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606# QsSwift
<p align="center">
<img src="https://github.com/techouse/qs-swift/raw/main/logo.png?raw=true" width="256" alt="QsSwift" />
</p>
A fast, flexible query string **encoding/decoding** library for Swift and [Objective-C](#objective-c).
Ported from [qs](https://www.npmjs.com/package/qs) for JavaScript.
[](https://github.com/techouse/qs-swift/releases/latest)
[](https://swiftpackageindex.com/techouse/qs-swift)
[](https://swiftpackageindex.com/techouse/qs-swift)
[](https://techouse.github.io/qs-swift/qsswift/documentation/qsswift/) [](https://techouse.github.io/qs-swift/qsobjc/documentation/qsobjc/)
[](LICENSE)
[](https://github.com/techouse/qs-swift/actions/workflows/test.yml)
[](https://codecov.io/gh/techouse/qs-swift)
[](https://app.codacy.com/gh/techouse/qs-swift/dashboard?utm_source=gh&utm_medium=referral&utm_content=&utm_campaign=Badge_grade)
[](https://github.com/sponsors/techouse)
[](https://github.com/techouse/qs-swift/stargazers)
---
## Highlights
- Nested maps & lists: `foo[bar][baz]=qux` ⇄ `["foo": ["bar": ["baz": "qux"]]]`
- Multiple list formats (indices, brackets, repeat, comma)
- Dot-notation (`a.b=c`) and optional dot-encoding (setting `decodeDotInKeys` automatically enables dot notation)
- UTF‑8 and ISO‑8859‑1 charsets; optional charset sentinel (`utf8=✓`)
- Custom encoders/decoders, sorting, filtering, strict/null handling
- Deterministic ordering with `OrderedDictionary` (swift-collections)
---
## Requirements
- Swift **5.10+**
- Platforms: macOS **12+**, iOS **13+**, tvOS **13+**, watchOS **8+**
---
## Installation (Swift Package Manager)
### Xcode
- File → Add Package Dependencies…
- Enter: https://github.com/techouse/qs-swift
- Add the Qs library to your target.
### Package.swift
```swift
// in your Package.swift
dependencies: [
.package(url: "https://github.com/techouse/qs-swift", from: "1.1.1")
],
targets: [
.target(
name: "YourApp",
dependencies: [
.product(name: "QsSwift", package: "qs-swift")
]
)
]
```
---
## Quick start
```swift
import QsSwift
// Decode
let decoded: [String: Any] = try Qs.decode("foo[bar]=baz&foo[list][]=a&foo[list][]=b")
// decoded == ["foo": ["bar": "baz", "list": ["a", "b"]]]
// Encode
let encoded: String = try Qs.encode(["foo": ["bar": "baz"]])
// encoded == "foo%5Bbar%5D=baz"
```
---
## Usage
### Simple
```swift
// Decode
let obj: [String: Any] = try Qs.decode("a=c")
// ["a": "c"]
// Encode
let qs: String = try Qs.encode(["a": "c"])
// "a=c"
```
---
## Decoding
### Nested maps
```swift
try Qs.decode("foo[bar]=baz")
// ["foo": ["bar": "baz"]]
try Qs.decode("a%5Bb%5D=c")
// ["a": ["b": "c"]]
try Qs.decode("foo[bar][baz]=foobarbaz")
// ["foo": ["bar": ["baz": "foobarbaz"]]]
```
### Depth (default: 5)
Beyond the configured depth, the remainder is kept literally:
```swift
let r = try Qs.decode("a[b][c][d][e][f][g][h][i]=j")
// r["a"]?["b"]?["c"]?["d"]?["e"]?["f"]?["[g][h][i]"] == "j"
```
Set `strictDepth: true` to **throw** instead of collapsing the remainder when the limit is exceeded.
