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ipip: Streaming Routing V1 HTTP API
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83 changes: 83 additions & 0 deletions src/ipips/ipip-0410.md
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---
title: "IPIP-0410: Streaming Routing V1 HTTP API"
date: 2023-05-12
ipip: proposal
editors:
- name: Henrique Dias
github: hacdias
url: https://hacdias.com/
relatedIssues:
- https://github.com/ipfs/specs/issues/344
- https://github.com/ipfs/boxo/pull/18
- https://github.com/ipfs/kubo/pull/9868
- https://github.com/ipfs/kubo/pull/9874
order: 410
tags: ['ipips']
---

Introduce backwards-compatible streaming support to the Routing V1 HTTP API.
For this, we use the `Accept` HTTP header (:cite[rfc9110]) for content type negotiation, as well
as the Newline Delimited JSON ([NDJSON]) format.

## Motivation

The main motivation for this change is to allow servers to respond faster to the
client with provider records, as soon as they are available. In the current state,
the client requests a list of providers for a CID from the server. Then, the client
has to wait for the server to collect their final list of providers. After that,
the server can respond with the full list of providers.

With streaming support, the server is able to respond with provider records as soon
as they are available. This reduces latency and allows for faster content discovery.

In addition, streaming responses may produce an unlimited amount of results, which
is not the case for non-streamed responses.

## Detailed Design

In summary, streaming is supported by using the `Accept` HTTP header, which is used
for content type negotiation as described in :cite[rfc9110]. The client sends an
`Accept` HTTP header starting with `application/x-ndjson`, which is the content
type for [NDJSON]. The following happens:

- The client adds the `Accept` HTTP header in the request starting with `application/x-ndjson`.
- The server checks the `Accept` HTTP header from the request and, if it contains
`application/x-ndjson`, they reply with NDJSON. If they don't support NDJSON, they
can reply with JSON.
- The server response MUST contain a `Content-Type` HTTP header indicating the
response type, which may be either `application/json` for non-streaming responses,
and `application/x-ndjson` for streamed responses.

For more details regarding the design, check :cite[http-routing-v1].

## Design Rationale

This feature is designed such that it does not break compatibility with existing
clients and servers. The `Accept` HTTP header is OPTIONAL. By default, the server
MUST respond with `application/json` unless the client explicitly asked for
`application/x-ndjson`. If the server does not support NDJSON, it is allowed
to still respond with non-streamed JSON.

### User Benefit

Users (clients) will benefit from this change as the servers will now be able
to respond more promptly to provider record requests. Instead of waiting for the whole
list to be constructed, servers can now return each provider record one by one,
in a streaming fashion.

### Compatibility

The introduced changes are backwards-compatible. The introduced header is completely
optional, and a server that does not support streaming is able to respond with a non-streaming
response to the client. Equally, non-streaming responses are the default. Therefore, a
client that does not support streaming will not receive a streamed response.

### Security

Security considerations are equivalent as the ones in :cite[ipip-0337].

### Copyright

Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).

[NDJSON]: http://ndjson.org/
21 changes: 20 additions & 1 deletion src/routing/http-routing-v1.md
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github: guseggert
- name: Masih H. Derkani
github: masih
- name: Henrique Dias
url: https://hacdias.com/
github: hacdias
xref:
- ipns-record
order: 0
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## Streaming

This API does not currently support streaming, however it can be added in the future through a backwards-compatible update by using a content type other than `application/json`.
JSON-based endpoints support streaming requests made by sending an `Accept` HTTP Header containing
`application/x-ndjson`. The response will be formatted as [Newline Delimited JSON (ndjson)](https://github.com/ndjson/ndjson-spec),
with one *read provider record* per line:


```json
{"Protocol": "<protocol_name>", "Schema": "<schema>", ...}
{"Protocol": "<protocol_name>", "Schema": "<schema>", ...}
{"Protocol": "<protocol_name>", "Schema": "<schema>", ...}
...
```

Streaming is backwards-compatible with clients that do not support streaming. Please note the following:

- Requests without an `Accept` header MUST default to regular, non-streaming, responses.
- The server MAY respond with non-streaming response even if the client requests streaming.
- The server MUST NOT respond with streaming response if the client did not request so.

## Error Codes

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