Upgrade golangci-lint and enable new rules

.golangci.yml

@@ -2,14 +2,19 @@ linters:
   enable:
     - deadcode
     - depguard
+    - dogsled
     - dupl
     - errcheck
+    - gochecknoinits
+    - gocognit
     - goconst
     - gocritic
     - gocyclo
+    - godox
     - gofmt
     - goimports
     - golint
+    - goprintffuncname
     - gosec
     - gosimple
     - govet
@@ -20,6 +25,7 @@ linters:
     - misspell
     - nakedret
     - prealloc
+    - rowserrcheck
     - scopelint
     - staticcheck
     - structcheck
@@ -29,3 +35,5 @@ linters:
     - unparam
     - unused
     - varcheck
+    - whitespace
+    - wsl

.travis.yml

@@ -6,7 +6,7 @@ go:
 env:
   - GO111MODULE=on
 before_install:
-  - curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $GOPATH/bin v1.18.0
+  - curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $GOPATH/bin v1.23.6
 script:
   - golangci-lint run
   - go test ./...

handler.go

@@ -64,6 +64,7 @@ func Handler(res http.ResponseWriter, req *http.Request) {
 	if req.Method != http.MethodGet {
 		res.Header().Set("Allow", http.MethodGet)
 		res.WriteHeader(http.StatusMethodNotAllowed)
+
 		return
 	}
 
@@ -73,6 +74,7 @@ func Handler(res http.ResponseWriter, req *http.Request) {
 	if writer == nil {
 		res.WriteHeader(http.StatusNotFound)
 		fmt.Fprintf(res, "error: unsupported file format")
+
 		return
 	}
 
@@ -84,6 +86,7 @@ func Handler(res http.ResponseWriter, req *http.Request) {
 	if err != nil {
 		res.WriteHeader(http.StatusBadRequest)
 		fmt.Fprintf(res, "error: invalid size")
+
 		return
 	}
 
@@ -107,13 +110,15 @@ func Handler(res http.ResponseWriter, req *http.Request) {
 	if err == ErrInvalidSize {
 		res.WriteHeader(http.StatusBadRequest)
 		fmt.Fprintf(res, "error: %s", err)
+
 		return
 	}
 
 	// Check if something else bad happened during generation.
 	if err != nil {
 		res.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintf(res, "error: %s", err)
+
 		return
 	}
 

handler_test.go

@@ -24,6 +24,7 @@ func isPrintable(s string) bool {
 			return false
 		}
 	}
+
 	return true
 }