Override depth:
```swift
let r = try Qs.decode("a[b][c][d][e][f][g][h][i]=j", options: .init(depth: 1))
// r["a"]?["b"]?["[c][d][e][f][g][h][i]"] == "j"
```
### Parameter limit & ignoring `?`
```swift
try Qs.decode("a=b&c=d", options: .init(parameterLimit: 1))
// ["a": "b"]
try Qs.decode("?a=b&c=d", options: .init(ignoreQueryPrefix: true))
// ["a": "b", "c": "d"]
```
### Custom delimiters (string or regex)
```swift
try Qs.decode("a=b;c=d", options: .init(delimiter: StringDelimiter(";")))
// ["a": "b", "c": "d"]
let delim = try RegexDelimiter("[;,]")
try Qs.decode("a=b;c=d", options: .init(delimiter: delim))
// ["a": "b", "c": "d"]
```
### Dot notation & “decode dots in keys”
```swift
try Qs.decode("a.b=c", options: .init(allowDots: true))
// ["a": ["b": "c"]]
let r = try Qs.decode(
"name%252Eobj.first=John&name%252Eobj.last=Doe",
options: .init(decodeDotInKeys: true)
)
// ["name.obj": ["first": "John", "last": "Doe"]]
```
_Note:_ `decodeDotInKeys` implies `allowDots`; you don’t need to set both.
### Empty lists & duplicates
```swift
try Qs.decode("foo[]&bar=baz", options: .init(allowEmptyLists: true))
// ["foo": [], "bar": "baz"]
try Qs.decode("foo=bar&foo=baz")
// ["foo": ["bar", "baz"]]
try Qs.decode("foo=bar&foo=baz", options: .init(duplicates: .first))
// ["foo": "bar"]
try Qs.decode("foo=bar&foo=baz", options: .init(duplicates: .last))
// ["foo": "baz"]
```
### Charset & sentinel
```swift
try Qs.decode("a=%A7", options: .init(charset: .isoLatin1))
// ["a": "§"]
try Qs.decode(
"utf8=%E2%9C%93&a=%C3%B8",
options: .init(charset: .isoLatin1, charsetSentinel: true)
)
// ["a": "ø"]
try Qs.decode(
"utf8=%26%2310003%3B&a=%F8",
options: .init(charset: .utf8, charsetSentinel: true)
)
// ["a": "ø"]
```
### Interpret numeric entities (`Ӓ`)
```swift
try Qs.decode(
"a=%26%239786%3B",
options: .init(charset: .isoLatin1, interpretNumericEntities: true)
)
// ["a": "☺"]
```
_Heads-up:_ If you also enable `comma: true`, entity interpretation happens **after** comma processing. When you use list syntax like `a[]=...`, a comma-joined scalar stays a **single** element (e.g. `["1,☺"]`) inside the list, matching the library’s tests and cross-port behavior.
### Lists
```swift
try Qs.decode("a[]=b&a[]=c")
// ["a": ["b", "c"]]
try Qs.decode("a[1]=c&a[0]=b")
// ["a": ["b", "c"]]
try Qs.decode("a[1]=b&a[15]=c")
// ["a": ["b", "c"]]
try Qs.decode("a[]=&a[]=b")
// ["a": ["", "b"]]
```
Large indices become a map by default:
```swift
let r = try Qs.decode("a[100]=b")
// ["a": ["100": "b"]]
```
Disable list parsing:
```swift
let r = try Qs.decode("a[]=b", options: .init(parseLists: false))
// ["a": ["0": "b"]]
```
Mix notations:
```swift
let r = try Qs.decode("a[0]=b&a[b]=c")
// ["a": ["0": "b", "b": "c"]]
```
Comma-separated values:
```swift
let r = try Qs.decode("a=b,c", options: .init(comma: true))
// ["a": ["b", "c"]]
```
---
## Encoding
### Basics
```swift
try Qs.encode(["a": "b"])
// "a=b"
try Qs.encode(["a": ["b": "c"]])
// "a%5Bb%5D=c"
```
Disable URI encoding for readability:
```swift
try Qs.encode(["a": ["b": "c"]], options: .init(encode: false))
// "a[b]=c"
```
Values-only encoding:
```swift
let input: [String: Any] = [
"a": "b",
"c": ["d", "e=f"],
"f": [["g"], ["h"]],
]
