Using Testcontainers in Swift

The Testcontainers for C/C++ library is compatible with native languages, and that includes Swift. To use the library in Swift, a few extra steps must be followed in order for it to be useable.

Using the generic Testcontainer C API

From the root of the repository:

cmake .
cmake --build .

The testcontainers-c header and library must be deployed to /usr manually:

sudo cp testcontainers-c/testcontainers-c.h /usr/include
sudo cp testcontainers-c/testcontainers-c.so /usr/lib/libtestcontainers-c.so

This is required so that Swift can actually find the header and library. On some systems, it may be required to deploy the *.so file to /usr/lib64 instead (such as openSUSE). Try this if Swift is unable to find the library at /usr/lib.

With a version of Swift 5.x installed, create a new project:

mkdir generic-container-swift && cd generic-container-swift
swift package init --type=executable

Inside of this project, create a new directory under Sources/ called CTestContainers. Create a CTestContainers.h file with the following content:

#include <testcontainers-c.h>

Then, create a file called module.modulemap in the same directory with this:

module CTestContainers [system] {
    header "CTestContainers.h"
    link "testcontainers-c"
    export *
}

Move main.swift into a subdirectory in Sources/ that matches the name of the project. You should end up with the following directory layout:

.
├── Package.swift
├── Sources
│   ├── CTestContainers
│   │   ├── CTestContainers.h
│   │   └── module.modulemap
│   └── generic-container-swift
│       └── main.swift

Then, add a the following definitions to the targets in Package.swift:

.systemLibrary(name: "CTestContainers")

It can be then included as a dependency for a target, like this:

.executableTarget(
    name: "generic-container-swift",
    dependencies: [
        "CTestContainers"
    ]
),

This module can then be imported and used from inside the application. However, the only challenge is dealing with C-style strings that are typically utf8 and are null terminated, so they require a bit of extra support for translation in Swift.

Here is the generic-containers demo translated into Swift, with an exstension to properly translate a String to a utf8 string for C:

import CTestContainers
import Glibc
import Foundation

extension String {
    func toCString() -> UnsafePointer<Int8> {
        return NSString(string: self).utf8String!
    }
}

let defaultImage = "wiremock/wiremock:3.0.1-1"
print("Using WireMock with the Testcontainers C binding (from Swift):")

print("Creating new container: \(defaultImage)")
let requestId = tc_new_container_request(defaultImage)
tc_with_exposed_tcp_port(requestId, 8080)
tc_with_wait_for_http(requestId, 8080, "/__admin/mappings".toCString())
tc_with_file(requestId, "test_data/hello.json".toCString(), "/home/wiremock/mappings/hello.json".toCString())
let ret = tc_run_container(requestId)
defer {
    free(ret.r2)
}
let containerId = ret.r0
if ret.r1 == 0 {
    print("Failed to run the container: \(String(cString: ret.r2))")
    exit(-1)
}

print("Sending HTTP request to the container")
let response = tc_send_http_get(containerId, 8080, "/hello")
defer {
    free(response.r1)
    free(response.r2)
}
if response.r0 == -1 {
    print("Failed to send HTTP request: \(String(cString: response.r2))")
    exit(-1)
}
if response.r0 != 200 {
    print("Received wrong response code: \(response.r0) instead of 200")
    print(String(cString: response.r1!))
    print(String(cString: response.r2!))
    exit(-1)
}
print("Server Response: HTTP-\(response.r0)")
print(String(cString: response.r1!))

Also, note that that free should be called to avoid memory leaks on the C strings returned from the library. This is missing from the existing C demos, but is an important consideration.

Using the WireMock Module

To use the wiremock module in Swift, all that needs to be done is to deploy the header and library in the same way as described above, and then add the following to CTestContainers.h:

#include <testcontainers-c-wiremock.h>

And the following to module.modulemap:

link "testcontainers-c-wiremock"

Then it is possible to use all the wiremock module helper functions from inside of Swift.