feat: vendor zzlib for unzip (#1174)

Download data of the registry suggest that ~10-18% struggle to unpack the registry archive, with the drop-off occurring in the `unzip` step. Being able to unpack the registry is a very crucial component of mason.nvim, which warrants vendoring [zzlib](https://github.com/zerkman/zzlib) to allow unpacking it entirely in Lua.

3 files changed, 788 insertions, 0 deletions

diff --git a/lua/mason-vendor/zzlib/inflate-bit32.lua b/lua/mason-vendor/zzlib/inflate-bit32.lua
new file mode 100644
index 00000000..fc426018
--- /dev/null
+++ b/lua/mason-vendor/zzlib/inflate-bit32.lua
@@ -0,0 +1,285 @@
+-- stylua: ignore start
+
+-- zzlib-bit32 - zlib decompression in Lua - version using bit/bit32 libraries
+
+-- Copyright (c) 2016-2023 Francois Galea <fgalea at free.fr>
+-- This program is free software. It comes without any warranty, to
+-- the extent permitted by applicable law. You can redistribute it
+-- and/or modify it under the terms of the Do What The Fuck You Want
+-- To Public License, Version 2, as published by Sam Hocevar. See
+-- the COPYING file or http://www.wtfpl.net/ for more details.
+
+
+local inflate = {}
+
+local bit = bit32 or bit
+
+inflate.band = bit.band
+inflate.rshift = bit.rshift
+
+function inflate.bitstream_init(file)
+  local bs = {
+    file = file,  -- the open file handle
+    buf = nil,    -- character buffer
+    len = nil,    -- length of character buffer
+    pos = 1,      -- position in char buffer, next to be read
+    b = 0,        -- bit buffer
+    n = 0,        -- number of bits in buffer
+  }
+  -- get rid of n first bits
+  function bs:flushb(n)
+    self.n = self.n - n
+    self.b = bit.rshift(self.b,n)
+  end
+  -- returns the next byte from the stream, excluding any half-read bytes
+  function bs:next_byte()
+    if self.pos > self.len then
+      self.buf = self.file:read(4096)
+      self.len = self.buf:len()
+      self.pos = 1
+    end
+    local pos = self.pos
+    self.pos = pos + 1
+    return self.buf:byte(pos)
+  end
+  -- peek a number of n bits from stream
+  function bs:peekb(n)
+    while self.n < n do
+      self.b = self.b + bit.lshift(self:next_byte(),self.n)
+      self.n = self.n + 8
+    end
+    return bit.band(self.b,bit.lshift(1,n)-1)
+  end
+  -- get a number of n bits from stream
+  function bs:getb(n)
+    local ret = bs:peekb(n)
+    self.n = self.n - n
+    self.b = bit.rshift(self.b,n)
+    return ret
+  end
+  -- get next variable-size of maximum size=n element from stream, according to Huffman table
+  function bs:getv(hufftable,n)
+    local e = hufftable[bs:peekb(n)]
+    local len = bit.band(e,15)
+    local ret = bit.rshift(e,4)
+    self.n = self.n - len
+    self.b = bit.rshift(self.b,len)
+    return ret
+  end
+  function bs:close()
+    if self.file then
+      self.file:close()
+    end
+  end
+  if type(file) == "string" then
+    bs.file = nil
+    bs.buf = file
+  else
+    bs.buf = file:read(4096)
+  end
+  bs.len = bs.buf:len()
+  return bs
+end
+
+local function hufftable_create(depths)
+  local nvalues = #depths
+  local nbits = 1
+  local bl_count = {}
+  local next_code = {}
+  for i=1,nvalues do
+    local d = depths[i]
+    if d > nbits then
+      nbits = d
+    end
+    bl_count[d] = (bl_count[d] or 0) + 1
+  end
+  local table = {}
+  local code = 0
+  bl_count[0] = 0
+  for i=1,nbits do
+    code = (code + (bl_count[i-1] or 0)) * 2
