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Using Content-Length to determine SIP message size #1148

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Using Content-Length to determine SIP message size #1148

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60 changes: 45 additions & 15 deletions layers/sip.go
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Original file line number Diff line number Diff line change
Expand Up @@ -180,7 +180,6 @@ var compactSipHeadersCorrespondance = map[string]string{
// -> The SIP Response code (if it's a response)
// -> The SIP Status line (if it's a response)
// You can easily know the type of the packet with the IsResponse boolean
//
type SIP struct {
BaseLayer

Expand Down Expand Up @@ -220,6 +219,7 @@ func decodeSIP(data []byte, p gopacket.PacketBuilder) error {
func NewSIP() *SIP {
s := new(SIP)
s.Headers = make(map[string][]string)
s.contentLength = -1
return s
}

Expand Down Expand Up @@ -297,20 +297,51 @@ func (s *SIP) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {

countLines++
}
s.BaseLayer = BaseLayer{Contents: data[:offset], Payload: data[offset:]}

s.setBaseLayer(data, offset, df)

return nil
}

// setBaseLayer is used to set the base layer of the SIP packet.
//
// According to "RFC3261 - 20.14 - Content-Length" the Content-Length header is mandatory
// for SIP packages transported over TCP. When transporting over UDP, the message
// body length CAN be determined by the length of the UDP datagram.
//
// So by using the Content-Length header, if present we can mark the packet as truncated if we do not
// have enough data. We are also able to limit the payload to the number bytes actually specified.
// If the header is not present, we can assume that the packet is transported over UDP we can then
// use the length of the UDP datagram as payload length (in this context this is the length of data).
func (s *SIP) setBaseLayer(data []byte, offset int, df gopacket.DecodeFeedback) {
// The content-length header was not present in the packet, we use the rest of the packet as payload
if s.contentLength == -1 {
s.contentLength = int64(len(data) - offset) // we should be able to trust contentLength even if not set
s.BaseLayer = BaseLayer{Contents: data[:offset], Payload: data[offset:]}
} else if s.contentLength == 0 {
// We have a zero Content-Length, no payload
s.BaseLayer = BaseLayer{Contents: data[:offset], Payload: []byte{}} // no payload
} else if len(data) < offset+int(s.contentLength) {
// Not enough data to fulfill the Content-Length. We set the packet as truncated
// and return what we have. The receiver of the packet will be able to determine this
// by comparing the SIP.ContentLength with the length of the SIP.Payload.
df.SetTruncated()
s.BaseLayer = BaseLayer{Contents: data[:offset], Payload: data[offset:]}
} else {
// we have at least enough data, to fulfill the Content-Length. But we only add the number
// of bytes specified in the Content-Length header to the payload.
s.BaseLayer = BaseLayer{Contents: data[:offset], Payload: data[offset : offset+int(s.contentLength)]}
}
}

// ParseFirstLine will compute the first line of a SIP packet.
// The first line will tell us if it's a request or a response.
//
// Examples of first line of SIP Prococol :
//
// Request : INVITE [email protected] SIP/2.0
// Response : SIP/2.0 200 OK
// Response : SIP/2.0 501 Not Implemented
// Examples of first line of SIP Protocol :
//
// Request : INVITE [email protected] SIP/2.0
// Response : SIP/2.0 200 OK
// Response : SIP/2.0 501 Not Implemented
func (s *SIP) ParseFirstLine(firstLine []byte) error {

var err error
Expand Down Expand Up @@ -372,13 +403,12 @@ func (s *SIP) ParseFirstLine(firstLine []byte) error {
//
// Examples of header :
//
// CSeq: 1 REGISTER
// Via: SIP/2.0/UDP there.com:5060
// Authorization:Digest username="UserB",
// realm="MCI WorldCom SIP",
// nonce="1cec4341ae6cbe5a359ea9c8e88df84f", opaque="",
// uri="sip:ss2.wcom.com", response="71ba27c64bd01de719686aa4590d5824"
//
// CSeq: 1 REGISTER
// Via: SIP/2.0/UDP there.com:5060
// Authorization:Digest username="UserB",
// realm="MCI WorldCom SIP",
// nonce="1cec4341ae6cbe5a359ea9c8e88df84f", opaque="",
// uri="sip:ss2.wcom.com", response="71ba27c64bd01de719686aa4590d5824"
func (s *SIP) ParseHeader(header []byte) (err error) {

