Change empty string checks to be more idiomatic (valyala#1684)

.golangci.yml

@@ -68,6 +68,9 @@ linters-settings:
       "all",
       "-ST1000", # at least one file in a package should have a package comment
     ]
+  gocritic:
+    enabled-checks:
+      - emptyStringTest
 
 issues:
   # Show all issues from a linter.

client.go

@@ -1825,7 +1825,7 @@ func newClientTLSConfig(c *tls.Config, addr string) *tls.Config {
 		c = c.Clone()
 	}
 
-	if len(c.ServerName) == 0 {
+	if c.ServerName == "" {
 		serverName := tlsServerName(addr)
 		if serverName == "*" {
 			c.InsecureSkipVerify = true

expvarhandler/expvar.go

@@ -53,7 +53,7 @@ func ExpvarHandler(ctx *fasthttp.RequestCtx) {
 
 func getExpvarRegexp(ctx *fasthttp.RequestCtx) (*regexp.Regexp, error) {
 	r := string(ctx.QueryArgs().Peek("r"))
-	if len(r) == 0 {
+	if r == "" {
 		return defaultRE, nil
 	}
 	rr, err := regexp.Compile(r)

fs.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"github.com/klauspost/compress/zstd"
 	"html"
 	"io"
 	"io/fs"
@@ -17,6 +16,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/klauspost/compress/zstd"
 	"github.com/andybalholm/brotli"
 	"github.com/klauspost/compress/gzip"
 	"github.com/valyala/bytebufferpool"
@@ -461,7 +461,7 @@ func (fs *FS) initRequestHandler() {
 	}
 
 	compressedFileSuffixes := fs.CompressedFileSuffixes
-	if len(compressedFileSuffixes["br"]) == 0 || len(compressedFileSuffixes["gzip"]) == 0 ||
+	if compressedFileSuffixes["br"] == "" || compressedFileSuffixes["gzip"] == "" ||
 		len(compressedFileSuffixes["zstd"]) == 0 || compressedFileSuffixes["br"] == compressedFileSuffixes["gzip"] ||
 		compressedFileSuffixes["br"] == compressedFileSuffixes["zstd"] ||
 		compressedFileSuffixes["gzip"] == compressedFileSuffixes["zstd"] {

header_test.go

@@ -2355,7 +2355,7 @@ type bufioPeekReader struct {
 }
 
 func (r *bufioPeekReader) Read(b []byte) (int, error) {
-	if len(r.s) == 0 {
+	if r.s == "" {
 		return 0, io.EOF
 	}
 

http.go

@@ -979,7 +979,7 @@ func (req *Request) MultipartForm() (*multipart.Form, error) {
 	}
 
 	req.multipartFormBoundary = string(req.Header.MultipartFormBoundary())
-	if len(req.multipartFormBoundary) == 0 {
+	if req.multipartFormBoundary == "" {
 		return nil, ErrNoMultipartForm
 	}
 
@@ -1035,7 +1035,7 @@ func marshalMultipartForm(f *multipart.Form, boundary string) ([]byte, error) {
 func WriteMultipartForm(w io.Writer, f *multipart.Form, boundary string) error {
 	// Do not care about memory allocations here, since multipart
 	// form processing is slow.
-	if len(boundary) == 0 {
+	if boundary == "" {
 		return errors.New("form boundary cannot be empty")
 	}
 

http_test.go

@@ -2214,7 +2214,7 @@ func testRequestSuccess(t *testing.T, method, requestURI, host, userAgent, body,
 	if string(req1.Header.Method()) != expectedMethod {
 		t.Fatalf("Unexpected method: %q. Expected %q", req1.Header.Method(), expectedMethod)
 	}
-	if len(requestURI) == 0 {
+	if requestURI == "" {
 		requestURI = "/"
 	}
 	if string(req1.Header.RequestURI()) != requestURI {
@@ -2467,7 +2467,7 @@ func testRequestPostArgsError(t *testing.T, req *Request, s string) {
 		t.Fatalf("Unexpected error when reading %q: %v", s, err)
 	}
 	ss := req.PostArgs().String()
-	if len(ss) != 0 {
+	if ss != "" {
 		t.Fatalf("unexpected post args: %q. Expecting empty post args", ss)
 	}
 }

server.go

@@ -1740,7 +1740,7 @@ func (s *Server) ServeTLSEmbed(ln net.Listener, certData, keyData []byte) error
 // This function allows programmer to handle multiple domains
 // in one server structure. See examples/multidomain.
 func (s *Server) AppendCert(certFile, keyFile string) error {
-	if len(certFile) == 0 && len(keyFile) == 0 {
+	if certFile == "" && keyFile == "" {
 		return errNoCertOrKeyProvided
 	}