+    next_code[i] = code
+  end
+  for i=1,nvalues do
+    local len = depths[i] or 0
+    if len > 0 then
+      local e = (i-1)*16 + len
+      local code = next_code[len]
+      local rcode = 0
+      for j=1,len do
+        rcode = rcode + bit.lshift(bit.band(1,bit.rshift(code,j-1)),len-j)
+      end
+      for j=0,2^nbits-1,2^len do
+        table[j+rcode] = e
+      end
+      next_code[len] = next_code[len] + 1
+    end
+  end
+  return table,nbits
+end
+
+local function block_loop(out,bs,nlit,ndist,littable,disttable)
+  local lit
+  repeat
+    lit = bs:getv(littable,nlit)
+    if lit < 256 then
+      table.insert(out,lit)
+    elseif lit > 256 then
+      local nbits = 0
+      local size = 3
+      local dist = 1
+      if lit < 265 then
+        size = size + lit - 257
+      elseif lit < 285 then
+        nbits = bit.rshift(lit-261,2)
+        size = size + bit.lshift(bit.band(lit-261,3)+4,nbits)
+      else
+        size = 258
+      end
+      if nbits > 0 then
+        size = size + bs:getb(nbits)
+      end
+      local v = bs:getv(disttable,ndist)
+      if v < 4 then
+        dist = dist + v
+      else
+        nbits = bit.rshift(v-2,1)
+        dist = dist + bit.lshift(bit.band(v,1)+2,nbits)
+        dist = dist + bs:getb(nbits)
+      end
+      local p = #out-dist+1
+      while size > 0 do
+        table.insert(out,out[p])
+        p = p + 1
+        size = size - 1
+      end
+    end
+  until lit == 256
+end
+
+local function block_dynamic(out,bs)
+  local order = { 17, 18, 19, 1, 9, 8, 10, 7, 11, 6, 12, 5, 13, 4, 14, 3, 15, 2, 16 }
+  local hlit = 257 + bs:getb(5)
+  local hdist = 1 + bs:getb(5)
+  local hclen = 4 + bs:getb(4)
+  local depths = {}
+  for i=1,hclen do
+    local v = bs:getb(3)
+    depths[order[i]] = v
+  end
+  for i=hclen+1,19 do
+    depths[order[i]] = 0
+  end
+  local lengthtable,nlen = hufftable_create(depths)
+  local i=1
+  while i<=hlit+hdist do
+    local v = bs:getv(lengthtable,nlen)
+    if v < 16 then
+      depths[i] = v
+      i = i + 1
+    elseif v < 19 then
+      local nbt = {2,3,7}
+      local nb = nbt[v-15]
+      local c = 0
+      local n = 3 + bs:getb(nb)
+      if v == 16 then
+        c = depths[i-1]
+      elseif v == 18 then
+        n = n + 8
+      end
+      for j=1,n do
+        depths[i] = c
+        i = i + 1
+      end
+    else
+      error("wrong entry in depth table for literal/length alphabet: "..v);
+    end
+  end
+  local litdepths = {} for i=1,hlit do table.insert(litdepths,depths[i]) end
+  local littable,nlit = hufftable_create(litdepths)
+  local distdepths = {} for i=hlit+1,#depths do table.insert(distdepths,depths[i]) end
+  local disttable,ndist = hufftable_create(distdepths)
+  block_loop(out,bs,nlit,ndist,littable,disttable)
+end
+
+local function block_static(out,bs)
+  local cnt = { 144, 112, 24, 8 }
+  local dpt = { 8, 9, 7, 8 }
+  local depths = {}
+  for i=1,4 do
+    local d = dpt[i]
+    for j=1,cnt[i] do
+      table.insert(depths,d)
+    end
+  end
+  local littable,nlit = hufftable_create(depths)
+  depths = {}
+  for i=1,32 do
+    depths[i] = 5
+  end
+  local disttable,ndist = hufftable_create(depths)
+  block_loop(out,bs,nlit,ndist,littable,disttable)
+end
+
+local function block_uncompressed(out,bs)
+  bs:flushb(bit.band(bs.n,7))
+  local len = bs:getb(16)
+  if bs.n > 0 then
+    error("Unexpected.. should be zero remaining bits in buffer.")
