From 0b3e9fa301f490c171264d0398cb1d93aabdd0a2 Mon Sep 17 00:00:00 2001
From: Carmel Eve <39550338+carmeleve@users.noreply.github.com>
Date: Fri, 13 Mar 2020 07:39:53 +0000
Subject: [PATCH] Handle scenario where message fragments never arrive (#56)

Co-authored-by: Ian Griffiths <Ian.Griffiths@endjin.com>
Co-authored-by: Carmel Eve <Carmel.Eve@endjin.com>
---
 .../NmeaAisMessageStreamProcessorBindings.cs  |  10 +
 .../NmeaLineToAisStreamAdapterSpecs.feature   |  29 ++
 ...NmeaLineToAisStreamAdapterSpecs.feature.cs | 289 ++++++++++++------
 .../NmeaLineToAisStreamAdapterSpecsSteps.cs   |  29 +-
 .../Ais/Net/NmeaLineToAisStreamAdapter.cs     |  75 ++++-
 .../Ais.Net/Ais/Net/NmeaParserOptions.cs      |  50 +++
 docs/adr/0002-missing-fragment-handling.md    |  17 ++
 7 files changed, 379 insertions(+), 120 deletions(-)
 create mode 100644 docs/adr/0002-missing-fragment-handling.md

diff --git a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaAisMessageStreamProcessorBindings.cs b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaAisMessageStreamProcessorBindings.cs
index ce329ed..3a54ee5 100644
--- a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaAisMessageStreamProcessorBindings.cs
+++ b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaAisMessageStreamProcessorBindings.cs
@@ -98,6 +98,16 @@ public void ThenTheMessageErrorReportShouldIncludeAnExceptionReportingThatItHasR
             Assert.AreEqual(expectedStart, e.Message.Substring(0, expectedStart.Length));
         }
 
+        [Then("the message error report (.*) should include an exception reporting that it received an incomplete set of fragments for a message")]
+        public void ThenTheMessageErrorReportShouldIncludeAnExceptionReportingThatItReceivedAnIncompleteSetOfFragmentsForAMessage(int errorCallNumber)
+        {
+            NmeaAisMessageStreamProcessorBindings.ErrorReport call = this.OnErrorCalls[errorCallNumber];
+            Assert.IsInstanceOf<ArgumentException>(call.Error);
+
+            var e = (ArgumentException)call.Error;
+            Assert.AreEqual("Received incomplete fragmented message.", e.Message);
+        }
+
         [Then("the message error report (.*) should include the line number (.*)")]
         public void ThenTheMessageErrorReportShouldIncludeTheLineNumber(int errorCallNumber, int lineNumber)
         {
diff --git a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature
index 732dd10..e896e82 100644
--- a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature
+++ b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature
@@ -88,6 +88,8 @@ Scenario: Interleaved multi-fragment messages
     And in ais message 1 the timestamp from the first NMEA line should be 1567686150
 
 Scenario: Interleaved single and multi-fragment messages
+	# This test interleaves more extensively than we ever see in reality, so we have to extend our reassembly window
+	Given I have configured a MaximumUnmatchedFragmentAge of 10
 	# ais.kystverket.no
 	When the line to message adapter receives '\s:42,c:1567684904*38\!AIVDM,1,1,,B,33m9UtPP@50wwE:VJW6LS67H01<@,0*3C'
 	# ais.kystverket.no
@@ -157,6 +159,8 @@ Scenario: Interleaved single and multi-fragment messages
     And in ais message 9 the timestamp from the first NMEA line should be 1567693618
 
 Scenario: Progress reports
+	# This test interleaves more extensively than we ever see in reality, so we have to extend our reassembly window
+	Given I have configured a MaximumUnmatchedFragmentAge of 10
 	# ais.kystverket.no
 	When the line to message adapter receives '\s:42,c:1567684904*38\!AIVDM,1,1,,B,33m9UtPP@50wwE:VJW6LS67H01<@,0*3C'
 	# ais.kystverket.no
@@ -238,6 +242,31 @@ Scenario: Line stream parser passes the same sentence of a two-part message twic
 	And the message error report 0 should include an exception reporting that it has received two message fragments with the same group id and position
 	And the message error report 0 should include the line number 2
 
+Scenario: Two-fragment message fragments received too many sentences in the middle
+	Given I have configured a MaximumUnmatchedFragmentAge of 1
+	# ais.kystverket.no
+	When the line to message adapter receives '\g:1-2-8055,s:99,c:1567685556*4E\!AIVDM,2,1,6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72'
+	# ais.kystverket.no
+	And the line to message adapter receives '\s:42,c:1567684904*38\!AIVDM,1,1,,B,33m9UtPP@50wwE:VJW6LS67H01<@,0*3C'
+	# ais.kystverket.no
+	And the line to message adapter receives '\s:3,c:1567692251*01\!AIVDM,1,1,,A,13m9WS001d0K==pR=D?HB6WD0pJV,0*54,0*63'
+	# ais.kystverket.no
+	And the line to message adapter receives '\g:2-2-8055*55\!AIVDM,2,2,6,B,j`888888880,2*2B'
+	Then INmeaAisMessageStreamProcessor.OnNext should have been called 2 times
+	Then INmeaAisMessageStreamProcessor.OnError should have been called 1 time
+	# ais.kystverket.no
+    And in ais message 0 the payload should be '33m9UtPP@50wwE:VJW6LS67H01<@' with padding of 0
+    And in ais message 0 the source from the first NMEA line should be 42
+    And in ais message 0 the timestamp from the first NMEA line should be 1567684904
+	# ais.kystverket.no
+    And in ais message 1 the payload should be '13m9WS001d0K==pR=D?HB6WD0pJV' with padding of 0
+    And in ais message 1 the source from the first NMEA line should be 3
+    And in ais message 1 the timestamp from the first NMEA line should be 1567692251
+	# ais.kystverket.no
+	And the message error report 0 should include the problematic line '\g:1-2-8055,s:99,c:1567685556*4E\!AIVDM,2,1,6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72'
+	And the message error report 0 should include an exception reporting that it received an incomplete set of fragments for a message
+	And the message error report 0 should include the line number 1
+
 
