create_exe.rs

//! Create a standalone native executable for a given Wasm file.

use super::ObjectFormat;
use crate::store::CompilerOptions;
use anyhow::{Context, Result};
use clap::Parser;
use std::env;
use std::fs;
use std::fs::File;
use std::io::prelude::*;
use std::io::BufWriter;
use std::path::{Path, PathBuf};
use std::process::Command;
use wasmer::*;
use wasmer_object::{emit_serialized, get_object_for_target};

/// The `prefixer` returns the a String to prefix each of the
/// functions in the static object generated by the
/// so we can assure no collisions.
#[cfg(feature = "static-artifact-create")]
pub type PrefixerFn = Box<dyn Fn(&[u8]) -> String + Send>;

const WASMER_MAIN_C_SOURCE: &[u8] = include_bytes!("wasmer_create_exe_main.c");
const WASMER_DESERIALIZE_HEADER: &str = include_str!("wasmer_deserialize_module.h");

#[derive(Debug, Clone)]
struct CrossCompile {
    /// Cross-compilation library path.
    library_path: Option<PathBuf>,

    /// Cross-compilation tarball library path.
    tarball: Option<PathBuf>,

    /// Specify `zig` binary path
    zig_binary_path: Option<PathBuf>,
}

struct CrossCompileSetup {
    target: Triple,
    zig_binary_path: PathBuf,
    library: PathBuf,
    working_dir: PathBuf,
}

#[derive(Debug, Parser)]
/// The options for the `wasmer create-exe` subcommand
pub struct CreateExe {
    /// Input file
    #[clap(name = "FILE", parse(from_os_str))]
    path: PathBuf,

    /// Output file
    #[clap(name = "OUTPUT PATH", short = 'o', parse(from_os_str))]
    output: PathBuf,

    /// Compilation Target triple
    ///
    /// Accepted target triple values must follow the
    /// ['target_lexicon'](https://crates.io/crates/target-lexicon) crate format.
    ///
    /// The recommended targets we try to support are:
    ///
    /// - "x86_64-linux-gnu"
    /// - "aarch64-linux-gnu"
    /// - "x86_64-apple-darwin"
    /// - "arm64-apple-darwin"
    #[clap(long = "target")]
    target_triple: Option<Triple>,

    // Cross-compile with `zig`
    /// Cross-compilation library path.
    #[clap(long = "library-path")]
    library_path: Option<PathBuf>,

    /// Cross-compilation tarball library path.
    #[clap(long = "tarball")]
    tarball: Option<PathBuf>,

    /// Specify `zig` binary path
    #[clap(long = "zig-binary-path")]
    zig_binary_path: Option<PathBuf>,

    /// Object format options
    ///
    /// This flag accepts two options: `symbols` or `serialized`.
    /// - (default) `symbols` creates an
    /// executable where all functions and metadata of the module are regular object symbols
    /// - `serialized` creates an executable where the module is zero-copy serialized as raw data
    #[clap(name = "OBJECT_FORMAT", long = "object-format", verbatim_doc_comment)]
    object_format: Option<ObjectFormat>,

    /// Header file for object input
    ///
    /// If given, the input `PATH` is assumed to be an object created with `wasmer create-obj` and
    /// this is its accompanying header file.
    #[clap(name = "HEADER", long = "header", verbatim_doc_comment)]
    header: Option<PathBuf>,

    #[clap(short = 'm')]
    cpu_features: Vec<CpuFeature>,

    /// Additional libraries to link against.
    /// This is useful for fixing linker errors that may occur on some systems.
    #[clap(short = 'l')]
    libraries: Vec<String>,

    #[clap(flatten)]
    compiler: CompilerOptions,
}

impl CreateExe {
    /// Runs logic for the `compile` subcommand
    pub fn execute(&self) -> Result<()> {
        let object_format = self.object_format.unwrap_or(ObjectFormat::Symbols);
        let working_dir = tempfile::tempdir()?;
        let starting_cd = env::current_dir()?;
        let output_path = starting_cd.join(&self.output);