+  end
+  local nlen = bs:getb(16)
+  if bit.bxor(len,nlen) ~= 65535 then
+    error("LEN and NLEN don't match")
+  end
+  for i=1,len do
+    table.insert(out,bs:next_byte())
+  end
+end
+
+function inflate.main(bs)
+  local last,type
+  local output = {}
+  repeat
+    local block
+    last = bs:getb(1)
+    type = bs:getb(2)
+    if type == 0 then
+      block_uncompressed(output,bs)
+    elseif type == 1 then
+      block_static(output,bs)
+    elseif type == 2 then
+      block_dynamic(output,bs)
+    else
+      error("unsupported block type")
+    end
+  until last == 1
+  bs:flushb(bit.band(bs.n,7))
+  return output
+end
+
+local crc32_table
+function inflate.crc32(s,crc)
+  if not crc32_table then
+    crc32_table = {}
+    for i=0,255 do
+      local r=i
+      for j=1,8 do
+        r = bit.bxor(bit.rshift(r,1),bit.band(0xedb88320,bit.bnot(bit.band(r,1)-1)))
+      end
+      crc32_table[i] = r
+    end
+  end
+  crc = bit.bnot(crc or 0)
+  for i=1,#s do
+    local c = s:byte(i)
+    crc = bit.bxor(crc32_table[bit.bxor(c,bit.band(crc,0xff))],bit.rshift(crc,8))
+  end
+  crc = bit.bnot(crc)
+  if crc<0 then
+    -- in Lua < 5.2, sign extension was performed
+    crc = crc + 4294967296
+  end
+  return crc
+end
+
+return inflate
diff --git a/lua/mason-vendor/zzlib/inflate-bwo.lua b/lua/mason-vendor/zzlib/inflate-bwo.lua
new file mode 100644
index 00000000..a64a46e9
--- /dev/null
+++ b/lua/mason-vendor/zzlib/inflate-bwo.lua
@@ -0,0 +1,283 @@
+-- stylua: ignore start
+
+-- zzlib - zlib decompression in Lua - version using Lua 5.3 bitwise operators
+
+-- Copyright (c) 2016-2023 Francois Galea <fgalea at free.fr>
+-- This program is free software. It comes without any warranty, to
+-- the extent permitted by applicable law. You can redistribute it
+-- and/or modify it under the terms of the Do What The Fuck You Want
+-- To Public License, Version 2, as published by Sam Hocevar. See
+-- the COPYING file or http://www.wtfpl.net/ for more details.
+
+
+local inflate = {}
+
+function inflate.band(x,y) return x & y end
+function inflate.rshift(x,y) return x >> y end
+
+function inflate.bitstream_init(file)
+  local bs = {
+    file = file,  -- the open file handle
+    buf = nil,    -- character buffer
+    len = nil,    -- length of character buffer
+    pos = 1,      -- position in char buffer, next to be read
+    b = 0,        -- bit buffer
+    n = 0,        -- number of bits in buffer
+  }
+  -- get rid of n first bits
+  function bs:flushb(n)
+    self.n = self.n - n
+    self.b = self.b >> n
+  end
+  -- returns the next byte from the stream, excluding any half-read bytes
+  function bs:next_byte()
+    if self.pos > self.len then
+      self.buf = self.file:read(4096)
+      self.len = self.buf:len()
+      self.pos = 1
+    end
+    local pos = self.pos
+    self.pos = pos + 1
+    return self.buf:byte(pos)
+  end
+  -- peek a number of n bits from stream
+  function bs:peekb(n)
+    while self.n < n do
+      self.b = self.b + (self:next_byte()<<self.n)
+      self.n = self.n + 8
+    end
+    return self.b & ((1<<n)-1)
+  end
+  -- get a number of n bits from stream
+  function bs:getb(n)
+    local ret = bs:peekb(n)
+    self.n = self.n - n
+    self.b = self.b >> n
+    return ret
+  end
+  -- get next variable-size of maximum size=n element from stream, according to Huffman table
+  function bs:getv(hufftable,n)
+    local e = hufftable[bs:peekb(n)]
+    local len = e & 15
+    local ret = e >> 4
+    self.n = self.n - len
+    self.b = self.b >> len
+    return ret
+  end
+  function bs:close()
+    if self.file then
+      self.file:close()
+    end
+  end
+  if type(file) == "string" then
+    bs.file = nil
+    bs.buf = file
+  else
+    bs.buf = file:read(4096)
+  end
+  bs.len = bs.buf:len()
