Provide a Zig string to a c lib function, converting a Zig String to a C string

Help
1

Hello,

I’m still learning Zig and I’m quite sure that I’m somewhat blindfold and I don’t got it.
But for now I need some help.

I’m using the Zap library for providing an embedded web server (Zig Zap).
I’m just going to enable the tls functionality, which is working so far, when I’m providing the path to my certificate file und key file by creating a string literal and assigning that string literal.

...
const CERT_FILE = "/workspaces/oauth2_02/certificates/srv-git2.crt";
const KEY_FILE = "/workspaces/oauth2_02/certificates/srv-git2.key";
...
    const tls = try zap.Tls.init(.{
        .server_name = "localhost:3000",
        .public_certificate_file = CERT_FILE,
        .private_key_file = KEY_FILE,
    });

...

That’s working.

Now I’m trying to read the file path from an .env file:
.env

CLIENT_CERTIFICATE_FILE="/workspace/oauth2_02/certificates/srv-git2.crt"
CLIENT_CERTIFICATE_KEY="/workspace/oauth2_02/certificates/srv-it2.key"

.zig

...
somehandler.clientCertificate = try std.process.getEnvVarOwned(allocator, "CLIENT_CERTIFICATE_FILE"),
...

const tls = try zap.Tls.init(.{
        .server_name = "localhost:3000",
        .public_certificate_file = somehandler.clientCertificate;
        .private_key_file = KEY_FILE,
    });

That is NOT working!

tls.public_certificate_file is type of [*:0]const u8; a C string.
somehandler.clientCertificate is type of const 8; a Zig string.

How can I convert that Zig string into a C string?

I’ve tried all this bufPrintZ, allocPrintZ, dupeZ stuff.
But I don’t got it working.

Maybe someone can just show me the right conversion.

Any help is realy appriciated!

BR SMF

2

What type of somehandler.clientCertificate is?
Probably, You can use dupeZ to achive it.

const tls = try zap.Tls.init(.{
      .server_name = "localhost:3000",
      .public_certificate_file = try allocator.dupe(u8, somehandler.clientCertificate);
      .private_key_file = KEY_FILE,
  });
3

Hi ktz_alias,

thank you for your help.

somehandler.clientCertificate is type of []const u8.

Trying

.public_certificate_file = try allocator.dupe(u8, somehandler.clientCertificate);

results in the following compile error:

src/main.zig:63:10: error: expected type '?[*:0]const u8', found '[]u8'
        .public_certificate_file = try allocator.dupe(u8, oauth2Handler.clientCertificate),
        ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Trying

.public_certificate_file = try allocator.dupe([]const u8, oauth2Handler.clientCertificate),

leads to the following compile error:

src/main.zig:63:80: error: expected type '[]const []const u8', found '[]const u8'
        .public_certificate_file = try allocator.dupe([]const u8, oauth2Handler.clientCertificate),
                                                                  ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~

I don’t understand this error.
But maybe there is another idea I haven’t seen until now.

BR SMF

4 
const str = try allocator.dupeZ(u8, somehandler.clientCertificate);
...
.public_certificate_file = str.ptr,

dupeZ to get a copy of the string that is zero terminated, .ptr to access the multi-item-pointer [*:0]u8, which can be automatically coerced to [*:0]const u8 and ?[*:0]const u8.

dupe expects the type of the slice element as first parameter not the type of the resulting slice. So if you pass it T dupe returns a []T and dupeZ returns a [:0]T.

3 Likes
5

Hi Sze,

yepp, that does the trick :+1: :+1:

Thank you very much for your help and your explanation.
I realy appriciated that.

BR SMF

1 Like