try Qs.encode(input, options: .init(encodeValuesOnly: true))
// "a=b&c[0]=d&c[1]=e%3Df&f[0][0]=g&f[1][0]=h"
```
Custom encoder:
```swift
let enc: ValueEncoder = { value, _, _ in
// e.g. map "č" → "c", otherwise describe
if let s = value as? String, s == "č" {
return "c"
}
return String(describing: value ?? "")
}
try Qs.encode(["a": ["b": "č"]], options: .init(encoder: enc))
// "a[b]=c"
```
### List formats
```swift
// indices (default when encode=false)
try Qs.encode(["a": ["b", "c"]], options: .init(encode: false))
// "a[0]=b&a[1]=c"
// brackets
try Qs.encode(["a": ["b", "c"]], options: .init(listFormat: .brackets, encode: false))
// "a[]=b&a[]=c"
// repeat
try Qs.encode(["a": ["b", "c"]], options: .init(listFormat: .repeatKey, encode: false))
// "a=b&a=c"
// comma
try Qs.encode(["a": ["b", "c"]], options: .init(listFormat: .comma, encode: false))
// "a=b,c"
```
_Note:_ When you select `.comma`, you can set `commaRoundTrip = true` to append `[]` for single‑element lists so they can decode back into arrays. Set `commaCompactNulls = true` to drop `NSNull`/`nil` entries before joining (e.g., `["one", NSNull(), nil, "two"]` → `one,two`). If all entries are `NSNull`/`nil`, the key is omitted; if filtering leaves a single item and `commaRoundTrip = true`, `[]` is preserved.
### Nested maps and dot notation
```swift
try Qs.encode(["a": ["b": ["c": "d", "e": "f"]]], options: .init(encode: false))
// "a[b][c]=d&a[b][e]=f"
try Qs.encode(["a": ["b": ["c": "d", "e": "f"]]], options: .init(allowDots: true, encode: false))
// "a.b.c=d&a.b.e=f"
```
Encode dots in keys:
```swift
try Qs.encode(
["name.obj": ["first": "John", "last": "Doe"]],
options: .init(allowDots: true, encodeDotInKeys: true)
)
// "name%252Eobj.first=John&name%252Eobj.last=Doe"
```
Empty lists, nulls, and other niceties:
```swift
// Allow empty lists (order preserved with OrderedDictionary input)
try Qs.encode(["foo": [Any](), "bar": "baz"], options: .init(allowEmptyLists: true, encode: false))
// e.g. "foo[]&bar=baz"
try Qs.encode(["a": ""]) // "a="
try Qs.encode(["a": [Any]()]) // ""
try Qs.encode(["a": ["b": [Any]()]]) // ""
try Qs.encode(["a": NSNull(), "b": Undefined()]) // "a="
try Qs.encode(["a": "b", "c": "d"], options: .init(addQueryPrefix: true)) // "?a=b&c=d"
try Qs.encode(["a": "b", "c": "d"], options: .init(delimiter: ";")) // "a=b;c=d"
```
### Dates
```swift
let date = Date(timeIntervalSince1970: 0.007) // 7 ms since epoch
// Default ISO-8601 with millisecond precision (encode=false example)
try Qs.encode(["a": date], options: .init(encode: false))
// "a=1970-01-01T00:00:00.007Z"
// Custom serializer (epoch millis)
try Qs.encode(
["a": date],
options: .init(
dateSerializer: { d in String(Int((d.timeIntervalSince1970 * 1000.0).rounded())) },
encode: false
)
)
// "a=7"
```
### Sorting and filtering
```swift
// Sort keys
let sort: Sorter = { a, b in
let la = String(describing: a ?? "")
let lb = String(describing: b ?? "")
return la.compare(lb).rawValue // -1/0/1
}
try Qs.encode(["a": "c", "z": "y", "b": "f"], options: .init(encode: false, sort: sort))
// "a=c&b=f&z=y"
// Function filter (drop/transform)
let date = Date(timeIntervalSince1970: 0.123) // 123 ms
let filter = FunctionFilter { prefix, value in
switch prefix {
