Program Listing for File b3_propagator.h¶
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)
#pragma once
#include "detail/context.h"
#include "detail/hex.h"
#include "detail/string.h"
#include "opentelemetry/trace/default_span.h"
#include "opentelemetry/trace/propagation/text_map_propagator.h"
#include <array>
OPENTELEMETRY_BEGIN_NAMESPACE
namespace trace
{
namespace propagation
{
static const nostd::string_view kB3CombinedHeader = "b3";
static const nostd::string_view kB3TraceIdHeader = "X-B3-TraceId";
static const nostd::string_view kB3SpanIdHeader = "X-B3-SpanId";
static const nostd::string_view kB3SampledHeader = "X-B3-Sampled";
/*
B3, single header:
b3: 80f198ee56343ba864fe8b2a57d3eff7-e457b5a2e4d86bd1-1-05e3ac9a4f6e3b90
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ ^ ^^^^^^^^^^^^^^^^
0 TraceId 31 33 SpanId 48 | 52 ParentSpanId 68
50 Debug flag
Multiheader version: X-B3-Sampled
X-B3-TraceId X-B3-SpanId X-B3-ParentSpanId (ignored)
*/
static const int kTraceIdHexStrLength = 32;
static const int kSpanIdHexStrLength = 16;
// The B3PropagatorExtractor class provides an interface that enables extracting context from
// headers of HTTP requests. HTTP frameworks and clients can integrate with B3Propagator by
// providing the object containing the headers, and a getter function for the extraction. Based on:
// https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/context/api-propagators.md#b3-extract
template <typename T>
class B3PropagatorExtractor : public TextMapPropagator<T>
{
public:
// Rules that manages how context will be extracted from carrier.
using Getter = nostd::string_view (*)(const T &carrier, nostd::string_view trace_type);
// Returns the context that is stored in the HTTP header carrier with the getter as extractor.
context::Context Extract(Getter getter,
const T &carrier,
context::Context &context) noexcept override
{
SpanContext span_context = ExtractImpl(getter, carrier);
nostd::shared_ptr<Span> sp{new DefaultSpan(span_context)};
return context.SetValue(kSpanKey, sp);
}
static TraceId TraceIdFromHex(nostd::string_view trace_id)
{
uint8_t buf[kTraceIdHexStrLength / 2];
detail::HexToBinary(trace_id, buf, sizeof(buf));
return TraceId(buf);
}
static SpanId SpanIdFromHex(nostd::string_view span_id)
{
uint8_t buf[kSpanIdHexStrLength / 2];
detail::HexToBinary(span_id, buf, sizeof(buf));
return SpanId(buf);
}
static TraceFlags TraceFlagsFromHex(nostd::string_view trace_flags)
{
if (trace_flags.length() != 1 || (trace_flags[0] != '1' && trace_flags[0] != 'd'))
{ // check for invalid length of flags and treat 'd' as sampled
return TraceFlags(0);
}
return TraceFlags(TraceFlags::kIsSampled);
}
private:
static SpanContext ExtractImpl(Getter getter, const T &carrier)
{
nostd::string_view trace_id_hex;
nostd::string_view span_id_hex;
nostd::string_view trace_flags_hex;
// first let's try a single-header variant
auto singleB3Header = getter(carrier, kB3CombinedHeader);
if (!singleB3Header.empty())
{
std::array<nostd::string_view, 3> fields{};
// https://github.com/openzipkin/b3-propagation/blob/master/RATIONALE.md
if (detail::SplitString(singleB3Header, '-', fields.data(), 3) < 2)
{
return SpanContext::GetInvalid();
}
trace_id_hex = fields[0];
span_id_hex = fields[1];
trace_flags_hex = fields[2];
}
else
{
trace_id_hex = getter(carrier, kB3TraceIdHeader);
span_id_hex = getter(carrier, kB3SpanIdHeader);
trace_flags_hex = getter(carrier, kB3SampledHeader);
}
if (!detail::IsValidHex(trace_id_hex) || !detail::IsValidHex(span_id_hex))
{
return SpanContext::GetInvalid();
}
TraceId trace_id = TraceIdFromHex(trace_id_hex);
SpanId span_id = SpanIdFromHex(span_id_hex);
if (!trace_id.IsValid() || !span_id.IsValid())
{
return SpanContext::GetInvalid();
}
return SpanContext(trace_id, span_id, TraceFlagsFromHex(trace_flags_hex), true);
}
};
// The B3Propagator class provides interface that enables extracting and injecting context into
// single header of HTTP Request.
template <typename T>
class B3Propagator : public B3PropagatorExtractor<T>
{
public:
// Rules that manages how context will be injected to carrier.
using Setter = void (*)(T &carrier,
nostd::string_view trace_type,
nostd::string_view trace_description);
// Sets the context for a HTTP header carrier with self defined rules.
void Inject(Setter setter, T &carrier, const context::Context &context) noexcept override
{
SpanContext span_context = detail::GetCurrentSpan(context);
if (!span_context.IsValid())
{
return;
}
char trace_identity[kTraceIdHexStrLength + kSpanIdHexStrLength + 3];
static_assert(sizeof(trace_identity) == 51, "b3 trace identity buffer size mismatch");
span_context.trace_id().ToLowerBase16({&trace_identity[0], kTraceIdHexStrLength});
trace_identity[kTraceIdHexStrLength] = '-';
span_context.span_id().ToLowerBase16(
{&trace_identity[kTraceIdHexStrLength + 1], kSpanIdHexStrLength});
trace_identity[kTraceIdHexStrLength + kSpanIdHexStrLength + 1] = '-';
trace_identity[kTraceIdHexStrLength + kSpanIdHexStrLength + 2] =
span_context.trace_flags().IsSampled() ? '1' : '0';
setter(carrier, kB3CombinedHeader, nostd::string_view(trace_identity, sizeof(trace_identity)));
}
};
template <typename T>
class B3PropagatorMultiHeader : public B3PropagatorExtractor<T>
{
public:
// Rules that manages how context will be injected to carrier.
using Setter = void (*)(T &carrier,
nostd::string_view trace_type,
nostd::string_view trace_description);
void Inject(Setter setter, T &carrier, const context::Context &context) noexcept override
{
SpanContext span_context = detail::GetCurrentSpan(context);
if (!span_context.IsValid())
{
return;
}
char trace_id[32];
TraceId(span_context.trace_id()).ToLowerBase16(trace_id);
char span_id[16];
SpanId(span_context.span_id()).ToLowerBase16(span_id);
char trace_flags[2];
TraceFlags(span_context.trace_flags()).ToLowerBase16(trace_flags);
setter(carrier, kB3TraceIdHeader, nostd::string_view(trace_id, sizeof(trace_id)));
setter(carrier, kB3SpanIdHeader, nostd::string_view(span_id, sizeof(span_id)));
setter(carrier, kB3SampledHeader, nostd::string_view(trace_flags + 1, 1));
}
};
} // namespace propagation
} // namespace trace
OPENTELEMETRY_END_NAMESPACE