生成策略与签名实现HTML POST直传Amazon S3桶报错排查

The error TypeError: a bytes-like object is required, not 'dict' pops up because you’re trying to base64-encode a Python dictionary directly—base64 only works on byte objects, not native data structures like dicts. Here’s how to fix this step by step:

Why the Error Happens #

AWS expects the policy document to be a minified UTF-8 JSON string (no extra whitespace) converted to bytes before base64 encoding. Your original code skips converting the dict to JSON bytes, hence the type mismatch.

Corrected Code with Explanations #

import base64
import hmac
import hashlib
import json  # Add JSON handling import

AWS_SECRET_ACCESS_KEY = 'AKIAIHHMU7Y4L2INOFRQ'
policy_document = {
    "expiration": "2019-01-01T00:00:00Z",
    "conditions": [
        {"bucket": "report-generation1"},
        ["starts-with", "$key", ""],
        {"acl": "private"},
        {"success_action_redirect": "localhost/"},  # Fixed trailing semicolon typo
        ["starts-with", "$Content-Type", ""],
        ["content-length-range", 0, 1048576]
    ]
}

# Step 1: Convert policy dict to minified JSON (required by AWS)
policy_json = json.dumps(policy_document, separators=(',', ':'))
# Step 2: Encode JSON string to UTF-8 bytes
policy_bytes = policy_json.encode('utf-8')
# Step 3: Base64 encode the bytes
policy = base64.b64encode(policy_bytes)

# Step 4: Encode secret key to bytes (HMAC requires byte input)
secret_key_bytes = AWS_SECRET_ACCESS_KEY.encode('utf-8')
# Step 5: Generate HMAC-SHA1 signature and base64 encode it
signature = base64.b64encode(hmac.new(secret_key_bytes, policy, hashlib.sha1).digest())

# Optional: Convert to strings for easy use in HTML form fields
policy_str = policy.decode('utf-8')
signature_str = signature.decode('utf-8')

Key Fixes & Notes #

• The separators=(',', ':') in json.dumps removes extra whitespace from the JSON, which is mandatory for AWS to validate the policy.
• Fixed a typo in success_action_redirect (removed the trailing semicolon inside the string).
• Converted the final policy and signature to strings so you can directly insert them into your HTML POST form’s hidden fields.

内容的提问来源于stack exchange，提问作者mrunal