case "b": return Undefined()
case "e[f]":
if let d = value as? Date {
return Int((d.timeIntervalSince1970 * 1000.0).rounded())
}
case "e[g][0]":
if let n = value as? NSNumber {
return n.intValue * 2
}
if let i = value as? Int {
return i * 2
}
default: break
}
return value
}
let input: [String: Any] = [
"a": "b",
"c": "d",
"e": ["f": date, "g": [2]],
]
try Qs.encode(input, options: .init(encode: false, filter: filter))
// "a=b&c=d&e[f]=123&e[g][0]=4"
// Iterable filter (whitelist keys/indices)
try Qs.encode(["a": "b", "c": "d", "e": "f"], options: .init(encode: false, filter: IterableFilter(["a", "e"])))
// "a=b&e=f"
```
### RFC 3986 vs RFC 1738 (spaces)
```swift
try Qs.encode(["a": "b c"]) // "a=b%20c" (RFC 3986 default)
try Qs.encode(["a": "b c"], options: .init(format: .rfc3986)) // "a=b%20c"
try Qs.encode(["a": "b c"], options: .init(format: .rfc1738)) // "a=b+c"
```
---
## `nil`, `NSNull`, and `Undefined` (null semantics)
Query strings don’t have a native null concept, so Qs uses a few conventions to mirror “JSON-style” semantics as
closely as possible:
- `NSNull()` – use this to represent an explicit “null-like” value.
- `Undefined()` – a special sentinel provided by `Qs` to mean “omit this key entirely”.
- `""` (empty string) – a real, present-but-empty value.
### Encoding behavior (Swift → query string)
| Input value | Default (`strictNullHandling: false`) | With `strictNullHandling: true` | With `skipNulls: true` |
|---------------------|---------------------------------------|---------------------------------|------------------------|
| `"foo"` | `a=foo` | `a=foo` | `a=foo` |
| `""` (empty string) | `a=` | `a=` | `a=` |
| `NSNull()` | `a=` | `a` (no `=` sign) | (omitted) |
| `Undefined()` | (omitted) | (omitted) | (omitted) |
Examples:
```swift
try Qs.encode(["a": NSNull()])
// "a="
try Qs.encode(["a": NSNull()], options: .init(strictNullHandling: true))
// "a" // bare key, no "="
try Qs.encode(["a": NSNull()], options: .init(skipNulls: true))
// "" // key omitted
try Qs.encode(["a": Undefined()])
// "" // always omitted, regardless of options
```
### Decoding behavior (query string → Swift)
| Input token | Default (`strictNullHandling: false`) | With `strictNullHandling: true` |
|-------------|---------------------------------------|---------------------------------|
| `a=` | `["a": ""]` | `["a": ""]` |
| `a` | `["a": ""]` | `["a": NSNull()]` |
Examples:
```swift
try Qs.decode("a&b=")
// ["a": "", "b": ""]
try Qs.decode("a&b=", options: .init(strictNullHandling: true))
// ["a": NSNull(), "b": ""]
```
### How this maps to JSON libraries
- In **Foundation**'s **JSONSerialization**, `NSNull` is the conventional stand-in for JSON `null`.
→ In Qs, use `NSNull()` to mean a `null`-like value.
- In **Codable**/**JSONEncoder**, whether missing keys are emitted or omitted often depends on how your model is
encoded (`encode` vs `encodeIfPresent`).
→ In `Qs`, use `Undefined()` to _always_ omit a key from the output.
- There is **[no native “null” in query strings]()**, so preserving a true “null round-trip” requires using:
- `NSNull()` on `encode` and `strictNullHandling: true` (so it renders as a bare key), and
- `strictNullHandling: true` on `decode` (so bare keys come back as `NSNull()`).
