add build-host tftp server

README.md

@@ -116,6 +116,22 @@ Assuming you have nixpkgs checked out in a peer directory of this one,
 
 Some of the tests require the emulated upstream connection to be running.
 
+## Hardware
+
+How you get the thing onto hardware will vary according to the device,
+but is likely to involve U-Boot and TFTP.
+
+There is a rudimentary TFTP server bundled with the system which runs
+from the command line, has an allowlist for client connections, and
+follows symlinks, so you can have your device download images direct
+from the `./result` directory without exposing `/nix/store/` to the
+internet or mucking about copying files to `/tftproot`. If the
+permitted device is to be given the IP address 192.168.8.251 you might
+do something like this:
+
+    $ NIX_PATH=nixpkgs=../nixpkgs:$NIX_PATH NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1 nix-build -I liminix-config=./tests/smoke/configuration.nix --arg device "import ./devices/gl-ar750.nix" -A outputs.tftpd -o tftpd
+    $  ./tftpd/bin/tufted -a 192.168.8.251 result
+
 
 ## Troubleshooting
 

default.nix

@@ -39,6 +39,7 @@ let
     # this exists so that you can run "nix-store -q --tree" on it and find
     # out what's in the image, which is nice if it's unexpectedly huge
     manifest = writeText "manifest.json" (builtins.toJSON config.filesystem.contents);
+    tftpd = nixpkgs.pkgs.buildPackages.tufted;
   };
 in {
   outputs = outputs // { default = outputs.${device.outputs.default}; };

overlay.nix

@@ -16,6 +16,8 @@ final: prev: {
     dbusSupport = false;
   };
 
+  tufted = final.callPackage ./pkgs/tufted {};
+
   pppoe = final.callPackage ./pkgs/pppoe {};
   ppp =
     (prev.ppp.override {

pkgs/tufted/default.nix

@@ -0,0 +1,44 @@
+{
+  lua5_3
+, stdenv
+, fennel
+, fetchFromGitHub
+, makeWrapper
+} :
+let
+  tufty-lua = lua.pkgs.buildLuaPackage {
+    pname = "tufty";
+    version = "1";
+    src = fetchFromGitHub {
+      owner = "telent";
+      repo = "tufty";
+      sha256 = "sha256-m5UEfcCNdG0Ku380cPhu1inNQmSfQJ5NcRIxLohUOh8=";
+      rev = "75c6d38713a82f4197f91dcb182a2e34f255bf7c";
+    };
+    buildPhase = ":";
+    installPhase = ''
+        mkdir -p "$out/share/lua/${lua5_3.luaversion}"
+        cp src/*.lua "$out/share/lua/${lua5_3.luaversion}/"
+      '';
+  };
+  lua = lua5_3.withPackages (ps: with ps; [
+    tufty-lua luasocket luaposix
+  ]);
+  fennel_ = (fennel.override { inherit lua; });
+in stdenv.mkDerivation {
+  pname = "tufted";
+  version = "1";
+  phases =  [ "unpackPhase" "installPhase" ];
+  buildInputs = [ lua fennel_ ];
+  nativeBuildInputs = [ makeWrapper ];
+  src = ./.;
+  installPhase = ''
+    mkdir -p $out/lib
+    cp tufted.fnl $out/lib
+    makeWrapper ${fennel_}/bin/fennel \
+      $out/bin/tufted \
+      --add-flags "--add-fennel-path $out/lib/?.fnl" \
+      --add-flags "--add-package-path $out/lib/?.lua" \
+      --add-flags "$out/lib/tufted.fnl"
+  '';
+}

pkgs/tufted/tufted.fnl

@@ -0,0 +1,51 @@
+(local tftp (require :tftp))
+(local { : realpath} (require :posix.stdlib))
+(local { : view } (require :fennel))
+
+(local options
+       (match arg
+         ["-a" ip-address dir]
+         { :allow ip-address :base-directory (realpath dir)}
+
+         [dir]
+         { :allow nil :base-directory (realpath dir)}
+
+         []
+         (error "missing command line parameters")
+         ))
+
+(print (.. "TFTP serving from " options.base-directory))
+
+(fn merge-pathname [directory filename]
+  (if (directory:match "/$")
+      (.. directory  filename)
+      (.. directory "/" filename)))
+
+(->
+ (tftp:listen
+  (fn [file host port]
+    (if (or (not options.allow) (= host options.allow))
+        (let [pathname (merge-pathname options.base-directory file)
+              f (io.open pathname "rb")
+              size (f:seek "end")]
+          (f:seek "set" 0)
+          (var eof? false)
+          (values
+           (fn handler [reqlen]
+             (let [bytes (f:read reqlen)]
+               (if eof?
+                   false
+                   bytes
+                   (values true bytes)
+                   (do
+                     ;; if the file length is divisible by the block
+                     ;; length, need to send an empty block at eof
+                     (set eof? true)
+                     (values true "")))))
+           size))
+        (error "host not allowed")))
+  nil
+  ["*"]
+  69)
+
+(os.exit))