flb_time_get(&tm);
ret = flb_ml_append_text(ml, stream_id, &tm, r->buf, len);
TEST_CHECK(ret == FLB_MULTILINE_OK);
}

TEST_CHECK(res.current_record == 0);

if (ml) {
flb_ml_destroy(ml);
}

flb_config_exit(config);
}

static void test_container_mix()
{
int i;
Expand Down Expand Up @@ -2149,5 +2324,8 @@ TEST_LIST = {
{ "issue_5504" , test_issue_5504},
{ "issue_10576" , test_issue_10576},
{ "issue_truncation_10576", test_issue_truncation_10576 },
{ "issue_6703" , test_issue_6703},
{ "issue_6703_disabled", test_issue_6703_disabled},
{ "issue_6703_all_empty", test_issue_6703_all_empty},
{ 0 }
};