Fix bug in provider cache aggregation rage loop

The loop responsible for aggregating contextual and chain level extended
providers ranges over the values fetched from indexers, passes the
values by reference but does not redeclare the value in each iteration.

Redeclare the value to make sure future iterations do not alter the
providers already added to slice.

While at it fix similar issues in other places.

find/client/provider_cache.go

@@ -114,6 +114,7 @@ func (pc *providerCache) getResults(ctx context.Context, pid peer.ID, ctxID []by
 		}
 		if pinfo.ExtendedProviders != nil {
 			for _, cxp := range pinfo.ExtendedProviders.Contextual {
+				cxp := cxp
 				wrapper.cxps[cxp.ContextID] = &cxp
 			}
 		}
@@ -141,6 +142,7 @@ func (pc *providerCache) getResults(ctx context.Context, pid peer.ID, ctxID []by
 	if contextualEpRecord, ok := wrapper.cxps[string(ctxID)]; ok {
 		override = contextualEpRecord.Override
 		for i, xpinfo := range contextualEpRecord.Providers {
+			xpinfo := xpinfo
 			xmd := contextualEpRecord.Metadatas[i]
 			// Skippng the main provider's record if its metadata is nil or is
 			// the same as the one retrieved from the indexer, because such EP
@@ -170,6 +172,7 @@ func (pc *providerCache) getResults(ctx context.Context, pid peer.ID, ctxID []by
 
 	// Adding chain-level EPs if such exist
 	for i, xpinfo := range wrapper.pinfo.ExtendedProviders.Providers {
+		xpinfo := xpinfo
 		xmd := wrapper.pinfo.ExtendedProviders.Metadatas[i]
 		// Skippng the main provider's record if its metadata is nil or is the
 		// same as the one retrieved from the indexer, because such EP record

find/client/provider_cache_test.go

@@ -0,0 +1,106 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/ipni/go-libipni/find/model"
+	"github.com/stretchr/testify/require"
+)
+
+func TestChainLevelExtendedProviderIsAsExpected(t *testing.T) {
+	var want []model.ProviderResult
+	err := json.Unmarshal([]byte(`[
+  {
+    "ContextID": "bG9ic3Rlcg==",
+    "Metadata": "YmFycmVsZXll",
+    "Provider": {
+      "ID": "12D3KooWNSRG5wTShNu6EXCPTkoH7dWsphKAPrbvQchHa5arfsDC",
+      "Addrs": [
+        "/ip4/209.94.92.6/tcp/24001"
+      ]
+    }
+  },
+  {
+    "ContextID": "bG9ic3Rlcg==",
+    "Metadata": "gBI=",
+    "Provider": {
+      "ID": "12D3KooWHf7cahZvAVB36SGaVXc7fiVDoJdRJq42zDRcN2s2512h",
+      "Addrs": [
+        "/ip4/209.94.92.6/tcp/24123"
+      ]
+    }
+  },
+  {
+    "ContextID": "bG9ic3Rlcg==",
+    "Metadata": "oBIA",
+    "Provider": {
+      "ID": "12D3KooWNSRG5wTShNu6EXCPTkoH7dWsphKAPrbvQchHa5arfsDC",
+      "Addrs": [
+        "/ip4/209.94.92.6/tcp/7575/http"
+      ]
+    }
+  }
+]`), &want)
+	require.NoError(t, err)
+
+	testServer := httptest.NewServer(http.HandlerFunc(func(res http.ResponseWriter, req *http.Request) {
+		_, err := res.Write([]byte(`{
+  "AddrInfo": {
+    "ID": "12D3KooWNSRG5wTShNu6EXCPTkoH7dWsphKAPrbvQchHa5arfsDC",
+    "Addrs": [
+      "/ip4/209.94.92.6/tcp/24001"
+    ]
+  },
+  "LastAdvertisement": {
+    "/": "baguqeerami47x7t3d4raobz7s2cq5np2fy2lhl3xh2ppiwuevxwbdamuikla"
+  },
+  "LastAdvertisementTime": "2023-06-28T12:21:06Z",
+  "Publisher": {
+    "ID": "12D3KooWNSRG5wTShNu6EXCPTkoH7dWsphKAPrbvQchHa5arfsDC",
+    "Addrs": [
+      "/ip4/209.94.92.6/tcp/24001"
+    ]
+  },
+  "IndexCount": 157535217,
+  "ExtendedProviders": {
+    "Providers": [
+      {
+        "ID": "12D3KooWHf7cahZvAVB36SGaVXc7fiVDoJdRJq42zDRcN2s2512h",
+        "Addrs": [
+          "/ip4/209.94.92.6/tcp/24123"
+        ]
+      },
+      {
+        "ID": "12D3KooWNSRG5wTShNu6EXCPTkoH7dWsphKAPrbvQchHa5arfsDC",
+        "Addrs": [
+          "/ip4/209.94.92.6/tcp/7575/http"
+        ]
+      }
+    ],
+    "Metadatas": [
+      "gBI=",
+      "oBIA"
+    ]
+  },
+  "FrozenAt": null
+}`))
+		require.NoError(t, err)
+	}))
+	defer func() { testServer.Close() }()
+
+	u, err := url.Parse(testServer.URL)
+	require.NoError(t, err)
+	subject, err := newProviderCache(u, nil)
+	require.NoError(t, err)
+
+	contextID := []byte("lobster")
+	metadata := []byte("barreleye")
+	got, err := subject.getResults(context.Background(), "fish", contextID, metadata)
+	require.NoError(t, err)
+	require.Equal(t, want, got)
+}