path: root/src/main.zig

const std = @import("std");
const log = std.log.scoped(.server);

// Web server for mfashby.net
// It does _not_ follow the unix philosophy (:
// Initially it replaces caddy, and it needs to be capable of these things 
// to actually be usable
//  - http(s) (otherwise it's not a web server...) ✅ https isn't supported because zig http server (in fact there's no TLS server implementation). For now I'll have to use haproxy
//  - routing, including virtual host              ✅
//  - serving static content from selected folders ✅
//  - executing CGI programs                       ✅
//  - reverse proxy                                ❌

// And I should probably test it thoroughly before exposing is to the 'net

// Future possibilities: 
//  - subsume some CGI programs directly into the web server e.g. my comments program
//  - and maybe even cgit (although I might scrap it in favour of stagit if I can figure out archive downloads
//  - do something about efficiency :) it's thread-per-request right now
pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{
        .thread_safe = true,
    }){};
    defer {
        log.info("deinit gpa", .{});
        _ = gpa.deinit();
    }
    const a = gpa.allocator();

    var pool: std.Thread.Pool = undefined;
    try std.Thread.Pool.init(&pool, .{ .allocator = a, .n_jobs = 32 });
    defer pool.deinit();

    var svr = std.http.Server.init(.{ .reuse_address = true, .reuse_port = true });
    const addr = try std.net.Address.parseIp("0.0.0.0", 8081);
    try svr.listen(addr);
    log.info("listening on {}", .{addr});
    while (true) {
        // Create the Response into the heap so that the ownership goes to the handling thread
        const res = try a.create(std.http.Server.Response);
        errdefer a.destroy(res);
        res.* = try svr.accept(.{ .allocator = a });
        errdefer res.deinit();
        try pool.spawn(handle, .{res});
    }
}

fn handle(res: *std.http.Server.Response) void {
    defer res.allocator.destroy(res);
    defer res.deinit();
    handleRoute(res) catch |e| {
        log.info("error {}", .{e});
        if (@errorReturnTrace()) |trace| {
            std.debug.dumpStackTrace(trace.*);
        }
        sendError(res, e) catch |e2| {
            log.info("error sending error {}", .{e2});
            if (@errorReturnTrace()) |trace| {
                std.debug.dumpStackTrace(trace.*);
            }
        };
    };
}

fn handleRoute(res: *std.http.Server.Response) !void {
    try res.wait();

    // Route, virtual host first
    var host: []const u8 = "";
    if (res.request.headers.getFirstValue("Host")) |host_header| {
        var spl = std.mem.splitScalar(u8, host_header, ':');
        host = spl.first();
    }

    const uri = std.Uri.parseWithoutScheme(res.request.target) catch {
        res.status = .bad_request;
        const msg = "bad request target";
        res.transfer_encoding = .{ .content_length = msg.len };
        try res.send();
        try res.writeAll(msg);
        try res.finish();
        return;
    };

    if (std.mem.eql(u8, host, "localhost")) {
        if (std.mem.startsWith(u8,  uri.path, "/api")) {
            try serveCgi(res, "/home/martin/dev/mfashby.net/comments/zig-out/bin/comments",
                &.{"DATABASE_URL","SMTP_USERNAME","SMTP_PASSWORD","NOTIFICATION_ADDRESS","SMTP_SERVER"});
        } else {
            try serveStatic(res, "public");
        }
    } else {
        const ans = "You have reached mfashby.net ... but did you mean to?";
        res.status = .ok;
        res.transfer_encoding = .{ .content_length = ans.len };
        try res.send();
        try res.writeAll(ans);
        try res.finish();
    }
}

fn serveCgi(res: *std.http.Server.Response, executable: []const u8,
            comptime env_copy: []const []const u8) !void {
    var child = std.ChildProcess.init(&.{executable}, res.allocator);
    child.stdin_behavior = .Pipe;
    child.stdout_behavior = .Pipe;
    child.stderr_behavior = .Pipe;

