Introduce locking for concurrent access control (#1557)

Fixes #1540

12 files changed, 100 insertions, 10 deletions

diff --git a/src/luarocks/cmd.lua b/src/luarocks/cmd.lua
index ca79c316..2db0c039 100644
--- a/src/luarocks/cmd.lua
+++ b/src/luarocks/cmd.lua
@@ -26,6 +26,7 @@ cmd.errorcodes = {
    UNSPECIFIED = 1,
    PERMISSIONDENIED = 2,
    CONFIGFILE = 3,
+   LOCK = 4,
    CRASH = 99
 }
 
@@ -477,6 +478,8 @@ Enabling completion for Fish:
       "To enable it, see '"..program.." help path'.")
    parser:flag("--global", "Use the system tree when `local_by_default` is `true`.")
    parser:flag("--no-project", "Do not use project tree even if running from a project folder.")
+   parser:flag("--force-lock", "Attempt to overwrite the lock for commands " ..
+      "that require exclusive access, such as 'install'")
    parser:flag("--verbose", "Display verbose output of commands executed.")
    parser:option("--timeout", "Timeout on network operations, in seconds.\n"..
       "0 means no timeout (wait forever). Default is "..
@@ -672,10 +675,28 @@ function cmd.run_command(description, commands, external_namespace, ...)
    end
 
    local cmd_mod = cmd_modules[args.command]
+
+   local lock
+   if cmd_mod.needs_lock then
+      lock, err = fs.lock_access(path.root_dir(cfg.root_dir), args.force_lock)
+      if not lock then
+         local try_force = args.force_lock
+                           and (" - failed to force the lock" .. (err and ": " .. err or ""))
+                           or  " - use --force-lock to overwrite the lock"
+         die("command '" .. args.command .. "' " ..
+             "requires exclusive access to " .. cfg.root_dir ..
+             try_force, cmd.errorcodes.LOCK)
+      end
+   end
+
    local call_ok, ok, err, exitcode = xpcall(function()
       return cmd_mod.command(args)
    end, error_handler)
 
+   if lock then
+      fs.unlock_access(lock)
+   end
+
    if not call_ok then
       die(ok, cmd.errorcodes.CRASH)
    elseif not ok then
diff --git a/src/luarocks/cmd/build.lua b/src/luarocks/cmd/build.lua
index 56f0e757..16c0aff2 100644
--- a/src/luarocks/cmd/build.lua
+++ b/src/luarocks/cmd/build.lua
@@ -180,4 +180,6 @@ function cmd_build.command(args)
    return name, version
 end
 
+cmd_build.needs_lock = true
+
 return cmd_build
diff --git a/src/luarocks/cmd/init.lua b/src/luarocks/cmd/init.lua
index 8bccb23f..dcd6b759 100644
--- a/src/luarocks/cmd/init.lua
+++ b/src/luarocks/cmd/init.lua
@@ -173,4 +173,6 @@ function init.command(args)
    return true
 end
 
+init.needs_lock = true
+
 return init
diff --git a/src/luarocks/cmd/install.lua b/src/luarocks/cmd/install.lua
index c2e947b2..b4f15cb8 100644
--- a/src/luarocks/cmd/install.lua
+++ b/src/luarocks/cmd/install.lua
@@ -255,4 +255,6 @@ function install.command(args)
    end
 end
 
+install.needs_lock = true
+
 return install
diff --git a/src/luarocks/cmd/make.lua b/src/luarocks/cmd/make.lua
index 8b313bb9..8147b5df 100644
--- a/src/luarocks/cmd/make.lua
+++ b/src/luarocks/cmd/make.lua
@@ -155,4 +155,6 @@ function make.command(args)
    end
 end
 
+make.needs_lock = true
+
 return make
diff --git a/src/luarocks/cmd/purge.lua b/src/luarocks/cmd/purge.lua
index c300e286..09380ef1 100644
--- a/src/luarocks/cmd/purge.lua
+++ b/src/luarocks/cmd/purge.lua
@@ -39,18 +39,10 @@ end
 function purge.command(args)
    local tree = args.tree
 
-   if type(tree) ~= "string" then
-      return nil, "The --tree argument is mandatory. "..util.see_help("purge")
-   end
-
-   local results = {}
-   if not fs.is_dir(tree) then
-      return nil, "Directory not found: "..tree
-   end
-
    local ok, err = fs.check_command_permissions(args)
    if not ok then return nil, err, cmd.errorcodes.PERMISSIONDENIED end
 
+   local results = {}
    search.local_manifest_search(results, path.rocks_dir(tree), queries.all())
 
    local sort = function(a,b) return vers.compare_versions(b,a) end
@@ -81,4 +73,6 @@ function purge.command(args)
    return writer.make_manifest(cfg.rocks_dir, "one")
 end
 
+purge.needs_lock = true
+
 return purge
diff --git a/src/luarocks/cmd/remove.lua b/src/luarocks/cmd/remove.lua
index 6bb69ad6..affeda25 100644
--- a/src/luarocks/cmd/remove.lua
+++ b/src/luarocks/cmd/remove.lua
@@ -72,4 +72,6 @@ function cmd_remove.command(args)
    return true
 end
 
