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API Gateways

API gateways in LangStream are HTTP/WebSocket endpoints that allow applications to interact with agents via message topics.
Messages contain a key, a value, and headers for metadata. This metadata is used to connect clients to topics and can be used to filter messages.​
LangStream applications can have three different gateway types:
Producer gateways are clients that create a message and write it to a topic.
Consumer gateways are clients that watch a topic for messages from a given position. This gateway can only be accessed via WebSocket.
Chat gateways create a producer client (questions-topic) and a consumer client (answers-topic) across one connection, optimized for "chat" style interactions between client and server. This gateway can only be accessed via WebSocket.
Service (topics) gateways create a producer client (input-topic) and a consumer client (output-topic), writing a single message and awaiting for the receivement of another message. This gateway can only be accessed via HTTP.
Service (agents) gateways send requests directly to a service agent and return the response to the client. This gateway can only be accessed via HTTP.
Example gateways
Given an application in tenant “my-super-cool-tenant” with an id of “some-application” and the following gateway manifest, 1 gateway of each type is created:
gateways:
  - id: "user-input"
    type: produce
    topic: "questions-topic"
​
  - id: "bot-output"
    type: consume
    topic: "answers-topic"
    
  - id: "chat"
    type: chat
    chat-options:
      questions-topic: questions-topic
      answers-topic: answers-topic
​
  - id: "service"
    type: service
    service-options:
      input-topic: questions-topic
      output-topic: answers-topic
The corresponding URLs to the gateways would be:
Produce gateway: ws://localhost:8091/produce/my-super-cool-tenant/some-application/user-input
Consume gateway: ws://localhost:8091/consume/my-super-cool-tenant/some-application/bot-output
Chat gateway: ws://localhost:8091/consume/my-super-cool-tenant/some-application/chat
Service gateway: http://localhost:8091/api/gateways/service/my-super-cool-tenant/some-application/service
The URL structure is ws://<control-plane-domain>:<api-gateway-port>/<gateway-type>/<tenant-name>/<application-id>/<gateway-id> for WebSocket.
The URL structure is http://<control-plane-domain>:<api-gateway-port>/api/gateways/<gateway-type>/<tenant-name>/<application-id>/<gateway-id> for HTTP.
Gateways configuration
Root
Node
Type
Description
gateways

​
​
The base node in the yaml. Holds the collection of gateways.
​
id
string (required)
An authentic name for the given gateway. Allowed characters are a-zA-Z0-9._-
​
type
string (required)
The type of gateway to create. Supported values are:
produce
consume
chat
Set to "produce" to use the gateway to create messages in the topic. Set to "consume" to use the gateway to consume messages in the topic. Set to "chat" to create a producer topic (answers-topic) and a consumer topic (questions-topic) and connect them through the gateway.
​
topic
string (required)
The mapping of a topic declared in pipeline.yaml manifest. This is where a gateway produces and consumes messages. This value must match the name of a topic in the pipeline manifest.
​
parameters
string[]
A string collection of labels to look for in the querystring. See Message filtering.​


headers
object
The values to use as headers on produced messages, that hold the given parameters.
​
authentication
object
Configuration of an identity provider. See Gateway authentication.​
​
produce-options
object
See headers.​
​
consume-options
object
See headers.​
​
chat-options
object
See chat-options.​
​
headers
map<String, String>
See headers.​
chat-options
Label
Type
Description
answers-topic
string
The name of the chat consumer topic, ex "input-topic".
questions-topic
string
The name of the chat producer topic, ex "output-topic".
headers
object
The values to use as headers on produced messages, that hold the given parameters. See headers.​
headers
Label
Type
Description
key
string
An identifier of the value. This can be thought of as the name. Allowed characters are a-zA-Z0-9._-
value-from-parameters
string
The mapped name to connect a querystring value in the Gateway URL to message headers. This must match a value set in the parameters collection.
value-from-authentication
string
The mapped name to connect a provided querysting value with the identity provider’s handshake value. See Gateway authentication.​
Example gateways manifest

Root	Node	Type	Description
gateways			The base node in the yaml. Holds the collection of gateways.
	id	string (required)	An authentic name for the given gateway. Allowed characters are a-zA-Z0-9._-
	type	string (required)	The type of gateway to create. Supported values are: produce consume chat Set to "produce" to use the gateway to create messages in the topic. Set to "consume" to use the gateway to consume messages in the topic. Set to "chat" to create a producer topic (answers-topic) and a consumer topic (questions-topic) and connect them through the gateway.
	topic	string (required)	The mapping of a topic declared in pipeline.yaml manifest. This is where a gateway produces and consumes messages. This value must match the name of a topic in the pipeline manifest.
	parameters	string[]	A string collection of labels to look for in the querystring. See Message filtering.
	headers	object	The values to use as headers on produced messages, that hold the given parameters.
	authentication	object	Configuration of an identity provider. See Gateway authentication.
	produce-options	object	See headers.
	consume-options	object	See headers.
	chat-options	object	See chat-options.
	headers	map<String, String>	See headers.

Label	Type	Description
answers-topic	string	The name of the chat consumer topic, ex "input-topic".
questions-topic	string	The name of the chat producer topic, ex "output-topic".
headers	object	The values to use as headers on produced messages, that hold the given parameters. See headers.

Label	Type	Description
key	string	An identifier of the value. This can be thought of as the name. Allowed characters are a-zA-Z0-9._-
value-from-parameters	string	The mapped name to connect a querystring value in the Gateway URL to message headers. This must match a value set in the parameters collection.
value-from-authentication	string	The mapped name to connect a provided querysting value with the identity provider’s handshake value. See Gateway authentication.

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