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 cachedFamily;
 const command = 'getconf GNU_LIBC_VERSION 2>&1 || true; ldd --version 2>&1 || true';
 let commandOut = '';
 
@@ -77,31 +79,61 @@ const familyFromCommand = (out) => {
  * @returns {Promise<?string>}
  */
 const family = async () => {
-  let family = null;
+  if (cachedFamily !== undefined) {
+    return cachedFamily;
+  }
+  cachedFamily = null;
   if (isLinux()) {
-    family = familyFromReport();
-    if (!family) {
-      const out = await safeCommand();
-      family = familyFromCommand(out);
+    try {
+      cachedFamily = await readFile(LDD_PATH)
+        .then(content => content.includes(MUSL))
+        .then(isMusl => isMusl ? MUSL : GLIBC);
+    } catch (e) {
+      // if permission model block access, we fallback to the old version
+      if (e.code === 'ERR_ACCESS_DENIED') {
+        cachedFamily = familyFromReport();
+        if (!cachedFamily) {
+          const out = await safeCommand();
+          cachedFamily = familyFromCommand(out);
+        }
+      } else {
+        // If ldd don't exist, accords https://wiki.musl-libc.org/faq.html we can assume
+        // that the system is musl because ldd is always present on non-musl linux.
+        cachedFamily = MUSL;
+      }
     }
   }
-  return family;
+  return cachedFamily;
 };
 
 /**
  * Returns the libc family when it can be determined, `null` otherwise.
  * @returns {?string}
  */
 const familySync = () => {
-  let family = null;
+  if (cachedFamily !== undefined) {
+    return cachedFamily;
+  }
+  cachedFamily = null;
   if (isLinux()) {
-    family = familyFromReport();
-    if (!family) {
-      const out = safeCommandSync();
-      family = familyFromCommand(out);
+    try {
+      cachedFamily = readFileSync(LDD_PATH).includes(MUSL) ? MUSL : GLIBC;
+    } catch (e) {
+      // if permission model block access, we fallback to the old version
+      if (e.code === 'ERR_ACCESS_DENIED') {
+        cachedFamily = familyFromReport();
+        if (!cachedFamily) {
+          const out = safeCommandSync();
+          cachedFamily = familyFromCommand(out);
+        }
+      } else {
+        // If ldd don't exist, accords https://wiki.musl-libc.org/faq.html we can assume
+        // that the system is musl because ldd is always present on non-musl linux.
+        cachedFamily = MUSL;
+      }
     }
   }
-  return family;
+  return cachedFamily;
 };
 
 /**

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