Use base64url::base64_urlencode() in encode64()

[wlandau]

Using base64url in encode64() decreases overhead. Relevant: #43, #44. Benchmarking code:

library(microbenchmark)
library(storr)

n <- 1000

cache_mangle <- storr::storr_rds(tempfile(), mangle_key = TRUE)
cache_no_mangle <- storr::storr_rds(tempfile(), mangle_key = FALSE)

for (i in seq_len(n)){
  cache_mangle$set(key = as.character(i), value = i)
  cache_no_mangle$set(key = as.character(i), value = i)
}

overhead <- function(cache, n){
  for (i in seq_len(n)){
    cache$get(key = as.character(i))
  }
}

benchmarks <- microbenchmark(
  overhead(cache_mangle, n),
  overhead(cache_no_mangle, n)
)

print(benchmarks)

Benchmarks with the native implementation:

#> Unit: milliseconds
#>                          expr      min        lq      mean    median
#>     overhead(cache_mangle, n) 98.03836 104.64194 108.22292 107.92887
#>  overhead(cache_no_mangle, n) 62.32374  65.64005  67.20944  66.88925
#>         uq       max neval cld
#>  111.33038 136.31826   100   b
#>   68.23469  95.06846   100  a

Benchmarks with this PR.

#> Unit: milliseconds
#>                          expr      min       lq     mean   median       uq
#>     overhead(cache_mangle, n) 83.93953 90.30987 94.06254 94.10564 97.07974
#>  overhead(cache_no_mangle, n) 62.71232 65.66816 68.68043 68.64221 70.61832
#>        max neval cld
#>  123.58915   100   b
#>   95.26984   100  a

Do you think this speedup is enough? I was hoping for more of an improvement.

Benchmarks if encode64() simply calls base64_urlencode() (without compatibility measures for char62, char63, or pad):

#> Unit: milliseconds
#>                          expr      min       lq     mean   median       uq
#>     overhead(cache_mangle, n) 76.86742 82.28243 84.44084 84.30136 86.61499
#>  overhead(cache_no_mangle, n) 63.01152 66.57724 69.32338 68.83174 70.57834
#>        max neval cld
#>   93.08793   100   b
#>  106.44841   100  a

[codecov-io]

Codecov Report

Merging #87 into master will decrease coverage by 0.17%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master      #87      +/-   ##
==========================================
- Coverage   99.91%   99.74%   -0.18%     
==========================================
  Files          15       15              
  Lines        1179     1176       -3     
==========================================
- Hits         1178     1173       -5     
- Misses          1        3       +2

Impacted Files	Coverage Δ
R/base64.R	93.93% <84.61%> (-6.07%)	⬇️

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[wlandau]

Given the benchmarks and the potential package dependency on base64url, I actually like #88 more than this PR.