        /* Making library_path, tarball zig_binary_path flags require that target_triple flag
         * is set cannot be encoded with structopt, so we have to perform cli flag validation
         * manually here */
        let cross_compile: Option<CrossCompile> = if self.target_triple.is_none()
            && (self.library_path.is_some()
                || self.tarball.is_some()
                || self.zig_binary_path.is_some())
        {
            return Err(anyhow!(
                "To cross-compile an executable, you must specify a target triple with --target"
            ));
        } else if self.target_triple.is_some() {
            Some(CrossCompile {
                library_path: self.library_path.clone(),
                zig_binary_path: self.zig_binary_path.clone(),
                tarball: self.tarball.clone(),
            })
        } else {
            None
        };

        let target = self
            .target_triple
            .as_ref()
            .map(|target_triple| {
                let mut features = self
                    .cpu_features
                    .clone()
                    .into_iter()
                    .fold(CpuFeature::set(), |a, b| a | b);
                // Cranelift requires SSE2, so we have this "hack" for now to facilitate
                // usage
                if target_triple.architecture == Architecture::X86_64 {
                    features |= CpuFeature::SSE2;
                }
                Target::new(target_triple.clone(), features)
            })
            .unwrap_or_default();

        env::set_current_dir(&working_dir)?;

        let cross_compilation: Option<CrossCompileSetup> = if let Some(mut cross_subc) =
            cross_compile.or_else(|| {
                if self.target_triple.is_some() {
                    Some(CrossCompile {
                        library_path: None,
                        tarball: None,
                        zig_binary_path: None,
                    })
                } else {
                    None
                }
            }) {
            if let ObjectFormat::Serialized = object_format {
                return Err(anyhow!(
                    "Cross-compilation with serialized object format is not implemented."
                ));
            }

            let target = if let Some(target_triple) = self.target_triple.clone() {
                target_triple
            } else {
                return Err(anyhow!(
                        "To cross-compile an executable, you must specify a target triple with --target"
                ));
            };
            if let Some(tarball_path) = cross_subc.tarball.as_mut() {
                if tarball_path.is_relative() {
                    *tarball_path = starting_cd.join(&tarball_path);
                    if !tarball_path.exists() {
                        return Err(anyhow!(
                            "Tarball path `{}` does not exist.",
                            tarball_path.display()
                        ));
                    } else if tarball_path.is_dir() {
                        return Err(anyhow!(
                            "Tarball path `{}` is a directory.",
                            tarball_path.display()
                        ));
                    }
                }
            }
            let zig_binary_path =
                find_zig_binary(cross_subc.zig_binary_path.as_ref().and_then(|p| {
                    if p.is_absolute() {
                        p.canonicalize().ok()
                    } else {
                        starting_cd.join(p).canonicalize().ok()
                    }
                }))?;
            let library = if let Some(v) = cross_subc.library_path.clone() {
                v
            } else {
                {
                    let libwasmer_path = if self
                        .target_triple
                        .clone()
                        .unwrap_or(Triple::host())
                        .operating_system
                        == wasmer_types::OperatingSystem::Windows
                    {
                        "lib/wasmer.lib"
                    } else {
                        "lib/libwasmer.a"
                    };
                    let libwasmer_headless_path = if self
                        .target_triple
                        .clone()
                        .unwrap_or(Triple::host())
                        .operating_system
                        == wasmer_types::OperatingSystem::Windows
                    {
                        "lib/wasmer.lib"
                    } else {
                        "lib/libwasmer-headless.a"
                    };
                    let filename = if let Some(local_tarball) = cross_subc.tarball {
                        let files = untar(local_tarball)?;
                        files.clone().into_iter().find(|f| f.contains(libwasmer_headless_path)).or_else(||
                        files.into_iter().find(|f| f.contains(libwasmer_path))).ok_or_else(|| {
                            anyhow!("Could not find libwasmer for {} target in the provided tarball path.", target)})?
                    } else {
                        #[cfg(feature = "http")]
                        {
                            let release = http_fetch::get_latest_release()?;
                            let tarball = http_fetch::download_release(release, target.clone())?;
                            let files = untar(tarball)?;
                            files.clone().into_iter().find(|f| f.contains(libwasmer_headless_path)).or_else(||
                            files.into_iter().find(|f| f.contains(libwasmer_path))).ok_or_else(|| {
                                anyhow!("Could not find libwasmer for {} target in the fetched release from Github: you can download it manually and specify its path with the --cross-compilation-library-path LIBRARY_PATH flag.", target)})?
                        }
                        #[cfg(not(feature = "http"))]
                        return Err(anyhow!("This wasmer binary isn't compiled with an HTTP request library (feature flag `http`). To cross-compile, specify the path of the non-native libwasmer or release tarball with the --library-path LIBRARY_PATH or --tarball TARBALL_PATH flag."));
                    };
                    filename.into()
                }
            };
            Some(CrossCompileSetup {
                target,
                zig_binary_path,
                library,
                working_dir: working_dir.path().to_path_buf(),
            })
        } else {
            None
        };

        let (store, compiler_type) = self.compiler.get_store_for_target(target.clone())?;

        println!("Compiler: {}", compiler_type.to_string());
        println!("Target: {}", target.triple());
        println!("Format: {:?}", object_format);

