many: replace most uses of strings.SplitN with Cut

In most cases Cut(s, sep) is clearer than strings.SplitN(s, sep, 2).

Change-Id: I375c15f778e43ff25b5b74c9ad0e96dac4615786
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/347889
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>

9 files changed, 45 insertions, 43 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 7b1e9349..3f243db7 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -27,6 +27,7 @@ import (
 	"cloud.google.com/go/storage"
 	"github.com/ghodss/yaml"
 	"golang.org/x/net/context/ctxhttp"
+	"golang.org/x/pkgsite/internal"
 	"golang.org/x/pkgsite/internal/derrors"
 	"golang.org/x/pkgsite/internal/log"
 	"golang.org/x/pkgsite/internal/secrets"
@@ -277,14 +278,14 @@ func (c *Config) DeploymentEnvironment() string {
 	if c.ServiceID == "" {
 		return "local"
 	}
-	parts := strings.SplitN(c.ServiceID, "-", 2)
-	if len(parts) == 1 {
+	before, _, found := internal.Cut(c.ServiceID, "-")
+	if !found {
 		return "prod"
 	}
-	if parts[0] == "" {
+	if before == "" {
 		return "unknownEnv"
 	}
-	return parts[0]
+	return before
 }
 
 // Application returns the name of the running application: "worker",
@@ -293,12 +294,12 @@ func (c *Config) Application() string {
 	if c.ServiceID == "" {
 		return "unknownApp"
 	}
-	parts := strings.SplitN(c.ServiceID, "-", 2)
+	before, after, found := internal.Cut(c.ServiceID, "-")
 	var svc string
-	if len(parts) == 1 {
-		svc = parts[0]
+	if !found {
+		svc = before
 	} else {
-		svc = parts[1]
+		svc = after
 	}
 	switch svc {
 	case "default":
diff --git a/internal/config/dynconfig/dynconfig.go b/internal/config/dynconfig/dynconfig.go
index 9c2e2342..29e65d17 100644
--- a/internal/config/dynconfig/dynconfig.go
+++ b/internal/config/dynconfig/dynconfig.go
@@ -40,12 +40,10 @@ func Read(ctx context.Context, location string) (_ *DynamicConfig, err error) {
 	log.Debugf(ctx, "reading dynamic config from %s", location)
 	var r io.ReadCloser
 	if strings.HasPrefix(location, "gs://") {
-		parts := strings.SplitN(location[5:], "/", 2)
-		if len(parts) != 2 {
+		bucket, object, found := internal.Cut(location[5:], "/")
+		if !found {
 			return nil, errors.New("bad GCS URL")
 		}
-		bucket := parts[0]
-		object := parts[1]
 		if err != nil {
 			return nil, err
 		}
diff --git a/internal/frontend/directory.go b/internal/frontend/directory.go
index 8dfa1934..bda7d9aa 100644
--- a/internal/frontend/directory.go
+++ b/internal/frontend/directory.go
@@ -59,7 +59,7 @@ func unitDirectories(directories []*DirectoryInfo) *Directories {
 	// subdirectories are grouped.
 	mappedDirs := make(map[string]*Directory)
 	for _, d := range directories {
-		prefix := strings.SplitN(d.Suffix, "/", 2)[0]
+		prefix, _, _ := internal.Cut(d.Suffix, "/")
 
