Hash overly long filenames

Fixes #5 (urls) by hashing filenames with sha256.
Original function(s) by Roberto Ierusalimschy, licensed
under MIT (see lib/sha256.lua)

Author: TheAMM

cat_osc.json

@@ -4,6 +4,7 @@
 		"src/license_blurb.lua",
 		"<version>",
 		"lib/helpers.lua",
+		"lib/sha256.lua",
 		"src/options.lua",
 		"src/thumbnailer_shared.lua",
 		"src/patched_osc.lua"

lib/sha256.lua

@@ -0,0 +1,241 @@
+-- SHA-256 code in Lua 5.2; based on the pseudo-code from
+-- Wikipedia (http://en.wikipedia.org/wiki/SHA-2)
+-- The original code here was written by Roberto Ierusalimschy, and is licensed under MIT (see http://lua-users.org/lists/lua-l/2014-08/msg00628.html)
+-- This version has been slightly modified for mpv_thumbnail_script.lua
+
+local _sha = function()
+  local band, rrotate, bxor, rshift, bnot =
+    bit32.band, bit32.rrotate, bit32.bxor, bit32.rshift, bit32.bnot
+
+  -- Initialize table of round constants
+  -- (first 32 bits of the fractional parts of the cube roots of the first
+  -- 64 primes 2..311):
+  local k = {
+     0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
+     0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+     0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
+     0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+     0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
+     0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+     0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
+     0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+     0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
+     0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+     0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
+     0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+     0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
+     0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+     0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
+     0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
+  }
+
+
+  -- transform a string of bytes in a string of hexadecimal digits
+  local function str2hexa (s)
+    local h = string.gsub(s, ".", function(c)
+                return string.format("%02x", string.byte(c))
+              end)
+    return h
+  end
+
+
+  -- transform number 'l' in a big-endian sequence of 'n' bytes
+  -- (coded as a string)
+  local function num2s (l, n)
+    local s = ""
+    for i = 1, n do
+      local rem = l % 256
+      s = string.char(rem) .. s
+      l = (l - rem) / 256
+    end
+    return s
+  end
+
+  -- transform the big-endian sequence of four bytes starting at
+  -- index 'i' in 's' into a number
+  local function s232num (s, i)
+    local n = 0
+    for i = i, i + 3 do
+      n = n*256 + string.byte(s, i)
+    end
+    return n
+  end
+
+
+  -- append the bit '1' to the message
+  -- append k bits '0', where k is the minimum number >= 0 such that the
+  -- resulting message length (in bits) is congruent to 448 (mod 512)
+  -- append length of message (before pre-processing), in bits, as 64-bit
+  -- big-endian integer
+  local function preproc (msg, len)
+    local extra = -(len + 1 + 8) % 64
+    len = num2s(8 * len, 8)    -- original len in bits, coded
+    msg = msg .. "\128" .. string.rep("\0", extra) .. len
+    assert(#msg % 64 == 0)
+    return msg
+  end
+
+
+  local function initH224 (H)
+    -- (second 32 bits of the fractional parts of the square roots of the
+    -- 9th through 16th primes 23..53)
+    H[1] = 0xc1059ed8
+    H[2] = 0x367cd507
+    H[3] = 0x3070dd17
+    H[4] = 0xf70e5939
+    H[5] = 0xffc00b31
+    H[6] = 0x68581511
+    H[7] = 0x64f98fa7
+    H[8] = 0xbefa4fa4
+    return H
+  end
+
+
+  local function initH256 (H)
+    -- (first 32 bits of the fractional parts of the square roots of the
+    -- first 8 primes 2..19):
+    H[1] = 0x6a09e667
+    H[2] = 0xbb67ae85
+    H[3] = 0x3c6ef372
+    H[4] = 0xa54ff53a
+    H[5] = 0x510e527f
+    H[6] = 0x9b05688c
+    H[7] = 0x1f83d9ab
+    H[8] = 0x5be0cd19
+    return H
+  end
+
+
+  local function digestblock (msg, i, H)
+
+      -- break chunk into sixteen 32-bit big-endian words w[1..16]
+      local w = {}
+      for j = 1, 16 do
+        w[j] = s232num(msg, i + (j - 1)*4)
+      end
+
+      -- Extend the sixteen 32-bit words into sixty-four 32-bit words:
+      for j = 17, 64 do
