Return empty response for not found to preserve compatability with cl…

…ients that expect non-nil response

find/client/client.go

@@ -55,8 +55,8 @@ func New(baseURL string, options ...Option) (*Client, error) {
 	}, nil
 }
 
-// Find looks up content entries by multihash. If no results are found then a
-// nil response without error is returned.
+// Find looks up content entries by multihash. If no results are found then an
+// empty response without error is returned.
 func (c *Client) Find(ctx context.Context, m multihash.Multihash) (*model.FindResponse, error) {
 	u := c.findURL.JoinPath(m.B58String())
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
@@ -72,7 +72,7 @@ func (c *Client) Find(ctx context.Context, m multihash.Multihash) (*model.FindRe
 	// Handle failed requests
 	if resp.StatusCode != http.StatusOK {
 		if resp.StatusCode == http.StatusNotFound {
-			return nil, nil
+			return &model.FindResponse{}, nil
 		}
 		return nil, fmt.Errorf("find query failed: %v", http.StatusText(resp.StatusCode))
 	}

find/client/dhash_client.go

@@ -99,7 +99,7 @@ func (c *DHashClient) PCache() *pcache.ProviderCache {
 
 // Find launches FindAsync in a separate go routine and assembles the result
 // into FindResponse as if it was a synchronous invocation. If no results are
-// found then a nil response without error is returned.
+// found then an empty response without error is returned.
 func (c *DHashClient) Find(ctx context.Context, mh multihash.Multihash) (*model.FindResponse, error) {
 	resChan := make(chan model.ProviderResult)
 	errChan := make(chan error, 1)
@@ -117,7 +117,7 @@ func (c *DHashClient) Find(ctx context.Context, mh multihash.Multihash) (*model.
 		return nil, err
 	}
 	if len(providerResults) == 0 {
-		return nil, nil
+		return &model.FindResponse{}, nil
 	}
 
 	return &model.FindResponse{

find/client/interface.go

@@ -13,13 +13,13 @@ import (
 // Finder is the interface implemented by all find clients.
 type Finder interface {
 	// Find queries for provider content records for a single multihash. If no
-	// results are found then a nil response without error is returned.
+	// results are found then an empty response without error is returned.
 	Find(context.Context, multihash.Multihash) (*model.FindResponse, error)
 }
 
 // FindBatch is a convenience function to lookup results for multiple
 // multihashes. This works with either the Client or DHashClient. If no results
-// are found then a nil response without error is returned.
+// are found then an empty response without error is returned.
 func FindBatch(ctx context.Context, finder Finder, mhs []multihash.Multihash) (*model.FindResponse, error) {
 	var resp *model.FindResponse
 	for i := range mhs {
@@ -41,5 +41,8 @@ func FindBatch(ctx context.Context, finder Finder, mhs []multihash.Multihash) (*
 			resp.MultihashResults = append(resp.MultihashResults, r.MultihashResults...)
 		}
 	}
+	if resp == nil {
+		resp = &model.FindResponse{}
+	}
 	return resp, nil
 }