 
 # TODO:
diff --git a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature.cs b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature.cs
index 2408a21..74ff7df 100644
--- a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature.cs
+++ b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecs.feature.cs
@@ -432,158 +432,161 @@ public virtual void InterleavedSingleAndMulti_FragmentMessages()
             {
                 this.ScenarioStart();
 #line 92
+ testRunner.Given("I have configured a MaximumUnmatchedFragmentAge of 10", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Given ");
+#line hidden
+#line 94
  testRunner.When("the line to message adapter receives \'\\s:42,c:1567684904*38\\!AIVDM,1,1,,B,33m9UtP" +
                         "P@50wwE:VJW6LS67H01<@,0*3C\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 94
+#line 96
  testRunner.And("the line to message adapter receives \'\\g:1-3-3451,s:27,c:1567686150*40\\!AIVDM,3,1" +
                         ",9,A,544MR0827oeaD<u0000lDdP4pTf0duAA,0*17\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 96
+#line 98
  testRunner.And("the line to message adapter receives \'\\s:42,c:1567684904*38\\!AIVDM,1,1,,A,B3m:H90" +
                         "0AP@b:79ae6:<OwnUoP06,0*78\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 98
+#line 100
  testRunner.And("the line to message adapter receives \'\\s:3,c:1567692251*01\\!AIVDM,1,1,,A,13m9WS00" +
                         "1d0K==pR=D?HB6WD0pJV,0*54\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 100
+#line 102
  testRunner.And("the line to message adapter receives \'\\g:1-2-8055,s:99,c:1567685556*4E\\!AIVDM,2,1" +
                         ",6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 102
+#line 104
  testRunner.And("the line to message adapter receives \'\\s:24,c:1567692878*35\\!AIVDM,1,1,,B,13o`9@7" +
                         "01j1Ej3vc;o3q@7SJ0D02,0*21\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 104
+#line 106
  testRunner.And("the line to message adapter receives \'\\g:2-3-3451*5F\\!AIVDM,3,2,9,A,<uH000167pF=2" +
                         "=nG0:0DRj0CQiC4jh00,0*4A\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 106
+#line 108
  testRunner.And("the line to message adapter receives \'\\s:67,c:1567693000*34\\!AIVDM,1,1,,,3CnWHf50" +
                         "000ga40TCHE0D0@R003B,0*4B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 108
+#line 110
  testRunner.And("the line to message adapter receives \'\\s:772,c:1567693246*07\\!AIVDM,1,1,,,13o7g20" +
                         "01P0Lv<rSdVHf2h3N0000,0*25\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 110
+#line 112
  testRunner.And("the line to message adapter receives \'\\g:2-2-8055*55\\!AIVDM,2,2,6,B,j`888888880,2" +
                         "*2B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 112
+#line 114
  testRunner.And("the line to message adapter receives \'\\s:722,c:1567693372*04\\!AIVDM,1,1,,A,13m63A" +
                         "?P00P`@GFTK3s>4?wR20Sf,0*71\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 114
+#line 116
  testRunner.And("the line to message adapter receives \'\\g:3-3-3451*5E\\!AIVDM,3,3,9,A,0000000,0*2F\'" +
                         "", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 116
+#line 118
  testRunner.And("the line to message adapter receives \'\\s:808,c:1567693618*0A\\!AIVDM,1,1,,B,B3o8B<" +
                         "00F8:0h694gOtbgwqUoP06,0*73\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 117
+#line 119
  testRunner.Then("INmeaAisMessageStreamProcessor.OnNext should have been called 10 times", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 119
+#line 121
     testRunner.And("in ais message 0 the payload should be \'33m9UtPP@50wwE:VJW6LS67H01<@\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 120
+#line 122
     testRunner.And("in ais message 0 the source from the first NMEA line should be 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 121
+#line 123
     testRunner.And("in ais message 0 the timestamp from the first NMEA line should be 1567684904", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 123
+#line 125
     testRunner.And("in ais message 1 the payload should be \'B3m:H900AP@b:79ae6:<OwnUoP06\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 124
+#line 126
     testRunner.And("in ais message 1 the source from the first NMEA line should be 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 125
+#line 127
     testRunner.And("in ais message 1 the timestamp from the first NMEA line should be 1567684904", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 127
+#line 129
     testRunner.And("in ais message 2 the payload should be \'13m9WS001d0K==pR=D?HB6WD0pJV\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 128
+#line 130
     testRunner.And("in ais message 2 the source from the first NMEA line should be 3", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 129
+#line 131
     testRunner.And("in ais message 2 the timestamp from the first NMEA line should be 1567692251", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 131
+#line 133
     testRunner.And("in ais message 3 the payload should be \'13o`9@701j1Ej3vc;o3q@7SJ0D02\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 132
+#line 134
     testRunner.And("in ais message 3 the source from the first NMEA line should be 24", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 133
+#line 135
     testRunner.And("in ais message 3 the timestamp from the first NMEA line should be 1567692878", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 135
+#line 137
     testRunner.And("in ais message 4 the payload should be \'3CnWHf50000ga40TCHE0D0@R003B\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 136
+#line 138
     testRunner.And("in ais message 4 the source from the first NMEA line should be 67", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 137
+#line 139
     testRunner.And("in ais message 4 the timestamp from the first NMEA line should be 1567693000", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 139
+#line 141
     testRunner.And("in ais message 5 the payload should be \'13o7g2001P0Lv<rSdVHf2h3N0000\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 140
+#line 142
     testRunner.And("in ais message 5 the source from the first NMEA line should be 772", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 141
+#line 143
     testRunner.And("in ais message 5 the timestamp from the first NMEA line should be 1567693246", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 143
+#line 145
     testRunner.And("in ais message 6 the payload should be \'53oGfN42=WRDhlHn221<4i@Dr22222222222220`1" +
                         "@O6640Ht50Skp4mR`4lj`888888880\' with padding of 2", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 144
+#line 146
     testRunner.And("in ais message 6 the source from the first NMEA line should be 99", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 145
+#line 147
     testRunner.And("in ais message 6 the timestamp from the first NMEA line should be 1567685556", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 147
+#line 149
     testRunner.And("in ais message 7 the payload should be \'13m63A?P00P`@GFTK3s>4?wR20Sf\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 148
+#line 150
     testRunner.And("in ais message 7 the source from the first NMEA line should be 722", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 149
+#line 151
     testRunner.And("in ais message 7 the timestamp from the first NMEA line should be 1567693372", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 151
+#line 153
     testRunner.And("in ais message 8 the payload should be \'544MR0827oeaD<u0000lDdP4pTf0duAA<uH000167" +
                         "pF=2=nG0:0DRj0CQiC4jh000000000\' with padding of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 152
+#line 154
     testRunner.And("in ais message 8 the source from the first NMEA line should be 27", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 153
+#line 155
     testRunner.And("in ais message 8 the timestamp from the first NMEA line should be 1567686150", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 155
+#line 157
     testRunner.And("in ais message 9 the payload should be \'B3o8B<00F8:0h694gOtbgwqUoP06\' with paddin" +
                         "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 156
+#line 158
     testRunner.And("in ais message 9 the source from the first NMEA line should be 808", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 157
+#line 159
     testRunner.And("in ais message 9 the timestamp from the first NMEA line should be 1567693618", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
@@ -596,7 +599,7 @@ public virtual void ProgressReports()
         {
             string[] tagsOfScenario = ((string[])(null));
             TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Progress reports", null, ((string[])(null)));
-#line 159
+#line 161
 this.ScenarioInitialize(scenarioInfo);
 #line hidden
             bool isScenarioIgnored = default(bool);
@@ -616,79 +619,82 @@ public virtual void ProgressReports()
             else
             {
                 this.ScenarioStart();
-#line 161
+#line 163
+ testRunner.Given("I have configured a MaximumUnmatchedFragmentAge of 10", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Given ");
