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Merged
merged 2 commits into from
Aug 14, 2019
Merged

Add decode function. #12

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8b0b6e7
Make encode function safe.
nsaunders Aug 12, 2019
fda176b
Add decode function.
nsaunders Aug 2, 2019
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8 changes: 6 additions & 2 deletions README.md
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Expand Up @@ -7,7 +7,8 @@

A `FormURLEncoded` datatype represents an ordered list of key-value pairs
with possible duplicates. `encode` function allows to transform `FormURLEncoded`
into a string according to `application/x-www-form-urlencoded`.
into a `Maybe String` according to `application/x-www-form-urlencoded`.
`decode` function transforms a string into a `Maybe FormURLEncoded` structure.

Documentation is available on [Pursuit][Pursuit].

Expand All @@ -23,7 +24,10 @@ Example:
> encode (fromArray [ Tuple "hey" Nothing
> , Tuple "Oh" (Just "Let's go!")
> ])
"hey&Oh=Let's%20go!"
Just "hey&Oh=Let's%20go!"

> decode "a=aa&b=bb"
Just (FormURLEncoded [(Tuple "a" (Just "aa")),(Tuple "b" (Just "bb"))])
```

## Contributing
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5 changes: 3 additions & 2 deletions bower.json
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Expand Up @@ -14,11 +14,12 @@
"package.json"
],
"dependencies": {
"purescript-globals": "^4.0.0",
"purescript-globals": "^4.1.0",
"purescript-maybe": "^4.0.0",
"purescript-newtype": "^3.0.0",
"purescript-prelude": "^4.0.0",
"purescript-strings": "^4.0.0",
"purescript-tuples": "^5.0.0"
"purescript-tuples": "^5.0.0",
"purescript-foldable-traversable": "^4.1.1"
}
}
23 changes: 17 additions & 6 deletions src/Data/FormURLEncoded.purs
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Expand Up @@ -4,9 +4,11 @@ import Prelude

import Data.Maybe (Maybe(..))
import Data.Newtype (class Newtype)
import Data.String (joinWith) as String
import Data.String (joinWith, split) as String
import Data.String.Pattern (Pattern(..))
import Data.Traversable (traverse)
import Data.Tuple (Tuple(..))
import Global.Unsafe (unsafeEncodeURIComponent)
import Global (decodeURIComponent, encodeURIComponent)

-- | `FormURLEncoded` is an ordered list of key-value pairs with possible duplicates.
newtype FormURLEncoded = FormURLEncoded (Array (Tuple String (Maybe String)))
Expand All @@ -29,9 +31,18 @@ instance showFormUrlEncoded :: Show FormURLEncoded where
show (FormURLEncoded kvs) = "(FormURLEncoded " <> show kvs <> ")"

-- | Encode `FormURLEncoded` as `application/x-www-form-urlencoded`.
encode :: FormURLEncoded -> String
encode = String.joinWith "&" <<< map encodePart <<< toArray
encode :: FormURLEncoded -> Maybe String
encode = map (String.joinWith "&") <<< traverse encodePart <<< toArray
where
encodePart = case _ of
Tuple k Nothing -> unsafeEncodeURIComponent k
Tuple k (Just v) -> unsafeEncodeURIComponent k <> "=" <> unsafeEncodeURIComponent v
Tuple k Nothing -> encodeURIComponent k
Tuple k (Just v) -> (\key val -> key <> "=" <> val) <$> encodeURIComponent k <*> encodeURIComponent v

-- | Decode `FormURLEncoded` from `application/x-www-form-urlencoded`.
decode :: String -> Maybe FormURLEncoded
decode = map FormURLEncoded <<< traverse decodePart <<< String.split (Pattern "&")
where
decodePart = String.split (Pattern "=") >>> case _ of
[k, v] -> (\key val -> Tuple key $ Just val) <$> decodeURIComponent k <*> decodeURIComponent v
[k] -> Tuple <$> decodeURIComponent k <*> pure Nothing
_ -> Nothing
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@thomashoneyman thomashoneyman Aug 3, 2019

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I'm not particularly familiar with decodeURIComponent, but is it possible that a key or value could cause an exception? For example, the MDN documentation provides this pair of examples, the first of which ought to succeed and the second of which ought to fail:

decodeURIComponent('JavaScript_%D1%88%D0%B5%D0%BB%D0%BB%D1%8B');
// "JavaScript_шеллы"

try { 
  var a = decodeURIComponent('%E0%A4%A'); 
} catch(e) { 
  console.error(e); 
}

// URIError: malformed URI sequence

neither of which contains the explicit pattern = or &, and I'm not sure which part of it causes the exception thrown in the second case.

Do you mind clarifying how the decode function avoids exceptions, and handles the same cases that the JavaScript decodeURIComponent function does? (Feel free to correct me if this question doesn't seem pertinent).

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@thomashoneyman thomashoneyman Aug 3, 2019

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Ideally the decode function in this library would:

  1. Successfully decode the same cases that the decodeURIComponent() function does
  2. Return Nothing for cases that would cause an exception in decodeURIComponent()

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@thomashoneyman thomashoneyman Aug 12, 2019

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Now that there are safe versions in -globals, can we update this @nsaunders?