perf(detect-libc): faster musl check by looking for ldd file

lib/detect-libc.js

@@ -5,7 +5,9 @@
 
 const childProcess = require('child_process');
 const { isLinux, getReport } = require('./process');
+const { LDD_PATH, readFile, readFileSync } = require('./filesystem');
 
+let cachedFilesystem;
 const command = 'getconf GNU_LIBC_VERSION 2>&1 || true; ldd --version 2>&1 || true';
 let commandOut = '';
 
@@ -72,14 +74,41 @@ const familyFromCommand = (out) => {
   return null;
 };
 
+const familyFromFilesystem = async () => {
+  if (cachedFilesystem !== undefined) {
+    return cachedFilesystem;
+  }
+  cachedFilesystem = null;
+  try {
+    cachedFilesystem = await readFile(LDD_PATH)
+      .then(content => content.includes(MUSL))
+      .then(isMusl => isMusl ? MUSL : GLIBC);
+  } catch (e) {}
+  return cachedFilesystem;
+};
+
+const familyFromFilesystemSync = () => {
+  if (cachedFilesystem !== undefined) {
+    return cachedFilesystem;
+  }
+  cachedFilesystem = null;
+  try {
+    cachedFilesystem = readFileSync(LDD_PATH).includes(MUSL) ? MUSL : GLIBC;
+  } catch (e) {}
+  return cachedFilesystem;
+};
+
 /**
  * Resolves with the libc family when it can be determined, `null` otherwise.
  * @returns {Promise<?string>}
  */
 const family = async () => {
   let family = null;
   if (isLinux()) {
-    family = familyFromReport();
+    family = await familyFromFilesystem();
+    if (!family) {
+      family = familyFromReport();
+    }
     if (!family) {
       const out = await safeCommand();
       family = familyFromCommand(out);
@@ -95,7 +124,10 @@ const family = async () => {
 const familySync = () => {
   let family = null;
   if (isLinux()) {
-    family = familyFromReport();
+    family = familyFromFilesystemSync();
+    if (!family) {
+      family = familyFromReport();
+    }
     if (!family) {
       const out = safeCommandSync();
       family = familyFromCommand(out);

lib/filesystem.js

@@ -0,0 +1,36 @@
+const fs = require('fs');
+
+/**
+ * The path where we can find the ldd
+ */
+const LDD_PATH = '/usr/bin/ldd';
+
+/**
+ * Read the content of a file synchronous
+ *
+ * @param {string} path
+ * @returns {string}
+ */
+const readFileSync = path => fs.readFileSync(path, 'utf-8');
+
+/**
+ * Read the content of a file
+ *
+ * @param {string} path
+ * @returns {Promise<string>}
+ */
+const readFile = path => new Promise((resolve, reject) => {
+  fs.readFile(path, 'utf-8', (err, data) => {
+    if (err) {
+      reject(err);
+    } else {
+      resolve(data);
+    }
+  });
+});
+
+module.exports = {
+  LDD_PATH,
+  readFileSync,
+  readFile
+};

test/fixtexture-file.txt

@@ -0,0 +1 @@
+1