// Ignore empty headers
Expand Down Expand Up @@ -529,7 +559,7 @@ func (s *SIP) GetUserAgent() string {
return s.GetFirstHeader("User-Agent")
}

// GetContentLength will return the parsed integer
// GetContentLength will return the parsed integer, or the actual payload size if the Contenet-Length header is missing
// Content-Length header of the current SIP packet
func (s *SIP) GetContentLength() int64 {
return s.contentLength
Expand Down
56 changes: 49 additions & 7 deletions layers/sip_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
package layers

import (
"bytes"
"testing"

"github.com/google/gopacket"
Expand All @@ -26,7 +27,6 @@ import (
// Expires:1800
// User-Agent:C530 IP/42.245.00.000.000
// Content-Length:0
//
var testPacketSIPRequest = []byte{
0x00, 0x07, 0x7d, 0x41, 0x2e, 0x40, 0x00, 0xd0, 0x03, 0x75, 0xe0, 0x00, 0x08, 0x00, 0x45, 0x00,
0x01, 0xf4, 0x73, 0x74, 0x00, 0x00, 0x75, 0x11, 0xca, 0x7f, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02,
Expand Down Expand Up @@ -74,7 +74,6 @@ var testPacketSIPRequest = []byte{
// Contact: <sip:[email protected]:5060>;expires=1800
// P-Associated-URI: <sip:[email protected]>
// Content-Length:0
//
var testPacketSIPResponse = []byte{
0x00, 0xd0, 0x00, 0x4a, 0x2c, 0x00, 0x00, 0x07, 0x7d, 0x41, 0x2e, 0x40, 0x08, 0x00, 0x45, 0x00,
0x01, 0xc1, 0x00, 0x00, 0x40, 0x00, 0x3f, 0x11, 0x34, 0x27, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01,
Expand Down Expand Up @@ -147,20 +146,54 @@ var testPacketSIPCompactInvite = []byte{
0x30, 0x3e, 0x0d, 0x0a, 0x6c, 0x3a, 0x30, 0x0d, 0x0a, 0x0d, 0x0a,
}

// Fourth packet is an INVITE with a payload
// This only contains the SIP Content and Payload, for more readability of the SIP layer
var testPacketSIPOnlyInviteWithPayload = []byte(
"INVITE sip:sip.provider.com SIP/2.0\r\n" +
"Via: SIP/2.0/TCP 172.16.254.66:5060;branch=z9hG4bK.xIOVvIsyy;rport\r\n" +
"From: \"Bob\" <sip:[email protected]>\r\n" +
"To: \"Alice\" <sip:[email protected]>\r\n" +
"Call-Id: 306366781@172_16_254_66\r\n" +
"CSeq: 1 INVITE\r\n" +
"Allow: INVITE,ACK,CANCEL,BYE,OPTIONS,INFO,SUBSCRIBE,NOTIFY,REFER,UPDATE\r\n" +
"Contact: <sip:[email protected]:5060>\r\n" +
"Content-Type: application/sdp\r\n" +
"Content-Length: 100\r\n" +
"\r\n" +
"v=0\r\n" +
"o=bob 4096 1976 IN IP4 172.16.254.66\r\n" +
"s=Talk\r\n" +
"c=IN 172.16.254.66\r\n" +
"t=0 0\r\n" +
"m=audio 6000 RTP/AVP 0",
)

// Fifth packet is an INVITE with an oversized payload
// This packet is generated by appending an extra attribute to the payload of the previous packet
var testOversizedPacketSIPOnlyInviteWithPayload = append(testPacketSIPOnlyInviteWithPayload, []byte("a=This_is_beyond_the_content_length\r\n")...)

