cmd/preprofile: clean up error handling

This CL adjusts error handling to be a bit more idiomatic. The
processing function returns errors, leaving main to log and exit on
error.

This CL contains no functional changes.

For #58102.

Change-Id: I9074127cc675e177d046474b7f01fbc37d0bd4c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/569335
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/cmd/preprofile/main.go b/src/cmd/preprofile/main.go
index 806f25fee8b6c6592a65221ca30ebb7dc62e50a1..ec42ceea22917a400c33b30584c1d0047bd8b9c6 100644 (file)
--- a/src/cmd/preprofile/main.go
+++ b/src/cmd/preprofile/main.go
@@ -6,7 +6,7 @@
 //
 // Usage:
 //
-//     go tool preprofile [-v] [-o output] [-i (pprof)input]
+//     go tool preprofile [-v] [-o output] -i input
 //
 //
 
@@ -32,45 +32,50 @@ import (
 // in current Go Compiler.
 // The format of the pre-processed output is as follows.
 //
-//     Header
-//     caller_name
+//      Header
+//      caller_name
 //      callee_name
 //      "call site offset" "call edge weight"
 //      ...
-//     caller_name
+//      caller_name
 //      callee_name
 //      "call site offset" "call edge weight"
 
 func usage() {
-       fmt.Fprintf(os.Stderr, "MUST have (pprof) input file \n")
-       fmt.Fprintf(os.Stderr, "usage: go tool preprofile [-v] [-o output] [-i (pprof)input] \n\n")
+       fmt.Fprintf(os.Stderr, "usage: go tool preprofile [-v] [-o output] -i input\n\n")
        flag.PrintDefaults()
        os.Exit(2)
 }
 
+var (
+       output  = flag.String("o", "", "output file path")
+       input   = flag.String("i", "", "input pprof file path")
+       verbose = flag.Bool("v", false, "enable verbose logging")
+)
+
 type NodeMapKey struct {
        CallerName     string
        CalleeName     string
        CallSiteOffset int // Line offset from function start line.
 }
 
-func readPprofFile(profileFile string, outputFile string, verbose bool) bool {
+func preprocess(profileFile string, outputFile string, verbose bool) error {
        // open the pprof profile file
        f, err := os.Open(profileFile)
        if err != nil {
-               log.Fatal("failed to open file " + profileFile)
-               return false
+               return fmt.Errorf("error opening profile: %w", err)
        }
        defer f.Close()
        p, err := profile.Parse(f)
        if err != nil {
-               log.Fatal("failed to Parse profile file.")
-               return false
+               return fmt.Errorf("error parsing profile: %w", err)
        }
 
        if len(p.Sample) == 0 {
                // We accept empty profiles, but there is nothing to do.
-               return false
+               //
+               // TODO(prattmic): write an "empty" preprocessed file.
+               return nil
        }
 
        valueIndex := -1
@@ -85,8 +90,7 @@ func readPprofFile(profileFile string, outputFile string, verbose bool) bool {
        }
 
        if valueIndex == -1 {
-               log.Fatal("failed to find CPU samples count or CPU nanoseconds value-types in profile.")
-               return false
+               return fmt.Errorf("failed to find CPU samples count or CPU nanoseconds value-types in profile.")
        }
 
        // The processing here is equivalent to cmd/compile/internal/pgo.createNamedEdgeMap.
@@ -131,7 +135,7 @@ func readPprofFile(profileFile string, outputFile string, verbose bool) bool {
                dirPath := filepath.Dir(outputFile)
                _, err := os.Stat(dirPath)
                if err != nil {
-                       log.Fatal("Directory does not exist: ", dirPath)
+                       return fmt.Errorf("directory does not exist: %s", dirPath)
                }
                base := filepath.Base(outputFile)
                outputFile = filepath.Join(dirPath, base)
@@ -139,8 +143,7 @@ func readPprofFile(profileFile string, outputFile string, verbose bool) bool {
                // write out NodeMap to a file
                fNodeMap, err = os.Create(outputFile)
                if err != nil {
-                       log.Fatal("Error creating output file:", err)
-                       return false
+                       return fmt.Errorf("Error creating output file: %w", err)
                }
 
                defer fNodeMap.Close() // Close the file when done writing
@@ -162,17 +165,9 @@ func readPprofFile(profileFile string, outputFile string, verbose bool) bool {
                count += 1
        }
 
-       if TotalEdgeWeight == 0 {
-               return false
-       }
-
-       return true
+       return nil
 }
 
-var dumpCode = flag.String("o", "", "dump output file ")
-var input = flag.String("i", "", "input pprof file ")
-var verbose = flag.Bool("v", false, "verbose log")
-
 func main() {
        log.SetFlags(0)
        log.SetPrefix("preprofile: ")
@@ -180,8 +175,11 @@ func main() {
        flag.Usage = usage
        flag.Parse()
        if *input == "" {
+               log.Print("Input pprof path required (-i)")
                usage()
-       } else {
-               readPprofFile(*input, *dumpCode, *verbose)
+       }
+
+       if err := preprocess(*input, *output, *verbose); err != nil {
+               log.Fatal(err)
        }
 }