codesnips
go 37 lines · 1 tab

Safe multipart uploads using temp files (bounded memory)

Leah Thompson Jan 2026
1 tab 
package api

import (
  "io"
  "net/http"
  "os"
)

func Upload(w http.ResponseWriter, r *http.Request) {
  r.Body = http.MaxBytesReader(w, r.Body, 20<<20) // 20 MiB
  if err := r.ParseMultipartForm(20 << 20); err != nil {
    http.Error(w, "invalid upload", http.StatusBadRequest)
    return
  }

  f, _, err := r.FormFile("file")
  if err != nil {
    http.Error(w, "missing file", http.StatusBadRequest)
    return
  }
  defer f.Close()

  tmp, err := os.CreateTemp("", "upload-*")
  if err != nil {
    http.Error(w, "server error", http.StatusInternalServerError)
    return
  }
  defer os.Remove(tmp.Name())
  defer tmp.Close()

  if _, err := io.Copy(tmp, f); err != nil {
    http.Error(w, "failed to save", http.StatusInternalServerError)
    return
  }

  w.WriteHeader(http.StatusCreated)
}
1 file · go Explain with highlit

Multipart uploads are a common DOS vector if you let them allocate unbounded memory. I cap the request with http.MaxBytesReader, keep ParseMultipartForm bounded, and copy the file stream into a temp file using io.Copy. This avoids holding the whole file in RAM and gives you an artifact you can scan, validate, and then push to object storage. The other detail is cleanup: if any validation fails, the temp file should be removed, and file descriptors must be closed. In production I also validate MIME type by sniffing the first bytes rather than trusting the client header, and I track upload metrics (bytes, errors) so abuse is visible. This pattern is pragmatic and safe for most services.

Related snips

go 
package api

import (
  "net/http"
  "runtime/debug"
)

Expose build metadata for debugging deploys

go observability build
by Leah Thompson 1 tab
ruby 
payload = {
  sub: user.id,
  iss: 'https://auth.example.com',
  aud: 'codesnips-api',
  exp: 15.minutes.from_now.to_i,
  iat: Time.now.to_i,

JWT issuance and verification without common footguns

jwt authentication api
by Kai Nakamura 2 tabs
typescript 
export interface RetryOptions {
  retries: number;
  baseMs: number;
  maxMs: number;
  signal?: AbortSignal;
  onRetry?: (attempt: number, delay: number, err: unknown) => void;

Exponential backoff with jitter for retries

typescript reliability retry
by codesnips 2 tabs
go 
package dbutil

import (
  "context"

  "github.com/jackc/pgconn"

Retry Postgres serialization failures with bounded attempts

go postgres transactions
by Leah Thompson 1 tab
bash 
#!/usr/bin/env bash
set -euo pipefail

export VAULT_ADDR="https://vault.internal:8200"
export VAULT_TOKEN="${VAULT_TOKEN:?missing VAULT_TOKEN}"

Secrets management with environment isolation and Vault

secrets-management vault environment-variables
by Kai Nakamura 1 tab
typescript 
import { randomBytes, createHash } from "crypto";
import jwt from "jsonwebtoken";
import { RefreshTokenStore } from "./store";

const ACCESS_SECRET = process.env.ACCESS_SECRET!;
const ACCESS_TTL = "15m";

JWT access + refresh token rotation (conceptual)

security node jwt
by codesnips 3 tabs

Share this code

Here's the card — post it anywhere.

Safe multipart uploads using temp files (bounded memory) — share card
Link copied