+cmd_remove.needs_lock = true
+
 return cmd_remove
diff --git a/src/luarocks/core/cfg.lua b/src/luarocks/core/cfg.lua
index 9c2728cc..81987cc9 100644
--- a/src/luarocks/core/cfg.lua
+++ b/src/luarocks/core/cfg.lua
@@ -238,6 +238,7 @@ local function make_defaults(lua_version, target_cpu, platforms, home)
          MKDIR = "mkdir",
          RMDIR = "rmdir",
          CP = "cp",
+         LN = "ln",
          LS = "ls",
          RM = "rm",
          FIND = "find",
diff --git a/src/luarocks/fetch.lua b/src/luarocks/fetch.lua
index 723af8b5..09f7a40b 100644
--- a/src/luarocks/fetch.lua
+++ b/src/luarocks/fetch.lua
@@ -33,21 +33,25 @@ function fetch.fetch_caching(url, mirroring)
    local name = repo_url:gsub("[/:]","_")
    local cache_dir = dir.path(cfg.local_cache, name)
    local ok = fs.make_dir(cache_dir)
-   if not ok then
+   local lock = ok and fs.lock_access(cache_dir)
+   if not (ok and lock) then
       cfg.local_cache = fs.make_temp_dir("local_cache")
       cache_dir = dir.path(cfg.local_cache, name)
       ok = fs.make_dir(cache_dir)
       if not ok then
          return nil, "Failed creating temporary cache directory "..cache_dir
       end
+      lock = fs.lock_access(cache_dir)
    end
 
    local cachefile = dir.path(cache_dir, filename)
    if cfg.aggressive_cache and (not name:match("^manifest")) and fs.exists(cachefile) then
+      fs.unlock_access(lock)
       return cachefile, nil, nil, true
    end
 
    local file, err, errcode, from_cache = fetch.fetch_url(url, cachefile, true, mirroring)
+   fs.unlock_access(lock)
    if not file then
       return nil, err or "Failed downloading "..url, errcode
    end
diff --git a/src/luarocks/fs/lua.lua b/src/luarocks/fs/lua.lua
index 174fdc88..ec497f88 100644
--- a/src/luarocks/fs/lua.lua
+++ b/src/luarocks/fs/lua.lua
@@ -283,6 +283,18 @@ end
 
 if lfs_ok then
 
+function fs_lua.lock_access(dirname, force)
+   fs.make_dir(dirname)
+   if force then
+      os.remove(dir.path(dirname, "lockfile.lfs"))
+   end
+   return lfs.lock_dir(dirname)
+end
+
+function fs_lua.unlock_access(lock)
+   return lock:free()
+end
+
 --- Run the given command.
 -- The command is executed in the current directory in the dir stack.
 -- @param cmd string: No quoting/escaping is applied to the command.
diff --git a/src/luarocks/fs/unix/tools.lua b/src/luarocks/fs/unix/tools.lua
index b7fd4de5..7106ed81 100644
--- a/src/luarocks/fs/unix/tools.lua
+++ b/src/luarocks/fs/unix/tools.lua
@@ -315,4 +315,43 @@ function tools.is_superuser()
    return fs.current_user() == "root"
 end
 
+function tools.lock_access(dirname, force)
+   fs.make_dir(dirname)
+
+   local tempfile = os.tmpname()
+   if not tempfile then
+      return nil, "failed creating temp file for locking"
+   end
+
+   local fd, fderr = io.open(tempfile, "w")
+   if not fd then
+      return nil, "failed opening temp file " .. tempfile .. " for locking: " .. fderr
+   end
+
+   local ok, werr = fd:write("lock file for " .. dirname)
+   if not ok then
+      return nil, "failed writing temp file " .. tempfile .. " for locking: " .. werr
+   end
+
+   fd:close()
+
+   local lockfile = dir.path(dirname, "lockfile.luarocks")
+
+   local force_flag = force and " -f" or ""
+
+   if fs.execute(vars.LN .. force_flag, tempfile, lockfile) then
+      return {
+         tempfile = tempfile,
+         lockfile = lockfile,
+      }
+   else
+      return nil, "File exists" -- same message as luafilesystem
+   end
+end
+
+function tools.unlock_access(lock)
+   os.remove(lock.lockfile)
+   os.remove(lock.tempfile)
+end
+
 return tools
diff --git a/src/luarocks/fs/win32/tools.lua b/src/luarocks/fs/win32/tools.lua
index 9bd050c6..be63063b 100644
--- a/src/luarocks/fs/win32/tools.lua
+++ b/src/luarocks/fs/win32/tools.lua
@@ -316,4 +316,13 @@ function tools.set_time(filename, time)
    return true -- FIXME
 end
 
+function tools.lock_access(dirname)
+   -- NYI
+   return {}
+end
+
+function tools.unlock_access(lock)
+   -- NYI
+end
+
 return tools