131 lines
3.5 KiB
Go
131 lines
3.5 KiB
Go
// -=-=- StartHere -=-=-
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//
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// # Chapter IX: Parallel DNS lookups
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//
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// The program we see here is _really_ similar to the one we
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// discussed in the previous chapter. The main difference
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// is the following: rather than performing DNS lookups
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// sequentially, we call a function that runs through the
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// list of resolvers and run them in parallel.
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//
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// Again, we are going to use low parallelism for the same
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// rationale mentioned in chapter09.
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//
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// (This file is auto-generated. Do not edit it directly! To apply
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// changes you need to modify `./internal/tutorial/measurex/chapter10/main.go`.)
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//
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// ## main.go
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//
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// The beginning of the program is pretty much the same.
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//
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// ```Go
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package main
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import (
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"context"
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"encoding/json"
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"flag"
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"fmt"
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"net/url"
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"time"
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"github.com/ooni/probe-cli/v3/internal/measurex"
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"github.com/ooni/probe-cli/v3/internal/runtimex"
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)
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type measurement struct {
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DNS []*measurex.DNSMeasurement
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Endpoints []*measurex.HTTPEndpointMeasurement
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}
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func print(v interface{}) {
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data, err := json.Marshal(v)
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runtimex.PanicOnError(err, "json.Marshal failed")
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fmt.Printf("%s\n", string(data))
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}
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func main() {
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URL := flag.String("url", "https://blog.cloudflare.com/", "URL to fetch")
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timeout := flag.Duration("timeout", 60*time.Second, "timeout to use")
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flag.Parse()
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ctx, cancel := context.WithTimeout(context.Background(), *timeout)
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defer cancel()
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parsed, err := url.Parse(*URL)
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runtimex.PanicOnError(err, "url.Parse failed")
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mx := measurex.NewMeasurerWithDefaultSettings()
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m := &measurement{}
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// ```
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//
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// The bulk of the difference is here. We create
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// a list of DNS resolvers. For each of them, we specify
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// the type and the endpoint address. (There is no
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// endpoint address for the system resolver, therefore
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// we leave its address empty.)
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//
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// ```Go
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resolvers := []*measurex.ResolverInfo{{
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Network: measurex.ResolverUDP,
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Address: "8.8.8.8:53",
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}, {
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Network: measurex.ResolverUDP,
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Address: "8.8.4.4:53",
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}, {
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Network: measurex.ResolverUDP,
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Address: "1.1.1.1:53",
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}, {
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Network: measurex.ResolverUDP,
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Address: "1.0.0.1:53",
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}, {
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Network: measurex.ResolverSystem,
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Address: "",
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}}
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// ```
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//
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// Then we call `LookupURLHostParallel`. This function runs
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// the queries that make sense given the input URL using a
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// pool of (currently three) background goroutines.
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//
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// When I say "queries that make sense", I mostly mean
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// that we only query for HTTPSSvc when the input URL
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// scheme is "https". Otherwise, if it's just "http", it
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// does not make sense to send this query.
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//
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// ```Go
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const parallelism = 3
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for dns := range mx.LookupURLHostParallel(ctx, parallelism, parsed, resolvers...) {
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m.DNS = append(m.DNS, dns)
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}
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// ```
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//
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// The rest of the program is exactly like in chapter09.
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//
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// ```Go
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headers := measurex.NewHTTPRequestHeaderForMeasuring()
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httpEndpoints, err := measurex.AllHTTPEndpointsForURL(parsed, headers, m.DNS...)
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runtimex.PanicOnError(err, "cannot get all the HTTP endpoints")
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cookies := measurex.NewCookieJar()
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for epnt := range mx.HTTPEndpointGetParallel(ctx, parallelism, cookies, httpEndpoints...) {
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m.Endpoints = append(m.Endpoints, epnt)
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}
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print(m)
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}
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// ```
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//
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// ## Running the example program
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//
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// Let us perform a vanilla run first:
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//
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// ```bash
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// go run -race ./internal/tutorial/measurex/chapter10 | jq
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// ```
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//
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// Take a look at the JSON output. Can you spot that
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// DNS queries are run in parallel?
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//
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// ## Conclusion
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//
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// We have seen how to run parallel DNS queries.
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//
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// -=-=- StopHere -=-=-
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