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# emacs + vi backup files
*~
.*.sw*
# various IDE junk
*.ipr
*.iml
*.iws
.project
.classpath
.settings
target
classes

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= Bandalore
http://github.com/cemerick/bandalore[Bandalore] is a Clojure client
library for Amazon's http://aws.amazon.com/sqs/[Simple Queue Service (SQS)]. It depends upon
the standard http://aws.amazon.com/sdkforjava/[AWS SDK for Java],
and provides a Clojure-idiomatic API for the SQS-related functionality
therein.
== "Installation"
+++<del>Bandalore is available in Maven central.</del>+++
*I'll get Bandalore releases to central in the next couple of days, promise. :-)*
Add it to your Maven project's `pom.xml`:
----
<dependency>
<groupId>cemerick</groupId>
<artifactId>bandalore</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
----
or your leiningen project.clj:
----
[cemerick/bandalore "0.0.1"]
----
== Usage
You should be familiar with http://aws.amazon.com/sqs/[SQS itself]
before sensibly using this library. That said, Bandalore's API
is well-documented.
You'll first need to load the library and create a SQS client object
to do anything:
----
(require '[cemerick.bandalore :as sqs])
(def client (sqs/create-client "your aws id" "your aws secret-key"))
----
You can create, delete, and list queues:
----
=> (sqs/create-queue client "foo")
"https://queue.amazonaws.com/499312652346/foo"
=> (sqs/list-queues client)
("https://queue.amazonaws.com/499312652346/foo")
=> (sqs/delete-queue client (first *1))
nil
=> (list-queues client)
nil
----
*Note that SQS is _eventually consistent_. This means that a created
queue won't necessarily show up in an immediate listing of queues,
messages aren't necessarily immediately available to be received, etc.*
You can send, receive, and delete messages:
----
=> (def q (sqs/create-queue client "foo"))
#'cemerick.bandalore-test/q
=> (sqs/send client q "my message body")
{:id "75d5d7a1-2274-4163-97b2-aa4c75f209ee", :body-md5 "05d358de00fc63dd2fa2026b77e112f6"}
=> (sqs/receive client q)
({:attrs #<HashMap {}>, :body "my message body", :body-md5 "05d358de00fc63dd2fa2026b77e112f6",
:id "75d5d7a1-2274-4163-97b2-aa4c75f209ee",
:receipt-handle "…very long string…"})
;;
;; …presumably do something with the received message(s)…
;;
=> (sqs/delete client q (first *1))
nil
=> (sqs/receive client q)
()
----
That's cleaner than having to interop directly with the Java SDK, but it's all
pretty pedestrian stuff. You can do more interesting things with some
simple higher-order functions and other nifty Clojure facilities.
=== Sending and receiving Clojure values
SQS' message bodies are strings, so you can stuff anything in them that you can
serialize to a string. That said, `pr-str` and `read-string` are too handy
to not use, assuming your consumers are using Clojure as well:
----
=> (sqs/send client q (pr-str {:a 5 :b "blah" :c 6.022e23}))
{:id "3756c302-866a-4fcc-a7a3-746e6f531f47", :body-md5 "60052fc2ffb835257c26b9957c6e9ffd"}
=> (-?> (sqs/receive client q) first :body read-string)
{:a 5, :b "blah", :c 6.022E23}
----
=== Sending seqs of messages
…with more gratuitous use of `pr-str` and `read-string` to send and receive
Clojure values:
----
=> (->> [:foo 'bar ["some vector" 42] #{#"silly place for a regex"}]
(map (comp (partial sqs/send client q) pr-str))
dorun)
nil
=> (map (comp read-string :body)
(sqs/receive client q :limit 10))
(bar ["some vector" 42])
=> (map (comp read-string :body)
(sqs/receive client q :limit 10))
(#{#"silly place for a regex"})
=> (map (comp read-string :body)
(sqs/receive client q :limit 10))
(:foo)
----
=== (Mostly) automatic deletion of consumed messages
When you're done processing a received message, you need to delete it from its
originaing queue:
----
; ensure our queue is empty to start
=> (get (sqs/queue-attrs client q) "ApproximateNumberOfMessages")
"0"
=> (dorun (map (partial sqs/send client q) (map str (range 100))))
nil
=> (get (sqs/queue-attrs client q) "ApproximateNumberOfMessages")
"100"
; received messages must be removed from the queue or they will
; be delivered again after their visibility timeout expires
=> (sqs/receive client q)
(…message seq…)
=> (get (sqs/queue-attrs client q) "ApproximateNumberOfMessages")
"100"
=> (->> (sqs/receive client q) first (sqs/delete client))
nil
=> (get (sqs/queue-attrs client q) "ApproximateNumberOfMessages")
"99"
----
Rather than trying to remember to do this, just use the
`deleting-consumer` "middleware" to produce a function that calls
the message-processing function you provide to it, and then
automatically deletes the processed message from the origining queue:
----
=> (doall (map
(sqs/deleting-consumer client (comp println :body))
(sqs/receive client q :limit 10)))
0
4
9
12
26
36
40
44
52
55
(nil nil nil nil nil nil nil nil nil nil)
=> (get (sqs/queue-attrs client q) "ApproximateNumberOfMessages")
"90"
----
=== Consuming queues as seqs
seqs being the _lingua franca_ of Clojure collections, it would be helpful if we
could treat an SQS queue as a seq of messages. While `receive` does return
a seq of messages, each `receive` call is limited to receiving a maximum of
10 messages, and there is no streaming or push counterpart in the SQS API.