 		// Skip internal directories that are not in the top level internal
 		// directory. For example, foo/internal and foo/internal/bar should
diff --git a/internal/frontend/search.go b/internal/frontend/search.go
index 5745c86a..ae601d8d 100644
--- a/internal/frontend/search.go
+++ b/internal/frontend/search.go
@@ -398,17 +398,17 @@ func searchQuery(r *http.Request) (q string, searchSymbols bool) {
 	if strings.HasPrefix(q, "#") {
 		return strings.TrimPrefix(q, "#"), true
 	}
-	if strings.Contains(q, ":") {
-		parts := strings.SplitN(q, ":", 2)
-		if searchModeSymbolKeyboardShortcuts[parts[0]] {
-			return parts[1], true
+	mode, query, found := internal.Cut(q, ":")
+	if found {
+		if searchModeSymbolKeyboardShortcuts[mode] {
+			return query, true
 		}
-		if searchModePackageKeyboardShortcuts[parts[0]] {
-			return parts[1], false
+		if searchModePackageKeyboardShortcuts[mode] {
+			return query, false
 		}
 		return q, false
 	}
-	mode := strings.TrimSpace(r.FormValue("m"))
+	mode = strings.TrimSpace(r.FormValue("m"))
 	if mode == searchModePackage {
 		return q, false
 	}
diff --git a/internal/frontend/symbol.go b/internal/frontend/symbol.go
index 5284acfb..f21f0c46 100644
--- a/internal/frontend/symbol.go
+++ b/internal/frontend/symbol.go
@@ -326,9 +326,9 @@ func addSymbol(s *Symbol, v string, sh *internal.SymbolHistory, builds []string)
 		return
 	}
 	for _, b := range builds {
-		parts := strings.SplitN(b, "/", 2)
+		goos, _, _ := internal.Cut(b, "/")
 		var build internal.BuildContext
-		switch parts[0] {
+		switch goos {
 		case "linux":
 			build = internal.BuildContextLinux
 		case "darwin":
diff --git a/internal/frontend/urlinfo.go b/internal/frontend/urlinfo.go
index 44559ba4..887b0994 100644
--- a/internal/frontend/urlinfo.go
+++ b/internal/frontend/urlinfo.go
@@ -52,8 +52,7 @@ func (e *userError) Unwrap() error {
 func extractURLPathInfo(urlPath string) (_ *urlPathInfo, err error) {
 	defer derrors.Wrap(&err, "extractURLPathInfo(%q)", urlPath)
 
-	parts := strings.SplitN(strings.TrimPrefix(urlPath, "/"), "@", 2)
-	if stdlib.Contains(parts[0]) {
+	if m, _, _ := internal.Cut(strings.TrimPrefix(urlPath, "/"), "@"); stdlib.Contains(m) {
 		return parseStdLibURLPath(urlPath)
 	}
 	return parseDetailsURLPath(urlPath)
@@ -92,16 +91,16 @@ func parseDetailsURLPath(urlPath string) (_ *urlPathInfo, err error) {
 	//   /<module-path>, @<version>/<suffix>
 	// or
 	//  /<module-path>/<suffix>, @<version>
-	parts := strings.SplitN(urlPath, "@", 2)
+	modulePath, rest, found := internal.Cut(urlPath, "@")
 	info := &urlPathInfo{
-		fullPath:         strings.TrimSuffix(strings.TrimPrefix(parts[0], "/"), "/"),
+		fullPath:         strings.TrimSuffix(strings.TrimPrefix(modulePath, "/"), "/"),
 		modulePath:       internal.UnknownModulePath,
 		requestedVersion: version.Latest,
 	}
-	if len(parts) != 1 {
+	if found {
 		// The urlPath contains a "@". Parse the version and suffix from
 		// parts[1], the string after the '@'.
-		endParts := strings.Split(parts[1], "/")
+		endParts := strings.Split(rest, "/")
 
 		// Parse the requestedVersion from the urlPath.
 		// The first path component after the '@' is the version.
@@ -137,8 +136,8 @@ func parseStdLibURLPath(urlPath string) (_ *urlPathInfo, err error) {
 
