I'm working on this app that allows users to upload PDF files to IPFS. A Document consists of the title, address (the uploader), price, description, and the file itself.


I've looked at other similar questions but none that I found solved my problem.


Whenever I fill out the information (as shown in the screenshot below), I always encounter this error that occurs in the onSubmit function.

Uncaught Error: invalid string value (arg="file", coderType="string", value=[{"path":"QmUqB9dWDCeZ5nth9YKRJTQ6PcnfrGPPx1vzdyNWV6rh8s","hash":"QmUqB9dWDCeZ5nth9YKRJTQ6PcnfrGPPx1vzdyNWV6rh8s","size":60035}]) at Object.n [as throwError] (web3.min.js:21199)



import React, { Component } from "react";
import MyContract from "./contracts/MyContract.json";
import Web3 from "web3";
import web3 from "./web3";
import ipfs from "./ipfs";
import storehash from "./storehash";

import "./styles/App.css";

class App extends Component {
  constructor(props) {
    this.state = {
      myContractHash: null,
      buffer: "",
      ethAddress: "",
      account: null

  async loadWeb3() {
    if (window.ethereum) {
      window.web3 = new Web3(window.ethereum);
      await window.ethereum.enable();
    } else if (window.web3) {
      window.web3 = new Web3(window.web3.currentProvider);
    } else {
      window.alert("Please switch to a browser that has an Ethereum wallet, such as MetaMask.");

  async loadBlockchain() {
    const web3 = window.web3;
    const accounts = await web3.eth.getAccounts();
    this.setState({ account: accounts[0] });

    const networkId = await web3.eth.net.getId();
    const networkData = MyContract.networks[networkId];

    if (networkData) {
      const contract = new web3.eth.Contract(MyContract.abi, networkData.address);
      this.setState({ contract });

      const myContractHash = await contract.methods.getHash().call();
      this.setState({ myContractHash });

  async componentWillMount() {
    await this.loadWeb3();
    await this.loadBlockchain();
  captureFile = (event) => {

    const file = event.target.files[0];

    let reader = new window.FileReader();
    reader.onloadend = () => this.convertToBuffer(reader);

  convertToBuffer = async (reader) => {
    // Convert file to buffer so that it can be uploaded to IPFS
    const buffer = await Buffer.from(reader.result);

  onSubmit = async (event) => {

    // Take the user's MetaMask address
    const accounts = await web3.eth.getAccounts();
    console.log("Sending from MetaMask account: " + accounts[0]);

    // To use the contract's methods
    this.MyContract = new web3.eth.Contract(

    // Retrieve the contract address from storehash.js
    const ethAddress= await storehash.options.address;
    // Save document to IPFS, return its hash, and set it to state
    await ipfs.add(this.state.buffer, (err, myContractHash) => {
      console.log(err, myContractHash);
      this.setState({ myContractHash: myContractHash[0].hash });

        .send({ from: this.account, gas: 5000000 });


  render() {
    return (
        <div className="header">
          <a href="/">
            <img src={require("./media/logo.png")} className="logo" />
          <div className="header-text">
            <span className="address">{this.state.account}</span>

        <div className="text-wrapper">
          <p className="heading">Publish a Document</p>
          <form onSubmit={this.onSubmit}>
            <input type="text" id="title" className="form-input" placeholder="Write title..." />
            <br />
            <input type="number" id="price" className="form-input" placeholder="0" />
            <br />
            <input type="textarea" id="description" className="form-input" placeholder="Write description..." />
            <br />
            <p>Choose a document to upload</p>
            <input type="file" onChange={this.captureFile} className="input-file" />

            <button type="submit">Publish</button>

        <div className="text-wrapper">
          <p className="heading">Feed</p>
      // <a href={`https://ipfs.infura.io/ipfs/${this.state.myContractHash}`}>Click to download the file</a>

export default App;


// SPDX-License-Identifier: MIT
pragma solidity >=0.5.16 <0.7.0;

contract MyContract {
  struct Document {
    string title;
    address payable uploader;
    uint256 price;
    string description;
    string file;

  string myContractHash;

  Document[] public documents;

  mapping(address => uint256[]) public filesUploaded;
  mapping(address => uint256[]) public documentsPublished;
  mapping(address => uint256[]) public documentsPurchased;

  // Setters
  function setHash(string memory ipfsHash) public {
    myContractHash = ipfsHash;

  // Getters
  function getHash() public view returns (string memory ipfsHash) {
    return myContractHash;

  function getDocument(uint256 i) public view returns (Document memory) {
    return documents[i];

  function getDocumentsPublishedTotal(address user) public view returns (uint256) {
    return documentsPublished[user].length;

  function getDocumentsPublished(address user, uint256 i) public view returns (uint256) {
    return documentsPublished[user][i];

  function getDocumentsPurchasedTotal(address user) public view returns (uint256) {
    return documentsPurchased[user].length;

  function getDocumentsPurchased(address user, uint256 i) public view returns (uint256) {
    return documentsPurchased[user][i];

  function publishDocument(
    string memory title,
    uint256 price,
    string memory description,
    string memory file
  ) public {
    require(bytes(title).length > 0 && bytes(title).length < 20, "Invalid title length");
    require(bytes(description).length > 0 && bytes(description).length < 10000, "Invalid description length");

    documents.push(Document(title, msg.sender, price, description, file));

  function isDocumentPurchased(uint256 i) public view returns (bool) {
    for (uint256 j = 0; j < documentsPurchased[msg.sender].length; j++) {
      if (documentsPurchased[msg.sender][j] == i) return true;
    return false;

  function purchaseDocument(uint256 i) setPause public payable {
    require(msg.sender != documents[i].uploader && !isDocumentPurchased(i));

    require(msg.value == documents[i].price, "Invalid price");



How do I solve this? Thank you for your help!

  • The message tells you that you are passing input parameter file to contract function publishDocument as a JSON object instead of as a string. – goodvibration Dec 24 '20 at 6:04
  • And BTW, please replace it from a screenshot to plaintext. – goodvibration Dec 24 '20 at 6:04
  • @goodvibration I've edited! – Wolfizzy Dec 24 '20 at 6:07
  • Great, do you understand the problem? – goodvibration Dec 24 '20 at 6:08
  • @goodvibration yes, but I'm not sure how to get it as a string. – Wolfizzy Dec 24 '20 at 6:11

Uncaught Error: invalid string value (arg="file", coderType="string", value=[{"path":"QmUqB9dWDCeZ5nth9YKRJTQ6PcnfrGPPx1vzdyNWV6rh8s","hash":"QmUqB9dWDCeZ5nth9YKRJTQ6PcnfrGPPx1vzdyNWV6rh8s","size":60035}]) at Object.n [as throwError] (web3.min.js:21199)

This error-message tells you that you are not passing the input argument file as a string.

And [{"path":"...","hash":"...","size":60035}] is indeed not a string, but an array of objects.

You may want to pass JSON.stringify(x) instead of x for this input argument.

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