The solution to this is `polling-receive`, which returns a lazy seq that
reaches out to SQS as necessary:
----
=> (map (sqs/deleting-consumer client :body)
(sqs/polling-receive client q :limit 10))
("3" "5" "7" "8" ... "81" "90" "91")
----
`polling-receive` accepts all of the same optional kwargs as `receive` does,
but adds two more to control its usage of `receive`:
:period - time in ms to wait after an unsuccessful `receive` request (default: 500)
:max-wait - maximum time in ms to wait to successfully receive messages before terminating
the lazy seq (default 5000ms)
Often queues are used to direct compute resources, so you'd like to be able to saturate
those boxen with as much work as your queue can offer up. The obvious solution
is to `pmap` across a seq of incoming messages, which you can do trivially with the seq
provided by `polling-receive`. Just make sure you tweak the `:max-wait` time so that,
assuming you want to continuously process incoming messages, the seq of messages doesn't
terminate because none have been available for a while.
Here's an example where one thread sends a message once a second for a minute,
and another consumes those messages using a lazy seq provided by `polling-receive`:
----
=> (defn send-dummy-messages
[client q count]
(future (doseq [n (range count)]
(Thread/sleep 100)
(sqs/send client q (str n)))))
#'cemerick.bandalore-test/send-dummy-messages
=> (defn consume-dummy-messages
[client q]
(future (dorun (map (sqs/deleting-consumer client (comp println :body))
(sqs/polling-receive client q :max-wait Integer/MAX_VALUE :limit 10)))))
#'cemerick.bandalore-test/consume-dummy-messages
=> (consume-dummy-messages client q) ;; start the consumer
#<core$future_call$reify__5500@a6f00bc: :pending>
=> (send-dummy-messages client q 1000) ;; start the sender
#<core$future_call$reify__5500@18986032: :pending>
3
4
1
0
2
8
5
7
...
----
You'd presumably want to set up some ways to control your consumer, but hopefully
you see that it would be trivial to parallelize the processing function being
wrapped by `deleting-consumer` using `pmap`, distribute processing among agents
if that's more appropriate, etc.
== Building Bandalore
Have maven. From the command line:
----
$ mvn clean install
----
The tests are all live, so you either need to add your AWS credentials to your
`~/.m2/settings.xml` file as properties, or specify them on the command line
using `-D` switches:
----
$ mvn -Daws.id=XXXXXXX -Daws.secret-key=YYYYYYY clean install
----
Or, you can skip the tests entirely if you're brave:
----
$ mvn -Dmaven.test.skip=true clean install
----
In any case, you'll find a built `.jar` file in the `target` directory, and in
its designated spot in `~/.m2/repository` (assuming you ran `install` rather than
e.g. `package`).
== Need Help?
Ping `cemerick` on freenode irc or twitter if you have questions
or would like to contribute patches.
== License
Copyright © 2011 Chas Emerick
Licensed under the EPL. (See the file epl-v10.html.)

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>cemerick</groupId>
<artifactId>bandalore</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>bandalore</name>
<description>A Clojure library for Amazon's Simple Queue Service (SQS).</description>
<parent>
<groupId>org.clojure</groupId>
<artifactId>pom.contrib</artifactId>
<version>0.0.20</version>
</parent>
<developers>
<developer>
<name>Chas Emerick</name>
<url>http://cemerick.com</url>
<email>cemerick@snowtide.com</email>
<timezone>-5</timezone>
</developer>
</developers>
<scm>
<connection>scm:git:git@github.com:cemerick/bandalore.git</connection>
<developerConnection>scm:git:git@github.com:cemerick/bandalore.git</developerConnection>
<url>git@github.com:cemerick/bandalore.git</url>
</scm>
<properties>
<clojure.version>1.2.0</clojure.version>
</properties>
<dependencies>
<dependency>
<groupId>com.amazonaws</groupId>
<artifactId>aws-java-sdk</artifactId>
<version>1.1.5</version>
</dependency>
<dependency>
<groupId>org.clojure</groupId>
<artifactId>clojure-contrib</artifactId>
<version>1.2.0</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>com.theoryinpractise</groupId>
<artifactId>clojure-maven-plugin</artifactId>
<executions>
<execution>
<id>clojure-test</id>
<configuration>
<clojureOptions>-Daws.id=${aws.id} -Daws.secret-key=${aws.secret-key}</clojureOptions>
</configuration>
</execution>
</executions>
<configuration>
<warnOnReflection>true</warnOnReflection>
</configuration>
</plugin>
</plugins>
</build>
</project>

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; Copyright (c) Chas Emerick. All rights reserved.
