### Example Bug Report

Source: https://github.com/apple/swift-asn1/blob/main/CONTRIBUTING.md

An example of a comprehensive bug report including commit hash, context, reproduction steps, and system information.

```text
Commit hash: b17a8a9f0f814c01a56977680cb68d8a779c951f

Context:
While testing my application that uses with swift-asn1, I noticed that ...

Steps to reproduce:
1. ...
2. ...
3. ...
4. ...

$ swift --version
Swift version 4.0.2 (swift-4.0.2-RELEASE)
Target: x86_64-unknown-linux-gnu

Operating system: Ubuntu Linux 16.04 64-bit

$ uname -a
Linux beefy.machine 4.4.0-101-generic #124-Ubuntu SMP Fri Nov 10 18:29:59 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

My system has IPv6 disabled.
```

--------------------------------

### Update CMakeLists Files using Script

Source: https://github.com/apple/swift-asn1/blob/main/CONTRIBUTING.md

Example of using curl to fetch and execute the update-cmake-lists.sh script with a specific configuration.

```bash
curl -s https://raw.githubusercontent.com/apple/swift-nio/main/scripts/update-cmake-lists.sh | CONFIG_JSON='{"targets":[{"name":"SwiftASN1","type":"source","exceptions":[]}]}' bash
```

--------------------------------

### Configure SwiftASN1 CMake Project

Source: https://github.com/apple/swift-asn1/blob/main/CMakeLists.txt

Sets up the project name, language, and build directories for the SwiftASN1 library.

```cmake
cmake_minimum_required(VERSION 3.19)

project(SwiftASN1
  LANGUAGES Swift)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules)

include(SwiftSupport)

option(BUILD_SHARED_LIBS "Build shared libraries by default" YES)

set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/swift)

set(CMAKE_POSITION_INDEPENDENT_CODE ${BUILD_SHARED_LIBS})

find_package(dispatch CONFIG)
find_package(Foundation CONFIG)

add_subdirectory(Sources)
add_subdirectory(cmake/modules)
```

--------------------------------

### Add SwiftASN1 product to target

Source: https://github.com/apple/swift-asn1/blob/main/README.md

Add the SwiftASN1 product to your target's dependencies to use the library in your code.

```swift
dependencies: [
    .product(name: "SwiftASN1", package: "swift-asn1"),
]
```

--------------------------------

### Configure and Export SwiftASN1 Targets

Source: https://github.com/apple/swift-asn1/blob/main/cmake/modules/CMakeLists.txt

Configures the project's CMake export files and exports the defined targets for external use.

```cmake
set(SWIFT_ASN1_EXPORTS_FILE ${CMAKE_CURRENT_BINARY_DIR}/SwiftASN1Exports.cmake)
configure_file(SwiftASN1Config.cmake.in
    ${CMAKE_CURRENT_BINARY_DIR}/SwiftASN1Config.cmake)

get_property(SWIFT_ASN1_EXPORTS GLOBAL PROPERTY SWIFT_ASN1_EXPORTS)
export(TARGETS ${SWIFT_ASN1_EXPORTS} FILE ${SWIFT_ASN1_EXPORTS_FILE})
```

--------------------------------

### Configure Git Commit Template

Source: https://github.com/apple/swift-asn1/blob/main/CONTRIBUTING.md

Command to configure Git to use the project's commit message template.

```bash
git config commit.template dev/git.commit.template
```

--------------------------------

### Add SwiftASN1 dependency to Package.swift

Source: https://github.com/apple/swift-asn1/blob/main/README.md

Include this dependency in your Package.swift file to integrate the library into your project.

```swift
dependencies: [
    .package(url: "https://github.com/apple/swift-asn1.git", .upToNextMajor(from: "1.0.0"))
]
```