func TestSIPMain(t *testing.T) {
expectedHeaders := map[string]string{"Call-ID": "306366781@172_16_254_66", "Contact": "<sip:[email protected]:5060>"}
_TestPacketSIP(t, testPacketSIPRequest, SIPMethodRegister, false, 3, expectedHeaders, "sip:sip.provider.com")
_TestPacketSIP(t, LinkTypeEthernet, testPacketSIPRequest, SIPMethodRegister, false, 3, expectedHeaders, "sip:sip.provider.com", []byte{})

expectedHeaders = map[string]string{"Call-ID": "306366781@172_16_254_66", "Contact": "<sip:[email protected]:5060>;expires=1800"}
_TestPacketSIP(t, testPacketSIPResponse, SIPMethodRegister, true, 3, expectedHeaders, "")
_TestPacketSIP(t, LinkTypeEthernet, testPacketSIPResponse, SIPMethodRegister, true, 3, expectedHeaders, "", []byte{})

expectedHeaders = map[string]string{"Call-ID": "306366781@172_16_254_66", "Contact": "<sip:[email protected]:5060>", "f": "\"Bob\" <sip:[email protected]>"}
_TestPacketSIP(t, testPacketSIPCompactInvite, SIPMethodInvite, false, 1, expectedHeaders, "sip:sip.provider.com")
_TestPacketSIP(t, LinkTypeEthernet, testPacketSIPCompactInvite, SIPMethodInvite, false, 1, expectedHeaders, "sip:sip.provider.com", []byte{})

expectedHeaders = map[string]string{"Call-ID": "306366781@172_16_254_66", "Contact": "<sip:[email protected]:5060>", "From": "\"Bob\" <sip:[email protected]>", "Content-Type": "application/sdp", "Content-Length": "100"}
expectedPayload := []byte("v=0\r\no=bob 4096 1976 IN IP4 172.16.254.66\r\ns=Talk\r\nc=IN 172.16.254.66\r\nt=0 0\r\nm=audio 6000 RTP/AVP 0")
_TestPacketSIP(t, LayerTypeSIP, testPacketSIPOnlyInviteWithPayload, SIPMethodInvite, false, 1, expectedHeaders, "sip:sip.provider.com", expectedPayload)

expectedHeaders = map[string]string{"Call-ID": "306366781@172_16_254_66", "Contact": "<sip:[email protected]:5060>", "From": "\"Bob\" <sip:[email protected]>", "Content-Type": "application/sdp", "Content-Length": "100"}
expectedPayload = []byte("v=0\r\no=bob 4096 1976 IN IP4 172.16.254.66\r\ns=Talk\r\nc=IN 172.16.254.66\r\nt=0 0\r\nm=audio 6000 RTP/AVP 0")
_TestPacketSIP(t, LayerTypeSIP, testOversizedPacketSIPOnlyInviteWithPayload, SIPMethodInvite, false, 1, expectedHeaders, "sip:sip.provider.com", expectedPayload)
}

func _TestPacketSIP(t *testing.T, packetData []byte, methodWanted SIPMethod, isResponse bool, wantedCseq int64, expectedHeaders map[string]string, expectedRequestURI string) {
func _TestPacketSIP(t *testing.T, firstLayerDecoder gopacket.Decoder, packetData []byte, methodWanted SIPMethod, isResponse bool, wantedCseq int64, expectedHeaders map[string]string, expectedRequestURI string, expectedPayload []byte) {

p := gopacket.NewPacket(packetData, LinkTypeEthernet, gopacket.Default)
p := gopacket.NewPacket(packetData, firstLayerDecoder, gopacket.Default)
if p.ErrorLayer() != nil {
t.Error("Failed to decode packet:", p.ErrorLayer().Error())
}
Expand Down Expand Up @@ -195,5 +228,14 @@ func _TestPacketSIP(t *testing.T, packetData []byte, methodWanted SIPMethod, isR
if got.GetCSeq() != wantedCseq {
t.Errorf("SIP Packet should be %d. Got : %d", wantedCseq, got.GetCSeq())
}

if got.contentLength != int64(len(got.Payload())) {
t.Errorf("SIP Payload length should be %d. Got : %d", got.contentLength, len(got.Payload()))
}

// Check payload
if bytes.Compare(got.Payload(), expectedPayload) != 0 {
t.Errorf("SIP Payload should be:\n\t%v\nGot:\n\t%v", expectedPayload, got.Payload())
}
}
}