sweet: add helper to write pprof files

Change-Id: I047004d6f79048b1c6ef244e4f273e6ca0b25f56
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/600056
Auto-Submit: Austin Clements <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

sweet/cmd/sweet/run.go

@@ -466,14 +466,8 @@ func mergeCPUProfiles(dir string) (string, error) {
 	}
 
 	out := filepath.Join(dir, "merged.cpu")
-	f, err := os.Create(out)
-	if err != nil {
-		return "", fmt.Errorf("error creating file: %w", err)
-	}
-	defer f.Close()
-
-	if err := p.Write(f); err != nil {
-		return "", fmt.Errorf("error writing merged profile: %w", err)
+	if err := sprofile.WritePprof(out, p); err != nil {
+		return "", err
 	}
 
 	return out, nil

sweet/common/profile/profile.go

@@ -6,6 +6,7 @@
 package profile
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 
@@ -21,6 +22,24 @@ func ReadPprof(filename string) (*profile.Profile, error) {
 	return profile.Parse(f)
 }
 
+func WritePprof(filename string, p *profile.Profile) error {
+	f, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	err = p.Write(f)
+	if err == nil {
+		err = f.Close()
+	}
+	if err != nil {
+		return fmt.Errorf("error writing profile %s: %s", filename, err)
+	}
+
+	return nil
+}
+
 // ReadDir reads all pprof profiles in dir whose name matches match(name).
 func ReadDirPprof(dir string, match func(string) bool) ([]*profile.Profile, error) {
 	entries, err := os.ReadDir(dir)