+        local v = w[j - 15]
+        local s0 = bxor(rrotate(v, 7), rrotate(v, 18), rshift(v, 3))
+        v = w[j - 2]
+        local s1 = bxor(rrotate(v, 17), rrotate(v, 19), rshift(v, 10))
+        w[j] = w[j - 16] + s0 + w[j - 7] + s1
+      end
+
+      -- Initialize hash value for this chunk:
+      local a, b, c, d, e, f, g, h =
+          H[1], H[2], H[3], H[4], H[5], H[6], H[7], H[8]
+
+      -- Main loop:
+      for i = 1, 64 do
+        local s0 = bxor(rrotate(a, 2), rrotate(a, 13), rrotate(a, 22))
+        local maj = bxor(band(a, b), band(a, c), band(b, c))
+        local t2 = s0 + maj
+        local s1 = bxor(rrotate(e, 6), rrotate(e, 11), rrotate(e, 25))
+        local ch = bxor (band(e, f), band(bnot(e), g))
+        local t1 = h + s1 + ch + k[i] + w[i]
+
+        h = g
+        g = f
+        f = e
+        e = d + t1
+        d = c
+        c = b
+        b = a
+        a = t1 + t2
+      end
+
+      -- Add (mod 2^32) this chunk's hash to result so far:
+      H[1] = band(H[1] + a)
+      H[2] = band(H[2] + b)
+      H[3] = band(H[3] + c)
+      H[4] = band(H[4] + d)
+      H[5] = band(H[5] + e)
+      H[6] = band(H[6] + f)
+      H[7] = band(H[7] + g)
+      H[8] = band(H[8] + h)
+
+  end
+
+
+  local function finalresult224 (H)
+    -- Produce the final hash value (big-endian):
+    return
+      str2hexa(num2s(H[1], 4)..num2s(H[2], 4)..num2s(H[3], 4)..num2s(H[4], 4)..
+               num2s(H[5], 4)..num2s(H[6], 4)..num2s(H[7], 4))
+  end
+
+
+  local function finalresult256 (H)
+    -- Produce the final hash value (big-endian):
+    return
+      str2hexa(num2s(H[1], 4)..num2s(H[2], 4)..num2s(H[3], 4)..num2s(H[4], 4)..
+               num2s(H[5], 4)..num2s(H[6], 4)..num2s(H[7], 4)..num2s(H[8], 4))
+  end
+
+
+  ----------------------------------------------------------------------
+  local HH = {}    -- to reuse
+
+  local function hash224 (msg)
+    msg = preproc(msg, #msg)
+    local H = initH224(HH)
+
+    -- Process the message in successive 512-bit (64 bytes) chunks:
+    for i = 1, #msg, 64 do
+      digestblock(msg, i, H)
+    end
+
+    return finalresult224(H)
+  end
+
+
+  local function hash256 (msg)
+    msg = preproc(msg, #msg)
+    local H = initH256(HH)
+
+    -- Process the message in successive 512-bit (64 bytes) chunks:
+    for i = 1, #msg, 64 do
+      digestblock(msg, i, H)
+    end
+
+    return finalresult256(H)
+  end
+  ----------------------------------------------------------------------
+  local mt = {}
+
+  local function new256 ()
+    local o = {H = initH256({}), msg = "", len = 0}
+    setmetatable(o, mt)
+    return o
+  end
+
+  mt.__index = mt
+
+  function mt:add (m)
+    self.msg = self.msg .. m
+    self.len = self.len + #m
+    local t = 0
+    while #self.msg - t >= 64 do
+      digestblock(self.msg, t + 1, self.H)
+      t = t + 64
+    end
+    self.msg = self.msg:sub(t + 1, -1)
+  end
+
+
+  function mt:close ()
+    self.msg = preproc(self.msg, self.len)
+    self:add("")
+    return finalresult256(self.H)
+  end
+  ----------------------------------------------------------------------
+
+  return {
+    hash224 = hash224,
+    hash256 = hash256,
+    new256 = new256,
+  }
+end
+local sha256 = _sha()

src/options.lua

@@ -12,6 +12,11 @@ local thumbnailer_options = {
     -- Only automatically thumbnail videos shorter than this (seconds)
     autogenerate_max_duration = 3600, -- 1 hour
 
+    -- MD5-sum filenames over this length
+    -- It's nice to know what files the thumbnails are (hence directory names)
+    -- but long URLs may approach filesystem limits.
+    hash_filename_length = 128,
+
     -- Use mpv to generate thumbnail even if ffmpeg is found in PATH
     -- ffmpeg does not handle ordered chapters (MKVs which rely on other MKVs)!
     -- mpv is a bit slower, but has better support overall (eg. subtitles in the previews)

src/thumbnailer_shared.lua

@@ -99,6 +99,10 @@ function Thumbnailer:get_thumbnail_template()
     end
 
     filename = filename:gsub('[^a-zA-Z0-9_.%-\' ]', '')
+    -- Hash overly long filenames (most likely URLs)
+    if #filename > thumbnailer_options.hash_filename_length then
+        filename = sha256.hash256(filename)
+    end
 
     local file_key = ("%s-%d"):format(filename, filesize)
     local file_template = join_paths(self.cache_directory, file_key, "%06d.bgra")