build.rs

// Derived from https://github.com/pellizzetti/router/blob/cc0ebcaf1d68184e1fe06f16534fddff76286b40/apollo-spaceport/build.rs
use protobuf_codegen::Customize;
use std::io::Write;
use std::path::Path;
use std::{
    error::Error,
    fs::File,
    io::{copy, Read},
};

fn main() -> Result<(), Box<dyn Error>> {
    // Skip building online from docs.rs
    if std::env::var_os("DOCS_RS").is_some() {
    } else {
        // Retrieve a live version of the reports.proto file
        let proto_url = "https://usage-reporting.api.apollographql.com/proto/reports.proto";
        let fut = reqwest::get(proto_url);

        cfg_if::cfg_if! {
            if #[cfg(not(target_arch = "wasm32"))] {
                let rt = tokio::runtime::Runtime::new().unwrap();
                let response = rt.block_on(fut)?;
                let mut content = rt.block_on(response.text())?;
            } else {
                let response = async_std::task::block_on(fut)?;
                let mut content = async_std::task::block_on(response.text())?;
            }
        }

        // Process the retrieved content to:
        //  - Insert a package Report; line after the import lines (currently only one) and before the first message definition
        //  - Remove the Apollo TS extensions [(js_use_toArray)=true] and [(js_preEncoded)=true] from the file
        //  Note: Only two in use at the moment. This may fail in future if new extensions are
        //  added to the source, so be aware future self. It will manifest as a protobuf compile
        //  error.
        let message = "\nmessage";
        let msg_index = content.find(message).ok_or("cannot find message string")?;
        content.insert_str(msg_index, "\npackage Report;\n");

        content = content.replace("[(js_use_toArray) = true]", "");
        content = content.replace("[(js_preEncoded) = true]", "");

        // Try to avoid writing out the same content since it will trigger unnecessary re-builds, which wastes time
        let write_content = match File::open("proto/reports.proto") {
            Ok(mut existing) => {
                let mut existing_content = String::new();
                existing.read_to_string(&mut existing_content)?;
                content != existing_content
            }
            Err(_) => true,
        };

        // Write the content out if they differ or an error occured trying to open proto file
        if write_content {
            let mut dest = File::create("proto/reports.proto")?;
            copy(&mut content.as_bytes(), &mut dest)?;
        }
    }

    // Process the proto files
    let proto_files = vec!["proto/reports.proto"];

    protobuf_codegen::Codegen::new()
        .pure()
        .cargo_out_dir("proto")
        .inputs(&proto_files)
        .include(".")
        .customize(Customize::default().gen_mod_rs(false))
        .run_from_script();

    let out_dir = std::env::var("OUT_DIR")?;
    let path = Path::new(&out_dir).join("proto").join("reports.rs");
    let content = std::fs::read_to_string(&path)?;

    let content = content
        .lines()
        .filter(|line| !(line.contains("#![") || line.contains("//!")))
        .fold(String::new(), |mut content, line| {
            content.push_str(line);
            content.push('\n');
            content
        });

    std::fs::remove_file(&path)?;
    let mut file = std::fs::File::create(&path)?;
    file.write_all(content.as_bytes())?;

    for file in proto_files {
        println!("cargo:rerun-if-changed={}", file);
    }

    Ok(())
}