+#line hidden
+#line 165
  testRunner.When("the line to message adapter receives \'\\s:42,c:1567684904*38\\!AIVDM,1,1,,B,33m9UtP" +
                         "P@50wwE:VJW6LS67H01<@,0*3C\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 163
+#line 167
  testRunner.And("the line to message adapter receives \'\\g:1-3-3451,s:27,c:1567686150*40\\!AIVDM,3,1" +
                         ",9,A,544MR0827oeaD<u0000lDdP4pTf0duAA,0*17\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 165
+#line 169
  testRunner.And("the line to message adapter receives \'\\s:42,c:1567684904*38\\!AIVDM,1,1,,A,B3m:H90" +
                         "0AP@b:79ae6:<OwnUoP06,0*78\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 167
+#line 171
  testRunner.And("the line to message adapter receives \'\\s:3,c:1567692251*01\\!AIVDM,1,1,,A,13m9WS00" +
                         "1d0K==pR=D?HB6WD0pJV,0*54,0*63\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 169
+#line 173
  testRunner.And("the line to message adapter receives \'\\g:1-2-8055,s:99,c:1567685556*4E\\!AIVDM,2,1" +
                         ",6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 171
+#line 175
  testRunner.And("the line to message adapter receives \'\\s:24,c:1567692878*35\\!AIVDM,1,1,,B,13o`9@7" +
                         "01j1Ej3vc;o3q@7SJ0D02,0*07\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 173
+#line 177
     testRunner.And("the line to message adapter receives a progress report of false, 6, 1234, 6, 1234" +
                         "", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 175
+#line 179
  testRunner.And("the line to message adapter receives \'\\g:2-3-3451*5F\\!AIVDM,3,2,9,A,<uH000167pF=2" +
                         "=nG0:0DRj0CQiC4jh00,0*4A\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 177
+#line 181
  testRunner.And("the line to message adapter receives \'\\s:67,c:1567693000*34\\!AIVDM,1,1,,,3CnWHf50" +
                         "000ga40TCHE0D0@R003B,0*4B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 179
+#line 183
  testRunner.And("the line to message adapter receives \'\\s:772,c:1567693246*07\\!AIVDM,1,1,,,13o7g20" +
                         "01P0Lv<rSdVHf2h3N0000,0*25\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 181
+#line 185
  testRunner.And("the line to message adapter receives \'\\g:2-2-8055*55\\!AIVDM,2,2,6,B,j`888888880,2" +
                         "*2B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 182
+#line 186
     testRunner.And("the line to message adapter receives a progress report of false, 10, 2345, 4, 111" +
                         "1", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 184
+#line 188
  testRunner.And("the line to message adapter receives \'\\s:722,c:1567693372*04\\!AIVDM,1,1,,A,13m63A" +
                         "?P00P`@GFTK3s>4?wR20Sf,0*71\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 186
+#line 190
  testRunner.And("the line to message adapter receives \'\\g:3-3-3451*5E\\!AIVDM,3,3,9,A,0000000,0*2F\'" +
                         "", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 188
+#line 192
  testRunner.And("the line to message adapter receives \'\\s:808,c:1567693618*0A\\!AIVDM,1,1,,B,B3o8B<" +
                         "00F8:0h694gOtbgwqUoP06,0*73\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 189
+#line 193
     testRunner.And("the line to message adapter receives a progress report of true, 13, 2445, 3, 100", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 190
+#line 194
  testRunner.Then("INmeaAisMessageStreamProcessor.Progress should have been called 3 times", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 191
+#line 195
     testRunner.And("progress report 0 was false, 6, 4, 1234, 6, 4, 1234", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 192
+#line 196
     testRunner.And("progress report 1 was false, 10, 7, 2345, 4, 3, 1111", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 193
+#line 197
     testRunner.And("progress report 2 was true, 13, 10, 2445, 3, 3, 100", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
@@ -701,7 +707,7 @@ public virtual void LineStreamParserReportsErrorInNon_FragmentedMessage()
         {
             string[] tagsOfScenario = ((string[])(null));
             TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Line stream parser reports error in non-fragmented message", null, ((string[])(null)));
-#line 195
+#line 199
 this.ScenarioInitialize(scenarioInfo);
 #line hidden
             bool isScenarioIgnored = default(bool);
@@ -721,21 +727,21 @@ public virtual void LineStreamParserReportsErrorInNon_FragmentedMessage()
             else
             {
                 this.ScenarioStart();
-#line 196
+#line 200
  testRunner.When("the line to message adapter receives an error report for content \'foobar\' with li" +
                         "ne number 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 197
+#line 201
  testRunner.Then("INmeaAisMessageStreamProcessor.OnError should have been called 1 time", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 198
+#line 202
  testRunner.And("the message error report 0 should include the problematic line \'foobar\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 199
+#line 203
  testRunner.And("the message error report 0 should include the exception reported by the line stre" +
                         "am parser", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 200
+#line 204
  testRunner.And("the message error report 0 should include the line number 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
@@ -748,7 +754,7 @@ public virtual void LineStreamParserReportsErrorInFirstFragmentOfTwo_PartMessage
         {
             string[] tagsOfScenario = ((string[])(null));
             TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Line stream parser reports error in first fragment of two-part message", null, ((string[])(null)));
-#line 202
+#line 206
 this.ScenarioInitialize(scenarioInfo);
 #line hidden
             bool isScenarioIgnored = default(bool);
@@ -768,25 +774,25 @@ public virtual void LineStreamParserReportsErrorInFirstFragmentOfTwo_PartMessage
             else
             {
                 this.ScenarioStart();
-#line 203
+#line 207
  testRunner.When("the line to message adapter receives an error report for content \'foobar\' with li" +
                         "ne number 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 205
+#line 209
  testRunner.And("the line to message adapter receives \'\\g:3-3-3451*5E\\!AIVDM,3,3,9,A,0000000,0*2F\'" +
                         "", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 206
+#line 210
  testRunner.Then("INmeaAisMessageStreamProcessor.OnError should have been called 1 time", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 207
+#line 211
  testRunner.And("the message error report 0 should include the problematic line \'foobar\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 208
+#line 212
  testRunner.And("the message error report 0 should include the exception reported by the line stre" +
                         "am parser", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 209
+#line 213
  testRunner.And("the message error report 0 should include the line number 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
@@ -799,7 +805,7 @@ public virtual void LineStreamParserReportsErrorInSecondFragmentOfTwo_PartMessag
         {
             string[] tagsOfScenario = ((string[])(null));
             TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Line stream parser reports error in second fragment of two-part message", null, ((string[])(null)));
-#line 211
+#line 215
 this.ScenarioInitialize(scenarioInfo);
 #line hidden
             bool isScenarioIgnored = default(bool);
@@ -819,25 +825,25 @@ public virtual void LineStreamParserReportsErrorInSecondFragmentOfTwo_PartMessag
             else
             {
                 this.ScenarioStart();
-#line 212
+#line 216
  testRunner.When("the line to message adapter receives \'\\g:1-2-8055,s:99,c:1567685556*4E\\!AIVDM,2,1" +
                         ",6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 213
+#line 217
  testRunner.And("the line to message adapter receives an error report for content \'foobar\' with li" +
                         "ne number 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 214
+#line 218
  testRunner.Then("INmeaAisMessageStreamProcessor.OnError should have been called 1 time", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 215
+#line 219
  testRunner.And("the message error report 0 should include the problematic line \'foobar\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 216
+#line 220
  testRunner.And("the message error report 0 should include the exception reported by the line stre" +
                         "am parser", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 217
+#line 221
  testRunner.And("the message error report 0 should include the line number 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
@@ -852,7 +858,7 @@ public virtual void LineStreamParserPassesAMessageWithPaddingThatIsTheFirstOfATw
             string[] tagsOfScenario = ((string[])(null));
             TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Line stream parser passes a message with padding that is the first of a two-part " +
                     "message", null, ((string[])(null)));
-#line 219
+#line 223
 this.ScenarioInitialize(scenarioInfo);
 #line hidden
             bool isScenarioIgnored = default(bool);
@@ -872,27 +878,27 @@ public virtual void LineStreamParserPassesAMessageWithPaddingThatIsTheFirstOfATw
             else
             {
                 this.ScenarioStart();
-#line 221
+#line 225
  testRunner.When("the line to message adapter receives \'\\g:1-2-8055,s:99,c:1567685556*4E\\!AIVDM,2,1" +
                         ",6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,1*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 223
+#line 227
  testRunner.And("the line to message adapter receives \'\\g:2-2-8055*55\\!AIVDM,2,2,6,B,j`888888880,2" +
                         "*2B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 224
+#line 228
  testRunner.Then("INmeaAisMessageStreamProcessor.OnError should have been called 1 time", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 226
+#line 230
  testRunner.And("the message error report 0 should include the problematic line \'\\g:1-2-8055,s:99," +
                         "c:1567685556*4E\\!AIVDM,2,1,6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht" +
                         "50Skp4mR`4l,1*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 227
+#line 231
  testRunner.And("the message error report 0 should include an exception reporting unexpected paddi" +
                         "ng on a non-terminal message fragment", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 228
+#line 232
  testRunner.And("the message error report 0 should include the line number 1", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
@@ -905,7 +911,7 @@ public virtual void LineStreamParserPassesTheSameSentenceOfATwo_PartMessageTwice
         {
             string[] tagsOfScenario = ((string[])(null));
             TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Line stream parser passes the same sentence of a two-part message twice", null, ((string[])(null)));
-#line 230
+#line 234
 this.ScenarioInitialize(scenarioInfo);
 #line hidden
             bool isScenarioIgnored = default(bool);
@@ -925,27 +931,114 @@ public virtual void LineStreamParserPassesTheSameSentenceOfATwo_PartMessageTwice
             else
             {
                 this.ScenarioStart();
-#line 232
+#line 236
  testRunner.When("the line to message adapter receives \'\\g:1-2-8055,s:99,c:1567685556*4E\\!AIVDM,2,1" +
                         ",6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
 #line hidden
-#line 234
+#line 238
  testRunner.And("the line to message adapter receives \'\\g:1-2-8055*55\\!AIVDM,2,1,6,B,j`888888880,0" +
                         "*2B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 235
+#line 239
  testRunner.Then("INmeaAisMessageStreamProcessor.OnError should have been called 1 time", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
 #line hidden
-#line 237
+#line 241
  testRunner.And("the message error report 0 should include the problematic line \'\\g:1-2-8055*55\\!A" +
                         "IVDM,2,1,6,B,j`888888880,0*2B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 238
+#line 242
  testRunner.And("the message error report 0 should include an exception reporting that it has rece" +
                         "ived two message fragments with the same group id and position", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
-#line 239
+#line 243
  testRunner.And("the message error report 0 should include the line number 2", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+            }
+            this.ScenarioCleanup();
+        }
+        
+        [NUnit.Framework.TestAttribute()]
+        [NUnit.Framework.DescriptionAttribute("Two-fragment message fragments received too many sentences in the middle")]
+        public virtual void Two_FragmentMessageFragmentsReceivedTooManySentencesInTheMiddle()
+        {
+            string[] tagsOfScenario = ((string[])(null));
+            TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Two-fragment message fragments received too many sentences in the middle", null, ((string[])(null)));
+#line 245
+this.ScenarioInitialize(scenarioInfo);
+#line hidden
+            bool isScenarioIgnored = default(bool);
+            bool isFeatureIgnored = default(bool);
+            if ((tagsOfScenario != null))
+            {
+                isScenarioIgnored = tagsOfScenario.Where(__entry => __entry != null).Where(__entry => String.Equals(__entry, "ignore", StringComparison.CurrentCultureIgnoreCase)).Any();
+            }
+            if ((this._featureTags != null))
+            {
+                isFeatureIgnored = this._featureTags.Where(__entry => __entry != null).Where(__entry => String.Equals(__entry, "ignore", StringComparison.CurrentCultureIgnoreCase)).Any();
+            }
+            if ((isScenarioIgnored || isFeatureIgnored))
+            {
+                testRunner.SkipScenario();
+            }
+            else
+            {
+                this.ScenarioStart();
+#line 246
+ testRunner.Given("I have configured a MaximumUnmatchedFragmentAge of 1", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Given ");
+#line hidden
+#line 248
+ testRunner.When("the line to message adapter receives \'\\g:1-2-8055,s:99,c:1567685556*4E\\!AIVDM,2,1" +
+                        ",6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht50Skp4mR`4l,0*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "When ");
+#line hidden
+#line 250
+ testRunner.And("the line to message adapter receives \'\\s:42,c:1567684904*38\\!AIVDM,1,1,,B,33m9UtP" +
+                        "P@50wwE:VJW6LS67H01<@,0*3C\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 252
+ testRunner.And("the line to message adapter receives \'\\s:3,c:1567692251*01\\!AIVDM,1,1,,A,13m9WS00" +
+                        "1d0K==pR=D?HB6WD0pJV,0*54,0*63\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 254
+ testRunner.And("the line to message adapter receives \'\\g:2-2-8055*55\\!AIVDM,2,2,6,B,j`888888880,2" +
+                        "*2B\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 255
+ testRunner.Then("INmeaAisMessageStreamProcessor.OnNext should have been called 2 times", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
+#line hidden
+#line 256
+ testRunner.Then("INmeaAisMessageStreamProcessor.OnError should have been called 1 time", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "Then ");
+#line hidden
+#line 258
+    testRunner.And("in ais message 0 the payload should be \'33m9UtPP@50wwE:VJW6LS67H01<@\' with paddin" +
+                        "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 259
+    testRunner.And("in ais message 0 the source from the first NMEA line should be 42", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 260
+    testRunner.And("in ais message 0 the timestamp from the first NMEA line should be 1567684904", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 262
+    testRunner.And("in ais message 1 the payload should be \'13m9WS001d0K==pR=D?HB6WD0pJV\' with paddin" +
+                        "g of 0", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 263
+    testRunner.And("in ais message 1 the source from the first NMEA line should be 3", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 264
+    testRunner.And("in ais message 1 the timestamp from the first NMEA line should be 1567692251", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 266
+ testRunner.And("the message error report 0 should include the problematic line \'\\g:1-2-8055,s:99," +
+                        "c:1567685556*4E\\!AIVDM,2,1,6,B,53oGfN42=WRDhlHn221<4i@Dr22222222222220`1@O6640Ht" +
+                        "50Skp4mR`4l,0*72\'", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 267
+ testRunner.And("the message error report 0 should include an exception reporting that it received" +
+                        " an incomplete set of fragments for a message", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
+#line hidden
+#line 268
+ testRunner.And("the message error report 0 should include the line number 1", ((string)(null)), ((TechTalk.SpecFlow.Table)(null)), "And ");
 #line hidden
             }
             this.ScenarioCleanup();
diff --git a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecsSteps.cs b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecsSteps.cs
index d977bfd..2fc81fc 100644
--- a/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecsSteps.cs
+++ b/Solutions/Ais.Net.Specs/Ais/Net/Specs/NmeaLineToAisStreamAdapterSpecsSteps.cs
@@ -12,22 +12,25 @@ namespace Ais.Net.Specs
     [Binding]
     public class NmeaLineToAisStreamAdapterSpecsSteps : IDisposable
     {
-        private readonly NmeaLineToAisStreamAdapter adapter;
-        private readonly NmeaAisMessageStreamProcessorBindings processor;
+        private readonly NmeaAisMessageStreamProcessorBindings processorBindings;
+        private readonly NmeaParserOptions parserOptions = new NmeaParserOptions();
+        private NmeaLineToAisStreamAdapter adapter;
         private bool adapterOnCompleteCalled = false;
         private Exception exceptionProvidedToProcessor;
         private int lineNumber = 1;
 
