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// Copyright 2020 New Relic Corporation. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
package newrelic
import (
"net/http"
)
// instrumentation.go contains helpers built on the lower level api.
// WrapHandle instruments http.Handler handlers with transactions. To
// instrument this code:
//
// http.Handle("/foo", myHandler)
//
// Perform this replacement:
//
// http.Handle(newrelic.WrapHandle(app, "/foo", myHandler))
//
// WrapHandle adds the Transaction to the request's context. Access it using
// FromContext to add attributes, create segments, or notice errors:
//
// func myHandler(rw ResponseWriter, req *Request) {
// if txn := newrelic.FromContext(req.Context()); nil != txn {
// txn.AddAttribute("customerLevel", "gold")
// }
// }
//
// This function is safe to call if app is nil.
func WrapHandle(app Application, pattern string, handler http.Handler) (string, http.Handler) {
if app == nil {
return pattern, handler
}
return pattern, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
txn := app.StartTransaction(pattern, w, r)
defer txn.End()
r = RequestWithTransactionContext(r, txn)
handler.ServeHTTP(txn, r)
})
}
// WrapHandleFunc instruments handler functions using transactions. To
// instrument this code:
//
// http.HandleFunc("/users", func(w http.ResponseWriter, req *http.Request) {
// io.WriteString(w, "users page")
// })
//
// Perform this replacement:
//
// http.HandleFunc(WrapHandleFunc(app, "/users", func(w http.ResponseWriter, req *http.Request) {
// io.WriteString(w, "users page")
// }))
//
// WrapHandleFunc adds the Transaction to the request's context. Access it using
// FromContext to add attributes, create segments, or notice errors:
//
// http.HandleFunc(WrapHandleFunc(app, "/users", func(w http.ResponseWriter, req *http.Request) {
// if txn := newrelic.FromContext(req.Context()); nil != txn {
// txn.AddAttribute("customerLevel", "gold")
// }
// io.WriteString(w, "users page")
// }))
//
// This function is safe to call if app is nil.
func WrapHandleFunc(app Application, pattern string, handler func(http.ResponseWriter, *http.Request)) (string, func(http.ResponseWriter, *http.Request)) {
p, h := WrapHandle(app, pattern, http.HandlerFunc(handler))
return p, func(w http.ResponseWriter, r *http.Request) { h.ServeHTTP(w, r) }
}
// NewRoundTripper creates an http.RoundTripper to instrument external requests
// and add distributed tracing headers. The RoundTripper returned creates an
// external segment before delegating to the original RoundTripper provided (or
// http.DefaultTransport if none is provided). If the Transaction parameter is
// nil then the RoundTripper will look for a Transaction in the request's
// context (using FromContext). Using a nil Transaction is STRONGLY recommended
// because it allows the same RoundTripper (and client) to be reused for
// multiple transactions.
func NewRoundTripper(txn Transaction, original http.RoundTripper) http.RoundTripper {
return roundTripperFunc(func(request *http.Request) (*http.Response, error) {
// The specification of http.RoundTripper requires that the request is never modified.
request = cloneRequest(request)
segment := StartExternalSegment(txn, request)
if nil == original {
original = http.DefaultTransport
}
response, err := original.RoundTrip(request)
segment.Response = response
segment.End()
return response, err
})
}
// cloneRequest mimics implementation of
// https://godoc.org/github.com/google/go-github/github#BasicAuthTransport.RoundTrip
func cloneRequest(r *http.Request) *http.Request {
// shallow copy of the struct
r2 := new(http.Request)
*r2 = *r
// deep copy of the Header
r2.Header = make(http.Header, len(r.Header))
for k, s := range r.Header {
r2.Header[k] = append([]string(nil), s...)
}
return r2
}
type roundTripperFunc func(*http.Request) (*http.Response, error)
func (f roundTripperFunc) RoundTrip(r *http.Request) (*http.Response, error) { return f(r) }
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