        #[cfg(not(windows))]
        let wasm_object_path = working_dir.path().join("wasm.o");
        #[cfg(windows)]
        let wasm_object_path = working_dir.path().join("wasm.obj");

        let wasm_module_path = starting_cd.join(&self.path);

        let static_defs_header_path: PathBuf = working_dir.path().join("static_defs.h");

        if let Some(header_path) = self.header.as_ref() {
            /* In this case, since a header file is given, the input file is expected to be an
             * object created with `create-obj` subcommand */
            let header_path = starting_cd.join(&header_path);
            std::fs::copy(&header_path, &static_defs_header_path)
                .context("Could not access given header file")?;
            let object_file_path = wasm_module_path;
            if let Some(setup) = cross_compilation.as_ref() {
                self.compile_zig(
                    output_path,
                    object_file_path,
                    static_defs_header_path,
                    setup,
                )?;
            } else {
                self.link(
                    static_defs_header_path,
                    LinkCode {
                        object_paths: vec![object_file_path, "main_obj.obj".into()],
                        output_path,
                        working_dir: working_dir.path().to_path_buf(),
                        ..Default::default()
                    },
                )?;
            }
        } else {
            match object_format {
                ObjectFormat::Serialized => {
                    let module = Module::from_file(&store, &wasm_module_path)
                        .context("failed to compile Wasm")?;
                    let bytes = module.serialize()?;
                    let mut obj = get_object_for_target(target.triple())?;
                    emit_serialized(&mut obj, &bytes, target.triple())?;
                    let mut writer = BufWriter::new(File::create(&wasm_object_path)?);
                    obj.write_stream(&mut writer)
                        .map_err(|err| anyhow::anyhow!(err.to_string()))?;
                    writer.flush()?;
                    drop(writer);
                    // Write down header file that includes deserialize function
                    {
                        let mut writer = BufWriter::new(File::create(&static_defs_header_path)?);
                        writer.write_all(WASMER_DESERIALIZE_HEADER.as_bytes())?;
                        writer.flush()?;
                    }

                    // write C src to disk
                    let c_src_path: PathBuf = working_dir.path().join("wasmer_main.c");
                    #[cfg(not(windows))]
                    let c_src_obj: PathBuf = working_dir.path().join("wasmer_main.o");
                    #[cfg(windows)]
                    let c_src_obj: PathBuf = working_dir.path().join("wasmer_main.obj");

                    {
                        let mut c_src_file = fs::OpenOptions::new()
                            .create_new(true)
                            .write(true)
                            .open(&c_src_path)
                            .context("Failed to open C source code file")?;
                        c_src_file.write_all(WASMER_MAIN_C_SOURCE)?;
                    }
                    run_c_compile(
                        &c_src_path,
                        &c_src_obj,
                        static_defs_header_path,
                        self.target_triple.clone(),
                    )
                    .context("Failed to compile C source code")?;
                    LinkCode {
                        object_paths: vec![c_src_obj, wasm_object_path],
                        output_path,
                        additional_libraries: self.libraries.clone(),
                        target: self.target_triple.clone(),
                        ..Default::default()
                    }
                    .run()
                    .context("Failed to link objects together")?;
                }
                #[cfg(not(feature = "static-artifact-create"))]
                ObjectFormat::Symbols => {
                    return Err(anyhow!("This version of wasmer-cli hasn't been compiled with static artifact support. You need to enable the `static-artifact-create` feature during compilation."));
                }
                #[cfg(feature = "static-artifact-create")]
                ObjectFormat::Symbols => {
                    let engine = store.engine();
                    let engine_inner = engine.inner();
                    let compiler = engine_inner.compiler()?;
                    let features = engine_inner.features();
                    let tunables = store.tunables();
                    let data: Vec<u8> = fs::read(wasm_module_path)?;
                    let prefixer: Option<PrefixerFn> = None;
                    let (module_info, obj, metadata_length, symbol_registry) =
                        Artifact::generate_object(
                            compiler, &data, prefixer, &target, tunables, features,
                        )?;