         public NmeaLineToAisStreamAdapterSpecsSteps(NmeaAisMessageStreamProcessorBindings processorBindings)
         {
-            this.adapter = new NmeaLineToAisStreamAdapter(processorBindings.Processor);
-            this.processor = processorBindings;
+            this.processorBindings = processorBindings;
         }
 
+        private NmeaLineToAisStreamAdapter Adapter =>
+            this.adapter ??= new NmeaLineToAisStreamAdapter(this.processorBindings.Processor, this.parserOptions);
+
         [Then("the message error report (.*) should include the exception reported by the line stream parser")]
         public void ThenTheMessageErrorReportShouldIncludeTheExceptionReportedByTheLineStreamParser(int errorCallNumber)
         {
-            NmeaAisMessageStreamProcessorBindings.ErrorReport call = this.processor.OnErrorCalls[errorCallNumber];
+            NmeaAisMessageStreamProcessorBindings.ErrorReport call = this.processorBindings.OnErrorCalls[errorCallNumber];
             Assert.AreSame(this.exceptionProvidedToProcessor, call.Error);
         }
 
@@ -35,11 +38,17 @@ public void Dispose()
         {
             if (!this.adapterOnCompleteCalled)
             {
-                this.adapter.OnCompleted();
+                this.Adapter.OnCompleted();
                 this.adapterOnCompleteCalled = true;
             }
 
