improve: port common code to C

This commit ports even more C++ code to C99, now, the codes available in the "common" folder.

loader/src/common/socket_utils.c

@@ -0,0 +1,95 @@
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/socket.h>
+
+#include <unistd.h>
+
+#include "logging.h"
+
+#include "socket_utils.h"
+
+/* TODO: Standardize how to log errors */
+int read_fd(int fd) {
+  char cmsgbuf[CMSG_SPACE(sizeof(int))];
+
+  int cnt = 1;
+  struct iovec iov = {
+    .iov_base = &cnt,
+    .iov_len = sizeof(cnt)
+  };
+
+  struct msghdr msg = {
+    .msg_iov = &iov,
+    .msg_iovlen = 1,
+    .msg_control = cmsgbuf,
+    .msg_controllen = sizeof(cmsgbuf)
+  };
+
+  ssize_t ret = recvmsg(fd, &msg, MSG_WAITALL);
+  if (ret == -1) {
+    PLOGE("recvmsg");
+
+    return -1;
+  }
+
+  struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+  if (cmsg == NULL) {
+    PLOGE("CMSG_FIRSTHDR");
+
+    return -1;
+  }
+
+  int sendfd;
+  memcpy(&sendfd, CMSG_DATA(cmsg), sizeof(int));
+
+  return sendfd;
+}
+
+char *read_string(int fd) {
+  size_t str_len = 0;
+  ssize_t read_bytes = read(fd, &str_len, sizeof(size_t));
+  if (read_bytes != (ssize_t)sizeof(size_t)) {
+    LOGE("Failed to read string length: Not all bytes were read (%zd != %zu).\n", read_bytes, sizeof(size_t));
+
+    return NULL;
+  }
+
+  char *buf = malloc(str_len + 1);
+  if (buf == NULL) {
+    PLOGE("allocate memory for string");
+
+    return NULL;
+  }
+
+  read_bytes = read(fd, buf, str_len);
+  if (read_bytes != (ssize_t)str_len) {
+    LOGE("Failed to read string: Promised bytes doesn't exist (%zd != %zu).\n", read_bytes, str_len);
+
+    free(buf);
+
+    return NULL;
+  }
+
+  if (str_len > 0) buf[str_len] = '\0';
+
+  return buf;
+}
+
+#define write_func(type)                    \
+  ssize_t write_## type(int fd, type val) { \
+    return write(fd, &val, sizeof(type));   \
+  }
+
+#define read_func(type)                     \
+  ssize_t read_## type(int fd, type *val) { \
+    return read(fd, val, sizeof(type));     \
+  }
+
+write_func(uint8_t)
+read_func(uint8_t)
+
+write_func(uint32_t)
+read_func(uint32_t)
+
+write_func(size_t)
+read_func(size_t)