                    let header_file_src = crate::c_gen::staticlib_header::generate_header_file(
                        &module_info,
                        &*symbol_registry,
                        metadata_length,
                    );
                    // Write object file with functions
                    let object_file_path: std::path::PathBuf =
                        working_dir.path().join("functions.o");
                    let mut writer = BufWriter::new(File::create(&object_file_path)?);
                    obj.write_stream(&mut writer)
                        .map_err(|err| anyhow::anyhow!(err.to_string()))?;
                    writer.flush()?;
                    // Write down header file that includes pointer arrays and the deserialize function
                    let mut writer = BufWriter::new(File::create(&static_defs_header_path)?);
                    writer.write_all(header_file_src.as_bytes())?;
                    writer.flush()?;
                    if let Some(setup) = cross_compilation.as_ref() {
                        self.compile_zig(
                            output_path,
                            object_file_path,
                            static_defs_header_path,
                            setup,
                        )?;
                    } else {
                        self.link(
                            static_defs_header_path,
                            LinkCode {
                                object_paths: vec![object_file_path, "main_obj.obj".into()],
                                output_path,
                                working_dir: working_dir.path().to_path_buf(),
                                ..Default::default()
                            },
                        )?;
                    }
                }
            }
        }

        if cross_compilation.is_some() {
            eprintln!(
                "✔ Cross-compiled executable for `{}` target compiled successfully to `{}`.",
                target.triple(),
                self.output.display(),
            );
        } else {
            eprintln!(
                "✔ Native executable compiled successfully to `{}`.",
                self.output.display(),
            );
        }

        Ok(())
    }

    fn compile_zig(
        &self,
        output_path: PathBuf,
        object_path: PathBuf,
        mut header_path: PathBuf,
        setup: &CrossCompileSetup,
    ) -> anyhow::Result<()> {
        debug_assert!(
            header_path.is_absolute(),
            "compile_zig() called with relative header file path {}",
            header_path.display()
        );
        let CrossCompileSetup {
            ref target,
            ref zig_binary_path,
            ref library,
            ref working_dir,
        } = setup;
        let c_src_path = working_dir.join("wasmer_main.c");
        let mut libwasmer_path = library.to_path_buf();

        println!("Library Path: {}", libwasmer_path.display());
        /* Cross compilation is only possible with zig */
        println!("Using zig binary: {}", zig_binary_path.display());
        let zig_triple = triple_to_zig_triple(target);
        eprintln!("Using zig target triple: {}", &zig_triple);

        let lib_filename = libwasmer_path
            .file_name()
            .unwrap()
            .to_str()
            .unwrap()
            .to_string();
        libwasmer_path.pop();
        {
            let mut c_src_file = fs::OpenOptions::new()
                .create_new(true)
                .write(true)
                .open(&c_src_path)
                .context("Failed to open C source code file")?;
            c_src_file.write_all(WASMER_MAIN_C_SOURCE)?;
        }

        if !header_path.is_dir() {
            header_path.pop();
        }

        /* Compile main function */
        let compilation = {
            let mut include_dir = libwasmer_path.clone();
            include_dir.pop();
            include_dir.push("include");

            let mut cmd = Command::new(zig_binary_path);
            let mut cmd_mut: &mut Command = cmd
                .arg("cc")
                .arg("-w")
                .arg("-fgnu-inline-asm")
                .arg("-fsanitize=undefined")
                .arg("-fsanitize-trap=undefined")
                .arg("-target")
                .arg(&zig_triple)
                .arg(&format!("-L{}", libwasmer_path.display()))
                .arg(&format!("-l:{}", lib_filename))
                .arg(&format!("-I{}", include_dir.display()))
                .arg(&format!("-I{}", header_path.display()));
            if !zig_triple.contains("windows") {
                cmd_mut = cmd_mut.arg("-lunwind");
            }
            cmd_mut
                .arg(&object_path)
                .arg(&c_src_path)
                .arg("-o")
                .arg(&output_path)
                .output()
                .context("Could not execute `zig`")?
        };
        if !compilation.status.success() {
            return Err(anyhow::anyhow!(String::from_utf8_lossy(
                &compilation.stderr
            )
            .to_string()));
        }
        Ok(())
    }