-            this.adapter.Dispose();
+            this.Adapter.Dispose();
+        }
+
+        [Given("I have configured a MaximumUnmatchedFragmentAge of (.*)")]
+        public void GivenIHaveConfiguredAMaximumUnmatchedFragmentAgeOf(int maximumUnmatchedFragmentAge)
+        {
+            this.parserOptions.MaximumUnmatchedFragmentAge = maximumUnmatchedFragmentAge;
         }
 
         [When("the line to message adapter receives '(.*)'")]
@@ -47,7 +56,7 @@ public void WhenTheLineToMessageAdapterReceives(string line)
         {
             byte[] ascii = Encoding.ASCII.GetBytes(line);
             var lineParser = new NmeaLineParser(ascii);
-            this.adapter.OnNext(lineParser, this.lineNumber++);
+            this.Adapter.OnNext(lineParser, this.lineNumber++);
         }
 
         [When("the line to message adapter receives an error report for content '(.*)' with line number (.*)")]
@@ -55,14 +64,14 @@ public void WhenTheLineToMessageAdapterReceivesAnErrorReportForContentWithLineNu
         {
             byte[] ascii = Encoding.ASCII.GetBytes(line);
             this.exceptionProvidedToProcessor = new ArgumentException("That was never 5 minutes");
-            this.adapter.OnError(ascii, this.exceptionProvidedToProcessor, lineNumber);
+            this.Adapter.OnError(ascii, this.exceptionProvidedToProcessor, lineNumber);
         }
 
         [When("the line to message adapter receives a progress report of (.*), (.*), (.*), (.*), (.*)")]
         public void WhenTheLineToMessageAdapterReceivesAProgressReportOfFalse(
             bool done, int totalLines, int totalTicks, int linesSinceLastUpdate, int ticksSinceLastUpdate)
         {
-            this.adapter.Progress(done, totalLines, totalTicks, linesSinceLastUpdate, ticksSinceLastUpdate);
+            this.Adapter.Progress(done, totalLines, totalTicks, linesSinceLastUpdate, ticksSinceLastUpdate);
         }
     }
 }
\ No newline at end of file
diff --git a/Solutions/Ais.Net/Ais/Net/NmeaLineToAisStreamAdapter.cs b/Solutions/Ais.Net/Ais/Net/NmeaLineToAisStreamAdapter.cs
index 1897c2d..5aacfd9 100644
--- a/Solutions/Ais.Net/Ais/Net/NmeaLineToAisStreamAdapter.cs
+++ b/Solutions/Ais.Net/Ais/Net/NmeaLineToAisStreamAdapter.cs
@@ -8,6 +8,7 @@ namespace Ais.Net
     using System.Buffers;
     using System.Collections.Generic;
     using System.Linq;
+    using System.Text;
 
     /// <summary>
     /// Processes NMEA message lines, and passes their payloads as complete AIS messages to an
@@ -18,7 +19,7 @@ public class NmeaLineToAisStreamAdapter : INmeaLineStreamProcessor, IDisposable
     {
         private readonly INmeaAisMessageStreamProcessor messageProcessor;
         private readonly NmeaParserOptions options;
-        private readonly Dictionary<int, IMemoryOwner<byte>[]> messageFragments = new Dictionary<int, IMemoryOwner<byte>[]>();
+        private readonly Dictionary<int, FragmentedMessage> messageFragments = new Dictionary<int, FragmentedMessage>();
         private int messagesProcessed = 0;
         private int messagesProcessedAtLastUpdate = 0;
 
