Day 14: Nim Assets (bundle your assets into single binary)

Today we will implement nimassets project heavily inspired by go-bindata

nimassets

Typically while developing projects we have assets like (icons, images, template files, css, javascript..etc) and It can be annoying to distribute them with your application or even risk losing them or misconfiguring paths or messed-up packaging script, so packaging all of them into the same binary would be an interesting option to have. these concerns were the reason to have something like go-bindata or Qt resource system

What do we expect?

  • Having single binary that has the actually resources into the executable.
  • Generating nim file out of the resources we want to bundle. Maybe something like nimassets -d=templatesdir -o=assetsfile.nim
  • Easy access to these bundled resources using getAsset proc
import assetsfile

echo assetsfile.getAsset("templatesdir/index.html")

The plan

So from a very highlevel

[ Resource1 ]                                
[ Resource2 ]   -> converter (nimassets) ->  [Nim file Represneting the resources list]
[ Resource3 ]                                

The generated file should look like


import os, tables, strformat, base64, ospaths

var assets = initTable[string, string]()

proc getAsset*(path: string): string = 
  result = assets[path].decode()

assets[RESOURCE1_PATH] = BASE64_ENCODE(RESOURCE1_CONTENT)
assets[RESOURCE2_PATH] = BASE64_ENCODE(RESOURCE2_CONTENT)
assets[RESOURCE3_PATH] = BASE64_ENCODE(RESOURCE3_CONTENT)
...
...
...
...

  • We store the resource path and its base64 encoded content in assets table
  • We will expose 1 proc getAsset that takes path and returns the content by decoding base64 content

Implementation

Let's go top down approach for the implementation

Command line arguments

const buildBranchName* = staticExec("git rev-parse --abbrev-ref HEAD") ## \
const buildCommit* = staticExec("git rev-parse HEAD")  ## \
# const latestTag* = staticExec("git describe --abbrev=0 --tags") ## \

const versionString* = fmt"0.1.0 ({buildBranchName}/{buildCommit})"

proc writeHelp() = 
    echo fmt"""
nimassets {versionString} (Bundle your assets into nim file)
    -h | --help         : show help
    -v | --version      : show version
    -o | --output       : output filename
    -f | --fast         : faster generation
    -d | --dir          : dir to include (recursively)
"""

proc writeVersion() =
    echo fmt"nimassets version {versionString}"

proc cli*() =
  var 
    compress, fast : bool = false
    dirs = newSeq[string]()
    output = "assets.nim"
  
  if paramCount() == 0:
    writeHelp()
    quit(0)
  
  for kind, key, val in getopt():
    case kind
    of cmdLongOption, cmdShortOption:
        case key
        of "help", "h": 
            writeHelp()
            quit()
        of "version", "v":
            writeVersion()
            quit()
        of "fast", "f": fast = true
        of "dir", "d": dirs.add(val)
        of "output", "o": output = val 
        else:
          discard
    else:
      discard 
  for d in dirs:
    if not dirExists(d):
      echo fmt"[-] Directory doesnt exist {d}"
      quit 2 # 2 means dir doesn't exist.
  # echo fmt"compress: {compress} fast: {fast} dirs:{dirs} output:{output}"
  createAssetsFile(dirs, output, fast, compress)

when isMainModule:
  cli()

Pretty simple, we accept list of directories (using -d or --dir flag) to bundle into a nim file defined using output flag (assets.nim by default)

--fast flag indicates if we should use threading or not to speed up a little compress used to allow compression we will pass it always as false

for version information (branch and commit id) we used some git commands combined with staticExec to ensure these values are available at compile time

createAssetsFile

this proc is the entry to our application as it receives seq of the directories we want to bundle, the output filename, code optimization, and will make use of compress flag in the future

proc createAssetsFile(dirs:seq[string], outputfile="assets.nim", fast=false, compress=false) =
  var generator: proc(s:string): string
  var data = assetsFileHeader

  if fast:
    generator = generateDirAssetsSpawn
  else:
    generator = generateDirAssetsSimple

  for d in dirs:
    data &= generator(d)
  
  writeFile(outputfile, data)

Here we write (the header of the assets file and the result of generating the bundle of each directory) to the outputfile

and either we bundle files one by one (using generateDirAssetsSimple) or separately (using generateDirAssetsSpawn)

generateDirAssetsSimple

proc generateDirAssetsSimple(dir:string): string =
  var key, val, valString: string

  for path in expandTilde(dir).walkDirRec():
    key = path
    val = readFile(path).encode()
    valString = " \"\"\"" & val & "\"\"\" "
    result &= fmt"""assets.add("{path}", {valString})""" & "\n\n"

We walk recursively on the directory using walkDirRec and write down the part assets[RESOURECE_PATH] = ENCODE_BASE64(RESOURCE CONTENT) for each file in the directory.

generateDirAssetsSpawn

proc handleFile(path:string): string {.thread.} =
  var val, valString: string
  val = readFile(path).encode()
  valString = " \"\"\"" & val & "\"\"\" "
  result = fmt"""assets.add("{path}", {valString})""" & "\n\n"

proc generateDirAssetsSpawn(dir: string): string = 
  var results = newSeq[FlowVar[string]]()
  for path in expandTilde(dir).walkDirRec():
    results.add(spawn handleFile(path))

  # wait till all of them are done.
  for r in results:
    result &= ^r

the same but as generateDirAssetsSimple but using spawn to do generate the assets table entry

And that's basically it.

nimassets

All of the code is based on nimassets project. Feel free to send a PR or report issues.