dot-request: --inbox, and xz compression past 400 KB

--inbox files into another inbox than dot: the path it posts to and the
namespace it signs in both follow it, so the key signs for that inbox only.
DOT_REQUEST_URL still overrides the whole URL for testing.

A signed request over 400 KB -- the inbox's limit on the wire -- now goes
xz -9e compressed with Content-Encoding: xz, which the inbox undoes before
checking anything; a smaller one goes as it is. --compress and --no-compress
override that either way. Compressing needs xz, so it joins the Brewfile;
without it a request that must be compressed is refused, never sent plain.

Checked against a local inbox: 148 KB sent plain, 740 KB compressed to 37 KB
and accepted, --no-compress over the limit refused with 413, --compress on a
small request accepted, a bad --inbox name refused before signing.

2 files changed, 48 insertions, 5 deletions

diff --git a/Brewfile b/Brewfile
index 6f3f465..bbf4f2a 100644
--- a/Brewfile
+++ b/Brewfile
@@ -26,6 +26,7 @@ brew "gh"                  # config/profile hands it the GitHub token
 brew "mosh"                # alacritty-mosh, mosh-tmux.sh
 brew "terminal-notifier"   # bin/notify
 brew "fswatch"             # bin/sz-wait-for
+brew "xz"                  # bin/dot-request, for requests over 400 KB
 brew "n"                   # node versions, under $N_PREFIX
 brew "bash-completion"
 brew "shellcheck"
diff --git a/bin/dot-request b/bin/dot-request
index c68418e..8dcb17f 100755
--- a/bin/dot-request
+++ b/bin/dot-request
@@ -19,15 +19,27 @@
 # key authorised for that inbox. Set DOT_REQUEST_URL to point somewhere else
 # when testing.
 #
+#   --inbox NAME     file into another inbox than dot. The key must be
+#                    authorised there too, and signs for that inbox only.
+#   --compress       send it xz-compressed (xz -9e), whatever its size
+#   --no-compress    send it as it is, whatever its size
+#
+# By default a signed request over 400 KB goes xz-compressed and a smaller one
+# as it is: the inbox takes 400 KB on the wire, and more than that only
+# compressed, up to what the inbox allows once decompressed. Compressing needs
+# xz; without it, a request that must be compressed is refused, not sent plain.
+#
 # Runs under macOS's /bin/bash 3.2.
 
 set -euo pipefail
 
 key=""
-url="${DOT_REQUEST_URL:-https://req.soarez.net/inbox/dot}"
+inbox="dot"
+compress=""   # empty: decided by size
+compress_over=$((400 * 1024))
 
 usage() {
-    sed -n '3,25p' "$0" | sed 's/^# \{0,1\}//'
+    sed -n '3,32p' "$0" | sed 's/^# \{0,1\}//'
     exit "${1:-0}"
 }
 
@@ -35,11 +47,23 @@ while [[ $# -gt 0 ]]; do
     case "$1" in
         --key) key="${2:-}"; shift 2 ;;
         --key=*) key="${1#--key=}"; shift ;;
+        --inbox) inbox="${2:-}"; shift 2 ;;
+        --inbox=*) inbox="${1#--inbox=}"; shift ;;
+        --compress) compress=yes; shift ;;
+        --no-compress) compress=no; shift ;;
         -h|--help) usage 0 ;;
         *) >&2 echo "dot-request: unknown argument: $1"; usage 1 ;;
     esac
 done
 
+# The inbox is a path segment there and a signature namespace here: held to
+# the same names the inbox itself accepts.
+if [[ ! "${inbox}" =~ ^[A-Za-z0-9_-]{1,32}$ ]]; then
+    >&2 echo "dot-request: --inbox: '${inbox}' is not an inbox name"
+    exit 1
+fi
+url="${DOT_REQUEST_URL:-https://req.soarez.net/inbox/${inbox}}"
+
 if [[ -z "${key}" ]]; then
     >&2 echo "dot-request: --key is required (the ssh key this machine signs with)"
     exit 1
@@ -70,12 +94,30 @@ fi
 # against the same one. It is what stops a request signed here being replayed
 # into a different inbox, and what stops this key being made to sign for
 # anything else.
-ssh-keygen -Y sign -q -f "${key}" -n sz-request:dot "${tmp}/request.md"
+ssh-keygen -Y sign -q -f "${key}" -n "sz-request:${inbox}" "${tmp}/request.md"
 cat "${tmp}/request.md" "${tmp}/request.md.sig" > "${tmp}/signed.md"
 
+# What is signed is the text; compression is only how it travels, undone by
+# the inbox before it checks anything.
+size="$(wc -c < "${tmp}/signed.md" | tr -d ' ')"
+if [[ -z "${compress}" ]]; then
+    if [[ "${size}" -gt "${compress_over}" ]]; then compress=yes; else compress=no; fi
+fi
+encoding=()
+body="${tmp}/signed.md"
+if [[ "${compress}" == yes ]]; then
+    if ! command -v xz >/dev/null; then
+        >&2 echo "dot-request: ${size} bytes needs compressing, and there is no xz here"
+        exit 1
+    fi
+    xz -9e -c "${tmp}/signed.md" > "${tmp}/signed.md.xz"
+    body="${tmp}/signed.md.xz"
+    encoding=(-H 'Content-Encoding: xz')
+fi
+
 code="$(curl -sS -o "${tmp}/reply" -w '%{http_code}' \
-    -X POST -H 'Content-Type: text/markdown' \
-    --data-binary "@${tmp}/signed.md" "${url}")"
+    -X POST -H 'Content-Type: text/markdown' ${encoding[@]+"${encoding[@]}"} \
+    --data-binary "@${body}" "${url}")"
 
 if [[ "${code}" == "201" ]]; then
     echo "submitted: $(cat "${tmp}/reply")"