[yellowstone] Add yellowstone server for endpoint registration.

lib/mammoth/include/mammoth/endpoint_client.h

@@ -12,6 +12,8 @@ class EndpointClient {
   template <typename Req, typename Resp>
   glcr::ErrorOr<glcr::Pair<Resp, z_cap_t>> CallEndpoint(const Req& req);
 
+  z_cap_t GetCap() { return cap_; }
+
  private:
   EndpointClient(uint64_t cap) : cap_(cap) {}
   z_cap_t cap_;

lib/mammoth/include/mammoth/port.h

@@ -1,17 +1,27 @@
 #pragma once
 
+#include <glacier/status/error_or.h>
+#include <glacier/string/string.h>
 #include <stdint.h>
 #include <zcall.h>
 
+// FIXME: Split send and receive.
 class Port {
  public:
+  static glcr::ErrorOr<Port> Create();
   Port(uint64_t port_cap);
 
+  glcr::ErrorCode RecvCap(uint64_t* num_bytes, char* msg, uint64_t* cap);
   z_err_t PollForIntCap(uint64_t* msg, uint64_t* cap);
 
   template <typename T>
   z_err_t WriteMessage(const T& obj, uint64_t cap);
 
+  glcr::ErrorCode WriteString(glcr::String str, uint64_t cap);
+
+  // FIXME: We can't create error_ors of ints
+  glcr::ErrorCode Duplicate(uint64_t* new_cap);
+
  private:
   uint64_t port_cap_;
 };

lib/mammoth/include/mammoth/process.h

@@ -1,8 +1,9 @@
 #pragma once
 
-#include <glacier/status/error_or.h>
+#include <glacier/status/error.h>
 #include <stdint.h>
 
 #include "mammoth/endpoint_client.h"
 
-glcr::ErrorOr<EndpointClient> SpawnProcessFromElfRegion(uint64_t program);
+glcr::ErrorCode SpawnProcessFromElfRegion(uint64_t program,
+                                          EndpointClient client);