Add a library for running external commands, providing timeouts and test injection.

go/exec/exec.go

+/*
+        A wrapper around the os/exec package that supports timeouts and testing.
+
+        Example usage:
+
+        Simple command with argument:
+        err := Run(&Command{
+                Name: "touch",
+                Args: []string{file},
+        })
+
+        More complicated example:
+        output := bytes.Buffer{}
+        err := Run(&Command{
+                Name: "make",
+                Args: []string{"all"},
+                // Set environment:
+                Env: []string{fmt.Sprintf("GOPATH=%s", projectGoPath)},
+                // Set working directory:
+                Dir: projectDir,
+                // Capture output:
+                CombinedOutput: &output,
+                // Set a timeout:
+                Timeout: 10*time.Minute,
+        })
+
+        Inject a Run function for testing:
+        var actualCommand *Command
+        SetRunForTesting(func(command *Command) error {
+                actualCommand = command
+                return nil
+        })
+        defer SetRunForTesting(DefaultRun)
+        TestCodeCallingRun()
+        expect.Equal(t, "touch", actualCommand.Name)
+        expect.Equal(t, 1, len(actualCommand.Args))
+        expect.Equal(t, file, actualCommand.Args[0])
+*/
+package exec
+
+import (
+        "bytes"
+        "fmt"
+        "io"
+        "os"
+        osexec "os/exec"
+        "reflect"
+        "strings"
+        "time"
+
+        "github.com/skia-dev/glog"
+)
+
+// WriteLog implements the io.Writer interface and writes to the given log function.
+type WriteLog struct {
+        LogFunc func(format string, args ...interface{})
+}
+
+func (wl WriteLog) Write(p []byte) (n int, err error) {
+        wl.LogFunc("%s", string(p))
+        return len(p), nil
+}
+
+var (
+        WriteInfoLog  = WriteLog{LogFunc: glog.Infof}
+        WriteErrorLog = WriteLog{LogFunc: glog.Errorf}
+)
+
+type Command struct {
+        // Name of the command, as passed to osexec.Command. Can be the path to a binary or the
+        // name of a command that osexec.Lookpath can find.
+        Name string
+        // Arguments of the command, not including Name.
+        Args []string
+        // The environment of the process. If nil, the current process's environment is used.
+        Env []string
+        // If Env is non-nil, adds the current process's PATH to Env.
+        InheritPath bool
+        // The working directory of the command. If nil, runs in the current process's current
+        // directory.
+        Dir string
+        // See docs for osexec.Cmd.Stdin.
+        Stdin io.Reader
+        // If true, duplicates stdout of the command to WriteInfoLog.
+        LogStdout bool
+        // Sends the stdout of the command to this Writer, e.g. os.File or bytes.Buffer.
+        Stdout io.Writer
+        // If true, duplicates stderr of the command to WriteErrorLog.
+        LogStderr bool
+        // Sends the stderr of the command to this Writer, e.g. os.File or bytes.Buffer.
+        Stderr io.Writer
+        // Sends the combined stdout and stderr of the command to this Writer, in addition to
+        // Stdout and Stderr. Only one goroutine will write at a time. Note: the Go runtime seems to
+        // combine stdout and stderr into one stream as long as LogStdout and LogStderr are false
+        // and Stdout and Stderr are nil. Otherwise, the stdout and stderr of the command could be
+        // arbitrarily reordered when written to CombinedOutput.
+        CombinedOutput io.Writer
+        // Time limit to wait for the command to finish. (Starts when Wait is called.) No limit if
+        // not specified.
+        Timeout time.Duration
+}
+
+// Divides commandLine at spaces; treats the first token as the program name and the other tokens
+// as arguments. Note: don't expect this function to do anything smart with quotes or escaped
+// spaces.
+func ParseCommand(commandLine string) Command {
+        programAndArgs := strings.Split(commandLine, " ")
+        return Command{Name: programAndArgs[0], Args: programAndArgs[1:]}
+}
+
+// Given io.Writers or nils, return a single writer that writes to all, or nil if no non-nil
+// writers. Also checks for non-nil io.Writer containing a nil value.