+  return bs
+end
+
+local function hufftable_create(depths)
+  local nvalues = #depths
+  local nbits = 1
+  local bl_count = {}
+  local next_code = {}
+  for i=1,nvalues do
+    local d = depths[i]
+    if d > nbits then
+      nbits = d
+    end
+    bl_count[d] = (bl_count[d] or 0) + 1
+  end
+  local table = {}
+  local code = 0
+  bl_count[0] = 0
+  for i=1,nbits do
+    code = (code + (bl_count[i-1] or 0)) * 2
+    next_code[i] = code
+  end
+  for i=1,nvalues do
+    local len = depths[i] or 0
+    if len > 0 then
+      local e = (i-1)*16 + len
+      local code = next_code[len]
+      local rcode = 0
+      for j=1,len do
+        rcode = rcode + ((1&(code>>(j-1))) << (len-j))
+      end
+      for j=0,2^nbits-1,2^len do
+        table[j+rcode] = e
+      end
+      next_code[len] = next_code[len] + 1
+    end
+  end
+  return table,nbits
+end
+
+local function block_loop(out,bs,nlit,ndist,littable,disttable)
+  local lit
+  repeat
+    lit = bs:getv(littable,nlit)
+    if lit < 256 then
+      table.insert(out,lit)
+    elseif lit > 256 then
+      local nbits = 0
+      local size = 3
+      local dist = 1
+      if lit < 265 then
+        size = size + lit - 257
+      elseif lit < 285 then
+        nbits = (lit-261) >> 2
+        size = size + ((((lit-261)&3)+4) << nbits)
+      else
+        size = 258
+      end
+      if nbits > 0 then
+        size = size + bs:getb(nbits)
+      end
+      local v = bs:getv(disttable,ndist)
+      if v < 4 then
+        dist = dist + v
+      else
+        nbits = (v-2) >> 1
+        dist = dist + (((v&1)+2) << nbits)
+        dist = dist + bs:getb(nbits)
+      end
+      local p = #out-dist+1
+      while size > 0 do
+        table.insert(out,out[p])
+        p = p + 1
+        size = size - 1
+      end
+    end
+  until lit == 256
+end
+
+local function block_dynamic(out,bs)
+  local order = { 17, 18, 19, 1, 9, 8, 10, 7, 11, 6, 12, 5, 13, 4, 14, 3, 15, 2, 16 }
+  local hlit = 257 + bs:getb(5)
+  local hdist = 1 + bs:getb(5)
+  local hclen = 4 + bs:getb(4)
+  local depths = {}
+  for i=1,hclen do
+    local v = bs:getb(3)
+    depths[order[i]] = v
+  end
+  for i=hclen+1,19 do
+    depths[order[i]] = 0
+  end
+  local lengthtable,nlen = hufftable_create(depths)
+  local i=1
+  while i<=hlit+hdist do
+    local v = bs:getv(lengthtable,nlen)
+    if v < 16 then
+      depths[i] = v
+      i = i + 1
+    elseif v < 19 then
+      local nbt = {2,3,7}
+      local nb = nbt[v-15]
+      local c = 0
+      local n = 3 + bs:getb(nb)
+      if v == 16 then
+        c = depths[i-1]
+      elseif v == 18 then
+        n = n + 8
+      end
+      for j=1,n do
+        depths[i] = c
+        i = i + 1
+      end
+    else
+      error("wrong entry in depth table for literal/length alphabet: "..v);
+    end
+  end
+  local litdepths = {} for i=1,hlit do table.insert(litdepths,depths[i]) end
+  local littable,nlit = hufftable_create(litdepths)
+  local distdepths = {} for i=hlit+1,#depths do table.insert(distdepths,depths[i]) end
+  local disttable,ndist = hufftable_create(distdepths)
+  block_loop(out,bs,nlit,ndist,littable,disttable)
+end
+
+local function block_static(out,bs)
+  local cnt = { 144, 112, 24, 8 }
+  local dpt = { 8, 9, 7, 8 }
+  local depths = {}
+  for i=1,4 do
+    local d = dpt[i]
+    for j=1,cnt[i] do
+      table.insert(depths,d)
+    end
+  end
+  local littable,nlit = hufftable_create(depths)
+  depths = {}
+  for i=1,32 do
+    depths[i] = 5
+  end
+  local disttable,ndist = hufftable_create(depths)
+  block_loop(out,bs,nlit,ndist,littable,disttable)
+end
+
+local function block_uncompressed(out,bs)
+  bs:flushb(bs.n&7)
+  local len = bs:getb(16)
+  if bs.n > 0 then
+    error("Unexpected.. should be zero remaining bits in buffer.")
