Skip to content

docs: refresh README for current SDK surface #19

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
wrossmorrow merged 1 commit into from
Oct 28, 2026
Merged

docs: refresh README for current SDK surface #19

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 30 additions & 12 deletions README.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,4 +1,3 @@

# An Envoy ExternalProcessor SDK (java)

## Overview
Expand All @@ -19,7 +18,7 @@ Implement the `extproc.RequestProcessor` interface, and pass an instance to the
```java
package myextproc;

import extproc.ExternalProcessorServer;
import com.github.wrossmorrow.extproc.ExternalProcessorServer;

public class MainClass {
public void main() {
Expand All @@ -37,7 +36,7 @@ You can also supply your own server implementation, and use `ExternalProcessor`:
```java
package myextproc;

import extproc.ExternalProcessor;
import com.github.wrossmorrow.extproc.ExternalProcessor;

ExternalProcessor service = new ExternalProcessor(new MyRequestProcessor());
```
Expand Down Expand Up @@ -99,7 +98,7 @@ Your `RequestProcessor` implementation can use whatever storage strategy for you
We also provide some convenience routines for operating on process phase stream responses, so that users of this SDK need to learn less (preferably nothing) about the specifics of the `envoy` datastructures. The gRPC stream response datastructures are complicated, and our aim is to utilize the `RequestContext` to guard and simplify the construction of responses with a simpler user interface.

In particular, the methods
```go
```java
RequestContext.continueAndReplace()
RequestContext.cancelRequest(int status, Map<String, String> headers, String body)
```
Expand Down Expand Up @@ -127,20 +126,23 @@ methods, requiring only names of headers to remove.

### Modifying Bodies

Two methods help modify bodies:
The `RequestContext` exposes body-modification helpers covering both buffered and streamed semantics:
```java
replaceBodyChunk(byte[] | String body)
clearBodyChunk()
replaceBody(byte[] body) // replace the whole (buffered) body
replaceBody(String body) // replace the whole (buffered) body
clearBody() // clear the whole (buffered) body
replaceBodyChunk(byte[] body) // replace a single chunk (buffered: the whole body)
replaceBodyChunk(String body) // replace a single chunk (buffered: the whole body)
clearBodyChunk() // clear a single chunk (buffered: the whole body)
```
These are the two options currently available in `envoy` ExtProcs: replace a chunk and clear the entire chunk. Note that with buffered bodies the "chunks" should be the entire body. See the [masker](#masker) example discussed below.

## Examples

You can run all the examples with
```shell
./gradlew clean build && docker-compose up --build
./gradlew clean build && docker compose up --build
```
The compose setup runs `envoy` (see `envoy.yaml`), a mock echo server (see `ghcr.io/wrossmorrow/simple-echo-server`), and several implementations of ExtProcs based on the SDK. These implementations are described below.
The compose setup runs `envoy` (see `envoy.yaml`), an upstream echo server (see `ghcr.io/wrossmorrow/simple-echo-server`), and several implementations of ExtProcs based on the SDK. These implementations are described below.

Here is some sample output with the compose setup running:
```shell
Expand All @@ -164,7 +166,7 @@ $ curl localhost:8080/hello -s -vvv | jq .
< x-extproc-response-seen: true
< x-extproc-duration-ns: echo=2000,dedup=3000,digest=4000,timer=5000,trivial=2000,noop=6000
< server: envoy
< x-request-id: c9792bc4-668a-4e99-a89b-da559b1a7e87
< x-request-id: c9792bc4-668a4e99-a89b-da559b1a7e87
< transfer-encoding: chunked
<
{ [597 bytes data]
Expand Down Expand Up @@ -200,7 +202,7 @@ $ curl localhost:8080/hello -s -vvv | jq .
"http"
],
"X-Request-Id": [
"c9792bc4-668a-4e99-a89b-da559b1a7e87"
"c9792bc4-668a4e99-a89b-da559b1a7e87"
]
},
"Body": "",
Expand Down Expand Up @@ -248,3 +250,19 @@ The `DigestRequestProcessor` computes a (SHA256) digest of the request, specific
### Dedup

The `DedupRequestProcessor` _uses_ a request digest as above and to reject requests when another request with the _same_ digest is still in flight (i.e., not yet responded to). You can utilize the `X-Echo-Delay` header to the proxied echo server to make one "long running" request in one terminal, and another similar request in another terminal and observe the second will have a `409` response. You can use a `PUT`/`POST`/`PATCH` and change the body in the second request and see it pass through. This is an example of "chained" external processors, as this depends on the `DigestRequestProcessor`.

### Logging

The `LoggingRequestProcessor` logs each phase as it processes the request, using the options' verbose stream/phase logs, and is a minimal example of a processor that observes phases without modifying them.

### Data

The `DataRequestProcessor` stores a custom value (`customId`) in the request context during the request phase and surfaces it to the client in the response via a header, demonstrating the custom-data surface.

### Router

The `RouterRequestProcessor` routes a request to an upstream based on a request header or JSON body, using the custom-data surface and clearing the route cache, demonstrating header/body-driven routing.

### Testing

The `TestingRequestProcessor` is the processor used by the testing harness: it applies a JSON action body across the phases of an exchange (append/add/overwrite/remove headers, clear/replace bodies, cancel), and supports an upstream override via the `x-route-to-upstream` header.
Loading