receiving-and-continuing-tracing.js

/* api-service */

app.use('/api/v1/whereami', async (req, res, next) => {
    const parentSpan = createContinuationSpan(tracer, req, 'whereami-request')
    
    const childSpan = tracer.startSpan('city-from-ip', {childOf: parentSpan})
    const _ = await axios.get(`http://ip-api.com/json/${req.ip}`)
    childSpan.finish()
    
    // Do more work and create more children spans.
        
    parentSpan.finish()
})

function createContinuationSpan(tracer, req, spanName) {
    const incomingSpanContext = tracer.extract(opentracing.FORMAT_HTTP_HEADERS, req.headers)
    
    if (incomingSpanContext == null) {
        return tracer.startSpan(spanName)
    }
    
    return tracer.startSpan(spanName, {childOf: incomingSpanContext})
}