check transport parameters after 0-RTT resumption (#3985)

* check new transport parameters do not contain redueced limits

* redefine ValidForUpdate and add tests

* fix test assertion and update comment

internal/wire/transport_parameter_test.go

@@ -612,5 +612,93 @@ var _ = Describe("Transport Parameters", func() {
 				Expect(p.ValidFor0RTT(saved)).To(BeFalse())
 			})
 		})
+
+		Context("client checks the parameters after successfully sending 0-RTT data", func() {
+			var p TransportParameters
+			saved := &TransportParameters{
+				InitialMaxStreamDataBidiLocal:  1,
+				InitialMaxStreamDataBidiRemote: 2,
+				InitialMaxStreamDataUni:        3,
+				InitialMaxData:                 4,
+				MaxBidiStreamNum:               5,
+				MaxUniStreamNum:                6,
+				ActiveConnectionIDLimit:        7,
+			}
+
+			BeforeEach(func() {
+				p = *saved
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxStreamDataBidiLocal was reduced", func() {
+				p.InitialMaxStreamDataBidiLocal = saved.InitialMaxStreamDataBidiLocal - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxStreamDataBidiLocal was increased", func() {
+				p.InitialMaxStreamDataBidiLocal = saved.InitialMaxStreamDataBidiLocal + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxStreamDataBidiRemote was reduced", func() {
+				p.InitialMaxStreamDataBidiRemote = saved.InitialMaxStreamDataBidiRemote - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxStreamDataBidiRemote was increased", func() {
+				p.InitialMaxStreamDataBidiRemote = saved.InitialMaxStreamDataBidiRemote + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxStreamDataUni was reduced", func() {
+				p.InitialMaxStreamDataUni = saved.InitialMaxStreamDataUni - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxStreamDataUni was increased", func() {
+				p.InitialMaxStreamDataUni = saved.InitialMaxStreamDataUni + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxData was reduced", func() {
+				p.InitialMaxData = saved.InitialMaxData - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxData was increased", func() {
+				p.InitialMaxData = saved.InitialMaxData + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the MaxBidiStreamNum was reduced", func() {
+				p.MaxBidiStreamNum = saved.MaxBidiStreamNum - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the MaxBidiStreamNum was increased", func() {
+				p.MaxBidiStreamNum = saved.MaxBidiStreamNum + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the MaxUniStreamNum reduced", func() {
+				p.MaxUniStreamNum = saved.MaxUniStreamNum - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the MaxUniStreamNum was increased", func() {
+				p.MaxUniStreamNum = saved.MaxUniStreamNum + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the ActiveConnectionIDLimit reduced", func() {
+				p.ActiveConnectionIDLimit = saved.ActiveConnectionIDLimit - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the ActiveConnectionIDLimit increased", func() {
+				p.ActiveConnectionIDLimit = saved.ActiveConnectionIDLimit + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+		})
 	})
 })

internal/wire/transport_parameters.go

@@ -481,6 +481,18 @@ func (p *TransportParameters) ValidFor0RTT(saved *TransportParameters) bool {
 		p.ActiveConnectionIDLimit == saved.ActiveConnectionIDLimit
 }
 
+// ValidForUpdate checks that the new transport parameters don't reduce limits after resuming a 0-RTT connection.
+// It is only used on the client side.
+func (p *TransportParameters) ValidForUpdate(saved *TransportParameters) bool {
+	return p.ActiveConnectionIDLimit >= saved.ActiveConnectionIDLimit &&
+		p.InitialMaxData >= saved.InitialMaxData &&
+		p.InitialMaxStreamDataBidiLocal >= saved.InitialMaxStreamDataBidiLocal &&
+		p.InitialMaxStreamDataBidiRemote >= saved.InitialMaxStreamDataBidiRemote &&
+		p.InitialMaxStreamDataUni >= saved.InitialMaxStreamDataUni &&
+		p.MaxBidiStreamNum >= saved.MaxBidiStreamNum &&
+		p.MaxUniStreamNum >= saved.MaxUniStreamNum
+}
+
 // String returns a string representation, intended for logging.
 func (p *TransportParameters) String() string {
 	logString := "&wire.TransportParameters{OriginalDestinationConnectionID: %s, InitialSourceConnectionID: %s, "