De-duplicate inodes when converting from the old state (#2792) (#2797)

When upgrading the registry file from 1.x versions, make sure
the new state doesn't contain any duplicate inodes, as these will cause
an invalid state. Fixes #2784.

CHANGELOG.asciidoc

@@ -43,6 +43,7 @@ https://github.com/elastic/beats/compare/v5.0.0-rc1...5.0[Check the HEAD diff]
 
 *Filebeat*
 - Fix issue when clean_removed and clean_inactive were used together that states were not directly removed from the registry.
+- Fix issue where upgrading a 1.x registry file resulted in duplicate state entries. {pull}2792[2792]
 
 *Winlogbeat*
 

filebeat/registrar/registrar.go

@@ -139,16 +139,8 @@ func (r *Registrar) loadAndConvertOldState(f *os.File) bool {
 	}
 
 	// Convert old states to new states
-	states := make([]file.State, len(oldStates))
 	logp.Info("Old registry states found: %v", len(oldStates))
-	counter := 0
-	for _, state := range oldStates {
-		// Makes timestamp time of migration, as this is the best guess
-		state.Timestamp = time.Now()
-		states[counter] = state
-		counter++
-	}
-
+	states := convertOldStates(oldStates)
 	r.states.SetStates(states)
 
 	// Rewrite registry in new format
@@ -159,6 +151,32 @@ func (r *Registrar) loadAndConvertOldState(f *os.File) bool {
 	return true
 }
 
+func convertOldStates(oldStates map[string]file.State) []file.State {
+	// Convert old states to new states
+	states := []file.State{}
+	for _, state := range oldStates {
+		// Makes timestamp time of migration, as this is the best guess
+		state.Timestamp = time.Now()
+
+		// Check for duplicates
+		dupe := false
+		for i, other := range states {
+			if state.FileStateOS.IsSame(other.FileStateOS) {
+				dupe = true
+				if state.Offset > other.Offset {
+					// replace other
+					states[i] = state
+					break
+				}
+			}
+		}
+		if !dupe {
+			states = append(states, state)
+		}
+	}
+	return states
+}
+
 func (r *Registrar) Start() error {
 
 	// Load the previous log file locations now, for use in prospector

filebeat/registrar/registrar_test.go

@@ -0,0 +1,59 @@
+// +build !windows,!integration
+
+package registrar
+
+import (
+	"sort"
+	"testing"
+
+	"github.com/elastic/beats/filebeat/input/file"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestConvertOldStates(t *testing.T) {
+	type io struct {
+		Name   string
+		Input  map[string]file.State
+		Output []string
+	}
+	tests := []io{
+		{
+			Name: "Simple test with three files",
+			Input: map[string]file.State{
+				"test":  file.State{Source: "test", FileStateOS: file.StateOS{Inode: 5}},
+				"test1": file.State{Source: "test1", FileStateOS: file.StateOS{Inode: 3}},
+				"test2": file.State{Source: "test2", FileStateOS: file.StateOS{Inode: 2}},
+			},
+			Output: []string{"test", "test1", "test2"},
+		},
+		{
+			Name: "De-duplicate inodes. Bigger offset wins (1)",
+			Input: map[string]file.State{
+				"test":  file.State{Source: "test", FileStateOS: file.StateOS{Inode: 2}},
+				"test1": file.State{Source: "test1", FileStateOS: file.StateOS{Inode: 3}},
+				"test2": file.State{Source: "test2", FileStateOS: file.StateOS{Inode: 2}, Offset: 2},
+			},
+			Output: []string{"test1", "test2"},
+		},
+		{
+			Name: "De-duplicate inodes. Bigger offset wins (2)",
+			Input: map[string]file.State{
+				"test":  file.State{Source: "test", FileStateOS: file.StateOS{Inode: 2}, Offset: 2},
+				"test1": file.State{Source: "test1", FileStateOS: file.StateOS{Inode: 3}},
+				"test2": file.State{Source: "test2", FileStateOS: file.StateOS{Inode: 2}, Offset: 0},
+			},
+			Output: []string{"test", "test1"},
+		},
+	}
+
+	for _, test := range tests {
+		result := convertOldStates(test.Input)
+		resultSources := []string{}
+		for _, state := range result {
+			resultSources = append(resultSources, state.Source)
+		}
+		sort.Strings(resultSources)
+		assert.Equal(t, test.Output, resultSources, test.Name)
+
+	}
+}