Workaround ziglang/zig#24443

Author: Techatrix

src/lsp.zig

@@ -1334,9 +1334,23 @@ pub fn ThreadSafeTransport(config: ThreadSafeTransportConfig) type {
     };
 }
 
-pub fn readJsonMessage(reader: *std.io.Reader, allocator: std.mem.Allocator) (std.io.Reader.ReadAllocError || BaseProtocolHeader.ParseError)![]u8 {
+pub fn readJsonMessage(
+    reader: *std.io.Reader,
+    allocator: std.mem.Allocator,
+) (std.io.Reader.Error || std.mem.Allocator.Error || BaseProtocolHeader.ParseError)![]u8 {
     const header: BaseProtocolHeader = try .parse(reader);
-    return try reader.readAlloc(allocator, header.content_length);
+
+    // Use `readAlloc` once https://github.com/ziglang/zig/issues/24443 has been resolved:
+    // return try reader.readAlloc(allocator, header.content_length);
+
+    const json_message = try allocator.alloc(u8, header.content_length);
+    errdefer allocator.free(json_message);
+    var writer: std.io.Writer = .fixed(json_message);
+    reader.streamExact(&writer, json_message.len) catch |err| switch (err) {
+        error.ReadFailed, error.EndOfStream => |e| return e,
+        error.WriteFailed => unreachable, // fixed buffer
+    };
+    return json_message;
 }
 
 test readJsonMessage {