+// http://devs.cloudimmunity.com/gotchas-and-common-mistakes-in-go-golang/index.html#nil_in_nil_in_vals
+func squashWriters(writers ...io.Writer) io.Writer {
+        nonNil := []io.Writer{}
+        for _, writer := range writers {
+                if writer != nil && !reflect.ValueOf(writer).IsNil() {
+                        nonNil = append(nonNil, writer)
+                }
+        }
+        switch len(nonNil) {
+        case 0:
+                return nil
+        case 1:
+                return nonNil[0]
+        default:
+                return io.MultiWriter(nonNil...)
+        }
+}
+
+func createCmd(command *Command) *osexec.Cmd {
+        cmd := osexec.Command(command.Name, command.Args...)
+        if len(command.Env) != 0 {
+                cmd.Env = command.Env
+                if command.InheritPath {
+                        cmd.Env = append(cmd.Env, "PATH="+os.Getenv("PATH"))
+                }
+        }
+        cmd.Dir = command.Dir
+        cmd.Stdin = command.Stdin
+        var stdoutLog io.Writer
+        if command.LogStdout {
+                stdoutLog = WriteInfoLog
+        }
+        cmd.Stdout = squashWriters(stdoutLog, command.Stdout, command.CombinedOutput)
+        var stderrLog io.Writer
+        if command.LogStderr {
+                stderrLog = WriteErrorLog
+        }
+        cmd.Stderr = squashWriters(stderrLog, command.Stderr, command.CombinedOutput)
+        return cmd
+}
+
+func start(cmd *osexec.Cmd) error {
+        if len(cmd.Env) == 0 {
+                glog.Infof("Executing %s", strings.Join(cmd.Args, " "))
+        } else {
+                glog.Infof("Executing %s with env %s",
+                        strings.Join(cmd.Args, " "), strings.Join(cmd.Env, " "))
+        }
+        err := cmd.Start()
+        if err != nil {
+                glog.Errorf("Unable to start command %s: %s", strings.Join(cmd.Args, " "), err)
+        }
+        return err
+}
+
+func waitSimple(cmd *osexec.Cmd) error {
+        err := cmd.Wait()
+        if err != nil {
+                glog.Errorf("Command exited with %s: %s", err, strings.Join(cmd.Args, " "))
+        }
+        return err
+}
+
+func wait(command *Command, cmd *osexec.Cmd) error {
+        if command.Timeout == 0 {
+                return waitSimple(cmd)
+        }
+        done := make(chan error)
+        go func() {
+                done <- cmd.Wait()
+        }()
+        select {
+        case <-time.After(command.Timeout):
+                if err := cmd.Process.Kill(); err != nil {
+                        return fmt.Errorf("Failed to kill timed out process: %s", err)
+                }
+                <-done // allow goroutine to exit
+                glog.Errorf("Command killed since it took longer than %f secs", command.Timeout.Seconds())
+                return fmt.Errorf("Command killed since it took longer than %f secs", command.Timeout.Seconds())
+        case err := <-done:
+                if err != nil {
+                        glog.Errorf("Command exited with %s: %s", err, strings.Join(cmd.Args, " "))
+                }
+                return err
+        }
+}
+
+// Default value of Run.
+func DefaultRun(command *Command) error {
+        cmd := createCmd(command)
+        if err := start(cmd); err != nil {
+                return err
+        }
+        return wait(command, cmd)
+}
+
+// Run runs command and waits for it to finish. If any failure, returns non-nil. If a timeout was
+// specified, returns an error once the command has exceeded that timeout.
+var Run func(command *Command) error = DefaultRun
+
+// SetRunForTesting replaces the Run function with a test version so that commands don't actually
+// run.
+func SetRunForTesting(testRun func(command *Command) error) {
+        Run = testRun
+}
+
+// Run method is convenience for Run(command).
+func (command *Command) Run() error {
+        return Run(command)
+}
+
+// RunSimple executes the given command line string; the command being run is expected to not care
+// what its current working directory is. Returns the combined stdout and stderr. May also return
+// an error if the command exited with a non-zero status or there is any other error.
+func RunSimple(commandLine string) (string, error) {
+        command := ParseCommand(commandLine)
+        output := bytes.Buffer{}
+        command.CombinedOutput = &output
+        err := Run(&command)
+        result := string(output.Bytes())
+        glog.Infof("StdOut + StdErr: %s\n", result)
+        return result, err
+}