Multithreaded C++ framework for AWS S3.
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Copyright 2011-2017 by the Digital Aggregates Corporation, Colorado, USA.


This software is licensed under the terms of the GNU General Public License (GNU GPL) version 3 as published by the Free Software Foundation (FSF). Alternative commercial licensing terms are available from the copyright holder.


This file is part of the Digital Aggregates Corporation Hayloft package. Hayloft presents a C++-based object oriented abstraction to the Amazon Web Service (AWS) Simple Storage System (S3). Why C++? Because part of my original goal was to develop an experimental framework that could be used in embedded applications. However, since I wrote this code in 2011, the Linux-based embedded targets that I've worked on professionally have become so powerful that there may be little reason not to use higher level languages like Python for embedded S3 applications.


You have to be pretty determined to use Hayloft because it has a lot of dependencies.

Hayloft has direct dependencies on Bryan Ischo's S3 library libs3 2.0, and on Digital Aggregates's Grandote C++ systems programming library.

libs3 depends on the cURL, SSL, Crypto, and XML2 libraries.

Grandote depends on the Digital Aggregates Diminuto C systems programming library, Google Test (or Google Mock), and the Digital Aggregates Google Test helper framework Lariat.

Diminuto depends on the standard pthread (POSIX thread), rt (real-time), dl (dynamic linker), and math libraries.

Hayloft can be used with the standard libs3-2 available as an Ubuntu package. But I chose to build it from scratch to patch in support for enabling verbose debugging in libcurl and to support the use of the Charles Web Debugging Proxy.

Grandote is a fork of the Digital Aggregates Desperadito C++ library ported to run on top of Diminuto. Desperadito is a fork of the Digital Aggregates Desperado C++ library plus some general purposes classes that were originally in Hayloft itself. Portions of Desperado, Desperadito, and Diminuto have found their way into some of the code bases of my clients. I am no longer maintaining Desperadito or Desperado.

NOTA BENE (2017)

This code worked when I wrote it six years ago in 2011. When I revisited it in 2017, it was horribly broken. Maybe I shouldn't be surprised, since so much has changed in the deep stack of frameworks, libraries, and technologies on which Hayloft depends. But the most mysterious thing is that while the extensive unit test suite that had always worked in 2011 now failed miserably, the example application - a sort of "Hello, World!" application that served as an example of how to use Hayloft in a C++ application that used AWS S3 - worked just fine.

Ultimately this turned out to be several issues, which is usually the way with these sorts of things.

The first was a subtle change in behavior in libcurl, which is used by libs3 to communicate with AWS. The fix was to change the decision making in Hayloft about whether it should return to the caller or continue driving the underlying cURL state machine in multiplexed operations. I believe this bug - which was in a couple of places - has been fixed.

The second was in the realm of eventual consistency, and consistency convergence, in distributed systems, something I experimented with when I first wrote this software. For example: you can create a bucket. But if you immediately check to see if the bucket exists, you may get a response that it does not. But if you then check a few minutes later, it's there. I recall that back in 2011 the unit test suite failed from time to time in a similar manner when I ran it during the peak Christmas shopping season; that's probably not a coincidence. Addressing this has mostly been a matter of tuning the unit tests to wait longer for consistency to converge.



Chip Overclock
Digital Aggregates Corporation
3440 Youngfield Street, #209
Wheat Ridge CO 80033 USA


Hayloft has been built and tested on the following targets.

Intel NUC5i7RYH
Intel Core i7-5557U @ 3.10GHz x 8
Ubuntu 16.04.3 "xenial"
Linux 4.10.0
gcc 5.4.0


C. Overclock, "'s Simple Storage Service and Hayloft",

C. Overclock, "Eventual Consistency and Hayloft",

C. Overclock, "Abstraction in C++ using I/O Functors",, Amazon Simple Storage Service, "Getting Started Guide (GSG)", 2017, Amazon Web Services, Amazon Simple Storage Service, "Developer Guide (DG)", 2006-03-01, Amazon Web Services, Amazon Simple Storage Service, "API Reference (AR)", 2006-03-01, Amazon Web Services, Amazon Simple Storage Service, "Console User Guide", 2017, Amazon Web Services

Amazon Simple Storage Service Team, "Best Practices for Using Amazon S3", 2008-11-10, Amazon Web Services

Jinesh Varia, "Cloud Architectures", 2008-06, Amazon Web Services

Jinesh Varia, "Architecting for the Cloud: Best Practices", 2010-01, Amazon Web Services

R. Fielding et al., "Hypertext Transfer Protocol -- HTTP/1.1", RFC2616, The Internet Society, June 1999


out/host/tst/unittest [ -d ]

Runs the Google Test-based unit test suite, optionally with debugging enabled. (Be forewarned that enabling debugging cause the unit test suite to generate a humongous amount of output when it runs.)

out/host/tst/example [ -d ]

Runs the example application, optionally with debugging enabled.


Deletes buckets and objects used by the unit test suite and by the example application. Useful if either program doesn't complete normally.

. etc/libs3.rc

Sets the environmental variables needed by the s3 utility that is part of the libs3 framework.


Contain the S3 authentication strings, bucket suffix string, and user agent name that are required by the comamnds described above. The unit test suite, for example, sets the environmental variables described below from the contents of these files.



This string is your twenty character AWS access key id, a sort of login (but not your AWS web login).


This string is your forty character AWS secret access key, a sort of password (but not your AWS web password) and encryption key.


This string is the DNS host name of the AWS S3 service. This host name may (or must) differ depending on the region the bucket is in. If not specified, the United States Standard end point, "", is used.


