DOC-4997 hiredis async API and integration examples

content/develop/clients/hiredis/connect.md

@@ -62,4 +62,83 @@ freeReplyObject(reply);
 redisFree(c);
 ```
 
+## Asynchronous connection
 
+You can also connect to Redis using an asynchronous API.
+The `redisAsyncConnect()` call that creates the context is
+similar to the synchronous function `redisConnect()`, but it returns the
+context object immediately before the connection is complete.
+It lets you supply callbacks to respond when a connection is successful
+or to handle any errors that may occur.
+
+The following code creates an asynchronous connection and
+sets the context callbacks:
+
+```c
+#include <stdio.h>
+
+#include "hiredis.h"
+#include "async.h"
+    .
+    .
+    .
+
+redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);
+
+if (c->err) {
+    printf("Error: %s\n", c->errstr);
+    return 1;
+}
+
+// Set callbacks to respond to successful or unsuccessful
+// connection and disconnection.
+redisAsyncSetConnectCallback(c, connectCallback);
+redisAsyncSetDisconnectCallback(c, disconnectCallback);
+
+char *key = "testkey";
+char *value = "testvalue";
+
+// Status reply is ignored.
+redisAsyncCommand(c, NULL, NULL, "SET %s %s", key, value);
+
+// Reply handled by `getCallback()` function.
+redisAsyncCommand(c, getCallback, key, "GET %s", key);
+```
+
+The callback functions have a simple signature that receives
+the context object and a status code. See
+[Handling errors]({{< relref "/develop/clients/hiredis/handle-replies#handling-errors" >}})
+for a list of the possible status codes.
+
+```c
+void connectCallback(const redisAsyncContext *c, int status) {
+    if (status != REDIS_OK) {
+        printf("Error: %s\n", c->errstr);
+        return;
+    }
+    printf("Connected...\n");
+}
+
+void disconnectCallback(const redisAsyncContext *c, int status) {
+    if (status != REDIS_OK) {
+        printf("Error: %s\n", c->errstr);
+        return;
+    }
+    printf("Disconnected...\n");
+}
+```
+
+Use the `redisAsyncCommand()` function to issue Redis commands
+with an asynchronous connection. This is similar to the equivalent
+synchronous function `redisCommand()` but also lets you supply a callback
+and a custom data pointer to process the response to the command. See
+[Construct asynchronous commands]({{< relref "/develop/clients/hiredis/issue-commands#construct-asynchronous-commands" >}}) for more
+information.
+
+Note that you should normally disconnect asynchronously from a
+callback when you have finished using the connection.
+Use `redisAsyncDisconnect()` to disconnect gracefully, letting
+pending commands execute and activate their callbacks.
+Use `redisAsyncFree()` to disconnect immediately. If you do this then
+any pending callbacks from commands that have already executed will be
+called with a `NULL` reply pointer.

content/develop/clients/hiredis/int-examples/_index.md

@@ -0,0 +1,22 @@
+---
+categories:
+- docs
+- develop
+- stack
+- oss
+- rs
+- rc
+- oss
+- kubernetes
+- clients
+description: Integrate hiredis with C++ and external frameworks.
+linkTitle: Integration guides
+title: Integration guides
+weight: 50
+---
+
+`hiredis` is compatible with C++ and the library source includes a set of
+[adapters](https://github.com/redis/hiredis/tree/master/adapters)
+to help you use it in conjunction with C and C++ libraries and frameworks.
+The pages in this section explain how to integrate `hiredis` into
+your app.

content/develop/clients/hiredis/int-examples/libevent-integration.md

@@ -0,0 +1,176 @@
+---
+categories:
+- docs
+- develop
+- stack
+- oss
+- rs
+- rc
+- oss
+- kubernetes
+- clients
+description: Use `hiredis` in conjunction with the `libevent` framework.
+linkTitle: libevent integration
+title: Integrate hiredis with a libevent app
+weight: 60
+---
+
+The [`libevent`](https://libevent.org/) library provides an
+implementation of an event loop that lets you call functions
+asynchronously in response to events. This guide explains
+how to use `hiredis` to connect to a Redis server from a
+`libevent` app.
+
+## Install `libevent`
+
+The [`libevent` home page](https://libevent.org/) has links to download
+all versions of the library, but you should use the latest version
+unless there is a specific version you need to target.
+
+When you have downloaded `libevent`, follow the instructions in the
+`README` file to compile and install the library.
