Update cURL example for unmanaged arraylist

zig-code/samples/curl.zig

@@ -1,9 +1,14 @@
-// compile with `zig build-exe zig-curl-test.zig --library curl --library c $(pkg-config --cflags libcurl)`
+//compile with `zig build-exe curl.zig -lcurl -lc $(pkg-config --cflags libcurl)`
 const std = @import("std");
 const cURL = @cImport({
     @cInclude("curl/curl.h");
 });
 
+const ResponseContext = struct {
+    buffer: std.ArrayList(u8),
+    allocator: std.mem.Allocator,
+};
+
 pub fn main() !void {
     var arena_state = std.heap.ArenaAllocator.init(std.heap.c_allocator);
     defer arena_state.deinit();
@@ -19,11 +24,14 @@ pub fn main() !void {
     const handle = cURL.curl_easy_init() orelse return error.CURLHandleInitFailed;
     defer cURL.curl_easy_cleanup(handle);
 
-    var response_buffer = std.ArrayList(u8).init(allocator);
+    var response_ctx = ResponseContext{
+        .buffer = std.ArrayList(u8).empty,
+        .allocator = allocator,
+    };
 
     // superfluous when using an arena allocator, but
     // important if the allocator implementation changes
-    defer response_buffer.deinit();
+    // defer response_ctx.buffer.deinit(allocator);
 
     // setup curl options
     if (cURL.curl_easy_setopt(handle, cURL.CURLOPT_URL, "https://ziglang.org") != cURL.CURLE_OK)
@@ -32,21 +40,26 @@ pub fn main() !void {
     // set write function callbacks
     if (cURL.curl_easy_setopt(handle, cURL.CURLOPT_WRITEFUNCTION, writeToArrayListCallback) != cURL.CURLE_OK)
         return error.CouldNotSetWriteCallback;
-    if (cURL.curl_easy_setopt(handle, cURL.CURLOPT_WRITEDATA, &response_buffer) != cURL.CURLE_OK)
+    if (cURL.curl_easy_setopt(handle, cURL.CURLOPT_WRITEDATA, &response_ctx) != cURL.CURLE_OK)
         return error.CouldNotSetWriteCallback;
 
     // perform
     if (cURL.curl_easy_perform(handle) != cURL.CURLE_OK)
         return error.FailedToPerformRequest;
 
-    std.log.info("Got response of {d} bytes", .{response_buffer.items.len});
-    std.debug.print("{s}\n", .{response_buffer.items});
+    std.log.info("Got response of {d} bytes", .{response_ctx.buffer.items.len});
+    std.debug.print("{s}\n", .{response_ctx.buffer.items});
 }
 
-fn writeToArrayListCallback(data: *anyopaque, size: c_uint, nmemb: c_uint, user_data: *anyopaque) callconv(.C) c_uint {
-    var buffer: *std.ArrayList(u8) = @alignCast(@ptrCast(user_data));
+fn writeToArrayListCallback(
+    data: *anyopaque,
+    size: usize,
+    nmemb: usize,
+    user_data: *anyopaque,
+) callconv(.c) usize {
+    var ctx: *ResponseContext = @ptrCast(@alignCast(user_data));
     var typed_data: [*]u8 = @ptrCast(data);
-    buffer.appendSlice(typed_data[0 .. nmemb * size]) catch return 0;
+    ctx.buffer.appendSlice(ctx.allocator, typed_data[0 .. nmemb * size]) catch return 0;
     return nmemb * size;
 }