    #[cfg(feature = "static-artifact-create")]
    fn link(&self, mut header_path: PathBuf, linkcode: LinkCode) -> anyhow::Result<()> {
        debug_assert!(
            header_path.is_absolute(),
            "link() called with relative header file path {}",
            header_path.display()
        );
        let c_src_path: PathBuf = linkcode.working_dir.join("wasmer_main.c");
        let mut libwasmer_path = get_libwasmer_path()?
            .canonicalize()
            .context("Failed to find libwasmer")?;

        println!("Using libwasmer file: {}", libwasmer_path.display());

        let lib_filename = libwasmer_path
            .file_name()
            .unwrap()
            .to_str()
            .unwrap()
            .to_string();
        libwasmer_path.pop();
        {
            let mut c_src_file = fs::OpenOptions::new()
                .create_new(true)
                .write(true)
                .open(&c_src_path)
                .context("Failed to open C source code file")?;
            c_src_file.write_all(WASMER_MAIN_C_SOURCE)?;
        }

        if !header_path.is_dir() {
            header_path.pop();
        }

        /* Compile main function */
        let compilation = {
            Command::new("cc")
                .arg("-c")
                .arg(&c_src_path)
                .arg(if linkcode.optimization_flag.is_empty() {
                    "-O2"
                } else {
                    linkcode.optimization_flag.as_str()
                })
                .arg(&format!("-L{}", libwasmer_path.display()))
                .arg(&format!("-I{}", get_wasmer_include_directory()?.display()))
                .arg(&format!("-l:{}", lib_filename))
                //.arg("-lwasmer")
                // Add libraries required per platform.
                // We need userenv, sockets (Ws2_32), advapi32 for some system calls and bcrypt for random numbers.
                //#[cfg(windows)]
                //    .arg("-luserenv")
                //    .arg("-lWs2_32")
                //    .arg("-ladvapi32")
                //    .arg("-lbcrypt")
                // On unix we need dlopen-related symbols, libmath for a few things, and pthreads.
                //#[cfg(not(windows))]
                .arg("-ldl")
                .arg("-lm")
                .arg("-pthread")
                .arg(&format!("-I{}", header_path.display()))
                .arg("-v")
                .arg("-o")
                .arg("main_obj.obj")
                .output()?
        };
        if !compilation.status.success() {
            return Err(anyhow::anyhow!(String::from_utf8_lossy(
                &compilation.stderr
            )
            .to_string()));
        }
        linkcode.run().context("Failed to link objects together")?;
        Ok(())
    }
}

fn triple_to_zig_triple(target_triple: &Triple) -> String {
    let arch = match target_triple.architecture {
        wasmer_types::Architecture::X86_64 => "x86_64".into(),
        wasmer_types::Architecture::Aarch64(wasmer_types::Aarch64Architecture::Aarch64) => {
            "aarch64".into()
        }
        v => v.to_string(),
    };
    let os = match target_triple.operating_system {
        wasmer_types::OperatingSystem::Linux => "linux".into(),
        wasmer_types::OperatingSystem::Darwin => "macos".into(),
        wasmer_types::OperatingSystem::Windows => "windows".into(),
        v => v.to_string(),
    };
    let env = match target_triple.environment {
        wasmer_types::Environment::Musl => "musl",
        wasmer_types::Environment::Gnu => "gnu",
        wasmer_types::Environment::Msvc => "msvc",
        _ => "none",
    };
    format!("{}-{}-{}", arch, os, env)
}

fn get_wasmer_dir() -> anyhow::Result<PathBuf> {
    Ok(PathBuf::from(
        env::var("WASMER_DIR")
            .or_else(|e| {
                option_env!("WASMER_INSTALL_PREFIX")
                    .map(str::to_string)
                    .ok_or(e)
            })
            .context("Trying to read env var `WASMER_DIR`")?,
    ))
}

fn get_wasmer_include_directory() -> anyhow::Result<PathBuf> {
    let mut path = get_wasmer_dir()?;
    path.push("include");
    Ok(path)
}

/// path to the static libwasmer
fn get_libwasmer_path() -> anyhow::Result<PathBuf> {
    let mut path = get_wasmer_dir()?;
    path.push("lib");

    // TODO: prefer headless Wasmer if/when it's a separate library.
    #[cfg(not(windows))]
    path.push("libwasmer.a");
    #[cfg(windows)]
    path.push("wasmer.lib");

    Ok(path)
}

/// path to library tarball cache dir
fn get_libwasmer_cache_path() -> anyhow::Result<PathBuf> {
    let mut path = get_wasmer_dir()?;
    path.push("cache");
    let _ = std::fs::create_dir(&path);
    Ok(path)
}

/// Compile the C code.
fn run_c_compile(
    path_to_c_src: &Path,
    output_name: &Path,
    mut header_path: PathBuf,
    target: Option<Triple>,
) -> anyhow::Result<()> {
    debug_assert!(
        header_path.is_absolute(),
        "run_c_compile() called with relative header file path {}",
        header_path.display()
    );

