解决方法如下：

1. 创建一个Lambda函数来读取S3中的文件。以下是一个示例代码：

import boto3

def lambda_handler(event, context):
    s3 = boto3.client('s3')
    bucket_name = 'your-bucket-name'
    file_name = 'your-file-name'
    
    response = s3.get_object(Bucket=bucket_name, Key=file_name)
    file_contents = response['Body'].read().decode('utf-8')
    
    return {
        'statusCode': 200,
        'body': file_contents
    }

2. 创建一个API网关来触发Lambda函数。以下是一个示例代码：

import boto3

def create_rest_api():
    client = boto3.client('apigateway')

    # 创建REST API
    api_name = 'MyAPI'
    response = client.create_rest_api(
        name=api_name,
        description='My API'
    )
    api_id = response['id']
    
    # 创建资源
    response = client.create_resource(
        restApiId=api_id,
        parentId='root',
        pathPart='read-file'
    )
    resource_id = response['id']
    
    # 创建方法
    response = client.put_method(
        restApiId=api_id,
        resourceId=resource_id,
        httpMethod='GET',
        authorizationType='NONE'
    )
    
    # 配置Lambda集成
    uri = 'arn:aws:apigateway:your-region:lambda:path/2015-03-31/functions/your-lambda-function-arn/invocations'
    response = client.put_integration(
        restApiId=api_id,
        resourceId=resource_id,
        httpMethod='GET',
        type='AWS',
        integrationHttpMethod='POST',
        uri=uri
    )
    
    # 部署API
    response = client.create_deployment(
        restApiId=api_id,
        stageName='prod'
    )
    
    # 获取API的URL
    url = f"https://{api_id}.execute-api.your-region.amazonaws.com/prod/read-file"
    return url

# 创建API网关并获取URL
api_url = create_rest_api()
print(api_url)

这样，你就可以通过访问api_url来从S3中读取文件了。