feat(collectors) basic implementation of boring collectors; sender via http(s) to hard coded api route

internal/collectors/memory/memory.go

@@ -0,0 +1,92 @@
+package memory
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+	"strings"
+
+	"bugs.watch/agent/internal/aggregate"
+)
+
+type Stats struct {
+	TotalKB     uint64
+	AvailableKB uint64
+}
+
+// Read reads MemTotal and MemAvailable from /proc/meminfo.
+// Values are in KB.
+func Read() (Stats, error) {
+	f, err := os.Open("/proc/meminfo")
+	if err != nil {
+		return Stats{}, err
+	}
+	defer f.Close()
+
+	var total uint64
+	var available uint64
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if strings.HasPrefix(line, "MemTotal:") {
+			fields := strings.Fields(line)
+			if len(fields) >= 2 {
+				if v, err := strconv.ParseUint(fields[1], 10, 64); err == nil {
+					total = v
+				}
+			}
+			continue
+		}
+
+		if strings.HasPrefix(line, "MemAvailable:") {
+			fields := strings.Fields(line)
+			if len(fields) >= 2 {
+				if v, err := strconv.ParseUint(fields[1], 10, 64); err == nil {
+					available = v
+				}
+			}
+			continue
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return Stats{}, err
+	}
+
+	return Stats{
+		TotalKB:     total,
+		AvailableKB: available,
+	}, nil
+}
+
+// UsedPercent returns used memory percentage based on MemTotal and MemAvailable.
+func UsedPercent(s Stats) float64 {
+	if s.TotalKB == 0 {
+		return 0
+	}
+
+	used := s.TotalKB - s.AvailableKB
+	return (float64(used) / float64(s.TotalKB)) * 100.0
+}
+
+// Collector implements a stateless memory usage collector.
+type Collector struct{}
+
+func New() *Collector {
+	return &Collector{}
+}
+
+func (c *Collector) Name() string {
+	return "memory"
+}
+
+func (c *Collector) Collect(window *aggregate.Window) {
+	stats, err := Read()
+	if err != nil {
+		return
+	}
+
+	window.AddMemory(UsedPercent(stats))
+}