system: move out of internal

Signed-off-by: Ophestra <cat@gensokyo.uk>

system/tmpfiles.go

@@ -0,0 +1,76 @@
+package system
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"syscall"
+)
+
+// CopyFile registers an Op that copies from src.
+// A buffer is initialised with size cap and the Op faults if bytes read exceed n.
+func (sys *I) CopyFile(payload *[]byte, src string, cap int, n int64) *I {
+	buf := new(bytes.Buffer)
+	buf.Grow(cap)
+
+	sys.lock.Lock()
+	sys.ops = append(sys.ops, &Tmpfile{payload, src, n, buf})
+	sys.lock.Unlock()
+
+	return sys
+}
+
+type Tmpfile struct {
+	payload *[]byte
+	src     string
+
+	n   int64
+	buf *bytes.Buffer
+}
+
+func (t *Tmpfile) Type() Enablement { return Process }
+func (t *Tmpfile) apply(sys *I) error {
+	sys.println("copying", t)
+
+	if t.payload == nil {
+		// this is a misuse of the API; do not return an error message
+		return errors.New("invalid payload")
+	}
+
+	if b, err := os.Stat(t.src); err != nil {
+		return sys.wrapErrSuffix(err,
+			fmt.Sprintf("cannot stat %q:", t.src))
+	} else {
+		if b.IsDir() {
+			return sys.wrapErrSuffix(syscall.EISDIR,
+				fmt.Sprintf("%q is a directory", t.src))
+		}
+		if s := b.Size(); s > t.n {
+			return sys.wrapErrSuffix(syscall.ENOMEM,
+				fmt.Sprintf("file %q is too long: %d > %d",
+					t.src, s, t.n))
+		}
+	}
+
+	if f, err := os.Open(t.src); err != nil {
+		return sys.wrapErrSuffix(err,
+			fmt.Sprintf("cannot open %q:", t.src))
+	} else if _, err = io.CopyN(t.buf, f, t.n); err != nil {
+		return sys.wrapErrSuffix(err,
+			fmt.Sprintf("cannot read from %q:", t.src))
+	}
+
+	*t.payload = t.buf.Bytes()
+	return nil
+}
+func (t *Tmpfile) revert(*I, *Criteria) error { t.buf.Reset(); return nil }
+
+func (t *Tmpfile) Is(o Op) bool {
+	t0, ok := o.(*Tmpfile)
+	return ok && t0 != nil &&
+		t.src == t0.src && t.n == t0.n
+}
+func (t *Tmpfile) Path() string   { return t.src }
+func (t *Tmpfile) String() string { return fmt.Sprintf("up to %d bytes from %q", t.n, t.src) }