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import logging
log = logging.getLogger(__name__)
ROOT = 'Root'
PARENT = 'Parent'
SAMPLE = 'Sampled'
HEADER_DELIMITER = ";"
class TraceHeader(object):
"""
The sampling decision and trace ID are added to HTTP requests in
tracing headers named ``X-Amzn-Trace-Id``. The first X-Ray-integrated
service that the request hits adds a tracing header, which is read
by the X-Ray SDK and included in the response. Learn more about
`Tracing Header <http://docs.aws.amazon.com/xray/latest/devguide/xray-concepts.html#xray-concepts-tracingheader>`_.
"""
def __init__(self, root=None, parent=None, sampled=None):
"""
:param str root: trace id
:param str parent: parent id
:param int sampled: 0 means not sampled, 1 means sampled
"""
self._root = root
self._parent = parent
self._sampled = None
if sampled is not None:
self._sampled = int(sampled)
@classmethod
def from_header_str(cls, header):
"""
Create a TraceHeader object from a tracing header string
extracted from a http request headers.
"""
if not header:
return cls()
try:
params = header.strip().split(HEADER_DELIMITER)
header_dict = {}
for param in params:
entry = param.split('=')
header_dict[entry[0]] = entry[1]
return cls(
root=header_dict.get(ROOT, None),
parent=header_dict.get(PARENT, None),
sampled=header_dict.get(SAMPLE, None),
)
except Exception:
log.warning("malformed tracing header %s, ignore.", header)
return cls()
def to_header_str(self):
"""
Convert to a tracing header string that can be injected to
outgoing http request headers.
"""
h_str = ''
if self.root:
h_str = ROOT + '=' + self.root
if self.parent:
h_str = h_str + HEADER_DELIMITER + PARENT + '=' + self.parent
if self.sampled is not None:
h_str = h_str + HEADER_DELIMITER + SAMPLE + '=' + str(self.sampled)
return h_str
@property
def root(self):
"""
Return trace id of the header
"""
return self._root
@property
def parent(self):
"""
Return the parent segment id in the header
"""
return self._parent
@property
def sampled(self):
"""
Return the sampling decision in the header.
It's either 0 or 1.
"""
return self._sampled
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