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HTTP-API-based Connectors

The CDK offers base classes that greatly simplify writing HTTP API-based connectors. Some of the most useful features include helper functionality for:

  • Authentication (basic auth, Oauth2, or any custom auth method)
  • Pagination
  • Handling rate limiting with static or dynamic backoff timing
  • Caching

All these features have sane off-the-shelf defaults but are completely customizable depending on your use case. They can also be combined with other stream features described in the full refresh streams and incremental streams sections.

Overview of HTTP Streams​

Just like any general HTTP request, the basic HTTPStream requires a url to perform the request, and instructions on how to parse the resulting response.

The full request path is broken up into two parts, the base url and the path. This makes it easy for developers to create a Source-specific base HTTPStream class, with the base url filled in, and individual streams for each available HTTP resource. The Stripe CDK implementation is a reification of this pattern.

The base url is set via the url_base property, while the path is set by implementing the abstract path function.

The parse_response function instructs the stream how to parse the API response. This returns an Iterable, whose elements are each later transformed into an AirbyteRecordMessage. API routes whose response contains a single record generally have a parse_reponse function that return a list of just that one response. Routes that return a list, usually have a parse_response function that return the received list with all elements. Pulling the data out from the response is sufficient, any deserialization is handled by the CDK.

Lastly, the HTTPStream must describe the schema of the records it outputs using JsonSchema. The simplest way to do this is by placing a .json file per stream in the schemas directory in the generated python module. The name of the .json file must match the lower snake case name of the corresponding Stream. Here are examples from the Stripe API.

You can also dynamically set your schema. See the schema docs for more information.

These four elements - the url_base property, the path function, the parse_response function and the schema file - are the bare minimum required to implement the HTTPStream, and can be seen in the same Stripe example.

This basic implementation gives us a Full-Refresh Airbyte Stream. We say Full-Refresh since the stream does not have state and will always indiscriminately read all data from the underlying API resource.

Authentication​

The CDK supports Basic and OAuth2.0 authentication via the TokenAuthenticator and Oauth2Authenticator classes respectively. Both authentication strategies are identical in that they place the api token in the Authorization header. The OAuth2Authenticator goes an additional step further and has mechanisms to, given a refresh token, refresh the current access token. Note that the OAuth2Authenticator currently only supports refresh tokens and not the full OAuth2.0 loop.

Using either authenticator is as simple as passing the created authenticator into the relevant HTTPStream constructor. Here is an example from the Stripe API.

Pagination​

Most APIs, when facing a large call, tend to return the results in pages. The CDK accommodates paging via the next_page_token function. This function is meant to extract the next page "token" from the latest response. The contents of a "token" are completely up to the developer: it can be an ID, a page number, a partial URL etc.. The CDK will continue making requests as long as the next_page_token continues returning non-None results. This can then be used in the request_params and other methods in HttpStream to page through API responses. Here is an example from the Stripe API.

Rate Limiting​

The CDK, by default, will conduct exponential backoff on the HTTP code 429 and any 5XX exceptions, and fail after 5 tries.

Retries are governed by the should_retry and the backoff_time methods. Override these methods to customise retry behavior. Here is an example from the Slack API.

Note that Airbyte will always attempt to make as many requests as possible and only slow down if there are errors. It is not currently possible to specify a rate limit Airbyte should adhere to when making requests.

Stream Slicing​

When implementing stream slicing in an HTTPStream each Slice is equivalent to a HTTP request; the stream will make one request per element returned by the stream_slices function. The current slice being read is passed into every other method in HttpStream e.g: request_params, request_headers, path, etc.. to be injected into a request. This allows you to dynamically determine the output of the request_params, path, and other functions to read the input slice and return the appropriate value.

Nested Streams & Caching​

It's possible to cache data from a stream onto a temporary file on disk.

This is especially useful when dealing with streams that depend on the results of another stream e.g: /employees/{id}/details. In this case, we can use caching to write the data of the parent stream to a file to use this data when the child stream synchronizes, rather than performing a full HTTP request again.

The caching mechanism works as follows: If the request is made for the first time, the returned value will be written to disk (all requests made by the read_records method will be written to the cache file). When the same request is made again, instead of making another HTTP request, the result will instead be read from disk. It is checked whether the required request is in the cache file, and if so, the data from this file is returned. However, if the check for the request's existence in the cache file fails, a new request will be made, and its result will be added to the cache file.

Caching can be enabled by overriding the use_cache property of the HttpStream class to return True.

The caching mechanism is related to parent streams. For child streams, there is an HttpSubStream class inheriting from HttpStream and overriding the stream_slices method that returns a generator of all parent entries.

To use caching in the parent/child relationship, perform the following steps:

  1. Turn on parent stream caching by overriding the use_cache property.
  2. Inherit child stream class from HttpSubStream class.

Example​

class Employees(HttpStream):
    ...

    @property
    def use_cache(self) -> bool:
        return True

class EmployeeDetails(HttpSubStream):
    ...
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