common/fdlimit: Move fdlimit files to separate package (#15850)

* common/fdlimit: Move fdlimit files to separate package

When go-ethereum is used as a library the calling program need to set
the FD limit.

This commit extract fdlimit files to a separate package so it can be
used outside of go-ethereum.

* common/fdlimit: Remove FdLimit from functions signature

* common/fdlimit: Rename fdlimit functions

4 files changed, 216 insertions, 0 deletions

diff --git a/common/fdlimit/fdlimit_freebsd.go b/common/fdlimit/fdlimit_freebsd.go
new file mode 100644
index 000000000..25caaafe2
--- /dev/null
+++ b/common/fdlimit/fdlimit_freebsd.go
@@ -0,0 +1,64 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+// +build freebsd
+
+package fdlimit
+
+import "syscall"
+
+// This file is largely identical to fdlimit_unix.go,
+// but Rlimit fields have type int64 on FreeBSD so it needs
+// an extra conversion.
+
+// Raise tries to maximize the file descriptor allowance of this process
+// to the maximum hard-limit allowed by the OS.
+func Raise(max uint64) error {
+	// Get the current limit
+	var limit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return err
+	}
+	// Try to update the limit to the max allowance
+	limit.Cur = limit.Max
+	if limit.Cur > int64(max) {
+		limit.Cur = int64(max)
+	}
+	if err := syscall.Setrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Current retrieves the number of file descriptors allowed to be opened by this
+// process.
+func Current() (int, error) {
+	var limit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return 0, err
+	}
+	return int(limit.Cur), nil
+}
+
+// Maximum retrieves the maximum number of file descriptors this process is
+// allowed to request for itself.
+func Maximum() (int, error) {
+	var limit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return 0, err
+	}
+	return int(limit.Max), nil
+}
diff --git a/common/fdlimit/fdlimit_test.go b/common/fdlimit/fdlimit_test.go
new file mode 100644
index 000000000..05e9f0b65
--- /dev/null
+++ b/common/fdlimit/fdlimit_test.go
@@ -0,0 +1,45 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package fdlimit
+
+import (
+	"fmt"
+	"testing"
+)
+
+// TestFileDescriptorLimits simply tests whether the file descriptor allowance
+// per this process can be retrieved.
+func TestFileDescriptorLimits(t *testing.T) {
+	target := 4096
+	hardlimit, err := Maximum()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hardlimit < target {
+		t.Skip(fmt.Sprintf("system limit is less than desired test target: %d < %d", hardlimit, target))
+	}
+
+	if limit, err := Current(); err != nil || limit <= 0 {
+		t.Fatalf("failed to retrieve file descriptor limit (%d): %v", limit, err)
+	}
+	if err := Raise(uint64(target)); err != nil {
+		t.Fatalf("failed to raise file allowance")
+	}
+	if limit, err := Current(); err != nil || limit < target {
+		t.Fatalf("failed to retrieve raised descriptor limit (have %v, want %v): %v", limit, target, err)
+	}
+}
diff --git a/common/fdlimit/fdlimit_unix.go b/common/fdlimit/fdlimit_unix.go
new file mode 100644
index 000000000..27c7e783f
--- /dev/null
+++ b/common/fdlimit/fdlimit_unix.go
@@ -0,0 +1,60 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+// +build linux darwin netbsd openbsd solaris
+
+package fdlimit
+
+import "syscall"
+
+// Raise tries to maximize the file descriptor allowance of this process
+// to the maximum hard-limit allowed by the OS.
+func Raise(max uint64) error {
+	// Get the current limit
+	var limit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return err
+	}
+	// Try to update the limit to the max allowance
+	limit.Cur = limit.Max
+	if limit.Cur > max {
+		limit.Cur = max
+	}
+	if err := syscall.Setrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Current retrieves the number of file descriptors allowed to be opened by this
+// process.
+func Current() (int, error) {
+	var limit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return 0, err
+	}
+	return int(limit.Cur), nil
+}
+
+// Maximum retrieves the maximum number of file descriptors this process is
+// allowed to request for itself.
+func Maximum() (int, error) {
+	var limit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &limit); err != nil {
+		return 0, err
+	}
+	return int(limit.Max), nil
+}
diff --git a/common/fdlimit/fdlimit_windows.go b/common/fdlimit/fdlimit_windows.go
new file mode 100644
index 000000000..efcd3220e
--- /dev/null
+++ b/common/fdlimit/fdlimit_windows.go
@@ -0,0 +1,47 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package fdlimit
+
+import "errors"
+
+// Raise tries to maximize the file descriptor allowance of this process
+// to the maximum hard-limit allowed by the OS.
+func Raise(max uint64) error {
+	// This method is NOP by design:
+	//  * Linux/Darwin counterparts need to manually increase per process limits
+	//  * On Windows Go uses the CreateFile API, which is limited to 16K files, non
+	//    changeable from within a running process
+	// This way we can always "request" raising the limits, which will either have
+	// or not have effect based on the platform we're running on.
+	if max > 16384 {
+		return errors.New("file descriptor limit (16384) reached")
+	}
+	return nil
+}
+
+// Current retrieves the number of file descriptors allowed to be opened by this
+// process.
+func Current() (int, error) {
+	// Please see Raise for the reason why we use hard coded 16K as the limit
+	return 16384, nil
+}
+
+// Maximum retrieves the maximum number of file descriptors this process is
+// allowed to request for itself.
+func Maximum() (int, error) {
+	return Current()
+}