+  end
+  local nlen = bs:getb(16)
+  if len~nlen ~= 65535 then
+    error("LEN and NLEN don't match")
+  end
+  for i=1,len do
+    table.insert(out,bs:next_byte())
+  end
+end
+
+function inflate.main(bs)
+  local last,type
+  local output = {}
+  repeat
+    local block
+    last = bs:getb(1)
+    type = bs:getb(2)
+    if type == 0 then
+      block_uncompressed(output,bs)
+    elseif type == 1 then
+      block_static(output,bs)
+    elseif type == 2 then
+      block_dynamic(output,bs)
+    else
+      error("unsupported block type")
+    end
+  until last == 1
+  bs:flushb(bs.n&7)
+  return output
+end
+
+local crc32_table
+function inflate.crc32(s,crc)
+  if not crc32_table then
+    crc32_table = {}
+    for i=0,255 do
+      local r=i
+      for j=1,8 do
+        r = (r >> 1) ~ (0xedb88320 & ~((r & 1) - 1))
+      end
+      crc32_table[i] = r
+    end
+  end
+  crc = (crc or 0) ~ 0xffffffff
+  for i=1,#s do
+    local c = s:byte(i)
+    crc = crc32_table[c ~ (crc & 0xff)] ~ (crc >> 8)
+  end
+  crc = (crc or 0) ~ 0xffffffff
+  if crc<0 then
+    -- in Lua < 5.2, sign extension was performed
+    crc = crc + 4294967296
+  end
+  return crc
+end
+
+return inflate
diff --git a/lua/mason-vendor/zzlib/init.lua b/lua/mason-vendor/zzlib/init.lua
new file mode 100644
index 00000000..2ca30039
--- /dev/null
+++ b/lua/mason-vendor/zzlib/init.lua
@@ -0,0 +1,220 @@
+-- stylua: ignore start
+
+-- zzlib - zlib decompression in Lua - Implementation-independent code
+
+-- Copyright (c) 2016-2023 Francois Galea <fgalea at free.fr>
+-- This program is free software. It comes without any warranty, to
+-- the extent permitted by applicable law. You can redistribute it
+-- and/or modify it under the terms of the Do What The Fuck You Want
+-- To Public License, Version 2, as published by Sam Hocevar. See
+-- the COPYING file or http://www.wtfpl.net/ for more details.
+
+
+local unpack = table.unpack or unpack
+local infl
+
+local lua_version = tonumber(_VERSION:match("^Lua (.*)"))
+if not lua_version or lua_version < 5.3 then
+  -- older version of Lua or Luajit being used - use bit/bit32-based implementation
+  infl = require("mason-vendor.zzlib.inflate-bit32")
+else
+  -- From Lua 5.3, use implementation based on bitwise operators
+  infl = require("mason-vendor.zzlib.inflate-bwo")
+end
+
+local zzlib = {}
+
+local function arraytostr(array)
+  local tmp = {}
+  local size = #array
+  local pos = 1
+  local imax = 1
+  while size > 0 do
+    local bsize = size>=2048 and 2048 or size
+    local s = string.char(unpack(array,pos,pos+bsize-1))
+    pos = pos + bsize
+    size = size - bsize
+    local i = 1
+    while tmp[i] do
+      s = tmp[i]..s
+      tmp[i] = nil
+      i = i + 1
+    end
+    if i > imax then
+      imax = i
+    end
+    tmp[i] = s
+  end
+  local str = ""
+  for i=1,imax do
+    if tmp[i] then
+      str = tmp[i]..str
+    end
+  end
+  return str
+end
+
+local function inflate_gzip(bs)
+  local id1,id2,cm,flg = bs.buf:byte(1,4)
+  if id1 ~= 31 or id2 ~= 139 then
+    error("invalid gzip header")
+  end
+  if cm ~= 8 then
+    error("only deflate format is supported")
+  end
+  bs.pos=11
+  if infl.band(flg,4) ~= 0 then
+    local xl1,xl2 = bs.buf.byte(bs.pos,bs.pos+1)
+    local xlen = xl2*256+xl1
+    bs.pos = bs.pos+xlen+2
+  end
+  if infl.band(flg,8) ~= 0 then
+    local pos = bs.buf:find("\0",bs.pos)
+    bs.pos = pos+1
+  end
+  if infl.band(flg,16) ~= 0 then
+    local pos = bs.buf:find("\0",bs.pos)
+    bs.pos = pos+1
+  end
+  if infl.band(flg,2) ~= 0 then
+    -- TODO: check header CRC16
+    bs.pos = bs.pos+2
+  end
+  local result = arraytostr(infl.main(bs))
