fix zip archives paths and add zip files test

- create_zip from a subdirectory wrote entry names with a leading
  '/', so the mounted archive looked empty
- memory_ostream did not support tellp(), so create_zip into a memory
  device wrote invalid offsets (-1) to the archive
- ZipFileDevice added missing parent directories for the first entry
  only
- ZipFileDevice::exists returned false for the archive root
- MemoryDevice::mkdirs recreated existing directories, dropping their
  content (mkdir("a/b") cleared "a"); overwriting a file duplicated its
  name in the directory listing

Added dev/tests/zip_files.lua: builds archives with file.create_zip
from memory device root, subdirectories and the real filesystem,
mounts them and checks reading, listing and read-only access.
memory_filesystem.lua got checks for the MemoryDevice issues.

Closes #544

dev/tests/memory_filesystem.lua

@@ -41,6 +41,17 @@ assert(entries[1] == "memtest:dir/subdir/a.txt")
 assert(entries[2] == "memtest:dir/subdir/b.txt")
 assert(entries[3] == "memtest:dir/subdir/other")
 
+debug.log("create sibling directory")
+file.mkdir("memtest:dir/subdir/sibling")
+assert(file.isfile("memtest:dir/subdir/a.txt"))
+assert(file.isdir("memtest:dir/subdir/other"))
+asserts.equals(4, #file.list("memtest:dir/subdir"))
+
+debug.log("overwrite file")
+file.write("memtest:dir/subdir/a.txt", "overwritten")
+asserts.equals("overwritten", file.read("memtest:dir/subdir/a.txt"))
+asserts.equals(4, #file.list("memtest:dir/subdir"))
+
 debug.log("remove tree")
 file.remove_tree("memtest:dir")
 assert(not file.isdir("memtest:dir"))

dev/tests/zip_files.lua

@@ -0,0 +1,118 @@
+local function sorted_list(path)
+    local entries = file.list(path)
+    table.sort(entries)
+    return entries
+end
+
+local function check_list(expected, path)
+    local entries = sorted_list(path)
+    asserts.equals(#expected, #entries)
+    for i, name in ipairs(expected) do
+        asserts.equals(name, entries[i])
+    end
+end
+
+local function join(root, name)
+    if root:sub(-1) == ":" then
+        return root..name
+    end
+    return root.."/"..name
+end
+
+local bytes = {0xDE, 0xAD, 0x00, 0xC0, 0xDE}
+
+local function create_tree(root)
+    file.mkdirs(join(root, "sub/deep"))
+    file.mkdir(join(root, "empty"))
+    file.write(join(root, "root.txt"), "root file")
+    file.write(join(root, "sub/a.txt"), "example, пример")
+    file.write_bytes(join(root, "sub/deep/binary"), bytes)
+end
+
+local function check_tree(m)
+    debug.log("check directories")
+    assert(file.exists(m..":"))
+    assert(file.isdir(m..":"))
+    assert(file.isdir(m..":sub"))
+    assert(file.isdir(m..":sub/deep"))
+    assert(file.isdir(m..":empty"))
+    assert(not file.isfile(m..":sub"))
+
+    debug.log("check files")
+    assert(file.isfile(m..":root.txt"))
+    assert(file.isfile(m..":sub/a.txt"))
+    assert(not file.isdir(m..":sub/a.txt"))
+    assert(not file.exists(m..":missing.txt"))
+    assert(not file.exists(m..":sub/missing.txt"))
+
+    debug.log("read files")
+    asserts.equals("root file", file.read(m..":root.txt"))
+    asserts.equals("example, пример", file.read(m..":sub/a.txt"))
+    asserts.equals(#"root file", file.length(m..":root.txt"))
+
+    local rbytes = file.read_bytes(m..":sub/deep/binary")
+    asserts.equals(#bytes, #rbytes)
+    for i, b in ipairs(bytes) do
+        asserts.equals(b, rbytes[i])
+    end
+
+    debug.log("read file with io_stream")
+    local stream = file.open(m..":root.txt", "r")
+    asserts.equals("root file", stream:read_line())
+    stream:close()
+
+    debug.log("list directories")
+    check_list({m..":empty", m..":root.txt", m..":sub"}, m..":")
+    check_list({m..":sub/a.txt", m..":sub/deep"}, m..":sub")
+    check_list({m..":sub/deep/binary"}, m..":sub/deep")
+    check_list({}, m..":empty")
+
+    debug.log("check read-only")
+    assert(not file.is_writeable(m..":"))
+    assert(not pcall(file.write, m..":new.txt", "text"))
+    local ok, created = pcall(file.mkdir, m..":newdir")
+    assert(not (ok and created))
+    assert(not file.exists(m..":newdir"))
+end
+
+local function check_zip(src, zipfile)
+    debug.log("create zip "..zipfile.." from "..src)
+    file.create_zip(src, zipfile)
+    assert(file.isfile(zipfile))
+
+    debug.log("mount "..zipfile)
+    local m = file.mount(zipfile)
+    check_tree(m)
+
+    debug.log("unmount "..m)
+    file.unmount(m)
+    assert(not pcall(file.read, m..":root.txt"))
+    assert(not pcall(file.unmount, m))
+end
+
+local mem = file.create_memory_device()
+local out = file.create_memory_device()
+
+debug.log("zip memory device root")
+create_tree(mem..":")
+check_zip(mem..":", out..":root.zip")
+
+debug.log("zip memory device subdirectory")
+create_tree(mem..":pack")
+check_zip(mem..":pack", out..":pack.zip")
+
+debug.log("zip nested subdirectory")
+create_tree(mem..":a/b/pack")
+check_zip(mem..":a/b/pack", out..":nested.zip")
+
+debug.log("zip real filesystem directory")
+if file.exists("config:ziptest") then
+    file.remove_tree("config:ziptest")
+end
+create_tree("config:ziptest/pack")
+check_zip("config:ziptest/pack", "config:ziptest/pack.zip")
+file.remove_tree("config:ziptest")
+
+debug.log("mount non-zip file")
+file.write(out..":text.txt", "not an archive")
+assert(not pcall(file.mount, out..":text.txt"))