Fix deadlock when the builder outputs a lot of data over stdio. Ref: g…

…olang/go#16787

Also improve developer experience by outputting logs incrementally.

Includes a small tweak in detect.ts to allow referencing the workflow in
this repository by commit.

Signed-off-by: Juliette Pretot <julsh@google.com>
Co-authored-by: Jason LeBrun <jibbl@google.com>

internal/builders/docker/pkg/builder.go

@@ -23,6 +23,7 @@ package pkg
 // Docker image.
 
 import (
+	"bufio"
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
@@ -36,6 +37,7 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
+	"sync"
 
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	slsa1 "github.com/in-toto/in-toto-golang/in_toto/slsa_provenance/v1"
@@ -476,34 +478,74 @@ func (c *GitClient) checkoutGitCommit() error {
 	return nil
 }
 
+type tempFileResult struct {
+	File *os.File
+	Err  error
+}
+
+// A helper function used by saveToTempFile to process one individual file.
+func saveOneTempFile(verbose bool, reader io.Reader, fileChannel chan tempFileResult, printChannel chan string) {
+	var allBytes []byte
+	scanner := bufio.NewScanner(reader)
+	for scanner.Scan() {
+		bytes := scanner.Bytes()
+		allBytes = append(allBytes, bytes...)
+		allBytes = append(allBytes, '\n')
+
+		if verbose {
+			printChannel <- string(bytes)
+		}
+	}
+
+	tmpfile, err := os.CreateTemp("", "log-*.txt")
+	if err != nil {
+		fileChannel <- tempFileResult{Err: err}
+		return
+	}
+	if _, err := tmpfile.Write(allBytes); err != nil {
+		tmpfile.Close()
+		fileChannel <- tempFileResult{Err: fmt.Errorf("couldn't write bytes to tempfile: %v", err)}
+	}
+
+	fileChannel <- tempFileResult{File: tmpfile}
+}
+
 // saveToTempFile creates a tempfile in `/tmp` and writes the content of the
 // given readers to that file.
+// It processes all provided readers concurrently.
 func saveToTempFile(verbose bool, readers ...io.Reader) ([]string, error) {
-	var files []string
+	if verbose {
+		fmt.Print("\n\n>>>>>>>>>>>>>> output from command <<<<<<<<<<<<<<\n")
+	}
+	var wg sync.WaitGroup
+	var fileChannel = make(chan tempFileResult, len(readers))
+	var printChannel = make(chan string)
+
 	for _, reader := range readers {
-		bytes, err := io.ReadAll(reader)
-		if err != nil {
-			return files, err
-		}
+		wg.Add(1)
+		go func(reader io.Reader) {
+			defer wg.Done()
+			saveOneTempFile(verbose, reader, fileChannel, printChannel)
+		}(reader)
+	}
 
-		if verbose {
-			if len(bytes) > 0 {
-				fmt.Print("\n\n>>>>>>>>>>>>>> output from command <<<<<<<<<<<<<<\n")
-				fmt.Printf("%s", bytes)
-				fmt.Print("=================================================\n\n\n")
-			}
-		}
+	// Close the channel once all goroutines have finished.
+	go func() {
+		wg.Wait()
+		close(printChannel)
+		close(fileChannel)
+	}()
 
-		tmpfile, err := os.CreateTemp("", "log-*.txt")
-		if err != nil {
-			return files, fmt.Errorf("couldn't create tempfile: %v", err)
-		}
+	for line := range printChannel {
+		fmt.Println(line)
+	}
 
-		if _, err := tmpfile.Write(bytes); err != nil {
-			tmpfile.Close()
-			return files, fmt.Errorf("couldn't write bytes to tempfile: %v", err)
+	var files []string
+	for result := range fileChannel {
+		if result.Err != nil {
+			return nil, result.Err
 		}
-		files = append(files, tmpfile.Name())
+		files = append(files, result.File.Name())
 	}
 
 	return files, nil