+  local crc = bs:getb(8)+256*(bs:getb(8)+256*(bs:getb(8)+256*bs:getb(8)))
+  bs:close()
+  if crc ~= infl.crc32(result) then
+    error("checksum verification failed")
+  end
+  return result
+end
+
+-- compute Adler-32 checksum
+local function adler32(s)
+  local s1 = 1
+  local s2 = 0
+  for i=1,#s do
+    local c = s:byte(i)
+    s1 = (s1+c)%65521
+    s2 = (s2+s1)%65521
+  end
+  return s2*65536+s1
+end
+
+local function inflate_zlib(bs)
+  local cmf = bs.buf:byte(1)
+  local flg = bs.buf:byte(2)
+  if (cmf*256+flg)%31 ~= 0 then
+    error("zlib header check bits are incorrect")
+  end
+  if infl.band(cmf,15) ~= 8 then
+    error("only deflate format is supported")
+  end
+  if infl.rshift(cmf,4) ~= 7 then
+    error("unsupported window size")
+  end
+  if infl.band(flg,32) ~= 0 then
+    error("preset dictionary not implemented")
+  end
+  bs.pos=3
+  local result = arraytostr(infl.main(bs))
+  local adler = ((bs:getb(8)*256+bs:getb(8))*256+bs:getb(8))*256+bs:getb(8)
+  bs:close()
+  if adler ~= adler32(result) then
+    error("checksum verification failed")
+  end
+  return result
+end
+
+local function inflate_raw(buf,offset,crc)
+  local bs = infl.bitstream_init(buf)
+  bs.pos = offset
+  local result = arraytostr(infl.main(bs))
+  if crc and crc ~= infl.crc32(result) then
+    error("checksum verification failed")
+  end
+  return result
+end
+
+function zzlib.gunzipf(filename)
+  local file,err = io.open(filename,"rb")
+  if not file then
+    return nil,err
+  end
+  return inflate_gzip(infl.bitstream_init(file))
+end
+
+function zzlib.gunzip(str)
+  return inflate_gzip(infl.bitstream_init(str))
+end
+
+function zzlib.inflate(str)
+  return inflate_zlib(infl.bitstream_init(str))
+end
+
+local function int2le(str,pos)
+  local a,b = str:byte(pos,pos+1)
+  return b*256+a
+end
+
+local function int4le(str,pos)
+  local a,b,c,d = str:byte(pos,pos+3)
+  return ((d*256+c)*256+b)*256+a
+end
+
+local function nextfile(buf,p)
+  if int4le(buf,p) ~= 0x02014b50 then
+    -- end of central directory list
+    return
+  end
+  -- local flag = int2le(buf,p+8)
+  local packed = int2le(buf,p+10)~=0
+  local crc = int4le(buf,p+16)
+  local namelen = int2le(buf,p+28)
+  local name = buf:sub(p+46,p+45+namelen)
+  local offset = int4le(buf,p+42)+1
+  p = p+46+namelen+int2le(buf,p+30)+int2le(buf,p+32)
+  if int4le(buf,offset) ~= 0x04034b50 then
+    error("invalid local header signature")
+  end
+  local size = int4le(buf,offset+18)
+  local extlen = int2le(buf,offset+28)
+  offset = offset+30+namelen+extlen
+  return p,name,offset,size,packed,crc
+end
+
+function zzlib.files(buf)
+  local p = #buf-21
+  if int4le(buf,p) ~= 0x06054b50 then
+    -- not sure there is a reliable way to locate the end of central directory record
+    -- if it has a variable sized comment field
+    error(".ZIP file comments not supported")
+  end
+  local cdoffset = int4le(buf,p+16)+1
+  return nextfile,buf,cdoffset
+end
+
+function zzlib.unzip(buf,arg1,arg2)
+  if type(arg1) == "number" then
+    -- mode 1: unpack data from specified position in zip file
+    return inflate_raw(buf,arg1,arg2)
+  end
+  -- mode 2: search and unpack file from zip file
+  local filename = arg1
+  for _,name,offset,size,packed,crc in zzlib.files(buf) do
+    if name == filename then
+      local result
+      if not packed then
+        -- no compression
+        result = buf:sub(offset,offset+size-1)
+      else
+        -- DEFLATE compression
+        result = inflate_raw(buf,offset,crc)
+      end
+      return result
+    end
+  end
+  error("file '"..filename.."' not found in ZIP archive")
+end
+
+return zzlib