- Fix failure to generate all possible combinations (#3132)

* - Fix failure to generate all possible combinations

Bug happens when the endorsement policy is set to k-out-of-n where (n - k) > 1.
For example, when there are 6 organizations and the endorsement policy is set
to majority (i.e. 4-out-of-6). The combinations calculated by chooseKoutOfN()
in original code are as below.
	[0 1 2 5], [0 1 2 5], [0 1 2 5], [0 1 3 5],
	[0 1 3 5], [0 1 4 5], [0 2 3 5], [0 2 3 5],
	[0 2 4 5], [0 3 4 5], [1 2 3 5], [1 2 3 5],
	[1 2 4 5], [1 3 4 5], [2 3 4 5]

Obviously, the function fails to find out all the possible combinations. Some of
 the combinations are overrided by child's call. This bug would trigger below
error sometimes when the alive peers are not within the above combinations.

	[discovery] chaincodeQuery -> ERRO 13a Failed constructing descriptor for
	chaincode chaincodes:<name:"XXXX" > ,: no peer combination can satisfy the
	endorsement policy

To fix it, the last line of choose() should be changed to pass a copy of
"currentSubGroup" to the recursive call instead, i.e.

	choose(n, targetAmount, i+1, append(make([]int, 0), currentSubGroup...), subGroups)

After applying the fix, the resulting combinations generated should be corrected
as below.
	[0 1 2 3], [0 1 2 4], [0 1 2 5], [0 1 3 4],
	[0 1 3 5], [0 1 4 5], [0 2 3 4], [0 2 3 5],
	[0 2 4 5], [0 3 4 5], [1 2 3 4], [1 2 3 5],
	[1 2 4 5], [1 3 4 5], [2 3 4 5]

Signed-off-by: Tim <96273851+timtim-git@users.noreply.github.com>

* - Fix failure to generate all possible combinations

Bug happens when the endorsement policy is set to k-out-of-n where (n - k) > 1.
For example, when there are 6 organizations and the endorsement policy is set
to majority (i.e. 4-out-of-6). The combinations calculated by chooseKoutOfN()
in original code are as below.
	[0 1 2 5], [0 1 2 5], [0 1 2 5], [0 1 3 5],
	[0 1 3 5], [0 1 4 5], [0 2 3 5], [0 2 3 5],
	[0 2 4 5], [0 3 4 5], [1 2 3 5], [1 2 3 5],
	[1 2 4 5], [1 3 4 5], [2 3 4 5]

Obviously, the function fails to find out all the possible combinations. Some of
 the combinations are overrided by child's call. This bug would trigger below
error sometimes when the alive peers are not within the above combinations.

	[discovery] chaincodeQuery -> ERRO 13a Failed constructing descriptor for
	chaincode chaincodes:<name:"XXXX" > ,: no peer combination can satisfy the
	endorsement policy

To fix it, the last line of choose() should be changed to pass a copy of
"currentSubGroup" to the recursive call instead, i.e.

	choose(n, targetAmount, i+1, append(make([]int, 0), currentSubGroup...), subGroups)

After applying the fix, the resulting combinations generated should be corrected
as below.
	[0 1 2 3], [0 1 2 4], [0 1 2 5], [0 1 3 4],
	[0 1 3 5], [0 1 4 5], [0 2 3 4], [0 2 3 5],
	[0 2 4 5], [0 3 4 5], [1 2 3 4], [1 2 3 5],
	[1 2 4 5], [1 3 4 5], [2 3 4 5]

Signed-off-by: Tim <96273851+timtim-git@users.noreply.github.com>

* - Update choose_test.go

Signed-off-by: Tim <96273851+timtim-git@users.noreply.github.com>

* - Fix build error

Signed-off-by: Tim <96273851+timtim-git@users.noreply.github.com>
(cherry picked from commit 21a17ee)

common/graph/choose.go

@@ -59,7 +59,14 @@ func choose(n int, targetAmount int, i int, currentSubGroup []int, subGroups *or
 		return
 	}
 	// We either pick the current element
-	choose(n, targetAmount, i+1, append(currentSubGroup, i), subGroups)
+	choose(n, targetAmount, i+1, concatInts(currentSubGroup, i), subGroups)
 	// Or don't pick it
 	choose(n, targetAmount, i+1, currentSubGroup, subGroups)
 }
+
+func concatInts(a []int, elements ...int) []int {
+	var res []int
+	res = append(res, a...)
+	res = append(res, elements...)
+	return res
+}

common/graph/choose_test.go

@@ -7,6 +7,7 @@ SPDX-License-Identifier: Apache-2.0
 package graph
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -24,3 +25,32 @@ func TestCombinationsExceed(t *testing.T) {
 	// N < K returns false
 	assert.False(t, CombinationsExceed(20, 30, 0))
 }
+
+func TestChooseKoutOfN(t *testing.T) {
+	expectedSets := indiceSets{
+		&indiceSet{[]int{0, 1, 2, 3}},
+		&indiceSet{[]int{0, 1, 2, 4}},
+		&indiceSet{[]int{0, 1, 2, 5}},
+		&indiceSet{[]int{0, 1, 3, 4}},
+		&indiceSet{[]int{0, 1, 3, 5}},
+		&indiceSet{[]int{0, 1, 4, 5}},
+		&indiceSet{[]int{0, 2, 3, 4}},
+		&indiceSet{[]int{0, 2, 3, 5}},
+		&indiceSet{[]int{0, 2, 4, 5}},
+		&indiceSet{[]int{0, 3, 4, 5}},
+		&indiceSet{[]int{1, 2, 3, 4}},
+		&indiceSet{[]int{1, 2, 3, 5}},
+		&indiceSet{[]int{1, 2, 4, 5}},
+		&indiceSet{[]int{1, 3, 4, 5}},
+		&indiceSet{[]int{2, 3, 4, 5}},
+	}
+	require.Equal(t, indiceSetsToStrings(expectedSets), indiceSetsToStrings(chooseKoutOfN(6, 4)))
+}
+
+func indiceSetsToStrings(sets indiceSets) []string {
+	var res []string
+	for _, set := range sets {
+		res = append(res, fmt.Sprintf("%v", set.indices))
+	}
+	return res
+}