def from_headers(self, headers):
"""Generate a SpanContext object from B3 propagation headers.
:type headers: dict
:param headers: HTTP request headers.
:rtype: :class:`~opencensus.trace.span_context.SpanContext`
:returns: SpanContext generated from B3 propagation headers.
"""
if headers is None:
return SpanContext(from_header=False)
trace_id, span_id, sampled = None, None, None
state = headers.get(_STATE_HEADER_KEY)
if state:
fields = state.split('-', 4)
if len(fields) == 1:
sampled = fields[0]
elif len(fields) == 2:
trace_id, span_id = fields
elif len(fields) == 3:
trace_id, span_id, sampled = fields
elif len(fields) == 4:
trace_id, span_id, sampled, _parent_span_id = fields
else:
return SpanContext(from_header=False)
else:
trace_id = headers.get(_TRACE_ID_KEY)
span_id = headers.get(_SPAN_ID_KEY)
sampled = headers.get(_SAMPLED_KEY)
if sampled is not None:
# The specification encodes an enabled tracing decision as "1".
# In the wild pre-standard implementations might still send "true".
# "d" is set in the single header case when debugging is enabled.
sampled = sampled.lower() in ('1', 'd', 'true')
else:
# If there's no incoming sampling decision, it was deferred to us.
# Even though we set it to False here, we might still sample
# depending on the tracer configuration.
sampled = False
trace_options = TraceOptions()
trace_options.set_enabled(sampled)
# TraceId and SpanId headers both have to exist
if not trace_id or not span_id:
return SpanContext(trace_options=trace_options)
# Convert 64-bit trace ids to 128-bit
if len(trace_id) == 16:
trace_id = '0' * 16 + trace_id
span_context = SpanContext(trace_id=trace_id,
span_id=span_id,
trace_options=trace_options,
from_header=True)
return span_context
def nope(*args, **kwargs):
trace_options = TraceOptions()
trace_options.set_enabled(False)
return SpanContext(trace_options=trace_options)