 	// This splits urlPath into either:
 	//   /<path>@<tag> or /<path>
-	parts := strings.SplitN(urlPath, "@", 2)
-	fullPath := strings.TrimSuffix(strings.TrimPrefix(parts[0], "/"), "/")
+	fullPath, tag, found := internal.Cut(urlPath, "@")
+	fullPath = strings.TrimSuffix(strings.TrimPrefix(fullPath, "/"), "/")
 	if !isValidPath(fullPath) {
 		return nil, &userError{
 			err:         fmt.Errorf("isValidPath(%q) is false", fullPath),
@@ -150,11 +149,11 @@ func parseStdLibURLPath(urlPath string) (_ *urlPathInfo, err error) {
 		fullPath:   fullPath,
 		modulePath: stdlib.ModulePath,
 	}
-	if len(parts) == 1 {
+	if !found {
 		info.requestedVersion = version.Latest
 		return info, nil
 	}
-	tag := strings.TrimSuffix(parts[1], "/")
+	tag = strings.TrimSuffix(tag, "/")
 	info.requestedVersion = stdlib.VersionForTag(tag)
 	if info.requestedVersion == "" {
 		return nil, &userError{
diff --git a/internal/godoc/dochtml/internal/render/linkify.go b/internal/godoc/dochtml/internal/render/linkify.go
index ae2a3fc8..cdb61110 100644
--- a/internal/godoc/dochtml/internal/render/linkify.go
+++ b/internal/godoc/dochtml/internal/render/linkify.go
@@ -21,6 +21,7 @@ import (
 	"github.com/google/safehtml"
 	"github.com/google/safehtml/legacyconversions"
 	"github.com/google/safehtml/template"
+	"golang.org/x/pkgsite/internal"
 	"golang.org/x/pkgsite/internal/godoc/internal/doc"
 	"golang.org/x/pkgsite/internal/log"
 )
@@ -152,15 +153,13 @@ func parseLink(line string) *Link {
 	if !strings.HasPrefix(line, "- ") && !strings.HasPrefix(line, "-\t") {
 		return nil
 	}
-	parts := strings.SplitN(line[2:], ",", 2)
-	if len(parts) != 2 {
+	text, href, found := internal.Cut(line[2:], ",")
+	if !found {
 		return nil
 	}
-	text := strings.TrimSpace(parts[0])
-	href := strings.TrimSpace(parts[1])
 	return &Link{
-		Text: text,
-		Href: href,
+		Text: strings.TrimSpace(text),
+		Href: strings.TrimSpace(href),
 	}
 }
 
diff --git a/internal/middleware/quota.go b/internal/middleware/quota.go
index a2601824..8fd6cd45 100644
--- a/internal/middleware/quota.go
+++ b/internal/middleware/quota.go
@@ -20,6 +20,7 @@ import (
 	"go.opencensus.io/stats"
 	"go.opencensus.io/stats/view"
 	"go.opencensus.io/tag"
+	"golang.org/x/pkgsite/internal"
 	"golang.org/x/pkgsite/internal/config"
 	"golang.org/x/pkgsite/internal/log"
 )
@@ -48,9 +49,9 @@ func recordQuotaMetric(ctx context.Context, blocked string) {
 }
 
 func ipKey(s string) string {
-	fields := strings.SplitN(s, ",", 2)
+	addr, _, _ := internal.Cut(s, ",")
 	// First field is the originating IP address.
-	origin := strings.TrimSpace(fields[0])
+	origin := strings.TrimSpace(addr)
 	ip := net.ParseIP(origin)
 	if ip == nil {
 		return ""
diff --git a/tests/search/main.go b/tests/search/main.go
index 2d1d5675..9acfa7ef 100755
--- a/tests/search/main.go
+++ b/tests/search/main.go
@@ -10,6 +10,7 @@ package main
 import (
 	"bufio"
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -257,12 +258,15 @@ func readImportedByCounts(filename string) (map[string]int, error) {
 		if line == "" || line[0] == '#' {
 			continue
 		}
-		parts := strings.SplitN(line, ", ", 2)
-		c, err := strconv.Atoi(parts[1])
+		path, count, found := internal.Cut(line, ", ")
+		if !found {
+			return nil, errors.New("missing comma")
+		}
+		c, err := strconv.Atoi(count)
 		if err != nil {
 			return nil, err
 		}
-		counts[parts[0]] = c
+		counts[path] = c
 	}
 	if err := scan.Err(); err != nil {
 		return nil, err