    #[cfg(not(windows))]
    let c_compiler = "cc";
    // We must use a C++ compiler on Windows because wasm.h uses `static_assert`
    // which isn't available in `clang` on Windows.
    #[cfg(windows)]
    let c_compiler = "clang++";

    if !header_path.is_dir() {
        header_path.pop();
    }

    let mut command = Command::new(c_compiler);
    let command = command
        .arg("-O2")
        .arg("-c")
        .arg(path_to_c_src)
        .arg(&format!("-I{}", header_path.display()))
        .arg(&format!("-I{}", get_wasmer_include_directory()?.display()));

    let command = if let Some(target) = target {
        command.arg("-target").arg(format!("{}", target))
    } else {
        command
    };

    let output = command.arg("-o").arg(output_name).output()?;

    if !output.status.success() {
        bail!(
            "C code compile failed with: stdout: {}\n\nstderr: {}",
            std::str::from_utf8(&output.stdout)
                .expect("stdout is not utf8! need to handle arbitrary bytes"),
            std::str::from_utf8(&output.stderr)
                .expect("stderr is not utf8! need to handle arbitrary bytes")
        );
    }
    Ok(())
}

/// Data used to run a linking command for generated artifacts.
#[derive(Debug)]
struct LinkCode {
    /// Path to the linker used to run the linking command.
    linker_path: PathBuf,
    /// String used as an optimization flag.
    optimization_flag: String,
    /// Paths of objects to link.
    object_paths: Vec<PathBuf>,
    /// Additional libraries to link against.
    additional_libraries: Vec<String>,
    /// Path to the output target.
    output_path: PathBuf,
    /// Path to the dir containing the static libwasmer library.
    libwasmer_path: PathBuf,
    /// The target to link the executable for.
    target: Option<Triple>,
    /// Working directory
    working_dir: PathBuf,
}

impl Default for LinkCode {
    fn default() -> Self {
        #[cfg(not(windows))]
        let linker = "cc";
        #[cfg(windows)]
        let linker = "clang";
        Self {
            linker_path: PathBuf::from(linker),
            optimization_flag: String::from("-O2"),
            object_paths: vec![],
            additional_libraries: vec![],
            output_path: PathBuf::from("a.out"),
            libwasmer_path: get_libwasmer_path().unwrap(),
            target: None,
            working_dir: env::current_dir().expect("could not get current dir from environment"),
        }
    }
}

impl LinkCode {
    fn run(&self) -> anyhow::Result<()> {
        let libwasmer_path = self
            .libwasmer_path
            .canonicalize()
            .context("Failed to find libwasmer")?;
        println!(
            "Using path `{}` as libwasmer path.",
            libwasmer_path.display()
        );
        let mut command = Command::new(&self.linker_path);
        let command = command
            .arg(&self.optimization_flag)
            .args(
                self.object_paths
                    .iter()
                    .map(|path| path.canonicalize().unwrap()),
            )
            .arg(&libwasmer_path);
        let command = if let Some(target) = &self.target {
            command.arg("-target").arg(format!("{}", target))
        } else {
            command
        };
        // Add libraries required per platform.
        // We need userenv, sockets (Ws2_32), advapi32 for some system calls and bcrypt for random numbers.
        #[cfg(windows)]
        let command = command
            .arg("-luserenv")
            .arg("-lWs2_32")
            .arg("-ladvapi32")
            .arg("-lbcrypt");
        // On unix we need dlopen-related symbols, libmath for a few things, and pthreads.
        #[cfg(not(windows))]
        let command = command.arg("-ldl").arg("-lm").arg("-pthread");
        let link_against_extra_libs = self
            .additional_libraries
            .iter()
            .map(|lib| format!("-l{}", lib));
        let command = command.args(link_against_extra_libs);
        let output = command.arg("-o").arg(&self.output_path).output()?;

        if !output.status.success() {
            bail!(
                "linking failed with: stdout: {}\n\nstderr: {}",
                std::str::from_utf8(&output.stdout)
                    .expect("stdout is not utf8! need to handle arbitrary bytes"),
                std::str::from_utf8(&output.stderr)
                    .expect("stderr is not utf8! need to handle arbitrary bytes")
            );
        }
        Ok(())
    }
}