    var env = std.process.EnvMap.init(res.allocator);
    try env.put("REQUEST_METHOD", @tagName(res.request.method));
    try env.put("REQUEST_URI", res.request.target);
    inline for (env_copy) |key| {
        try env.put(key, std.os.getenv(key) orelse "");
    }
    var clb = [_]u8{0}**30;
    if (res.request.method == .POST) {
        if (res.request.content_length) |cl| {
            try env.put("CONTENT_LENGTH", try std.fmt.bufPrint(&clb, "{}", .{cl}));
        }
    }
    child.env_map = &env;
    try child.spawn();
    
    if (res.request.method == .POST) {
        if (res.request.content_length) |cl| {
            log.info("sending {} data as CGI body", .{cl});
            try pump(res.reader(), child.stdin.?.writer(), cl);
        } else {
            _ = try pumpUnknown(res.reader(), child.stdin.?.writer());
        }
    }
    var stdout = std.ArrayList(u8).init(res.allocator);
    var stderr = std.ArrayList(u8).init(res.allocator);
    defer stdout.deinit();
    defer stderr.deinit();
    defer {
        if (stderr.items.len>0) {
            log.err("CGI error: {s}", .{stderr.items});
        }
    }
    try child.collectOutput(&stdout, &stderr, 1_000_000);
    const term = try child.wait();
    if (term.Exited != 0) {
        return error.ProcessError;
    }

    var fbs = std.io.fixedBufferStream(stdout.items);
    var reader = fbs.reader();
    var headerLine = std.ArrayList(u8).init(res.allocator);
    defer headerLine.deinit();
    while (true) {
        headerLine.clearRetainingCapacity();
        try reader.streamUntilDelimiter(headerLine.writer(), '\r', 8192);
        _ = try reader.skipBytes(1, .{}); // \n
        if (headerLine.items.len == 0) {
            break;
        }
        var spl = std.mem.splitScalar(u8, headerLine.items, ':');
        const key = try std.ascii.allocLowerString(res.allocator, spl.first());
        defer res.allocator.free(key);
        if (std.mem.eql(u8, key, "status")) {
            const value = spl.rest();
            var spl2 = std.mem.splitScalar(u8, std.mem.trim(u8, value, " "), ' ');
            res.status = @enumFromInt(try std.fmt.parseInt(u16, spl2.first(), 10));
            log.info("status from CGI {}", .{res.status});
        } else if (std.mem.eql(u8, key, "content-length")) {
            const value = spl.rest();
            res.transfer_encoding = .{.content_length = try std.fmt.parseInt(usize, value, 10)};
            log.info("transfer_encoding from CGI {}", .{res.transfer_encoding});
        } else {
            const value = spl.rest();
            try res.headers.append(key, std.mem.trim(u8, value, " "));
            log.info("header from CGI {s}: {s}", .{key, value});
        }
    }

    if (res.transfer_encoding == .content_length) {
        try res.send();
        try pump(reader, res.writer(), res.transfer_encoding.content_length);
    } else {
        res.transfer_encoding = .chunked;
        try res.send();
        _ = try pumpUnknown(reader, res.writer());
    }
    try res.finish();
}

fn serveStatic(res: *std.http.Server.Response, dirname: []const u8) !void {
    const dirpath = try std.fs.realpathAlloc(res.allocator, dirname);
    defer res.allocator.free(dirpath);

    // Path massaging
    const uri = std.Uri.parseWithoutScheme(res.request.target) catch {
        res.status = .bad_request;
        const msg = "bad request target";
        res.transfer_encoding = .{ .content_length = msg.len };
        try res.send();
        try res.writeAll(msg);
        try res.finish();
        return;
    };
    var requested_path = uri.path;
    requested_path = try std.fs.path.join(res.allocator, &.{ dirpath, requested_path });


    const path = std.fs.realpathAlloc(res.allocator, requested_path) catch |e| {
        res.status = switch (e) {
            error.FileNotFound => .not_found,
            error.AccessDenied => .forbidden,
            error.BadPathName => .bad_request,
            else => .internal_server_error,
        };
        const msg = try std.fmt.allocPrint(res.allocator, "error: {}", .{e});
        defer res.allocator.free(msg);
        res.transfer_encoding = .{ .content_length = msg.len };
        try res.send();
        try res.writeAll(msg);
        try res.finish();
        return;
    };

