os += ReadFile

Add convenient utility to read whole file and return its content
similarly to Go. The code is taken from wendelin.core:

https://lab.nexedi.com/nexedi/wendelin.core/blob/wendelin.core-2.0.alpha1-18-g38dde766/wcfs/client/wcfs_misc.cpp#L246-281

golang/os.cpp

@@ -49,6 +49,7 @@ namespace sys = golang::internal::syscall;
 using std::tuple;
 using std::make_tuple;
 using std::tie;
+using std::vector;
 
 // golang::os::
 namespace golang {
@@ -211,6 +212,38 @@ error _File::Stat(struct stat *st) {
 }
 
 
+tuple<string, error> ReadFile(const string& path) {
+    // errctx is ok as returned by all calls.
+    File  f;
+    error err;
+
+    tie(f, err) = Open(path);
+    if (err != nil)
+        return make_tuple("", err);
+
+    string data;
+    vector<char> buf(4096);
+
+    while (1) {
+        int n;
+        tie(n, err) = f->Read(&buf[0], buf.size());
+        data.append(&buf[0], n);
+        if (err != nil) {
+            if (err == io::EOF_)
+                err = nil;
+            break;
+        }
+    }
+
+    error err2 = f->Close();
+    if (err == nil)
+        err = err2;
+    if (err != nil)
+        data = "";
+    return make_tuple(data, err);
+}
+
+
 // pipe
 
 tuple<File, File, error> Pipe() {

golang/os.h

@@ -26,6 +26,7 @@
 //  - `Open` opens file @path.
 //  - `Pipe` creates new pipe.
 //  - `NewFile` wraps OS-level file-descriptor into File.
+//  - `ReadFile` returns content of file @path.
 //  - `Signal` represents OS-level signal.
 //
 // See also https://golang.org/pkg/os for Go os package documentation.
@@ -105,6 +106,9 @@ LIBGOLANG_API std::tuple<File, error> NewFile(int sysfd, const string& name);
 // Pipe creates connected pair of files.
 LIBGOLANG_API std::tuple</*r*/File, /*w*/File, error> Pipe();
 
+// ReadFile returns content of file @path.
+LIBGOLANG_API std::tuple<string, error> ReadFile(const string& path);
+
 
 // Signal represents an OS signal.
 //

golang/os_test.cpp

@@ -87,6 +87,12 @@ void __test_os_fileio_cpp(const string& tmpd) {
 
     err = f->Close();
     ASSERT(err == nil);
+
+    // readfile
+    string data;
+    tie(data, err) = os::ReadFile(tpath);
+    ASSERT(err == nil);
+    ASSERT_EQ(data, "hello world\n");
 }
 
 void _test_os_pipe_cpp() {