Add getExecOutput function (#814)

* Add getExecOutput function

* Add tests for exec output

* Modify tests to not rely on buffer size, but only test larger output

* Handle split multi-byte characters + PR feedback

* Fix tests

* Lint

* Update how split byte are sent for tests

packages/exec/src/exec.ts

@@ -1,7 +1,8 @@
-import {ExecOptions} from './interfaces'
+import {StringDecoder} from 'string_decoder'
+import {ExecOptions, ExecOutput, ExecListeners} from './interfaces'
 import * as tr from './toolrunner'
 
-export {ExecOptions}
+export {ExecOptions, ExecOutput, ExecListeners}
 
 /**
  * Exec a command.
@@ -28,3 +29,63 @@ export async function exec(
   const runner: tr.ToolRunner = new tr.ToolRunner(toolPath, args, options)
   return runner.exec()
 }
+
+/**
+ * Exec a command and get the output.
+ * Output will be streamed to the live console.
+ * Returns promise with the exit code and collected stdout and stderr
+ *
+ * @param     commandLine           command to execute (can include additional args). Must be correctly escaped.
+ * @param     args                  optional arguments for tool. Escaping is handled by the lib.
+ * @param     options               optional exec options.  See ExecOptions
+ * @returns   Promise<ExecOutput>   exit code, stdout, and stderr
+ */
+
+export async function getExecOutput(
+  commandLine: string,
+  args?: string[],
+  options?: ExecOptions
+): Promise<ExecOutput> {
+  let stdout = ''
+  let stderr = ''
+
+  //Using string decoder covers the case where a mult-byte character is split
+  const stdoutDecoder = new StringDecoder('utf8')
+  const stderrDecoder = new StringDecoder('utf8')
+
+  const originalStdoutListener = options?.listeners?.stdout
+  const originalStdErrListener = options?.listeners?.stderr
+
+  const stdErrListener = (data: Buffer): void => {
+    stderr += stderrDecoder.write(data)
+    if (originalStdErrListener) {
+      originalStdErrListener(data)
+    }
+  }
+
+  const stdOutListener = (data: Buffer): void => {
+    stdout += stdoutDecoder.write(data)
+    if (originalStdoutListener) {
+      originalStdoutListener(data)
+    }
+  }
+
+  const listeners: ExecListeners = {
+    ...options?.listeners,
+    stdout: stdOutListener,
+    stderr: stdErrListener
+  }
+
+  const exitCode = await exec(commandLine, args, {...options, listeners})
+
+  //flush any remaining characters
+  stdout += stdoutDecoder.end()
+  stderr += stderrDecoder.end()
+
+  //return undefined for stdout/stderr if they are empty
+  return {
+    exitCode,
+    stdout,
+    stderr
+  }
+}