--------------------------------

### Run CI Checks Locally with act

Source: https://github.com/apple/swift-asn1/blob/main/CONTRIBUTING.md

Command to run Github Actions workflows locally using 'act' for CI checks, specifically the 'cmake-lists' job.

```bash
act --container-architecture linux/amd64 pull_request -j cmake-lists -W ./.github/workflows/pull_request.yml  --bind
```

--------------------------------

### Built-in ASN.1 Types

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/index.md

A list of common ASN.1 types implemented within the library.

```APIDOC
## Built-in ASN.1 Types

### Description
Commonly used ASN.1 types provided by the library.

### Protocols

- `ASN1IntegerRepresentable`

### Types

- `IntegerBytesCollection`
- `GeneralizedTime`
- `ASN1BitString`
- `UTCTime`
- `ASN1OctetString`
- `ASN1Any`
- `ASN1Null`
- `ASN1ObjectIdentifier`
- `ASN1UTF8String`
- `ASN1PrintableString`
- `ASN1BMPString`
- `ASN1IA5String`
- `ASN1TeletexString`
- `ASN1UniversalString`
```

--------------------------------

### Initialize ECDSASignature from DER encoded data

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Implement the DERImplicitlyTaggable protocol to decode an ECDSASignature from DER encoded data. This involves parsing a SEQUENCE node and recursively decoding its INTEGER components.

```swift
extension ECDSASignature: DERImplicitlyTaggable {
    init(derEncoded rootNode: ASN1Node, withIdentifier identifier: ASN1Identifier) throws {
        self = try DER.sequence(rootNode, identifier: identifier) {
            // TODO
        }
    }
}
```

```swift
init(derEncoded rootNode: ASN1Node, withIdentifier identifier: ASN1Identifier) throws {
    self = try DER.sequence(rootNode, identifier: identifier) {
        let r = try ArraySlice<UInt8>(derEncoded: &nodes)
        let s = try ArraySlice<UInt8>(derEncoded: &nodes)

        return ECDSASignature(r: r, s: s)
    }
}
```

--------------------------------

### DER Serialization API

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/index.md

This section outlines the components used for serializing ASN.1 structures into DER-encoded data.

```APIDOC
## DER Serialization

### Description
Components for serializing ASN.1 structures into DER-encoded data.

### Types

- `DER/Serializer`

### Protocols

- `DERSerializable`
- `DERImplicitlyTaggable`
```

--------------------------------

### Decode Explicitly Tagged INTEGER

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Use this initializer to decode an explicitly tagged INTEGER within a SEQUENCE. It requires the root node and specifies the tag number and class for the explicit tag.

```swift
init(derEncoded rootNode: ASN1Node) throws {
    self = try DER.sequence(rootNode, identifier: .sequence) { nodes in
        let value = try ASN1.explicitlyTagged(&nodes, tagNumber: 0, tagClass: .contextSpecific) {
            try Int64(derEncoded: $0)
        }

        return ContainsExplicitTag(value: value)
    }
}
```

--------------------------------

### PEM Parsing and Serialization

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/index.md

APIs for handling Privacy-Enhanced Mail (PEM) encoded data.

```APIDOC
## PEM Parsing and Serialization

### Description
Protocols and types for parsing and serializing PEM-encoded data.

### Protocols

- `PEMRepresentable`
- `PEMParseable`
- `PEMSerializable`

### Types

- `PEMDocument`
```

--------------------------------

### DER Parsing API

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/index.md

This section details the functions and protocols related to parsing DER-encoded data into ASN.1 structures.

```APIDOC
## DER Parsing

### Description
Functions and protocols for parsing DER-encoded data.

### Functions

- `DER/parse(_:)-72yd1`
- `DER/parse(_:)-6uo24`

### Protocols

- `DERParseable`
- `DERImplicitlyTaggable`
- `DERSerializable`
```

--------------------------------

### ASN.1 Node Representation

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/index.md

Details on the `ASN1Node` structure used to represent ASN.1 objects in a tree-like format.

```APIDOC
## ASN.1 Node Representation

### Description
Represents an ASN.1 object as a tree of nodes.

### Types

- `ASN1Node`
- `ASN1NodeCollection`
- `ASN1Identifier`
```

