Implement deno.readlink() (#797)

7 files changed, 133 insertions, 1 deletions

diff --git a/BUILD.gn b/BUILD.gn
index 50346dfed..dd995c00f 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -83,6 +83,7 @@ ts_sources = [
   "js/read_file.ts",
   "js/remove.ts",
   "js/rename.ts",
+  "js/read_link.ts",
   "js/stat.ts",
   "js/symlink.ts",
   "js/text_encoding.ts",
diff --git a/js/deno.ts b/js/deno.ts
index dd6539163..3bbda69e8 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -5,8 +5,9 @@ export { env, exit } from "./os";
 export { mkdirSync, mkdir } from "./mkdir";
 export { makeTempDirSync, makeTempDir } from "./make_temp_dir";
 export { removeSync, remove, removeAllSync, removeAll } from "./remove";
-export { readFileSync, readFile } from "./read_file";
 export { renameSync, rename } from "./rename";
+export { readFileSync, readFile } from "./read_file";
+export { readlinkSync, readlink } from "./read_link";
 export { FileInfo, statSync, lstatSync, stat, lstat } from "./stat";
 export { symlinkSync, symlink } from "./symlink";
 export { writeFileSync, writeFile } from "./write_file";
diff --git a/js/read_link.ts b/js/read_link.ts
new file mode 100644
index 000000000..6bd613389
--- /dev/null
+++ b/js/read_link.ts
@@ -0,0 +1,46 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import * as fbs from "gen/msg_generated";
+import { flatbuffers } from "flatbuffers";
+import { assert } from "./util";
+import * as dispatch from "./dispatch";
+
+/**
+ * Returns the destination of the named symbolic link synchronously.
+ *
+ *     import { readlinkSync } from "deno";
+ *     const targetPath = readlinkSync("symlink/path");
+ */
+export function readlinkSync(name: string): string {
+  return res(dispatch.sendSync(...req(name)));
+}
+
+/**
+ * Returns the destination of the named symbolic link.
+ *
+ *     import { readlink } from "deno";
+ *     const targetPath = await readlink("symlink/path");
+ */
+export async function readlink(name: string): Promise<string> {
+  return res(await dispatch.sendAsync(...req(name)));
+}
+
+function req(
+  name: string
+): [flatbuffers.Builder, fbs.Any, flatbuffers.Offset] {
+  const builder = new flatbuffers.Builder();
+  const name_ = builder.createString(name);
+  fbs.Readlink.startReadlink(builder);
+  fbs.Readlink.addName(builder, name_);
+  const msg = fbs.Readlink.endReadlink(builder);
+  return [builder, fbs.Any.Readlink, msg];
+}
+
+function res(baseRes: null | fbs.Base): string {
+  assert(baseRes !== null);
+  assert(fbs.Any.ReadlinkRes === baseRes!.msgType());
+  const res = new fbs.ReadlinkRes();
+  assert(baseRes!.msg(res) !== null);
+  const path = res.path();
+  assert(path !== null);
+  return path!;
+}
diff --git a/js/read_link_test.ts b/js/read_link_test.ts
new file mode 100644
index 000000000..2df6b30d0
--- /dev/null
+++ b/js/read_link_test.ts
@@ -0,0 +1,44 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import { test, testPerm, assert, assertEqual } from "./test_util.ts";
+import * as deno from "deno";
+
+testPerm({ write: true }, function readlinkSyncSuccess() {
+  const testDir = deno.makeTempDirSync() + "/test-readlink-sync";
+  const target = testDir + "/target";
+  const symlink = testDir + "/symln";
+  deno.mkdirSync(target);
+  // TODO Add test for Windows once symlink is implemented for Windows.