@@ -81,13 +82,16 @@ public void OnNext(in NmeaLineParser parsedLine, int lineNumber)
 
                 int groupId = sentenceGrouping.GroupId;
 
-                if (!this.messageFragments.TryGetValue(groupId, out IMemoryOwner<byte>[] fragments))
+                if (!this.messageFragments.TryGetValue(groupId, out FragmentedMessage fragments))
                 {
-                    fragments = new IMemoryOwner<byte>[sentenceGrouping.SentencesInGroup];
+                    fragments = new FragmentedMessage(
+                        new IMemoryOwner<byte>[sentenceGrouping.SentencesInGroup],
+                        lineNumber);
                     this.messageFragments.Add(groupId, fragments);
                 }
 
-                if (fragments[sentenceGrouping.SentenceNumber - 1] != null)
+                IMemoryOwner<byte>[] fragmentMemoryOwners = fragments.MemoryOwners;
+                if (fragmentMemoryOwners[sentenceGrouping.SentenceNumber - 1] != null)
                 {
                     this.messageProcessor.OnError(
                         parsedLine.Line,
@@ -96,21 +100,21 @@ public void OnNext(in NmeaLineParser parsedLine, int lineNumber)
                 }
 
                 IMemoryOwner<byte> buffer = MemoryPool<byte>.Shared.Rent(parsedLine.Line.Length);
-                fragments[sentenceGrouping.SentenceNumber - 1] = buffer;
+                fragmentMemoryOwners[sentenceGrouping.SentenceNumber - 1] = buffer;
                 parsedLine.Line.CopyTo(buffer.Memory.Span);
 
                 bool allFragmentsReceived = true;
                 int totalPayloadSize = 0;
 
-                for (int i = 0; i < fragments.Length; ++i)
+                for (int i = 0; i < fragmentMemoryOwners.Length; ++i)
                 {
-                    if (fragments[i] == null)
+                    if (fragmentMemoryOwners[i] == null)
                     {
                         allFragmentsReceived = false;
                         break;
                     }
 
-                    var storedParsedLine = new NmeaLineParser(fragments[i].Memory.Span, this.options.ThrowWhenTagBlockContainsUnknownFields);
+                    var storedParsedLine = new NmeaLineParser(fragmentMemoryOwners[i].Memory.Span, this.options.ThrowWhenTagBlockContainsUnknownFields);
                     totalPayloadSize += storedParsedLine.Payload.Length;
                 }
 
@@ -122,9 +126,9 @@ public void OnNext(in NmeaLineParser parsedLine, int lineNumber)
                         Span<byte> reassemblyBuffer = reassembly.Memory.Span;
                         uint finalPadding = 0;
 
-                        for (int i = 0; i < fragments.Length; ++i)
+                        for (int i = 0; i < fragmentMemoryOwners.Length; ++i)
                         {
-                            var storedParsedLine = new NmeaLineParser(fragments[i].Memory.Span, this.options.ThrowWhenTagBlockContainsUnknownFields);
+                            var storedParsedLine = new NmeaLineParser(fragmentMemoryOwners[i].Memory.Span, this.options.ThrowWhenTagBlockContainsUnknownFields);
                             ReadOnlySpan<byte> payload = storedParsedLine.Payload;
                             payload.CopyTo(reassemblyBuffer.Slice(reassemblyIndex, payload.Length));
                             reassemblyIndex += payload.Length;
@@ -132,7 +136,7 @@ public void OnNext(in NmeaLineParser parsedLine, int lineNumber)
                         }
 
                         this.messageProcessor.OnNext(
-                            new NmeaLineParser(fragments[0].Memory.Span, this.options.ThrowWhenTagBlockContainsUnknownFields),
+                            new NmeaLineParser(fragmentMemoryOwners[0].Memory.Span, this.options.ThrowWhenTagBlockContainsUnknownFields),
                             reassemblyBuffer.Slice(0, totalPayloadSize),
                             finalPadding);
                         this.messagesProcessed += 1;
@@ -146,6 +150,40 @@ public void OnNext(in NmeaLineParser parsedLine, int lineNumber)
                 this.messageProcessor.OnNext(parsedLine, parsedLine.Payload, parsedLine.Padding);
                 this.messagesProcessed += 1;
             }
+
+            if (this.messageFragments.Count > 0)
+            {
+                Span<int> fragmentGroupIdsToRemove = stackalloc int[this.messageFragments.Count];
+                int fragmentToRemoveCount = 0;
+                foreach (KeyValuePair<int, FragmentedMessage> kv in this.messageFragments)
+                {
+                    int sentencesSinceFirstFragment = lineNumber - kv.Value.LineNumber;
+                    if (sentencesSinceFirstFragment > this.options.MaximumUnmatchedFragmentAge)
+                    {
+                        fragmentGroupIdsToRemove[fragmentToRemoveCount++] = kv.Key;
+                    }
+                }
+
+                for (int i = 0; i < fragmentToRemoveCount; ++i)
+                {
+                    int groupId = fragmentGroupIdsToRemove[i];
+                    FragmentedMessage fragmentedMessage = this.messageFragments[groupId];
+                    IMemoryOwner<byte> lastMemoryOwner = fragmentedMessage.MemoryOwners.Last(mo => mo != null);
+
+                    ReadOnlySpan<byte> line = lastMemoryOwner.Memory.Span;
+                    int endOfMessages = line.IndexOf((byte)0);
+                    if (endOfMessages >= 0)
+                    {
+                        line = line.Slice(0, endOfMessages);
+                    }
+
+                    this.messageProcessor.OnError(
+                        line,
+                        new ArgumentException("Received incomplete fragmented message."),
+                        fragmentedMessage.LineNumber);
+                    this.FreeMessageFragments(groupId);
+                }
+            }
         }
 
