lite: fix HTTP provider error handling

Fixes #4739, kind of. See #4740 for the proper fix.

---

For contributor use:

- [x] Wrote tests
- [x] Updated CHANGELOG_PENDING.md
- [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
- [x] Updated relevant documentation (`docs/`) and code comments
- [x] Re-reviewed `Files changed` in the Github PR explorer
- [x] Applied Appropriate Labels

CHANGELOG_PENDING.md

@@ -28,3 +28,5 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 - [txindex] [\#4466](https://github.com/tendermint/tendermint/pull/4466) Allow to index an event at runtime (@favadi)
 
 ### BUG FIXES:
+
+- [light] [\#4741](https://github.com/tendermint/tendermint/pull/4741) Correctly return  `ErrSignedHeaderNotFound` and `ErrValidatorSetNotFound` on corresponding RPC errors (@erikgrinaker)

lite2/provider/http/http.go

@@ -3,6 +3,7 @@ package http
 import (
 	"errors"
 	"fmt"
+	"regexp"
 	"strings"
 
 	"github.com/tendermint/tendermint/lite2/provider"
@@ -11,6 +12,9 @@ import (
 	"github.com/tendermint/tendermint/types"
 )
 
+// This is very brittle, see: https://github.com/tendermint/tendermint/issues/4740
+var regexpMissingHeight = regexp.MustCompile(`height \d+ (must be less than or equal to|is not available)`)
+
 // http provider uses an RPC client to obtain the necessary information.
 type http struct {
 	chainID string
@@ -62,7 +66,7 @@ func (p *http) SignedHeader(height int64) (*types.SignedHeader, error) {
 	commit, err := p.client.Commit(h)
 	if err != nil {
 		// TODO: standartise errors on the RPC side
-		if strings.Contains(err.Error(), "height must be less than or equal") {
+		if regexpMissingHeight.MatchString(err.Error()) {
 			return nil, provider.ErrSignedHeaderNotFound
 		}
 		return nil, err
@@ -92,7 +96,7 @@ func (p *http) ValidatorSet(height int64) (*types.ValidatorSet, error) {
 	res, err := p.client.Validators(h, 0, maxPerPage)
 	if err != nil {
 		// TODO: standartise errors on the RPC side
-		if strings.Contains(err.Error(), "height must be less than or equal") {
+		if regexpMissingHeight.MatchString(err.Error()) {
 			return nil, provider.ErrValidatorSetNotFound
 		}
 		return nil, err

lite2/provider/http/http_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/tendermint/tendermint/abci/example/kvstore"
+	"github.com/tendermint/tendermint/lite2/provider"
 	"github.com/tendermint/tendermint/lite2/provider/http"
 	litehttp "github.com/tendermint/tendermint/lite2/provider/http"
 	rpcclient "github.com/tendermint/tendermint/rpc/client"
@@ -33,6 +34,7 @@ func TestNewProvider(t *testing.T) {
 
 func TestMain(m *testing.M) {
 	app := kvstore.NewApplication()
+	app.RetainBlocks = 5
 	node := rpctest.StartTendermint(app)
 
 	code := m.Run()
@@ -73,8 +75,25 @@ func TestProvider(t *testing.T) {
 	assert.Nil(t, sh.ValidateBasic(chainID))
 
 	// historical queries now work :)
-	lower := sh.Height - 5
+	lower := sh.Height - 3
 	sh, err = p.SignedHeader(lower)
 	assert.Nil(t, err, "%+v", err)
 	assert.Equal(t, lower, sh.Height)
+
+	// fetching missing heights (both future and pruned) should return appropriate errors
+	_, err = p.SignedHeader(1000)
+	require.Error(t, err)
+	assert.Equal(t, provider.ErrSignedHeaderNotFound, err)
+
+	_, err = p.ValidatorSet(1000)
+	require.Error(t, err)
+	assert.Equal(t, provider.ErrValidatorSetNotFound, err)
+
+	_, err = p.SignedHeader(1)
+	require.Error(t, err)
+	assert.Equal(t, provider.ErrSignedHeaderNotFound, err)
+
+	_, err = p.ValidatorSet(1)
+	require.Error(t, err)
+	assert.Equal(t, provider.ErrValidatorSetNotFound, err)
 }