minecraft-assets/data/minecraft/recipes/hopper.json

{
  "type": "minecraft:crafting_shaped",
  "category": "redstone",
  "key": {
    "C": {
      "item": "minecraft:chest"
    },
    "I": {
      "item": "minecraft:iron_ingot"
    }
  },
  "pattern": [
    "I I",
    "ICI",
    " I "
  ],
  "result": {
    "item": "minecraft:hopper"
  }
}