If specified, this string is is appended without further punctuation to each bucket name specified in any of the Bucket constructors (BucketCreate, etc.) prior to the bucket name being canonicalized by Hayloft. Canonicalized bucket names have to be globally unique and form a legal internet Domain Name Service (DNS) domain name. Although domain names are case insensitive, S3 requires that they be all lower case. Furthermore, when using HTTPS, the security certificate only works if your bucket name contains no periods. I use a suffix like "-hayloft-diag-com". An application creating a bucket using BucketCreate("Me") and using the default end point name and the default virtual path style URL will hence see the name canonicalized into an S3 bucket name "". Canonicalized bucket names are what you will see in a ServiceManifest.


If specified, this string is passed to S3 in the User-Agent HTTP header to identify your application.


This string is the default AWS region to use. If not specified, the United States Standard region is used (which is actually specified by omitting the region parameter altogether in messages to S3).


If specified, this string contains a sixteen bit number, encoded using the normal C syntax rules for octal, decimal, or hexadecimal numbers, to specify a sixteen bit logging mask at run time. The bits in the mask which of the sixteen log levels are enabled via the expression (1 << LEVEL) where LEVEL is one of the following log levels. So for example the DEBUG level is enabled if bit (1 << DEBUG) or 0x0010 is set. The different log levels found in com/diag/grandote/Log.h are the transitive closure of common logging mechanisms from GNU/Linux, Apache, Java, etc. (This is implemented in the Grandote library.)


FINEST           0		0x0001
FINER            1		0x0002
FINE             2		0x0004
TRACE            3		0x0008
DEBUG            4		0x0010
INFORMATION      5		0x0020
CONFIGURATION    6		0x0040
NOTICE           7		0x0080
WARNING          8		0x0100
ERROR            9		0x0200
SEVERE          10		0x0400
CRITICAL        11		0x0800
ALERT           12		0x1000
FATAL           13		0x2000
EMERGENCY       14		0x4000
PRINT           15		0x8000


0xff80			errors, warnings, notices of unusual events (default)
0xffc0			plus convergence and retry events like timeouts
0xffe0			plus output from show functions
0xfff0			plus debug output

The Grandote log levels are mapped to the appropriate log levels in the underlying logging mechanism. For example, SYSLOG has eight log levels.


These environmental variables can be used with the unit test suite to place a timeout (in milliseconds) for servicing each individual Bucket or Object request, and a limit (in iterations) for serving multiple Bucket or Object requests. Defining the NOLIMIT and NOTIMEOUT environmental variables (regardless of value) uses the maximum possible values.


Enables debug mode in the Hayloft framework and in the unit test suite. Several Hayloft functions alter their behavior if this environmental variable is defined (regardless of value). For example, HTTP is used as the default protocol instead of HTTPS.


This string specifies the IP address and port used for the cURL PROXY option used in conjunction with the Charles Web Debugging Proxy application. Typically this will be the local host address and Charles port "". This capability is only available if your libs3 sources have been patched with the patch file in the Hayloft distribution, and is only necessary if you are using Charles to spy on the communication between your system and S3. This might be useful for debugging.

libcurl and Charles don't seem to play well together when switching back and forth between HTTP and HTTPS. HTTPS is the default. Running the entire unit test suite with proxying enabled seems to cause Charles to break the BucketTest.Explicit unit test, which is the only unit test that uses HTTP. Running that unit test all by itself works fine. Running all unit tests without Charles works fine. As far as I can tell, libcurl is not reusing an existing HTTPS socket connection when switching to HTTP for BucketTest.Explicit, which I thought might be the problem.


This string, if it is equal to "1", turns on the cURL VERBOSE option. This causes CURL, the URL library used by libs3, to log just about everything it does. This might be useful for debugging.


If S3 does not maintain a bandwidth of at least the LOW_SPEED_LIMIT in bytes per second during a window of LOW_SPEED_TIME seconds, libcurl will terminate the connection. libs3 sets these parameters to 1024 and 15 respectively. These strings, when converted to long values, can be used to change this limit. Typically you'll want to set them lower. I find that even with a good broadband internet connection using a pretty sizeable Pentium server I sometimes see only around 660B/s. I suspect this is my broadband provider throttling my uplink speed. This will be an issue during ObjectGet and ObjectPut Actions.


Plexes are different approaches to managing the execution of Actions. You can see examples of all of them in the unit test suite. Briefly here are the different Plexes you can use.


When you use a constructor that doesn't specify a Plex, you are using the synchronous interface. The Action will be started inside the Action constructor and the calling thread will block until the Action completes. It is up to you to decide whether you need to restart the Action for any reason.


The Simplex uses the synchronous interface but doesn't start the Action automatically. You must start it manually using its start method. The calling thread will block in the start method until the Action completes. It is up to you to decide whether you need to restart the Action for any reason.


The Multiplex uses the asynchronous interface. You must start the Action manually using the start method, and then use the methods provided by the Multiplex to drive the underlying state machines inside libs3 and libcurl to talk to S3. Typically you will run these Multiplex methods in the foreground thread. It is possible to run them in a background thread, but you are responsible for any synchronization. It is up to you to decide whether you need to restart the Action for any reason.


Complex uses the asynchronous interface. You don't start the Action at all, but instead submit it to the Complex background thread for starting. You can call the wait method which will block your thread until a specific Action has completed. Complex automatically retries any Actions that complete due to a recoverable error, or for errors which are likely to be caused by eventual consistency issues. Complex can run many Actions simultaneously. Once an Action completes, either it has completed for a reason that is non-retryable (including success), it has already been retried too many times, or it failed to start or to reset upon a restart.