stringdude.go

package main

import (
  "bufio"
	"bytes"
	"fmt"
	"os"
)

type State int

const (
	INSIDE State = iota
	OUTSIDE
	ESCAPED
)

type Machine struct {
	state     State
	Stringbuf bytes.Buffer
	Output    *bufio.Writer
}

func (m *Machine) Tick(inchar rune) {
	incomingState := m.state

	if m.state == ESCAPED {
		m.state = INSIDE
	} else {
		switch inchar {
		case '"':
			switch m.state {
			case OUTSIDE:
				m.state = INSIDE
			case INSIDE:
				// Do stuff with content of Stringbuf
				m.state = OUTSIDE
			}
		case '\\':
			if m.state == INSIDE {
				m.state = ESCAPED
			}
		}
	}

	if (m.state == INSIDE || m.state == ESCAPED) && (incomingState == INSIDE || incomingState == ESCAPED) {
		m.Stringbuf.WriteRune(inchar)
	}
	if m.state == OUTSIDE || incomingState == OUTSIDE {
		m.Output.WriteRune(inchar)
	}

}

func main() {
	test := "[1,2,\"three \\\"thirty\", 4, \"four\", {\"what\":\"yeah\"}]"
	machine := Machine{OUTSIDE, bytes.Buffer{}, bufio.NewWriter(os.Stdout)}
	for _, char := range test {
		machine.Tick(char)
	}
	fmt.Printf("stringbuf: %v\n", machine.Stringbuf.String())
	machine.Output.Flush()
}

I've got this basically working. It takes an io.Reader and gives me a new io.Reader -- all JSON flowing through it has each string go through a transformer that takes a string and spits out a new string. Now I just need to figure out how to describe what I want to it.

func rewriteJson(in io.Reader, trans transformer) io.Reader {
    pr, pw := io.Pipe()

    go func() {
        m := newMachine(os.Stdout, trans)
        pw.CloseWithError(m.rage(bufio.NewReader(in)))
    }()

    return pr
}

func main() {
    test := "[1,2,\"three \\\"thirty\", 4, \"four\", {\"what\":\"yeah\"}]"
    r := rewriteJson(strings.NewReader(test), strings.Title)
    _, err := io.Copy(os.Stdout, r)
    if err != nil {
        panic(err)
    }
}

Applied: https://github.com/couchbaselabs/consolio/blob/master/tools/confsed/confsed.go#L39

You point this thing to a URL and give it a JSON map and it issues a new request that looks just like the original, but to the destination you want, and then rewrites the results, retaining headers and stuff. Probably not the most correct behavior for a proxy, but it does the thing I want.