Fix limit headers and instrument stenoread.

Change limits to int64, so we can request more than 4G of bytes.
Read limits from read headers, not (empty) write headers.
Instrument stenoread with --limit-packets and --limit-bytes flags, so you can
request limits.

base/base.go

@@ -331,7 +331,7 @@ func PacketsToFile(in *PacketChan, out io.Writer, limit Limit) error {
 			return fmt.Errorf("error writing packet: %v", err)
 		}
 		count++
-		if limit.ShouldStopAfter(Limit{Bytes: len(p.Data) + pcapHeaderSize, Packets: 1}) {
+		if limit.ShouldStopAfter(Limit{Bytes: int64(len(p.Data) + pcapHeaderSize), Packets: 1}) {
 			return nil
 		}
 	}
@@ -382,10 +382,10 @@ func Watchdog(d time.Duration, msg string) *time.Timer {
 // Limit is the amount of data we want to return, or the amount taken by a
 // single upload.
 type Limit struct {
-	Bytes, Packets int
+	Bytes, Packets int64
 }
 
-func dec(a *int, b int) bool {
+func dec(a *int64, b int64) bool {
 	if *a != 0 && b != 0 {
 		*a -= b
 		return *a <= 0
@@ -404,12 +404,12 @@ func (a *Limit) ShouldStopAfter(b Limit) bool {
 // LimitFromHeaders returns a Limit based on HTTP headers.
 func LimitFromHeaders(h http.Header) (a Limit, err error) {
 	if limitStr := h.Get("Steno-Limit-Bytes"); limitStr != "" {
-		if a.Bytes, err = strconv.Atoi(limitStr); err != nil {
+		if a.Bytes, err = strconv.ParseInt(limitStr, 0, 64); err != nil {
 			return
 		}
 	}
 	if limitStr := h.Get("Steno-Limit-Packets"); limitStr != "" {
-		if a.Packets, err = strconv.Atoi(limitStr); err != nil {
+		if a.Packets, err = strconv.ParseInt(limitStr, 0, 64); err != nil {
 			return
 		}
 	}

env/env.go

@@ -88,7 +88,7 @@ func (e *Env) handleQuery(w http.ResponseWriter, r *http.Request) {
 	w = httputil.Log(w, r, true)
 	defer log.Print(w)
 
-	limit, err := base.LimitFromHeaders(w.Header())
+	limit, err := base.LimitFromHeaders(r.Header)
 	if err != nil {
 		http.Error(w, "Invalid Limit Headers", http.StatusBadRequest)
 		return

stenoread

@@ -31,12 +31,37 @@ See README.md for more details on the Stenographer query language.
 
 Set the STENOGRAPHER_CONFIG environmental variable to point to your stenographer
 config if it's in a nonstandard place (defaults to /etc/stenographer/config).
+
+$0 arguments are given before the filter.  These include:
+  --limit-bytes X    :  Stop output once we've exceeded X bytes
+  --limit-packets X  :  Stop output once we've exceeded X packets
+
+For example:
+  # Print first 6 packets or 2K bytes, whichever comes first,
+  # from source IP 1.1.1.1
+  $0 --limit-packets 6 --limit-bytes 2048 'host 1.1.1.1'
 EOF
   exit 1
 fi
 
-STENOQUERY="$1"
-shift
+HEADERS=""
+while true; do
+  case "$1" in
+    --limit-packets)
+      HEADERS="$HEADERS --header Steno-Limit-Packets:$2"
+      shift 2
+      ;;
+    --limit-bytes)
+      HEADERS="$HEADERS --header Steno-Limit-Bytes:$2"
+      shift 2
+      ;;
+    *)
+      STENOQUERY="$1"
+      shift
+      break
+      ;;
+  esac
+done
 
 TCPDUMP=$(PATH=$PATH:/usr/local/sbin:/usr/sbin:/sbin which tcpdump)
 STENOCURL=$(PATH=$(dirname "$0"):$PATH which stenocurl)
@@ -46,5 +71,5 @@ echo "Running stenographer query '$STENOQUERY', piping to 'tcpdump $@'" >&2
     -d "$STENOQUERY" \
     --silent \
     --max-time 890 \
-    --show-error |
+    --show-error $HEADERS |
     "$TCPDUMP" -r /dev/stdin -s 0 "$@"

thread/thread.go

@@ -358,7 +358,7 @@ func (t *Thread) ExportDebugHandlers(mux *http.ServeMux) {
 	mux.HandleFunc(prefix+"/packets", func(w http.ResponseWriter, r *http.Request) {
 		w = httputil.Log(w, r, false)
 		defer log.Print(w)
-		limit, err := base.LimitFromHeaders(w.Header())
+		limit, err := base.LimitFromHeaders(r.Header)
 		if err != nil {
 			http.Error(w, "Bad limit headers", http.StatusBadRequest)
 			return