refactor(std/http): move io functions to http/io.ts (#4126)

std/http/mock.ts

@@ -0,0 +1,26 @@
+/** Create dummy Deno.Conn object with given base properties */
+export function mockConn(base: Partial<Deno.Conn> = {}): Deno.Conn {
+  return {
+    localAddr: {
+      transport: "tcp",
+      hostname: "",
+      port: 0
+    },
+    remoteAddr: {
+      transport: "tcp",
+      hostname: "",
+      port: 0
+    },
+    rid: -1,
+    closeRead: (): void => {},
+    closeWrite: (): void => {},
+    read: async (): Promise<number | Deno.EOF> => {
+      return 0;
+    },
+    write: async (): Promise<number> => {
+      return -1;
+    },
+    close: (): void => {},
+    ...base
+  };
+}