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Don't pass pointers

Browse Source 
I was uneasy: functions were returning values and mutating arguments
(specifically `response &Response`)--I was mixing meat with dairy, and
the result wasn't kosher.

Now I only return values, and don't mutate.

According to canonical [Go Code Review
Comments](https://github.com/golang/go/wiki/CodeReviewComments#pass-values):

> Don't pass pointers as function arguments just to save a few bytes. If
a function refers to its argument x only as *x throughout, then the
argument shouldn't be a pointer. Common instances of this include
passing a pointer to a string (*string) or a pointer to an interface
value (*io.Reader). In both cases the value itself is a fixed size and
can be passed directly. This advice does not apply to large structs, or
even small structs that might grow.
This commit is contained in:
Brian Cunnie
2021-12-24 09:49:24 -08:00
parent dd4eb3b426
commit d43990ed50
2 changed files with 36 additions and 73 deletions
Download Patch File Download Diff File Expand all files Collapse all files

78
bosh-release/src/sslip.io-dns-server/xip/xip.go
View File

@@ -180,7 +180,7 @@ type Response struct {
func QueryResponse(queryBytes []byte, sourceAddr net.IP) (responseBytes []byte, logMessage string, err error) {
var queryHeader dnsmessage.Header
var p dnsmessage.Parser
var response = &Response{}
var response Response
if queryHeader, err = p.Start(queryBytes); err != nil {
return nil, "", err
@@ -191,11 +191,12 @@ func QueryResponse(queryBytes []byte, sourceAddr net.IP) (responseBytes []byte,
if q, err = p.Question(); err != nil {
return nil, "", err
}
response.Header = ResponseHeader(queryHeader, dnsmessage.RCodeSuccess)
logMessage, err = processQuestion(q, response, sourceAddr)
response, logMessage, err = processQuestion(q, sourceAddr)
if err != nil {
return nil, "", err
}
response.Header.ID = queryHeader.ID
response.Header.RecursionDesired = queryHeader.RecursionDesired
b := dnsmessage.NewBuilder(nil, response.Header)
b.EnableCompression()
@@ -235,8 +236,20 @@ func QueryResponse(queryBytes []byte, sourceAddr net.IP) (responseBytes []byte,
return responseBytes, logMessage, nil
}
func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.IP) (logMessage string, err error) {
func processQuestion(q dnsmessage.Question, sourceAddr net.IP) (response Response, logMessage string, err error) {
logMessage = q.Type.String() + " " + q.Name.String() + " ? "
response = Response{
Header: dnsmessage.Header{
ID: 0, // this will later be replaced with query.ID
Response: true,
OpCode: 0,
Authoritative: true, // We're able to white label domains by always being authoritative
Truncated: false,
RecursionDesired: false, // this will later be replaced with query.RecursionDesired
RecursionAvailable: false, // We are not recursing servers, so recursion is never available. Prevents DDOS
RCode: dnsmessage.RCodeSuccess, // assume success, may be replaced later
},
}
if IsAcmeChallenge(q.Name.String()) { // thanks @NormanR
// delegate everything to its stripped (remove "_acme-challenge.") address, e.g.
// dig _acme-challenge.127-0-0-1.sslip.io mx → NS 127-0-0-1.sslip.io
@@ -258,7 +271,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
}
return nil
})
return logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
return response, logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
}
response.Answers = append(response.Answers,
// 1 or more A records; A records > 1 only available via Customizations
@@ -282,7 +295,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
ip := net.IP(nameToA.A[:])
logMessages = append(logMessages, ip.String())
}
return logMessage + strings.Join(logMessages, ", "), nil
return response, logMessage + strings.Join(logMessages, ", "), nil
}
case dnsmessage.TypeAAAA:
{
@@ -298,7 +311,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
}
return nil
})
return logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
return response, logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
}
response.Answers = append(response.Answers,
// 1 or more AAAA records; AAAA records > 1 only available via Customizations
@@ -322,7 +335,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
ip := net.IP(nameToAAAA.AAAA[:])
logMessages = append(logMessages, ip.String())
}
return logMessage + strings.Join(logMessages, ", "), nil
return response, logMessage + strings.Join(logMessages, ", "), nil
}
case dnsmessage.TypeALL:
{
@@ -330,7 +343,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
// https://blog.cloudflare.com/rfc8482-saying-goodbye-to-any/
// Google (8.8.8.8) returns every record they can find (A, AAAA, SOA, NS, MX, ...).
response.Header.RCode = dnsmessage.RCodeNotImplemented
return logMessage + "NotImplemented", nil
return response, logMessage + "NotImplemented", nil
}
case dnsmessage.TypeCNAME:
{
@@ -347,7 +360,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
}
return nil
})
return logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
return response, logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
}
response.Answers = append(response.Answers,
// 1 CNAME record, via Customizations
@@ -364,7 +377,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
}
return nil
})
return logMessage + cname.CNAME.String(), nil
return response, logMessage + cname.CNAME.String(), nil
}
case dnsmessage.TypeMX:
{
@@ -373,7 +386,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
// We can be sure that len(mailExchangers) > 1, but we check anyway
if len(mailExchangers) == 0 {
return "", errors.New("no MX records, but there should be one")
return response, "", errors.New("no MX records, but there should be one")
}
response.Answers = append(response.Answers,
// 1 or more A records; A records > 1 only available via Customizations
@@ -395,7 +408,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
for _, mailExchanger := range mailExchangers {
logMessages = append(logMessages, strconv.Itoa(int(mailExchanger.Pref))+" "+mailExchanger.MX.String())
}
return logMessage + strings.Join(logMessages, ", "), nil
return response, logMessage + strings.Join(logMessages, ", "), nil
}
case dnsmessage.TypeNS:
{
@@ -418,7 +431,7 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
}
return nil
})
return logMessage + soaLogMessage(soaResource), nil
return response, logMessage + soaLogMessage(soaResource), nil
}
case dnsmessage.TypeTXT:
{
@@ -448,12 +461,12 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
})
logMessages = append(logMessages, nameServer.NS.String())
}
return logMessage + "nil, NS " + strings.Join(logMessages, ", "), nil
return response, logMessage + "nil, NS " + strings.Join(logMessages, ", "), nil
}
var txts []dnsmessage.TXTResource
txts, err = TXTResources(q.Name.String(), sourceAddr.String())
if err != nil {
return "", err
return response, "", err
}
response.Answers = append(response.Answers,
// 1 or more TXT records via Customizations
@@ -483,9 +496,9 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
logMessageTXTss = append(logMessageTXTss, `["`+strings.Join(logMessageTXTs, `", "`)+`"]`)
}
if len(logMessageTXTss) == 0 {
return logMessage + "nil, SOA " + soaLogMessage(SOAResource(q.Name)), nil
return response, logMessage + "nil, SOA " + soaLogMessage(SOAResource(q.Name)), nil
}
return logMessage + strings.Join(logMessageTXTss, ", "), nil
return response, logMessage + strings.Join(logMessageTXTss, ", "), nil
}
default:
{
@@ -500,17 +513,17 @@ func processQuestion(q dnsmessage.Question, response *Response, sourceAddr net.I
}
return nil
})
return logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
return response, logMessage + "nil, SOA " + soaLogMessage(soaResource), nil
}
}
// The following is flagged as "Unreachable code" in Goland, and that's expected
return "", errors.New("unexpectedly fell through processQuestion()")
return response, "", errors.New("unexpectedly fell through processQuestion()")
}
// NSResponse sets the Answers/Authorities depending whether we're delegating or authoritative
// (whether it's an "_acme-challenge." domain or not). Either way, it supplies the Additionals
// (IP addresses of the nameservers).
func NSResponse(name dnsmessage.Name, response *Response, logMessage string) (string, error) {
func NSResponse(name dnsmessage.Name, response Response, logMessage string) (Response, string, error) {
nameServers := NSResources(name.String())
var logMessages []string
if response.Header.Authoritative {
@@ -584,28 +597,7 @@ func NSResponse(name dnsmessage.Name, response *Response, logMessage string) (st
for _, nameServer := range nameServers {
logMessages = append(logMessages, nameServer.NS.String())
}
return logMessage + strings.Join(logMessages, ", "), nil
}
// ResponseHeader returns a pre-fab DNS response header.
// We are almost always authoritative (exception: _acme-challenge TXT records)
// We are not recursing
// servers, so recursion is never available. We're able to
// "white label" domains by indiscriminately matching every query that comes
// our way. Not being recursive has the added benefit of not being usable as an
// amplifier in a DDOS attack. We pass in the RCODE, which is normally RCodeSuccess
// but can also be a failure (e.g. ANY type we return RCodeNotImplemented)
func ResponseHeader(query dnsmessage.Header, rcode dnsmessage.RCode) dnsmessage.Header {
return dnsmessage.Header{
ID: query.ID,
Response: true,
OpCode: 0,
Authoritative: true,
Truncated: false,
RecursionDesired: query.RecursionDesired,
RecursionAvailable: false,
RCode: rcode,
}
return response, logMessage + strings.Join(logMessages, ", "), nil
}
// NameToA returns an []AResource that matched the hostname