         /// <inheritdoc/>
@@ -185,7 +223,7 @@ private void FreeRentedBuffers()
 
         private void FreeMessageFragments(int groupId)
         {
-            IMemoryOwner<byte>[] fragments = this.messageFragments[groupId];
+            IMemoryOwner<byte>[] fragments = this.messageFragments[groupId].MemoryOwners;
             for (int i = 0; i < fragments.Length; ++i)
             {
                 fragments[i]?.Dispose();
@@ -193,5 +231,18 @@ private void FreeMessageFragments(int groupId)
 
             this.messageFragments.Remove(groupId);
         }
+
+        private struct FragmentedMessage
+        {
+            public FragmentedMessage(IMemoryOwner<byte>[] memoryOwners, int lineNumber)
+            {
+                this.MemoryOwners = memoryOwners;
+                this.LineNumber = lineNumber;
+            }
+
+            public IMemoryOwner<byte>[] MemoryOwners { get; }
+
+            public int LineNumber { get; }
+        }
     }
 }
diff --git a/Solutions/Ais.Net/Ais/Net/NmeaParserOptions.cs b/Solutions/Ais.Net/Ais/Net/NmeaParserOptions.cs
index 35a2971..70872a3 100644
--- a/Solutions/Ais.Net/Ais/Net/NmeaParserOptions.cs
+++ b/Solutions/Ais.Net/Ais/Net/NmeaParserOptions.cs
@@ -14,5 +14,55 @@ public class NmeaParserOptions
         /// fields in an NMEA tag block should be treated as a non-recoverable error.
         /// </summary>
         public bool ThrowWhenTagBlockContainsUnknownFields { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets a value determining how long the <see cref="NmeaLineToAisStreamAdapter"/>
+        /// will wait for further related fragments after receiving a message fragment.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// Some AIS messages are typically split across multiple NMEA message. E.g., type 5
+        /// messages are on the large side and are normally split. Message-oriented methods such as
+        /// <see cref="NmeaStreamParser.ParseFileAsync(string, INmeaAisMessageStreamProcessor, NmeaParserOptions)"/>
+        /// deal with this for you, using the <see cref="NmeaLineToAisStreamAdapter"/> to combine
+        /// fragments, enabling processors to see the whole reassembled payload. But what should
+        /// happen if we receive an incomplete set of fragments? E.g., we might receive the first
+        /// fragment but the 2nd is lost due to transmission errors.
+        /// </para>
+        /// <para>
+        /// We must not hang onto message fragments indefinitely because the grouping identifiers
+        /// used to reunite them are recycled. When relying on the fragment number at the NMEA
+        /// sentence layer, it appears that the group is identified with a single non-zero decimal
+        /// digit, meaning that there can be at most 9 fragmented messages in progress at any time.
+        /// Many sources provide grouping information at the tag block level, where it is common
+        /// to use more digits. (4-digit group ids seem common.) But since applications may be
+        /// processing millions of messages per hour, even the tag-level group identifiers get
+        /// reused pretty frequently.
+        /// </para>
+        /// <para>
+        /// It is therefore necessary to limited how long we wait for all of the fragments of
+        /// a message to arrive. Otherwise, any time a fragment goes missing, we would
+        /// misidentify a later fragment: when the group identifier is reused, we would
+        /// incorrectly attempt to pair this new fragment with the older one. At best, this
+        /// causes us to report an error—if we get two "part 1" fragments for the same group,
+        /// we report this as an error. But if we are unlucky, we could lose the 2nd fragment
+        /// of a message and then later lose the 1st fragment of an unrelated message that
+        /// happens to have recycled the group id, and we will erroneously combine the
+        /// payloads of two unrelated messages and report them as a correctly-received
+        /// single message.
+        /// </para>
+        /// <para>
+        /// To avoid this, we limit the lifetime of unmatched message fragments. We measure
+        /// this lifetime in received messages, not elapsed time, because recycling of group
+        /// ids is driven by the number of messages that arrive.
+        /// </para>
+        /// <para>
+        /// In practice, we very rarely see message fragments interleaved with other messages
+        /// at all. Most of the time, the 2nd fragment appears immediately after the 1st if
+        /// it appears at all. So the default age of 8 is more than enough for the data
+        /// sources we've seen to date, and is small enough to work with single-digit group ids.
+        /// </para>
+        /// </remarks>
+        public int MaximumUnmatchedFragmentAge { get; set; } = 8;
     }
 }
diff --git a/docs/adr/0002-missing-fragment-handling.md b/docs/adr/0002-missing-fragment-handling.md
new file mode 100644
index 0000000..1f6f131
--- /dev/null
+++ b/docs/adr/0002-missing-fragment-handling.md
@@ -0,0 +1,17 @@
+# Missing fragment handling
+
+## Status
+
+Accepted.
+
+## Context
+
+Some AIS data sources include NMEA sentences that are not correctly formed. We sometimes see truncated messages, for example. This causes problems when a corrupt message was a fragment. At some point we need to let go of the fragment because its fellow fragments are never going to arrive.
+
+## Decision
+
+We default to abandoning fragmented messages if 8 other messages have arrived since the first fragment. This is configurable, but we chose 8 because there's a limit of 9 fragmented messages in progress at any one time if you use the AIVDM-level group identifiers. It is configurable because systems that provide tag block group identifiers often use larger group IDs (e.g., 4 digits are common), making it possible for more to be in flight at once. But in practice, most message fragments are adjacent, so a large window is usaully unnecessary.
+
+## Consequences
+
+Missing fragments can now be reported. We can also avoid the problems that can occur when fragment group identifiers are reused, as they inevitably will be in long message streams. By abandoning doomed messages early we avoid the problem where a later reuse of the same id is misidentified as being part of the same message we had earlier.
\ No newline at end of file