Trace invariant checks

[Kyle-Verhoog]

• HTTP headers
  • Trace count matches (trace_count_header)
  • Library version included (meta_tracer_version_header)
• Trace payload size (trace_content_length)
• Consistent trace ID in trace chunk
• Traces are non-empty
• Required span properties
• No collisions in trace ids across traces
• No collisions in span ids within a trace
• No multiple root spans
• No circular references in spans
• Tags are within the permitted size limits
• Type checks
  • Span properties
    • IDs are 64-bit integers
  • All keys are strings
  • Values in metrics are numeric
  • Values in meta are string or numeric
• No duplicate values between meta and metrics
• All referenced spans exist
• Value checks
  • Sampling tags
• Span type checks
  • eg. "type: redis" has "host" and "port" tags in meta
  • eg. "type: web" has resource