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refactor(netxlite): introduce the getaddrinfo transport (#775)
This diff modifies the system resolver to use a getaddrinf transport. Obviously the transport is a fake, but its existence will allow us to observe DNS events more naturally. A lookup using the system resolver would be a ANY lookup that will contain all the resolved IP addresses into the same response. This change was also part of websteps-illustrated, albeit the way in which I did it there was less clean than what we have here. Ref issue: ooni/probe#2096
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,125 @@ | ||
| package netxlite | ||
|
|
||
| // | ||
| // DNS over getaddrinfo: fake transport to allow us to observe | ||
| // lookups using getaddrinfo as a DNSTransport. | ||
| // | ||
|
|
||
| import ( | ||
| "context" | ||
| "net" | ||
| "time" | ||
|
|
||
| "github.com/miekg/dns" | ||
| "github.com/ooni/probe-cli/v3/internal/model" | ||
| ) | ||
|
|
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| // dnsOverGetaddrinfoTransport is a DNSTransport using getaddrinfo. | ||
| type dnsOverGetaddrinfoTransport struct { | ||
| testableTimeout time.Duration | ||
| testableLookupHost func(ctx context.Context, domain string) ([]string, error) | ||
| } | ||
|
|
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| var _ model.DNSTransport = &dnsOverGetaddrinfoTransport{} | ||
|
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| func (txp *dnsOverGetaddrinfoTransport) RoundTrip( | ||
| ctx context.Context, query model.DNSQuery) (model.DNSResponse, error) { | ||
| if query.Type() != dns.TypeANY { | ||
| return nil, ErrNoDNSTransport | ||
| } | ||
| addrs, err := txp.lookup(ctx, query.Domain()) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| resp := &dnsOverGetaddrinfoResponse{ | ||
| addrs: addrs, | ||
| query: query, | ||
| } | ||
| return resp, nil | ||
| } | ||
|
|
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| type dnsOverGetaddrinfoResponse struct { | ||
| addrs []string | ||
| query model.DNSQuery | ||
| } | ||
|
|
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| func (txp *dnsOverGetaddrinfoTransport) lookup( | ||
| ctx context.Context, hostname string) ([]string, error) { | ||
| // This code forces adding a shorter timeout to the domain name | ||
| // resolutions when using the system resolver. We have seen cases | ||
| // in which such a timeout becomes too large. One such case is | ||
| // described in https://github.com/ooni/probe/issues/1726. | ||
| addrsch, errch := make(chan []string, 1), make(chan error, 1) | ||
| ctx, cancel := context.WithTimeout(ctx, txp.timeout()) | ||
| defer cancel() | ||
| go func() { | ||
| addrs, err := txp.lookupfn()(ctx, hostname) | ||
| if err != nil { | ||
| errch <- err | ||
| return | ||
| } | ||
| addrsch <- addrs | ||
| }() | ||
| select { | ||
| case <-ctx.Done(): | ||
| return nil, ctx.Err() | ||
| case addrs := <-addrsch: | ||
| return addrs, nil | ||
| case err := <-errch: | ||
| return nil, err | ||
| } | ||
| } | ||
|
|
||
| func (txp *dnsOverGetaddrinfoTransport) timeout() time.Duration { | ||
| if txp.testableTimeout > 0 { | ||
| return txp.testableTimeout | ||
| } | ||
| return 15 * time.Second | ||
| } | ||
|
|
||
| func (txp *dnsOverGetaddrinfoTransport) lookupfn() func(ctx context.Context, domain string) ([]string, error) { | ||
| if txp.testableLookupHost != nil { | ||
| return txp.testableLookupHost | ||
| } | ||
| return TProxy.DefaultResolver().LookupHost | ||
| } | ||
|
|
||
| func (txp *dnsOverGetaddrinfoTransport) RequiresPadding() bool { | ||
| return false | ||
| } | ||
|
|
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| func (txp *dnsOverGetaddrinfoTransport) Network() string { | ||
| return TProxy.DefaultResolver().Network() | ||
| } | ||
|
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| func (txp *dnsOverGetaddrinfoTransport) Address() string { | ||
| return "" | ||
| } | ||
|
|
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| func (txp *dnsOverGetaddrinfoTransport) CloseIdleConnections() { | ||
| // nothing | ||
| } | ||
|
|
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| func (r *dnsOverGetaddrinfoResponse) Query() model.DNSQuery { | ||
| return r.query | ||
| } | ||
|
|
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| func (r *dnsOverGetaddrinfoResponse) Bytes() []byte { | ||
| return nil | ||
| } | ||
|
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| func (r *dnsOverGetaddrinfoResponse) Rcode() int { | ||
| return 0 | ||
| } | ||
|
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| func (r *dnsOverGetaddrinfoResponse) DecodeHTTPS() (*model.HTTPSSvc, error) { | ||
| return nil, ErrNoDNSTransport | ||
| } | ||
|
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| func (r *dnsOverGetaddrinfoResponse) DecodeLookupHost() ([]string, error) { | ||
| return r.addrs, nil | ||
| } | ||
|
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| func (r *dnsOverGetaddrinfoResponse) DecodeNS() ([]*net.NS, error) { | ||
| return nil, ErrNoDNSTransport | ||
| } |
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