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When fighting the good cyber-fight, one often has to process domain names. Our good friend @alexcpsec was in need of Punycode/IDNA processing in R which begat the newly-minted punycode R package. Much of the following has been culled from open documentation, so if you are already “in the know” about Punycode & IDNA, skip to the R code bits.

#### What is ‘Punycode’?

Punycode is a simple and efficient transfer encoding syntax designed for use with Internationalized Domain Names in Applications. It uniquely and reversibly transforms a Unicode string into an ASCII string. ASCII characters in the Unicode string are represented literally, and non-ASCII characters are represented by ASCII characters that are allowed in host name labels (letters, digits, and hyphens).

#### What is ‘IDNA’?

Until now, there has been no standard method for domain names to use characters outside the ASCII repertoire. The IDNA document defines internationalized domain names (IDNs) and a mechanism called IDNA for handling them in a standard fashion. IDNs use characters drawn from a large repertoire (Unicode), but IDNA allows the non-ASCII characters to be represented using only the ASCII characters already allowed in so-called host names today. This backward-compatible representation is required in existing protocols like DNS, so that IDNs can be introduced with no changes to the existing infrastructure. IDNA is only meant for processing domain names, not free text.

#### Why domain validation?

Organizations that manage some Top Level Domains (TLDs) have published tables with characters they accept within the domain. The reason may be to reduce complexity that come from using the full Unicode range, and to protect themselves from future (backwards incompatible) changes in the IDN or Unicode specifications. Libidn (and, hence, this package) implements an infrastructure for defining and checking strings against such tables.

#### Working with punycode

All three functions in the package are vectorized at the C-level.

For encoding and decoding operations, you pass in vectors of domain names and the functions return encoded or decoded character vectors. If there are any issues during the conversion of a particular domain name, the function will substitute Invalid for the domain name.

For the TLD validation function, any character set or conversion issue will cause FALSE to be returned. Otherwise the function will return TRUE.

#### Usage

devtools::install_github("hrbrmstr/punycode")
library(punycode)

ascii_doms <- c("xn------qpeiobbci9acacaca2c8a6ie7b9agmy.net",
"xn----0mcgcx6kho30j.com",
"xn----9hciecaaawbbp1b1cd.net",
"xn----ctbeewwhe7i.com",
"xn----ieuycya4cyb1b7jwa4fc8h4718bnq8c.com",
"xn----ny6a58fr8c8rtpsucir8k1bo62a.net",
"xn----peurf0asz4dzaln0qm161er8pd.biz",
"xn----twfb7ei8dwjzbf9dg.com",
"xn----ymcabp2br3mk93k.com")

intnl_doms <- c("ثبت-دومین.com",
"טיול-לפיליפינים.net",
"бизнес-тренер.com",
"новый-год.com",
"東京ライブ-バルーンスタンド.com",
"看護師高収入-求人.net",
"ユベラ-贅沢ポリフェノール.biz",
"เด็ก-ภูเก็ต.com",
"ایران-هاست.com")

for_valid <- c("gr€€n.no", "זגורי-אימפריה-לצפייה-ישירה.net", "ثبت-دومین.com",
"טיול-לפיליפינים.net", "xn------qpeiobbci9acacaca2c8a6ie7b9agmy.net", "xn----0mcgcx6kho30j.com",
"xn----9hciecaaawbbp1b1cd.net", "rudis.net")

# encoding

puny_encode(ascii_doms)

##  [1] "זגורי-אימפריה-לצפייה-ישירה.net"  "ثبت-دومین.com"                   "טיול-לפיליפינים.net"
##  [4] "бизнес-тренер.com"               "новый-год.com"                   "東京ライブ-バルーンスタンド.com"
##  [7] "看護師高収入-求人.net"           "ユベラ-贅沢ポリフェノール.biz"   "เด็ก-ภูเก็ต.com"
## [10] "ایران-هاست.com"

# decoding

puny_decode(intnl_doms)

## [1] "xn----0mcgcx6kho30j.com"                   "xn----9hciecaaawbbp1b1cd.net"
## [5] "xn----ieuycya4cyb1b7jwa4fc8h4718bnq8c.com" "xn----ny6a58fr8c8rtpsucir8k1bo62a.net"
## [7] "xn----peurf0asz4dzaln0qm161er8pd.biz"      "xn----twfb7ei8dwjzbf9dg.com"
## [9] "xn----ymcabp2br3mk93k.com"

# validation

puny_tld_check(for_valid)

## [1] FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE


#### Fin

If you find any errors or need more functionality, post an issue on github and/or drop a note in the comments.