server: Add JSON-RPC scaffolding code.

Author: frabert

include/vast/server/io.hpp

@@ -0,0 +1,103 @@
+// Copyright (c) 2024-present, Trail of Bits, Inc.
+
+#pragma once
+
+#include <memory>
+#include <span>
+#include <stdexcept>
+#include <string>
+
+#include <stdio.h>
+
+#include <gap/core/crtp.hpp>
+
+#include "vast/Util/Warnings.hpp"
+
+namespace vast::server {
+    class connection_closed : public std::runtime_error
+    {
+      public:
+        connection_closed() : std::runtime_error("Connection closed") {}
+
+        connection_closed(const char *what) : std::runtime_error(what) {}
+    };
+
+    struct io_adapter
+    {
+        virtual ~io_adapter() = default;
+
+        virtual void close() {}
+
+        virtual size_t read_some(std::span< char > dst)        = 0;
+        virtual size_t write_some(std::span< const char > dst) = 0;
+
+        // Upon completion, `dst` is filled with data.
+        void read_all(std::span< char > dst) {
+            while (!dst.empty()) {
+                size_t nread = read_some(dst);
+                dst          = dst.subspan(nread);
+            }
+        }
+
+        // Upon completion, all of the data in `src` is written to the client..
+        void write_all(std::span< const char > src) {
+            while (!src.empty()) {
+                size_t nwritten = write_some(src);
+                src             = src.subspan(nwritten);
+            }
+        }
+
+        char read() {
+            char res[1];
+            read_all(res);
+            return res[0];
+        }
+    };
+
+    class file_adapter final : public io_adapter
+    {
+        FILE *ifd;
+        FILE *ofd;
+
+      public:
+        file_adapter(FILE *ifd = stdin, FILE *ofd = stdout) : ifd(ifd), ofd(ofd) {
+            VAST_ASSERT(ifd != nullptr);
+            VAST_ASSERT(ofd != nullptr);
+
+            setvbuf(ofd, NULL, _IONBF, 0);
+        }
+
+        size_t read_some(std::span< char > dst) override {
+            size_t nread = fread(dst.data(), 1, dst.size_bytes(), ifd);
+            if (nread == 0 && (feof(ifd) || ferror(ifd))) {
+                throw connection_closed{};
+            }
+            return nread;
+        }
+
+        size_t write_some(std::span< const char > src) override {
+            size_t nwritten = fwrite(src.data(), 1, src.size_bytes(), ofd);
+            if (src.size() != 0 && nwritten == 0) {
+                throw connection_closed{};
+            }
+            return nwritten;
+        }
+    };
+
+    class sock_adapter final : public io_adapter
+    {
+      public:
+        struct impl;
+
+        size_t read_some(std::span< char > dst) override;
+        size_t write_some(std::span< const char > src) override;
+        ~sock_adapter();
+        void close() override;
+
+        static std::unique_ptr< sock_adapter > create_unix_socket(const std::string &path);
+
+      private:
+        std::unique_ptr< struct impl > pimpl;
+        sock_adapter(std::unique_ptr< impl > pimpl);
+    };
+} // namespace vast::server