Helper programs to repro JSON deserialize mem use

JSON deserialize of arrays is inefficient for memory. This is a minimal
reproducer to show that it uses lots more memory than expected.

Build each program separately, run gen and then you can run goread for
the repro and some memory usage stats.

src/cmd/jsondebug/common/helpers.go

@@ -0,0 +1,31 @@
+package common
+
+import (
+	"fmt"
+	"runtime"
+)
+
+const (
+	NumItems = 300000
+	ItemSize = 1024
+	FileName = "input.json"
+)
+
+type Foo struct {
+	A []byte
+}
+
+func PrintMemUsage() {
+	var m runtime.MemStats
+
+	runtime.ReadMemStats(&m)
+	// For info on each, see: https://golang.org/pkg/runtime/#MemStats
+	fmt.Printf("Alloc = %v MiB", bToMb(m.Alloc))
+	fmt.Printf("\tTotalAlloc = %v MiB", bToMb(m.TotalAlloc))
+	fmt.Printf("\tSys = %v MiB", bToMb(m.Sys))
+	fmt.Printf("\tNumGC = %v\n", m.NumGC)
+}
+
+func bToMb(b uint64) uint64 {
+	return b / 1024 / 1024
+}

src/cmd/jsondebug/gen/gen.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"github.com/alcionai/corso/src/cmd/jsondebug/common"
+)
+
+func main() {
+	buf := make([]byte, common.ItemSize)
+	data := make([]common.Foo, 0, common.NumItems)
+
+	for i := 0; i < common.NumItems; i++ {
+		n, err := rand.Read(buf)
+		if err != nil {
+			fmt.Printf("Error reading random data: %v\n", err)
+			return
+		} else if n != common.ItemSize {
+			fmt.Printf(
+				"Short read for item data: wanted %d, got %d\n",
+				common.ItemSize,
+				n,
+			)
+			return
+		}
+
+		item := common.Foo{A: buf}
+		data = append(data, item)
+	}
+
+	f, err := os.Create(common.FileName)
+	if err != nil {
+		fmt.Printf("Error making output file: %v\n", err)
+		return
+	}
+
+	defer f.Close()
+
+	enc := json.NewEncoder(f)
+	if err := enc.Encode(data); err != nil {
+		fmt.Printf("Error writing json to file: %v\n", err)
+		return
+	}
+}

src/cmd/jsondebug/goread/read.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"github.com/alcionai/corso/src/cmd/jsondebug/common"
+)
+
+func main() {
+	f, err := os.Open(common.FileName)
+	if err != nil {
+		fmt.Printf("Error opening input file: %v\n", err)
+		return
+	}
+
+	defer f.Close()
+
+	dec := json.NewDecoder(f)
+
+	output := []common.Foo{}
+
+	if err := dec.Decode(&output); err != nil {
+		fmt.Printf("Error decoding input: %v\n", err)
+		return
+	}
+
+	common.PrintMemUsage()
+}