#[cfg(feature = "http")]
mod http_fetch {
    use anyhow::{anyhow, Context, Result};
    use http_req::{
        request::Request,
        response::{Response, StatusCode},
        uri::Uri,
    };
    use std::convert::TryFrom;

    pub fn get_latest_release() -> Result<serde_json::Value> {
        let mut writer = Vec::new();
        let uri = Uri::try_from("https://api.github.com/repos/wasmerio/wasmer/releases").unwrap();

        let response = Request::new(&uri)
            .header("User-Agent", "wasmer")
            .header("Accept", "application/vnd.github.v3+json")
            .timeout(Some(std::time::Duration::new(30, 0)))
            .send(&mut writer)
            .map_err(anyhow::Error::new)
            .context("Could not lookup wasmer repository on Github.")?;

        if response.status_code() != StatusCode::new(200) {
            return Err(anyhow!(
                "Github API replied with non-200 status code: {}",
                response.status_code()
            ));
        }

        let v: std::result::Result<serde_json::Value, _> = serde_json::from_reader(&*writer);
        let mut response = v.map_err(anyhow::Error::new)?;

        if let Some(releases) = response.as_array_mut() {
            releases.retain(|r| {
                r["tag_name"].is_string() && !r["tag_name"].as_str().unwrap().is_empty()
            });
            releases.sort_by_cached_key(|r| r["tag_name"].as_str().unwrap_or_default().to_string());
            if let Some(latest) = releases.pop() {
                return Ok(latest);
            }
        }

        Err(anyhow!(
            "Could not get expected Github API response.\n\nReason: response format is not recognized:\n{:#?}", ""
        ))
    }

    pub fn download_release(
        mut release: serde_json::Value,
        target_triple: wasmer::Triple,
    ) -> Result<std::path::PathBuf> {
        let check_arch = |name: &str| -> bool {
            match target_triple.architecture {
                wasmer_types::Architecture::X86_64 => {
                    name.contains("x86_64") || name.contains("amd64")
                }
                wasmer_types::Architecture::Aarch64(wasmer_types::Aarch64Architecture::Aarch64) => {
                    name.contains("arm64") || name.contains("aarch64")
                }
                _ => false,
            }
        };

        let check_vendor = |name: &str| -> bool {
            match target_triple.vendor {
                wasmer_types::Vendor::Apple => {
                    name.contains("apple") || name.contains("macos") || name.contains("darwin")
                }
                wasmer_types::Vendor::Pc => name.contains("windows"),
                _ => true,
            }
        };
        let check_os = |name: &str| -> bool {
            match target_triple.operating_system {
                wasmer_types::OperatingSystem::Darwin => {
                    name.contains("apple") || name.contains("darwin") || name.contains("macos")
                }
                wasmer_types::OperatingSystem::Windows => name.contains("windows"),
                wasmer_types::OperatingSystem::Linux => name.contains("linux"),
                _ => false,
            }
        };
        let check_env = |name: &str| -> bool {
            match target_triple.environment {
                wasmer_types::Environment::Musl => name.contains("musl"),
                _ => !name.contains("musl"),
            }
        };

        if let Ok(mut cache_path) = super::get_libwasmer_cache_path() {
            match std::fs::read_dir(&cache_path).and_then(|r| {
                r.map(|res| res.map(|e| e.path()))
                    .collect::<Result<Vec<_>, std::io::Error>>()
            }) {
                Ok(mut entries) => {
                    entries.retain(|p| p.to_str().map(|p| check_arch(p)).unwrap_or(true));
                    entries.retain(|p| p.to_str().map(|p| check_vendor(p)).unwrap_or(true));
                    entries.retain(|p| p.to_str().map(|p| check_os(p)).unwrap_or(true));
                    entries.retain(|p| p.to_str().map(|p| check_env(p)).unwrap_or(true));
                    if entries.len() == 1 {
                        cache_path.push(&entries[0]);
                        if cache_path.exists() {
                            eprintln!(
                                "Using cached tarball to cache path `{}`.",
                                cache_path.display()
                            );
                            return Ok(cache_path);
                        }
                    }
                }
                Err(_ioerr) => {}
            }
        }
        if let Some(assets) = release["assets"].as_array_mut() {
            assets.retain(|a| {
                if let Some(name) = a["name"].as_str() {
                    check_arch(name)
                } else {
                    false
                }
            });
            assets.retain(|a| {
                if let Some(name) = a["name"].as_str() {
                    check_vendor(name)
                } else {
                    false
                }
            });
            assets.retain(|a| {
                if let Some(name) = a["name"].as_str() {
                    check_os(name)
                } else {
                    false
                }
            });
            assets.retain(|a| {
                if let Some(name) = a["name"].as_str() {
                    check_env(name)
                } else {
                    false
                }
            });