; The use and distribution terms for this software are covered by the
; Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
; which can be found in the file epl-v10.html at the root of this distribution.
; By using this software in any fashion, you are agreeing to be bound by
; the terms of this license.
; You must not remove this notice, or any other, from this software.
(ns cemerick.bandalore
(:import com.amazonaws.services.sqs.AmazonSQSClient
(com.amazonaws.services.sqs.model
AddPermissionRequest ChangeMessageVisibilityRequest CreateQueueRequest
DeleteMessageRequest DeleteQueueRequest GetQueueAttributesRequest
ListQueuesRequest Message ReceiveMessageRequest ReceiveMessageResult
RemovePermissionRequest SendMessageRequest SendMessageResult
SetQueueAttributesRequest))
(:refer-clojure :exclude (send)))
(defn create-client
"Creates a synchronous AmazonSQSClient using the provided account id, secret key,
and optional com.amazonaws.ClientConfiguration."
([id secret-key]
(create-client id secret-key (com.amazonaws.ClientConfiguration.)))
([id secret-key client-config]
(AmazonSQSClient. (com.amazonaws.auth.BasicAWSCredentials. id secret-key)
(.withUserAgent client-config "Bandalore - SQS for Clojure"))))
(defn create-queue
"Creates a queue with the given name, returning the corresponding URL string.
Returns successfully if the queue already exists.
Specify an optional :visibility keyword arg to set the new queue's default
visibility timeout in seconds."
[^AmazonSQSClient client queue-name & {:keys [visibility]}]
(->> (if visibility
(CreateQueueRequest. queue-name visibility)
(CreateQueueRequest. queue-name))
(.createQueue client)
.getQueueUrl))
(defn delete-queue
"Deletes the queue specified by the given URL string."
[^AmazonSQSClient client queue-url]
(.deleteQueue client (DeleteQueueRequest. queue-url)))
(defn list-queues
"Returns a seq of all queues' URL strings."
[^AmazonSQSClient client]
(->> (ListQueuesRequest.)
(.listQueues client)
.getQueueUrls
seq))
(defn queue-attrs
"Gets or sets the attributes of a queue specified by its URL string.
When setting attributes on a queue, the attribute map must have String keys
and values."
([^AmazonSQSClient client queue-url]
(->>
(.withAttributeNames (GetQueueAttributesRequest. queue-url) #{"All"})
(.getQueueAttributes client)
.getAttributes
(into {})))
([^AmazonSQSClient client queue-url attr-map]
(.setQueueAttributes client
(SetQueueAttributesRequest. queue-url attr-map))))
(defn send
"Sends a new message with the given string body to the queue specified
by the string URL. Returns a map with :id and :body-md5 slots."
[^AmazonSQSClient client queue-url message]
(let [resp (.sendMessage client (SendMessageRequest. queue-url message))]
{:id (.getMessageId resp)
:body-md5 (.getMD5OfMessageBody resp)}))
(defn- message-map
[queue-url ^Message msg]
{:attributes (.getAttributes msg)
:body (.getBody msg)
:body-md5 (.getMD5OfBody msg)
:id (.getMessageId msg)
:receipt-handle (.getReceiptHandle msg)
:source-queue queue-url})
(defn receive
"Receives one or more messages from the queue specified by the given URL.
Optionally accepts keyword arguments:
:limit - between 1 (default) and 10, the maximum number of messages to receive
:visibility - seconds the received messages should not be delivered to other
receivers; defaults to the queue's visibility attribute
:attributes - a collection of string names of :attributes to include in
received messages; e.g. #{\"All\"} will include all attributes,
#{\"SentTimestamp\"} will include only the SentTimestamp attribute, etc.
Defaults to the empty set (i.e. no attributes will be included in
received messages).
See the SQS documentation for all support message attributes.
Returns a seq of maps with these slots:
:attributes - message attributes
:body - the string body of the message
:body-md5 - the MD5 checksum of :body
:id - the message's ID
:receipt-handle - the ID used to delete the message from the queue after
it has been fully processed.