    defer res.allocator.free(path);
    if (!std.mem.startsWith(u8, path, dirpath)) {
        res.status = .bad_request;
        const msg = try std.fmt.allocPrint(res.allocator, "Trying to escape the root directory {s}", .{path});
        defer res.allocator.free(msg);
        res.transfer_encoding = .{ .content_length = msg.len };
        try res.send();
        try res.writeAll(msg);
        try res.finish();
        return;
    }
    const f = std.fs.openFileAbsolute(path, .{}) catch |e| {
        res.status = switch (e) {
            error.FileNotFound => .not_found,
            error.AccessDenied => .forbidden,
            error.BadPathName, error.NameTooLong => .bad_request,
            else => .internal_server_error,
        };
        const msg = try std.fmt.allocPrint(res.allocator, "error: {}", .{e});
        defer res.allocator.free(msg);
        res.transfer_encoding = .{ .content_length = msg.len };
        try res.send();
        try res.writeAll(msg);
        try res.finish();
        return;
    };
    defer f.close();
    const stat = try f.stat();
    switch (stat.kind) {
        .file => {
            res.transfer_encoding = .{ .content_length = stat.size };
            try res.send();
            try pump(f.reader(), res.writer(), stat.size);
            try res.finish();
        },
        .directory => {
            const index_path = try std.fs.path.join(res.allocator, &.{path, "index.html"});
            defer res.allocator.free(index_path);
            const index_f = std.fs.openFileAbsolute(index_path, .{}) catch |e| {
                res.status = switch (e) {
                    error.FileNotFound => .not_found,
                    error.AccessDenied => .forbidden,
                    error.BadPathName, error.NameTooLong => .bad_request,
                    else => .internal_server_error,
                };
                const msg = try std.fmt.allocPrint(res.allocator, "error: {}", .{e});
                defer res.allocator.free(msg);
                res.transfer_encoding = .{ .content_length = msg.len };
                try res.send();
                try res.writeAll(msg);
                try res.finish();
                return;
            };
            defer index_f.close();
            const index_stat = try index_f.stat();
            res.transfer_encoding = .{ .content_length = index_stat.size };
            try res.send();
            try pump(index_f.reader(), res.writer(), index_stat.size);
            try res.finish();  
        },
        else => {
            const msg = "unable to serve unsupported file kind";
            res.status = .unavailable_for_legal_reasons;
            res.transfer_encoding = .{.content_length = msg.len};
            try res.send();
            try res.writeAll(msg);
            try res.finish();
        }
    }
    
}

fn pumpUnknown(reader: anytype, writer: anytype) !usize {
    var read: usize = 0;
    var buf: [1024]u8 = undefined;
    while (true) {
        const sz = try reader.read(&buf);
        if (sz == 0) break;
        read += sz;
        try writer.writeAll(buf[0..sz]);
    }
    return read;
}

fn pump(reader: anytype, writer: anytype, expected: usize) !void {
    var read: usize = 0;
    var buf: [1024]u8 = undefined;
    while (true) {
        const sz = try reader.read(&buf);
        if (sz == 0) break;
        read += sz;
        if (read > expected) return error.TooMuchData;
        try writer.writeAll(buf[0..sz]);
    }
    if (read != expected) {
        return error.NotEnoughData;
    }
}


fn sendError(res: *std.http.Server.Response, e: anyerror) !void {
    switch (res.state) {
        .first, .start, .waited => {
            if (res.state != .waited) {
                try res.wait();
            }
            const errmsg = try std.fmt.allocPrint(res.allocator, "Error: {}", .{e});
            defer res.allocator.free(errmsg);
            // Now send an error
            res.status = .internal_server_error;
            res.transfer_encoding = .{ .content_length = errmsg.len };
            try res.send();
            try res.writeAll(errmsg);
            try res.finish();
        },
        .responded, .finished => {
            // Too late!
            log.err("can't send an error, response already sent, state {}", .{res.state});
        },
    }
}