29
bosh-release/src/sslip.io-dns-server/xip/xip_test.go
View File

@@ -16,38 +16,9 @@ import (
var _ = Describe("Xip", func() {
var (
err error
headerId uint16
)
rand.Seed(GinkgoRandomSeed()) // Set to ginkgo's seed so that it's different each test & we can reproduce failures if necessary
Describe("ResponseHeader()", func() {
It("returns a header with the ID", func() {
headerId = uint16(rand.Int31())
Expect(xip.ResponseHeader(dnsmessage.Header{
ID: headerId,
Response: false,
OpCode: 0,
Authoritative: false,
Truncated: false,
RecursionDesired: false,
RecursionAvailable: false,
}, dnsmessage.RCodeSuccess)).To(Equal(dnsmessage.Header{
ID: headerId, // taken from the query
Response: true,
OpCode: 0,
Authoritative: true,
Truncated: false,
RecursionDesired: false, // taken from the query
RecursionAvailable: false,
RCode: 0,
}))
})
It("returns the header with the passed-in RCode", func() {
Expect(xip.ResponseHeader(dnsmessage.Header{}, dnsmessage.RCodeNotImplemented).
RCode).To(Equal(dnsmessage.RCodeNotImplemented))
})
})
Describe("CNAMEResources()", func() {
It("returns nil by default", func() {
randomDomain := random8ByteString() + ".com."