A Pydantic model for validating S3 URLs

s3path.py

import re
from pydantic import BaseModel, Field, computed_field

class S3Path(BaseModel):
    """Pydantic Model for S3 URLs"""
    
    # https://docs.aws.amazon.com/AmazonS3/latest/userguide/bucketnamingrules.html
    _s3_pattern = re.compile(
        r'^s3://'
        r'(?=[a-z0-9])'  # Bucket name must start with a letter or digit
        r'(?!(^xn--|sthree-|sthree-configurator|.+-s3alias$))'  # Bucket name must not start with xn--, sthree-, sthree-configurator or end with -s3alias
        r'(?!.*\.\.)'  # Bucket name must not contain two adjacent periods
        r'[a-z0-9][a-z0-9.-]{1,61}[a-z0-9]'  # Bucket naming constraints
        r'(?<!\.-$)'  # Bucket name must not end with a period followed by a hyphen
        r'(?<!\.$)'  # Bucket name must not end with a period
        r'(?<!-$)'  # Bucket name must not end with a hyphen
        r'(/([a-zA-Z0-9._-]+/?)*)?$'  # key naming constraints
    )    
    url : str = Field(...,
                      strip_whitespace = True,
                      pattern = _s3_pattern,
                      min_length=8,
                      max_length=1023)

    def s3_url_parts(self):
        #path_parts=self.url.replace('s3://', '').split("/")
        path_parts=self.url[5:].split("/")
        bucket=path_parts.pop(0)
        key='/'.join(path_parts)
        return (bucket, key)
    
    @computed_field
    @property
    def bucket(self) -> str:
        """Add bucket name as a computed property"""
        return self.s3_url_parts()[0]
    
    @computed_field
    @property
    def key(self) -> str:
        """Add key as a computed property"""
        return self.s3_url_parts()[1]
    
good_urls = [
    's3://my-bucket/',
    's3://my.bucket.name/my-key',
    's3://123-bucket/another/key/path',
    's3://bucket/this/is/a/folder/',
    's3://my-bucket/some/key/path/file.txt',
    's3://10-bucket-01/nested.folder/structure/file.jpg',
    's3://my-bucket/with-key']

bad_urls = [
    's3://',
    's3://my',
    'https://my-bucket/',
    's3://bucket-name/with/white space/in/key', 
    's3:/my-bucket/',
    's3://my_bucket/',
    's3://My-Bucket/',
    's3://123.bucketname./invalid',
    's3://123.bucketname.-/invalid',
    's3://123.bucket..name/invalid',
    's3://-bucket-starts-with-hyphen/',
    's3://bucket-ends-with-hyphen-/',
    's3://my-bucket/ends/with/slash//',
    's3://toolongnameofthebucketwhichexceedssixtyfourcharacterslongforthisexample/',
    's3://my-bucket/?query=parameters',
    's3://my-bucket/this/path/has/a/tab/char\there'
    ]

print(f'Validating {len(good_urls)} good urls')
good_fails = []
for url in good_urls:
    try:
        print(S3Path(url = url).model_dump())
    except Exception as e:
        print(f"Error for good {url}: {e}")
        good_fails.append(url)

print(f'Validating {len(bad_urls)} bad urls')
bad_fails = []
for url in bad_urls:
    try:
        print(S3Path(url = url).model_dump())
        print(f'Error bad url passes : {url}')
        bad_fails.append(url)
    except Exception as e:
        pass

print(f'Good urls that failed validation: {good_fails}')
print(f'Bad urls that failed validation: {bad_fails}')

See pydantic/pydantic#4271 for discussions on this issue