:source-queue - the URL of the queue from which the message was received"
[^AmazonSQSClient client queue-url & {:keys [limit visibility ^java.util.Collection attributes]
:or {limit 1
attributes #{"All"}}}]
(let [req (-> (ReceiveMessageRequest. queue-url)
(.withMaxNumberOfMessages (-> limit (min 10) (max 1)))
(.withAttributeNames attributes))
req (if visibility (.withVisibilityTimeout req visibility) req)]
(->> (.receiveMessage client req)
.getMessages
(map (partial message-map queue-url)))))
(defn polling-receive
"Receives one or more messages from the queue specified by the given URL.
Returns a lazy seq of messages from multiple receive calls, performed
as the seq is consumed.
Accepts the same keyword arguments as `receive`, in addition to:
:period - time in ms to wait after an unsuccessful `receive` request (default: 500)
:max-wait - maximum time in ms to wait to successfully receive messages before
terminating the lazy seq (default 5000)"
[client queue-url & {:keys [period max-wait]
:or {period 500
max-wait 5000}
:as receive-opts}]
(let [waiting (atom 0)
receive-opts (mapcat identity receive-opts)
message-seq (fn message-seq []
(lazy-seq
(if-let [msgs (seq (apply receive client queue-url receive-opts))]
(do
(reset! waiting 0)
(concat msgs (message-seq)))
(do
(when (<= (swap! waiting + period) max-wait)
(Thread/sleep period)
(message-seq))))))]
(message-seq)))
(defn- receipt-handle
[msg-ish]
(cond
(string? msg-ish) msg-ish
(map? msg-ish) (:receipt-handle msg-ish)
:else (.getReceiptHandle ^Message msg-ish)))
(defn delete
"Deletes a message from the queue from which it was received.
The message must be a message map provided by `receive` or `polling-receive`
if the `queue-url` is not provided explicitly. Otherwise,
`message` may be a message map, Message object,
or the :receipt-handle value from a received message map."
([^AmazonSQSClient client message]
(delete client (:source-queue message) message))
([^AmazonSQSClient client queue-url message]
(->> message
receipt-handle
(DeleteMessageRequest. queue-url)
(.deleteMessage client))))
(defn deleting-consumer
"Some minor middleware for simplifying the deletion of processed messages
from their originating queue. Given a client and a function `f`, returns
a function that accepts a single message (as provided by `receive` and `polling-receive`);
it calls `f` with that message, and then deletes the message from its
originating queue. `f`'s return value is passed along."
[client f]
(fn [message]
(let [ret (f message)]
(delete client message)
ret)))
(defn change-message-visibility
"Updates the visibility timeout for a single message in the queue identified by the
given URL.
`message` may be a message map, Message object,
or the :receipt-handle value from a received message map."
[^AmazonSQSClient client queue-url message visibility-timeout]
(.changeMessageVisibility client
(ChangeMessageVisibilityRequest.
queue-url (receipt-handle message) visibility-timeout)))
;; ResponseMetadata getCachedResponseMetadata(AmazonWebServiceRequest request)
;; Returns additional metadata for a previously executed successful, request, typically used for debugging issues where a service isn't acting as expected.
;; void removePermission(RemovePermissionRequest removePermissionRequest)
; The RemovePermission action revokes any permissions in the queue policy that matches the specified Label parameter.
;; void addPermission(AddPermissionRequest addPermissionRequest)
;;The AddPermission action adds a permission to a queue for a specific principal.

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src/test/clojure/cemerick/bandalore_test.clj Normal file
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(ns cemerick.bandalore-test
(:use cemerick.bandalore
clojure.test
clojure.contrib.core)
(:refer-clojure :exclude (send)))
; kill the verbose aws logging
(.setLevel (java.util.logging.Logger/getLogger "com.amazonaws")
java.util.logging.Level/WARNING)
(def client
(let [id (System/getProperty "aws.id")
secret-key (System/getProperty "aws.secret-key")]
(assert (and id secret-key))
(create-client id secret-key)))
(def *test-queue-url* nil)
(defn- uuid
[]
(str (java.util.UUID/randomUUID)))
(defn- test-queue-name
[]
(str "bandalore-test-" (uuid)))
(defmacro defqueuetest
[name & body]
`(deftest ~name
(binding [*test-queue-url* (create-queue client (test-queue-name))]
(try
(is *test-queue-url*)
~@body
(finally
(delete-queue client *test-queue-url*))))))
(defqueuetest listing-queues
(let [msg (uuid)]
(send client *test-queue-url* msg)
(is ((set (list-queues client)) *test-queue-url*))))