Make C struct match the binary API more closely

Also make the internal conversion function return errors properly

build.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const Step = std.Build.Step;
 
 // Although this function looks imperative, note that its job is to
 // declaratively construct a build graph that will be executed by an external
@@ -37,13 +38,29 @@ pub fn build(b: *std.Build) void {
     exe_mod.addImport("zaprus", lib_mod);
     exe_mod.addImport("clap", b.dependency("clap", .{}).module("clap"));
 
-    const lib = b.addLibrary(.{
+    const static_lib = b.addLibrary(.{
         .linkage = .static,
         .name = "zaprus",
         .root_module = lib_mod,
     });
+    static_lib.addIncludePath(.{ .cwd_relative = "include" });
+    static_lib.linkLibC();
 
-    b.installArtifact(lib);
+    b.installArtifact(static_lib);
+
+    const dynamic_lib = b.addLibrary(.{
+        .linkage = .dynamic,
+        .name = "zaprus",
+        .root_module = lib_mod,
+    });
+    dynamic_lib.addIncludePath(.{ .cwd_relative = "include" });
+    dynamic_lib.linkLibC();
+
+    b.installArtifact(dynamic_lib);
+
+    // C Headers
+    const c_header = b.addInstallHeaderFile(b.path("include/zaprus.h"), "zaprus.h");
+    b.getInstallStep().dependOn(&c_header.step);
 
     // This creates another `std.Build.Step.Compile`, but this one builds an executable
     // rather than a static library.

include/zaprus.h

@@ -0,0 +1,51 @@
+// client
+
+#include<stdint.h>
+#include<stdlib.h>
+
+int zaprus_init(void);
+
+int zaprus_deinit(void);
+
+int zaprus_send_relay(const char* payload, size_t len, char dest[4]);
+
+int zaprus_send_initial_connection(const char* payload, size_t len, uint16_t initial_port);
+
+struct SaprusMessage* zaprus_connect(const char* payload, size_t len);
+
+// message
+#define SAPRUS_RELAY_MESSAGE_TYPE 0x003C
+#define SAPRUS_FILE_TRANSFER_MESSAGE_TYPE 0x8888
+#define SAPRUS_CONNECTION_MESSAGE_TYPE 0x00E9
+
+struct SaprusMessage {
+  uint16_t packet_type;
+  uint16_t payload_len;
+  union {
+    struct {
+      struct {
+	char dest[4];
+      };
+    } relay;
+    struct {
+      struct {
+	uint16_t src_port;
+	uint16_t dest_port;
+	uint32_t seq_num;
+	uint32_t msg_id;
+	char _reserved;
+	char options;
+      };
+      
+    } connection;
+  } headers;
+  char *payload;
+};
+
+// ptr should be freed by the caller.
+int zaprus_message_to_bytes(struct SaprusMessage msg, char** ptr, size_t* len);
+
+// Return value should be destroyed with zaprus_message_deinit.
+struct SaprusMessage* zaprus_message_from_bytes(const char* bytes, size_t len);
+
+void zaprus_message_deinit(struct SaprusMessage* msg);

src/c_api.zig

@@ -0,0 +1,115 @@
+const c = @cImport({
+    @cInclude("zaprus.h");
+});
+
+fn zigToCMessage(msg: ?*zaprus.Message) !?*c.SaprusMessage {
+    if (msg) |m| {
+        var res = c.SaprusMessage{
+            .packet_type = @intFromEnum(m.*),
+        };
+        switch (m.*) {
+            .relay => |r| {
+                res.headers.relay = .{
+                    .unnamed_0 = .{
+                        .dest = r.header.dest,
+                    },
+                };
+                res.payload_len = @intCast(r.payload.len);
+                res.payload = (try allocator.alloc(u8, r.payload.len)).ptr;
+            },
+            .connection => |con| {
+                res.headers.connection = .{
+                    .unnamed_0 = .{
+                        .src_port = con.header.src_port,
+                        .dest_port = con.header.dest_port,
+                        .seq_num = con.header.seq_num,
+                        .msg_id = con.header.msg_id,
+                        ._reserved = con.header.reserved,
+                        .options = @bitCast(con.header.options),
+                    },
+                };
+
+                res.payload_len = @intCast(con.payload.len);
+                res.payload = (try allocator.alloc(u8, con.payload.len)).ptr;
+            },
+            .file_transfer => return zaprus.Error.NotImplementedSaprusType,
+            else => return zaprus.Error.UnknownSaprusType,
+        }
+        return &res;
+    } else return null;
+}
+
+fn cToZigMessage(msg: ?*c.SaprusMessage) ?*zaprus.Message {
+    _ = msg;
+    return @constCast(&zaprus.Message{
+        .relay = .{
+            .header = .{ .dest = @splat(0) },
+            .payload = &.{0},
+        },
+    });
+}
+
+// client
+export fn zaprus_init() c_int {
+    SaprusClient.init() catch return 1;
+    return 0;
+}
+
+export fn zaprus_deinit() c_int {
+    SaprusClient.deinit();
+    return 0;
+}
+
+export fn zaprus_send_relay(payload: [*]const u8, len: usize, dest: [*]u8) c_int {
+    SaprusClient.sendRelay(payload[0..len], dest[0..4].*, allocator) catch return 1;
+    return 0;
+}
+
+export fn zaprus_send_initial_connection(payload: [*]const u8, len: usize, initial_port: u16) c_int {
+    _ = SaprusClient.sendInitialConnection(payload[0..len], initial_port, allocator) catch return 1;
+    return 0;
+}
+
+export fn zaprus_connect(payload: [*]const u8, len: usize) ?*c.SaprusMessage {
+    if (SaprusClient.connect(payload[0..len], allocator)) |msg| {
+        return zigToCMessage(@constCast(&(msg.?))) catch null;
+    } else |_| {
+        return null;
+    }
+}
+
+// message
+
+/// ptr should be freed by the caller.
+export fn zaprus_message_to_bytes(msg: c.SaprusMessage, ptr: *[*]u8, len: *usize) c_int {
+    if (cToZigMessage(@constCast(&msg))) |m| {
+        const bytes = m.toBytes(allocator) catch return 1;
+        ptr.* = bytes.ptr;
+        len.* = bytes.len;
+        return 0;
+    } else return 1;
+}
+
+/// Return value should be destroyed with zaprus_message_deinit.
+export fn zaprus_message_from_bytes(bytes: [*]const u8, len: usize) ?*c.SaprusMessage {
+    if (zaprus.Message.fromBytes(bytes[0..len], allocator)) |msg| {
+        return zigToCMessage(@constCast(&msg)) catch null;
+    } else |_| return null;
+}
+
+export fn zaprus_message_deinit(msg: *c.SaprusMessage) void {
+    // noop
+    _ = msg;
+    // msg.*.deinit(allocator);
+}
+
+const std = @import("std");
+
+const zaprus = @import("./root.zig");
+const SaprusClient = zaprus.Client;
+
+const allocator = std.heap.c_allocator;
+
+test {
+    std.testing.refAllDeclsRecursively(@This());
+}

src/root.zig

@@ -1,2 +1,4 @@
 pub const Client = @import("Client.zig");
 pub usingnamespace @import("message.zig");
+
+pub usingnamespace @import("c_api.zig");