Generalize Querier REST Pagination

.pending/improvements/sdk/4601-Implement-gener

@@ -0,0 +1,2 @@
+#4601 Implement generic pangination helper function to be used in
+REST handlers and queriers.

client/utils.go

@@ -0,0 +1,30 @@
+package client
+
+// Paginate returns the correct starting and ending index for a paginated query,
+// given that client provides a desired page and limit of objects and the handler
+// provides the total number of objects. If the start page is invalid, non-positive
+// values are returned signaling the request is invalid.
+//
+// NOTE: The start page is assumed to be 1-indexed.
+func Paginate(numObjs, page, limit, defLimit int) (start, end int) {
+	if page == 0 {
+		// invalid start page
+		return -1, -1
+	} else if limit == 0 {
+		limit = defLimit
+	}
+
+	start = (page - 1) * limit
+	end = limit + start
+
+	if end >= numObjs {
+		end = numObjs
+	}
+
+	if start >= numObjs {
+		// page is out of bounds
+		return -1, -1
+	}
+
+	return start, end
+}

client/utils_test.go

@@ -0,0 +1,61 @@
+package client_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/cosmos/cosmos-sdk/client"
+)
+
+func TestPaginate(t *testing.T) {
+	testCases := []struct {
+		name                           string
+		numObjs, page, limit, defLimit int
+		expectedStart, expectedEnd     int
+	}{
+		{
+			"all objects in a single page",
+			100, 1, 100, 100,
+			0, 100,
+		},
+		{
+			"page one of three",
+			75, 1, 25, 100,
+			0, 25,
+		},
+		{
+			"page two of three",
+			75, 2, 25, 100,
+			25, 50,
+		},
+		{
+			"page three of three",
+			75, 3, 25, 100,
+			50, 75,
+		},
+		{
+			"end is greater than total number of objects",
+			75, 2, 50, 100,
+			50, 75,
+		},
+		{
+			"invalid start page",
+			75, 4, 25, 100,
+			-1, -1,
+		},
+		{
+			"invalid zero start page",
+			75, 0, 25, 100,
+			-1, -1,
+		},
+	}
+
+	for i, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			start, end := client.Paginate(tc.numObjs, tc.page, tc.limit, tc.defLimit)
+			require.Equal(t, tc.expectedStart, start, "invalid result; test case #%d", i)
+			require.Equal(t, tc.expectedEnd, end, "invalid result; test case #%d", i)
+		})
+	}
+}

x/slashing/querier.go

@@ -5,6 +5,7 @@ import (
 
 	abci "github.com/tendermint/tendermint/abci/types"
 
+	"github.com/cosmos/cosmos-sdk/client"
 	"github.com/cosmos/cosmos-sdk/codec"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
@@ -65,27 +66,15 @@ func querySigningInfos(ctx sdk.Context, req abci.RequestQuery, k Keeper) ([]byte
 		return nil, sdk.ErrInternal(fmt.Sprintf("failed to parse params: %s", err))
 	}
 
-	if params.Limit == 0 {
-		// set the default limit to max bonded if no limit was provided
-		params.Limit = int(k.sk.MaxValidators(ctx))
-	}
-
 	var signingInfos []ValidatorSigningInfo
 
 	k.IterateValidatorSigningInfos(ctx, func(consAddr sdk.ConsAddress, info ValidatorSigningInfo) (stop bool) {
 		signingInfos = append(signingInfos, info)
 		return false
 	})
 
-	// get pagination bounds
-	start := (params.Page - 1) * params.Limit
-	end := params.Limit + start
-	if end >= len(signingInfos) {
-		end = len(signingInfos)
-	}
-
-	if start >= len(signingInfos) {
-		// page is out of bounds
+	start, end := client.Paginate(len(signingInfos), params.Page, params.Limit, int(k.sk.MaxValidators(ctx)))
+	if start < 0 || end < 0 {
 		signingInfos = []ValidatorSigningInfo{}
 	} else {
 		signingInfos = signingInfos[start:end]

x/staking/keeper/querier.go

@@ -6,6 +6,7 @@ import (
 
 	abci "github.com/tendermint/tendermint/abci/types"
 
+	"github.com/cosmos/cosmos-sdk/client"
 	"github.com/cosmos/cosmos-sdk/codec"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/x/staking/types"
@@ -55,11 +56,6 @@ func queryValidators(ctx sdk.Context, req abci.RequestQuery, k Keeper) ([]byte,
 		return nil, sdk.ErrInternal(fmt.Sprintf("failed to parse params: %s", err))
 	}
 
-	stakingParams := k.GetParams(ctx)
-	if params.Limit == 0 {
-		params.Limit = int(stakingParams.MaxValidators)
-	}
-
 	validators := k.GetAllValidators(ctx)
 	filteredVals := make([]types.Validator, 0, len(validators))
 
@@ -69,15 +65,8 @@ func queryValidators(ctx sdk.Context, req abci.RequestQuery, k Keeper) ([]byte,
 		}
 	}
 
-	// get pagination bounds
-	start := (params.Page - 1) * params.Limit
-	end := params.Limit + start
-	if end >= len(filteredVals) {
-		end = len(filteredVals)
-	}
-
-	if start >= len(filteredVals) {
-		// page is out of bounds
+	start, end := client.Paginate(len(filteredVals), params.Page, params.Limit, int(k.GetParams(ctx).MaxValidators))
+	if start < 0 || end < 0 {
 		filteredVals = []types.Validator{}
 	} else {
 		filteredVals = filteredVals[start:end]

x/supply/keeper/querier.go

@@ -5,6 +5,7 @@ import (
 
 	abci "github.com/tendermint/tendermint/abci/types"
 
+	"github.com/cosmos/cosmos-sdk/client"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/x/supply/types"
 )
@@ -32,20 +33,9 @@ func queryTotalSupply(ctx sdk.Context, req abci.RequestQuery, k Keeper) ([]byte,
 	}
 
 	totalSupply := k.GetSupply(ctx).Total
-	totalSupplyLen := len(totalSupply)
 
-	if params.Limit == 0 {
-		params.Limit = totalSupplyLen
-	}
-
-	start := (params.Page - 1) * params.Limit
-	end := params.Limit + start
-	if end >= totalSupplyLen {
-		end = totalSupplyLen
-	}
-
-	if start >= totalSupplyLen {
-		// page is out of bounds
+	start, end := client.Paginate(len(totalSupply), params.Page, params.Limit, 100)
+	if start < 0 || end < 0 {
 		totalSupply = sdk.Coins{}
 	} else {
 		totalSupply = totalSupply[start:end]