webhooker/internal/handlers/delivery_result_view.go

package handlers

import (
	"time"

	"github.com/dustin/go-humanize"
	"sneak.berlin/go/webhooker/internal/delivery"
)

// maxRenderedResponseBytes caps how many bytes of one stored
// delivery response body reach the event log page.
//
// The bound is enforced here and in SQL, because this page's
// memory profile must not depend on a constant in another
// package staying where it is, or on every stored row having
// been written by the delivery engine under its own cap.
//
// It happens to equal that engine cap, so a row written by the
// engine reaches this one exactly and is never cut twice.
// Nothing here may assume the two differ: see view.
const maxRenderedResponseBytes = 4096

// deliveryResultColumns is the delivery attempt projection.
// The casts to blob are load-bearing for the same reason they
// are in eventLogColumns: they make substr and length count
// bytes rather than characters, and they make SQLite do the
// cut, so an oversized stored response never becomes a Go
// string at all.
const deliveryResultColumns = "delivery_id, attempt_num, created_at, " +
	"success, status_code, error, duration, " +
	"substr(cast(response_body as blob), 1, ?) AS response_body, " +
	"length(cast(response_body as blob)) AS response_bytes"

// DeliveryResultView is the display-safe projection of one
// delivery attempt for the event log page. It carries a
// capped response body plus the true stored size, so the page
// can mark a response as truncated without holding the whole
// thing.
//
// Both Error and ResponseBody have been through the target's
// Redactor. The engine already masks the URL out of the
// errors it stores, so for errors this is a second line; for
// response bodies it is the only line, and its reach is what
// delivery.Redactor documents.
type DeliveryResultView struct {
	AttemptNum int
	Success    bool

	// Ran is how long ago the attempt was recorded, and RanUTC the
	// full timestamp the page shows on hover.
	Ran    string
	RanUTC string

	// StatusCode is 0 when the attempt never got a response,
	// which is why the page asks HasStatusCode rather than
	// printing the number.
	StatusCode int

	// Error is the stored failure message, redacted.
	Error string

	// DurationMS is how long the attempt took.
	DurationMS int64

	// ResponseBody holds at most maxRenderedResponseBytes
	// bytes of the stored response, redacted. It is remote
	// content and must only ever be rendered escaped.
	ResponseBody string

	// ResponseBytes is the size of the stored response body,
	// before the cut and before redaction. It is what the
	// remote sent only when ResponseSizeKnown is set.
	ResponseBytes int64

	// ResponseShownBytes is how much of that the page is
	// showing. It is the size of the cut, taken before
	// redaction, so the truncation marker reports what SQLite
	// returned rather than how much the marker substitution
	// then changed the length.
	ResponseShownBytes int

	// ResponseTruncated reports that the body shown may be
	// incomplete, so the page owes the reader a marker. Every
	// body that reaches the cap counts, because one the
	// delivery engine cut at its own equal cap is
	// indistinguishable from a complete one.
	ResponseTruncated bool

	// ResponseSizeKnown reports that ResponseBytes is the whole
	// response the remote sent, so the marker may quote it. It
	// is false for a body that only reaches the cap, where how
	// much came after it was never recorded.
	ResponseSizeKnown bool
}

// HasStatusCode reports whether the attempt got as far as an
// HTTP response. A transport failure stores no status code,
// and rendering that as "0" would read as a real status.
func (v DeliveryResultView) HasStatusCode() bool {
	return v.StatusCode != 0
}

// deliveryResultRow is one row of the delivery attempt
// projection. Its response body arrives already cut to the
// cap by SQLite, with the true size beside it.
type deliveryResultRow struct {
	DeliveryID    string
	AttemptNum    int
	CreatedAt     time.Time
	Success       bool
	StatusCode    int
	Error         string
	Duration      int64
	ResponseBody  []byte
	ResponseBytes int64
}

// view projects a loaded row for rendering, stripping the
// target's own credential out of the two fields a remote peer
// gets to influence.
func (r *deliveryResultRow) view(
	redactor delivery.Redactor,
) DeliveryResultView {
	body := r.ResponseBody

	// Two different cuts can have shortened this body, and the
	// row records only one of them. SQLite cuts here, whenever
	// the stored value is larger than the cap. The delivery
	// engine cut earlier, whenever the remote sent more than
	// its own maxBodyLog — which is this same number, so such a
	// row stores the cut length as its whole length and nothing
	// in it separates a response that ended at the cap from one
	// severed there.
	//
	// So a body that reaches the cap is treated as cut either
	// way. Gating on ResponseBytes alone would assume the two
	// caps differ, and they do not: under the current engine
	// that gate never opens.
	cut := r.ResponseBytes > int64(len(body)) ||
		len(body) >= maxRenderedResponseBytes

	// The row holds more than the page shows only in the first
	// of those cases. In the second the stored row is all there
	// is, and its size is a floor rather than the true one.
	sizeKnown := r.ResponseBytes > int64(len(body))

	// Only a cut response can have been left mid-sequence,
	// exactly as with an event body.
	if cut {
		body = trimPartialRune(body)
	}

	// A cut body goes through RedactCut: the remote controls
	// the padding ahead of a credential it echoes, so it
	// controls where the cut falls inside that credential, and
	// the severed prefix left behind matches no secret whole.
	rendered := string(body)
	if cut {
		rendered = redactor.RedactCut(rendered)
	} else {
		rendered = redactor.Redact(rendered)
	}

	return DeliveryResultView{
		AttemptNum:         r.AttemptNum,
		Success:            r.Success,
		Ran:                humanize.Time(r.CreatedAt),
		RanUTC:             r.CreatedAt.UTC().Format(time.DateTime) + " UTC",
		StatusCode:         r.StatusCode,
		Error:              redactor.Redact(r.Error),
		DurationMS:         r.Duration,
		ResponseBody:       rendered,
		ResponseBytes:      r.ResponseBytes,
		ResponseShownBytes: len(body),
		ResponseTruncated:  cut,
		ResponseSizeKnown:  sizeKnown,
	}
}