+  // See https://github.com/denoland/deno/issues/815.
+  if (deno.platform !== "win32") {
+    deno.symlinkSync(target, symlink);
+    const targetPath = deno.readlinkSync(symlink);
+    assertEqual(targetPath, target);
+  }
+});
+
+test(function readlinkSyncNotFound() {
+  let caughtError = false;
+  let data;
+  try {
+    data = deno.readlinkSync("bad_filename");
+  } catch (e) {
+    caughtError = true;
+    assertEqual(e.kind, deno.ErrorKind.NotFound);
+  }
+  assert(caughtError);
+  assertEqual(data, undefined);
+});
+
+testPerm({ write: true }, async function readlinkSuccess() {
+  const testDir = deno.makeTempDirSync() + "/test-readlink";
+  const target = testDir + "/target";
+  const symlink = testDir + "/symln";
+  deno.mkdirSync(target);
+  // TODO Add test for Windows once symlink is implemented for Windows.
+  // See https://github.com/denoland/deno/issues/815.
+  if (deno.platform !== "win32") {
+    deno.symlinkSync(target, symlink);
+    const targetPath = await deno.readlink(symlink);
+    assertEqual(targetPath, target);
+  }
+});
diff --git a/js/unit_tests.ts b/js/unit_tests.ts
index ae9db2a28..578a65c6d 100644
--- a/js/unit_tests.ts
+++ b/js/unit_tests.ts
@@ -11,6 +11,7 @@ import "./mkdir_test.ts";
 import "./make_temp_dir_test.ts";
 import "./stat_test.ts";
 import "./rename_test.ts";
+import "./read_link_test.ts";
 import "./blob_test.ts";
 import "./timers_test.ts";
 import "./symlink_test.ts";
diff --git a/src/handlers.rs b/src/handlers.rs
index eef091174..964baabf8 100644
--- a/src/handlers.rs
+++ b/src/handlers.rs
@@ -56,6 +56,7 @@ pub extern "C" fn msg_from_js(i: *const isolate, buf: deno_buf) {
     msg::Any::Remove => handle_remove,
     msg::Any::ReadFile => handle_read_file,
     msg::Any::Rename => handle_rename,
+    msg::Any::Readlink => handle_read_link,
     msg::Any::Symlink => handle_symlink,
     msg::Any::SetEnv => handle_set_env,
     msg::Any::Stat => handle_stat,
@@ -702,3 +703,31 @@ fn handle_symlink(i: *const isolate, base: &msg::Base) -> Box<Op> {
     }()))
   }
 }
+
+fn handle_read_link(_i: *const isolate, base: &msg::Base) -> Box<Op> {
+  let msg = base.msg_as_readlink().unwrap();
+  let cmd_id = base.cmd_id();
+  let name = String::from(msg.name().unwrap());
+  Box::new(futures::future::result(|| -> OpResult {
+    debug!("handle_read_link {}", name);
+    let path = fs::read_link(Path::new(&name))?;
+    let builder = &mut FlatBufferBuilder::new();
+    let path_off = builder.create_string(path.to_str().unwrap());
+    let msg = msg::ReadlinkRes::create(
+      builder,
+      &msg::ReadlinkResArgs {
+        path: Some(path_off),
+        ..Default::default()
+      },
+    );
+    Ok(serialize_response(
+      cmd_id,
+      builder,
+      msg::BaseArgs {
+        msg: Some(msg.as_union_value()),
+        msg_type: msg::Any::ReadlinkRes,
+        ..Default::default()
+      },
+    ))
+  }()))
+}
diff --git a/src/msg.fbs b/src/msg.fbs
index ee3930729..6358668b7 100644
--- a/src/msg.fbs
+++ b/src/msg.fbs
@@ -20,6 +20,8 @@ union Any {
   ReadFileRes,
   WriteFile,
   Rename,
+  Readlink,
+  ReadlinkRes,
   Symlink,
   Stat,
   StatRes,
@@ -202,6 +204,14 @@ table Rename {
   newpath: string;
 }
 
+table Readlink {
+  name: string;
+}
+
+table ReadlinkRes {
+  path: string;
+}
+
 table Symlink {
   oldname: string;
   newname: string;