            if assets.len() == 1 {
                let browser_download_url =
                    if let Some(url) = assets[0]["browser_download_url"].as_str() {
                        url.to_string()
                    } else {
                        return Err(anyhow!(
                            "Could not get download url from Github API response."
                        ));
                    };
                let filename = browser_download_url
                    .split('/')
                    .last()
                    .unwrap_or("output")
                    .to_string();
                let mut file = std::fs::File::create(&filename)?;
                println!("Downloading {} to {}", browser_download_url, &filename);
                let download_thread: std::thread::JoinHandle<Result<Response, anyhow::Error>> =
                    std::thread::spawn(move || {
                        let uri = Uri::try_from(browser_download_url.as_str())?;
                        let mut response = Request::new(&uri)
                            .header("User-Agent", "wasmer")
                            .send(&mut file)
                            .map_err(anyhow::Error::new)
                            .context("Could not lookup wasmer artifact on Github.")?;
                        if response.status_code() == StatusCode::new(302) {
                            let redirect_uri =
                                Uri::try_from(response.headers().get("Location").unwrap().as_str())
                                    .unwrap();
                            response = Request::new(&redirect_uri)
                                .header("User-Agent", "wasmer")
                                .send(&mut file)
                                .map_err(anyhow::Error::new)
                                .context("Could not lookup wasmer artifact on Github.")?;
                        }
                        Ok(response)
                    });
                let _response = download_thread
                    .join()
                    .expect("Could not join downloading thread");
                match super::get_libwasmer_cache_path() {
                    Ok(mut cache_path) => {
                        let _ = std::fs::create_dir_all(&cache_path);
                        cache_path.push(&filename);
                        if !cache_path.exists() {
                            if let Err(err) = std::fs::copy(&filename, &cache_path) {
                                eprintln!(
                                    "Could not store tarball to cache path `{}`: {}",
                                    cache_path.display(),
                                    err
                                );
                            } else {
                                eprintln!(
                                    "Cached tarball to cache path `{}`.",
                                    cache_path.display()
                                );
                            }
                        }
                    }
                    Err(err) => {
                        eprintln!(
                            "Could not determine cache path for downloaded binaries.: {}",
                            err
                        );
                    }
                }
                return Ok(filename.into());
            }
        }
        Err(anyhow!("Could not get release artifact."))
    }
}

fn untar(tarball: std::path::PathBuf) -> Result<Vec<String>> {
    let files = std::process::Command::new("tar")
        .arg("-tf")
        .arg(&tarball)
        .output()
        .expect("failed to execute process")
        .stdout;

    let files_s = String::from_utf8(files)?;

    let files = files_s
        .lines()
        .filter(|p| !p.ends_with('/'))
        .map(|s| s.to_string())
        .collect::<Vec<String>>();

    let _output = std::process::Command::new("tar")
        .arg("-xf")
        .arg(&tarball)
        .output()
        .expect("failed to execute process");
    Ok(files)
}

fn find_zig_binary(path: Option<PathBuf>) -> Result<PathBuf> {
    use std::env::split_paths;
    use std::ffi::OsStr;
    #[cfg(unix)]
    use std::os::unix::ffi::OsStrExt;
    let path_var = std::env::var("PATH").unwrap_or_default();
    #[cfg(unix)]
    let system_path_var = std::process::Command::new("getconf")
        .args(&["PATH"])
        .output()
        .map(|output| output.stdout)
        .unwrap_or_default();
    let retval = if let Some(p) = path {
        if p.exists() {
            p
        } else {
            return Err(anyhow!("Could not find `zig` binary in {}.", p.display()));
        }
    } else {
        let mut retval = None;
        for mut p in split_paths(&path_var).chain(split_paths(
            #[cfg(unix)]
            {
                &OsStr::from_bytes(&system_path_var[..])
            },
            #[cfg(not(unix))]
            {
                OsStr::new("")
            },
        )) {
            p.push("zig");
            if p.exists() {
                retval = Some(p);
                break;
            }
        }
        retval.ok_or_else(|| anyhow!("Could not find `zig` binary in PATH."))?
    };

    let version = std::process::Command::new(&retval)
        .arg("version")
        .output()
        .with_context(|| {
            format!(
                "Could not execute `zig` binary at path `{}`",
                retval.display()
            )
        })?
        .stdout;
    let version_slice = if let Some(pos) = version
        .iter()
        .position(|c| !(c.is_ascii_digit() || (*c == b'.')))
    {
        &version[..pos]
    } else {
        &version[..]
    };

    if version_slice < b"0.10.0".as_ref() {
        Err(anyhow!("`zig` binary in PATH (`{}`) is not a new enough version (`{}`): please use version `0.10.0` or newer.", retval.display(), String::from_utf8_lossy(version_slice)))
    } else {
        Ok(retval)
    }
}