--------------------------------

### Decode Implicitly Tagged INTEGER

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Initializes a ContainsImplicitTag object by decoding a SEQUENCE containing an implicitly tagged INTEGER.

```swift
init(derEncoded rootNode: ASN1Node) throws {
    self = try DER.sequence(rootNode, identifier: .sequence) {
        let value = try Int64(derEncoded: &nodes, withIdentifier: .init(tagWithNumber: 0, tagClass: .contextSpecific))

        return ContainsImplicitTag(value: value)
    }
}
```

--------------------------------

### Encode Explicitly Tagged INTEGER

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Implement this method to serialize an explicitly tagged INTEGER. It appends a constructed node to the coder and serializes the value with the specified explicit tag.

```swift
func serialize(into coder: inout DER.Serializer) throws {
    try coder.appendConstructedNode(identifier: .sequence) { coder in
        try coder.serialize(self.value, explicitlyTaggedWithTagNumber: 0, tagClass: .contextSpecific)
    }
}
```

--------------------------------

### Serialize ECDSASignature to DER format

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Implement the DERImplicitlyTaggable protocol to serialize an ECDSASignature into DER format. This uses DER.Serializer to append a constructed node and recursively serialize its components.

```swift
func serialize(into coder: inout DER.Serializer, withIdentifier identifier: ASN1Identifier) throws {
    try coder.appendConstructedNode(identifier: identifier) {
        coder in
        try coder.serialize(self.r)
        try coder.serialize(self.s)
    }
}
```

--------------------------------

### Define ECDSASignature with DERImplicitlyTaggable

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Defines the ECDSASignature struct conforming to DERImplicitlyTaggable, including default identifier, properties, and initializers for decoding and encoding.

```swift
struct ECDSASignature: DERImplicitlyTaggable {
    static var defaultIdentifier: ASN1Identifier {
        .sequence
    }

    var r: ArraySlice<UInt8>
    var s: ArraySlice<UInt8>

    init(r: ArraySlice<UInt8>, s: ArraySlice<UInt8>) {
        self.r = r
        self.s = s
    }

    init(derEncoded rootNode: ASN1Node, withIdentifier identifier: ASN1Identifier) throws {
        self = try DER.sequence(rootNode, identifier: identifier) { nodes in
            let r = try ArraySlice<UInt8>(derEncoded: &nodes)
            let s = try ArraySlice<UInt8>(derEncoded: &nodes)

            return ECDSASignature(r: r, s: s)
        }
    }

    func serialize(into coder: inout DER.Serializer, withIdentifier identifier: ASN1Identifier) throws {
        try coder.appendConstructedNode(identifier: identifier) { coder in
            try coder.serialize(self.r)
            try coder.serialize(self.s)
        }
    }
}
```

--------------------------------

### Define ECDSASignature Struct

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Define a Swift struct to represent the ECDSA signature, which consists of two INTEGER fields. Use ArraySlice<UInt8> to store the raw bytes of these arbitrary-sized integers.

```swift
struct ECDSASignature {
    var r: ArraySlice<UInt8>

    var s: ArraySlice<UInt8>

    init(r: ArraySlice<UInt8>, s: ArraySlice<UInt8>) {
        self.r = r
        self.s = s
    }
}
```

--------------------------------

### Encode Implicitly Tagged INTEGER

Source: https://github.com/apple/swift-asn1/blob/main/Sources/SwiftASN1/Docs.docc/DecodingASN1.md

Serializes a ContainsImplicitTag object by encoding its value into a SEQUENCE with an implicitly tagged INTEGER.

```swift
func serialize(into coder: inout DER.Serializer) throws {
    try coder.appendConstructedNode(identifier: .sequence) {
        try self.value.serialize(into: &coder, withIdentifier: .init(tagWithNumber: 0, tagClass: .contextSpecific))
    }
}
```

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