split plan 9 codes to internal/procstatus

make it testable on other platforms.

internal/procstatus/procstatus.go

@@ -0,0 +1,63 @@
+/*
+Package procstatus provides methods to access contents of /proc/{pid}/status
+for Plan 9.
+*/
+package procstatus
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// GetRSS retrives resident set size (RSS) for a process.
+func GetRSS(pid int) (uint, error) {
+	name := fmt.Sprintf("/proc/%d/status", pid)
+	r, err := os.Open(name)
+	if err != nil {
+		return 0, err
+	}
+	defer r.Close()
+	return readMemSize(r)
+}
+
+// readMemSize parses and extracts "amount of memory" (10th entry) from
+// /proc/{pid}/status.
+func readMemSize(r io.Reader) (uint, error) {
+	/*
+	 * proc/<n>/status contains process's status separated by a space.
+	 * 1. [27]the process name
+	 * 2. [27]the user name
+	 * 3. [11]the process status
+	 * 4. [11]the time current process has spent in user mode (ms)
+	 * 5. [11]the time current process has spent in system calls (ms)
+	 * 6. [11]the time current process has spent in real elapsed time (ms)
+	 * 7. [11]the time children and descendants's; user mode (ms)
+	 * 8. [11]the time children and descendants's; system calls (ms)
+	 * 9. [11]the time children and descendants's; real elapsed time (ms)
+	 * 10. [11]the amount of memory (kb)
+	 * 11. [11]the base scheduling priority
+	 * 12. [11]the current scheduling priority
+	 */
+	const nAllFields = (27+1)*2 + (11+1)*10 // +1: a space
+	const xAmountOfMemory = (27+1)*2 + (11+1)*7
+
+	buf := make([]byte, nAllFields)
+	n, err := r.Read(buf)
+	if err != nil {
+		return 0, fmt.Errorf("failed to read /proc/{pid}/status: %w", err)
+	}
+	if n != len(buf) {
+		return 0, errors.New("insufficient process status")
+	}
+	p := xAmountOfMemory
+	s := strings.TrimSpace(string(buf[p : p+11]))
+	msize, err := strconv.ParseUint(s, 10, 32)
+	if err != nil {
+		return 0, fmt.Errorf("failed to parse 10th field: %w", err)
+	}
+	return uint(msize) * 1024, nil
+}

phymem_plan9_test.go → internal/procstatus/procstatus_test.go

@@ -1,4 +1,4 @@
-package phymem
+package procstatus
 
 import (
 	"fmt"
@@ -12,10 +12,10 @@ func TestReadMemSize(t *testing.T) {
 	r := strings.NewReader(s)
 	msize, err := readMemSize(r)
 	if err != nil {
-		t.Fatal("readMemSize:", err)
+		t.Fatal(err)
 	}
 	const want = 236 * 1024
 	if msize != want {
-		t.Errorf("readMemSize(%q) = %d; want %d", s, msize, want)
+		t.Errorf("readMemSize failed: want=%d got=%d", want, msize)
 	}
 }

phymem_plan9.go

@@ -12,6 +12,7 @@ import (
 // for test.
 const providedCurrent = true
 
+// Current get physical memory which used by current process.
 func Current() (uint, error) {
 	name := fmt.Sprintf("/proc/%d/status", os.Getpid())
 	r, err := os.Open(name)