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Fix W3C tracestate parsing #360

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Fix W3C tracestate parsing #360

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375aa16
APMS-20291 Fix W3C tracestate parsing
datadog-prod-us1-3[bot] Aug 25, 2026
6a84a5e
Merge main into PR #360
bm1549 Aug 28, 2026
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44 changes: 41 additions & 3 deletions src/datadog/w3c_propagation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -222,6 +222,25 @@ Optional<std::string> extract_traceparent(ExtractedData& result,
return nullopt;
}

bool is_valid_datadog_trace_state(StringView datadog_trace_state) {
const std::size_t end = datadog_trace_state.size();
std::size_t item_begin = 0;
while (item_begin < end) {
const std::size_t item_end = datadog_trace_state.find(';', item_begin);
const StringView item =
datadog_trace_state.substr(item_begin, item_end - item_begin);
item_begin = item_end == StringView::npos ? end : item_end + 1;

const StringView trimmed_item = trim(item);
if (trimmed_item.data() != item.data() ||
trimmed_item.size() != item.size()) {
return false;
}
}

return true;
}

// Fill the specified `result` with information parsed from the specified
// `datadog_trace_state`. `datadog_trace_state` is the value of the "dd" entry
// in the W3C "tracestate" header.
Expand Down Expand Up @@ -326,16 +345,18 @@ void parse_w3c_tracestate_member(
ExtractedData& result, StringView member,
std::unordered_map<std::string, std::string>& span_tags,
std::string& other_w3c_tracestate,
std::size_t& other_w3c_tracestate_member_count) {
std::size_t& other_w3c_tracestate_member_count,
bool& has_datadog_trace_state) {
const std::size_t separator = member.find('=');
const StringView key = member.substr(0, separator);
const StringView member_value = separator == StringView::npos
? StringView{}
: member.substr(separator + 1);
if (key == "dd") {
has_datadog_trace_state = true;
if (member_value.size() > max_datadog_tracestate_value_size) {
span_tags[tags::internal::propagation_error] = "extract_max_size";
} else {
} else if (is_valid_datadog_trace_state(member_value)) {
parse_datadog_trace_state(result, member_value);
}
} else if (key == "ot") {
Expand Down Expand Up @@ -367,12 +388,29 @@ void parse_w3c_tracestate(
std::unordered_map<std::string, std::string>& span_tags) {
std::string other_w3c_tracestate;
std::size_t other_w3c_tracestate_member_count = 0;
bool has_datadog_trace_state = false;
for_each_w3c_tracestate_member(w3c_tracestate, [&](StringView member) {
parse_w3c_tracestate_member(result, member, span_tags, other_w3c_tracestate,
other_w3c_tracestate_member_count);
other_w3c_tracestate_member_count,
has_datadog_trace_state);
return true;
});

if (has_datadog_trace_state) {
std::string canonical_other_w3c_tracestate;
for_each_w3c_tracestate_member(
other_w3c_tracestate, [&](StringView member) {
if (!member.empty()) {
if (!canonical_other_w3c_tracestate.empty()) {
canonical_other_w3c_tracestate += ',';
}
append(canonical_other_w3c_tracestate, member);
}
return true;
});
other_w3c_tracestate = std::move(canonical_other_w3c_tracestate);
}

if (!other_w3c_tracestate.empty()) {
result.additional_w3c_tracestate = std::move(other_w3c_tracestate);
}
Expand Down
27 changes: 27 additions & 0 deletions test/test_span.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -815,6 +815,33 @@ TEST_SPAN("injecting W3C tracestate header") {
// The "s:0" comes from the sampling decision in `traceparent_drop`.
"dd=s:0;p:$parent_id;foo:bar;boing:boing"},

{__LINE__,
"trim outer tracestate OWS",
{
{"traceparent",
"00-00000000000000000000000000000001-0000000000000001-01"},
{"tracestate", "foo=1 , dd=s:2;o:some , bar=2"},
},
"dd=s:2;p:$parent_id;o:some,foo=1,bar=2"},

{__LINE__,
"skip dd entry with interior OWS",
{
{"traceparent",
"00-00000000000000000000000000000001-0000000000000001-01"},
{"tracestate", "foo=1,dd=s:0;t.dm:934086a686-4; t.x:y"},
},
"dd=s:1;p:$parent_id,foo=1"},

{__LINE__,
"skip dd entry with whitespace-only subentry",
{
{"traceparent",
"00-00000000000000000000000000000001-0000000000000001-01"},
{"tracestate", "foo=1,dd=s:0; ;t.x:y"},
},
"dd=s:1;p:$parent_id,foo=1"},

{__LINE__,
"all of the above",
{
Expand Down
143 changes: 143 additions & 0 deletions test/test_tracer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -997,6 +997,149 @@ TEST_TRACER("span extraction") {
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with trailing semicolon",
traceparent_keep, // traceparent
"foo=1,dd=s:2;o:some;", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with trailing semicolon and OWS",
traceparent_keep, // traceparent
"foo=1,dd=s:2;o:some; \t", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with double semicolon",
traceparent_keep, // traceparent
"foo=1,dd=s:2;;o:some", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with leading semicolon",
traceparent_keep, // traceparent
"foo=1,dd=;s:2;o:some", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with interior OWS",
traceparent_keep, // traceparent
"foo=1,dd=s:0;t.dm:934086a686-4; t.x:y", // tracestate
1, // expected_sampling_priority
nullopt, // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with OWS after first subentry",
traceparent_keep, // traceparent
"foo=1,dd=s:0; t.dm:934086a686-4", // tracestate
1, // expected_sampling_priority
nullopt, // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with whitespace-only subentry",
traceparent_keep, // traceparent
"foo=1,dd=s:0; ;t.x:y", // tracestate
1, // expected_sampling_priority
nullopt, // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"dd entry with whitespace-only first subentry",
traceparent_keep, // traceparent
"foo=1,dd= ;s:2;o:some", // tracestate
1, // expected_sampling_priority
nullopt, // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"outer empty list member before dd",
traceparent_keep, // traceparent
"foo=1,,dd=s:2;o:some", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"outer empty list member after dd",
traceparent_keep, // traceparent
"dd=s:2;o:some,,foo=1", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"outer OWS around list members",
traceparent_keep, // traceparent
"foo=1 , dd=s:2;o:some , bar=2", // tracestate
2, // expected_sampling_priority
"some", // expected_origin
{}, // expected_trace_tags
"foo=1,bar=2", // expected_additional_w3c_tracestate
nullopt, // expected_additional_datadog_w3c_tracestate
"0000000000000000", // expected_datadog_w3c_parent_id,
},

{
__LINE__,
"origin, trace tags, parent, and extra fields",
Expand Down
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