+
+## Create a simple app
+
+For a real project, you would build your code with a makefile, but for
+this simple test, you can just place it in a file called `main.c` and
+build it with the following command (assuming you used `make install` to
+install the `libhiredis` and `libevent` libraries):
+
+```bash
+cc main.c -L/usr/local/lib -lhiredis -levent
+```
+
+See [Build and install]({{< relref "/develop/clients/hiredis#build-and-install" >}})
+to learn how to build `hiredis`, if you have not already done so.
+
+Add the following header files from the `hiredis` folder to your project folder:
+
+-   `hiredis.h`
+-   `async.h`
+-   `adapters/libevent.h`
+
+You should include the `libevent.h` file in a folder called `adapters` but you
+don't need the other headers in the original `adapters` folder for this
+example.
+
+Now, add the following code in `main.c`. An explanation follows the
+code example:
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+
+#include "hiredis.h"
+#include "async.h"
+#include "adapters/libevent.h"
+
+// Callback for the `GET` command. 
+void getCallback(redisAsyncContext *c, void *r, void *privdata) {
+    redisReply *reply = r;
+    char *key = privdata;
+
+    if (reply == NULL) {
+        if (c->errstr) {
+            printf("errstr: %s\n", c->errstr);
+        }
+        return;
+    }
+
+    printf("Key: %s, value: %s\n", key, reply->str);
+
+    /* Disconnect after receiving the reply to GET */
+    redisAsyncDisconnect(c);
+}
+
+// Callback to respond to successful or unsuccessful connection.
+void connectCallback(const redisAsyncContext *c, int status) {
+    if (status != REDIS_OK) {
+        printf("Error: %s\n", c->errstr);
+        return;
+    }
+    printf("Connected...\n");
+}
+
+// Callback to respond to intentional or unexpected disconnection.
+void disconnectCallback(const redisAsyncContext *c, int status) {
+    if (status != REDIS_OK) {
+        printf("Error: %s\n", c->errstr);
+        return;
+    }
+    printf("Disconnected...\n");
+}
+
+
+int main (int argc, char **argv) {
+#ifndef _WIN32
+    signal(SIGPIPE, SIG_IGN);
+#endif
+
+    // Create the libevent `event_base` object to track all
+    // events.
+    struct event_base *base = event_base_new();
+
+    redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);
+
+    if (c->err) {
+        printf("Error: %s\n", c->errstr);
+        return 1;
+    }
+
+    // Use the Redis libevent adapter to attach the Redis connection
+    // to the libevent main loop.
+    redisLibeventAttach(c,base);
+
+    redisAsyncSetConnectCallback(c, connectCallback);
+    redisAsyncSetDisconnectCallback(c, disconnectCallback);
+
+    char *key = "testkey";
+    char *value = "testvalue";
+
+    redisAsyncCommand(c, NULL, NULL, "SET %s %s", key, value);
+    redisAsyncCommand(c, getCallback, key, "GET %s", key);
+
+    // Run the event loop.
+    event_base_dispatch(base);
+
+    return 0;
+}
+```
+
+The code calls
+[`event_base_new()`](https://libevent.org/doc/event_8h.html#af34c025430d445427a2a5661082405c3)
+to initialize the core
+[`event_base`](https://libevent.org/doc/structevent__base.html)
+object that manages the event loop. It then creates a standard
+[asynchronous connection]({{< relref "/develop/clients/hiredis/connect#asynchronous-connection" >}})
+to Redis and uses the `libevent` adapter function `redisLibeventAttach()` to
+attach the connection to the event loop.
+
+After setting the [connection callbacks]({{< relref "/develop/clients/hiredis/connect#asynchronous-connection" >}}), the code issues two asynchronous
+Redis commands (see
+[Construct asynchronous commands]({{< relref "/develop/clients/hiredis/issue-commands#construct-asynchronous-commands" >}})
+for more information).
+The final step is to call
+[`event_base_dispatch()`](https://libevent.org/doc/event_8h.html#a19d60cb72a1af398247f40e92cf07056)
+to start the event loop. This will wait for the commands to be processed and
+then exit when the Redis connection is closed in the `getCallback()` function.
+
+## Run the code
+
+If you compile and run the code, you will see the following output,
+showing that the callbacks executed correctly:
+
+```
+Connected...
+Key: testkey, value: testvalue
+Disconnected...
+```
+
+You can use the
+[`KEYS`]({{< relref "/commands/keys" >}}) command from
+[`redis-cli`]({{< relref "/develop/tools/cli" >}}) or
+[Redis Insight]({{< relref "/develop/tools/insight" >}}) to check
+that the "testkey" string key was added to the Redis database.