Round-trip tip:
```swift
// Encode with a null-like value:
let out = try Qs.encode(["a": NSNull()], options: .init(strictNullHandling: true))
// "a"
// Decode back to NSNull:
let back = try Qs.decode(out, options: .init(strictNullHandling: true))
// ["a": NSNull()]
```
If you simply want to drop keys when a value is not present, prefer `Undefined()` (or `skipNulls: true` when values are
`NSNull()`), rather than encoding `NSNull()` itself.
---
## API surface
- `Qs.decode(_:, options:) -> [String: Any]`
- `Qs.encode(_:, options:) -> String`
- `DecodeOptions` / `EncodeOptions` – configuration knobs
- `Duplicates` / `ListFormat` / `Format` – enums matching qs.js semantics
- `Undefined` – sentinel used by filters to omit keys
---
## Ordering notes
- If `options.sort != nil`, that comparator decides order.
- If `options.sort == nil` and `options.encode == false`, key order follows **input traversal** (use `OrderedDictionary`
for stability).
- Arrays always preserve input order.
---
## Safety tips
- Keep `depth` and `parameterLimit` reasonable for untrusted inputs (defaults are sane).
- `allowEmptyLists`, `allowSparseLists`, and `parseLists` let you tune behavior for edge cases.
- Use `strictNullHandling` to differentiate `nil` (no `=`) from empty string (`=`).
---
## Bench (optional)
A tiny micro‑bench harness lives in `Bench/` (separate SPM package). It’s excluded from the main library.
```bash
cd Bench
make profile
```
---
## Objective-C
An Objective‑C bridge is included as [`QsObjC`](Sources/QsObjC) (facade + delegate-style hooks).
See the [QsObjC README](Sources/QsObjC/README.md) for installation, options, and examples. → [Docs](https://techouse.github.io/qs-swift/qsobjc/documentation/qsobjc/)
---
## Linux support
**Experimental** (Swift 6.0+)
On Linux, QsSwift uses [ReerKit](https://swiftpackageindex.com/reers/ReerKit)’s [`WeakMap`](https://github.com/reers/ReerKit/blob/main/Sources/ReerKit/Utility/Weak/WeakMap.swift)
to emulate [`NSMapTable.weakToWeakObjects()`](Sources/QsSwift/Internal/NSMapTable%2BLinux.swift) (weak keys **and** weak
values) for the encoder’s cycle‑detection side‑channel. This works around CoreFoundation APIs that aren’t available in
swift‑corelibs‑foundation on Linux.
#### Caveats
- Some tests that construct *self‑referential* `NSArray`/`NSDictionary` graphs are wrapped in `withKnownIssue` because
swift‑corelibs‑foundation can crash when creating those graphs. (Apple platforms are unaffected.)
- CI includes an **experimental Ubuntu** job and is marked `continue-on-error` while Linux behavior stabilizes.
---
Special thanks to the authors of [qs](https://www.npmjs.com/package/qs) for JavaScript:
- [Jordan Harband](https://github.com/ljharb)
- [TJ Holowaychuk](https://github.com/visionmedia/node-querystring)
---
## Other ports
| Port | Repository | Package |
|----------------------------|-------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Dart | [techouse/qs](https://github.com/techouse/qs) | [](https://pub.dev/packages/qs_dart) |
| Python | [techouse/qs_codec](https://github.com/techouse/qs_codec) | [](https://pypi.org/project/qs-codec/) |
| Kotlin / JVM + Android AAR | [techouse/qs-kotlin](https://github.com/techouse/qs-kotlin) | [](https://central.sonatype.com/artifact/io.github.techouse/qs-kotlin) |
| .NET / C# | [techouse/qs-net](https://github.com/techouse/qs-net) | [](https://www.nuget.org/packages/QsNet) |
| Node.js (original) | [ljharb/qs](https://github.com/ljharb/qs) | [](https://www.npmjs.com/package/qs) |
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## License
BSD 3‑Clause © [techouse](https://github.com/techouse)