Go Programming

Go Programming


Fuzz Testing (Fuzzing) | Write a Fuzz Test with Go (Golang)

How to write a fuzz test with Go (Golang) | Demo

Want to write a fuzz test? In this video, we are joined by Saba, a Software Engineering Manager at Google, who shows how to write a fuzz test for a simple reverse string function, run the go command, and understand the log. You will need Go 1.18 to write a fuzz test!

Go 1.18 installation instructions → https://goo.gle/3AbDsoA 

0:00 - Intro
0:19 - Prerequisites for Fuzzing
0:56 - Demo
6:16 - Wrap up

#go #golang #programming 

What is GEEK

Buddha Community

Fuzz Testing (Fuzzing) | Write a Fuzz Test with Go (Golang)
Fannie  Zemlak

Fannie Zemlak


What's new in the go 1.15

Go announced Go 1.15 version on 11 Aug 2020. Highlighted updates and features include Substantial improvements to the Go linker, Improved allocation for small objects at high core counts, X.509 CommonName deprecation, GOPROXY supports skipping proxies that return errors, New embedded tzdata package, Several Core Library improvements and more.

As Go promise for maintaining backward compatibility. After upgrading to the latest Go 1.15 version, almost all existing Golang applications or programs continue to compile and run as older Golang version.

#go #golang #go 1.15 #go features #go improvement #go package #go new features

Generis: Versatile Go Code Generator


Versatile Go code generator.


Generis is a lightweight code preprocessor adding the following features to the Go language :

  • Generics.
  • Free-form macros.
  • Conditional compilation.
  • HTML templating.
  • Allman style conversion.


package main;


import (


#define DebugMode
#as true

// ~~

#define HttpPort
#as 8080

// ~~

#define WriteLine( {{text}} )
#as log.Println( {{text}} )

// ~~

#define local {{variable}} : {{type}};
#as var {{variable}} {{type}};

// ~~

#define DeclareStack( {{type}}, {{name}} )
    // -- TYPES

    type {{name}}Stack struct
        ElementArray []{{type}};

    // -- INQUIRIES

    func ( stack * {{name}}Stack ) IsEmpty(
        ) bool
        return len( stack.ElementArray ) == 0;

    // -- OPERATIONS

    func ( stack * {{name}}Stack ) Push(
        element {{type}}
        stack.ElementArray = append( stack.ElementArray, element );

    // ~~

    func ( stack * {{name}}Stack ) Pop(
        ) {{type}}
            element : {{type}};

        element = stack.ElementArray[ len( stack.ElementArray ) - 1 ];

        stack.ElementArray = stack.ElementArray[ : len( stack.ElementArray ) - 1 ];

        return element;

// ~~

#define DeclareStack( {{type}} )
#as DeclareStack( {{type}}, {{type:PascalCase}} )

// -- TYPES

DeclareStack( string )
DeclareStack( int32 )


func HandleRootPage(
    response_writer http.ResponseWriter,
    request * http.Request
        boolean : bool;
        natural : uint;
        integer : int;
        real : float64;
        text : string;
        integer_stack : Int32Stack;

    boolean = true;
    natural = 10;
    integer = 20;
    real = 30.0;
    text = "text";
    escaped_url_text = "&escaped text?";
    escaped_html_text = "<escaped text/>";

    integer_stack.Push( 10 );
    integer_stack.Push( 20 );
    integer_stack.Push( 30 );

    #write response_writer
        <!DOCTYPE html>
        <html lang="en">
                <meta charset="utf-8">
                <title><%= request.URL.Path %></title>
                <% if ( boolean ) { %>
                    <%= "URL : " + request.URL.Path %>
                    <%@ natural %>
                    <%# integer %>
                    <%& real %>
                    <%~ text %>
                    <%^ escaped_url_text %>
                    <%= escaped_html_text %>
                    <%= "<%% ignored %%>" %>
                    <%% ignored %%>
                <% } %>
                Stack :
                <% for !integer_stack.IsEmpty() { %>
                    <%# integer_stack.Pop() %>
                <% } %>

// ~~

func main()
    http.HandleFunc( "/", HandleRootPage );

    #if DebugMode
        WriteLine( "Listening on http://localhost:HttpPort" );

        http.ListenAndServe( ":HttpPort", nil )


#define directive

Constants and generic code can be defined with the following syntax :

#define old code
#as new code

#define old code

#as new code


#define parameter

The #define directive can contain one or several parameters :

{{variable name}} : hierarchical code (with properly matching brackets and parentheses)
{{variable name#}} : statement code (hierarchical code without semicolon)
{{variable name$}} : plain code
{{variable name:boolean expression}} : conditional hierarchical code
{{variable name#:boolean expression}} : conditional statement code
{{variable name$:boolean expression}} : conditional plain code

They can have a boolean expression to require they match specific conditions :

HasText text
HasPrefix prefix
HasSuffix suffix
HasIdentifier text
expression && expression
expression || expression
( expression )

The #define directive must not start or end with a parameter.

#as parameter

The #as directive can use the value of the #define parameters :

{{variable name}}
{{variable name:filter function}}
{{variable name:filter function:filter function:...}}

Their value can be changed through one or several filter functions :

ReplacePrefix old_prefix new_prefix
ReplaceSuffix old_suffix new_suffix
ReplaceText old_text new_text
ReplaceIdentifier old_identifier new_identifier
AddPrefix prefix
AddSuffix suffix
RemovePrefix prefix
RemoveSuffix suffix
RemoveText text
RemoveIdentifier identifier

#if directive

Conditional code can be defined with the following syntax :

#if boolean expression
    #if boolean expression
    #if boolean expression

The boolean expression can use the following operators :

expression && expression
expression || expression
( expression )

#write directive

Templated HTML code can be sent to a stream writer using the following syntax :

#write writer expression
    <% code %>
    <%@ natural expression %>
    <%# integer expression %>
    <%& real expression %>
    <%~ text expression %>
    <%= escaped text expression %>
    <%! removed content %>
    <%% ignored tags %%>


  • There is no operator precedence in boolean expressions.
  • The --join option requires to end the statements with a semicolon.
  • The #writer directive is only available for the Go language.


Install the DMD 2 compiler (using the MinGW setup option on Windows).

Build the executable with the following command line :

dmd -m64 generis.d

Command line

generis [options]


--prefix # : set the command prefix
--parse INPUT_FOLDER/ : parse the definitions of the Generis files in the input folder
--process INPUT_FOLDER/ OUTPUT_FOLDER/ : reads the Generis files in the input folder and writes the processed files in the output folder
--trim : trim the HTML templates
--join : join the split statements
--create : create the output folders if needed
--watch : watch the Generis files for modifications
--pause 500 : time to wait before checking the Generis files again
--tabulation 4 : set the tabulation space count
--extension .go : generate files with this extension


generis --process GS/ GO/

Reads the Generis files in the GS/ folder and writes Go files in the GO/ folder.

generis --process GS/ GO/ --create

Reads the Generis files in the GS/ folder and writes Go files in the GO/ folder, creating the output folders if needed.

generis --process GS/ GO/ --create --watch

Reads the Generis files in the GS/ folder and writes Go files in the GO/ folder, creating the output folders if needed and watching the Generis files for modifications.

generis --process GS/ GO/ --trim --join --create --watch

Reads the Generis files in the GS/ folder and writes Go files in the GO/ folder, trimming the HTML templates, joining the split statements, creating the output folders if needed and watching the Generis files for modifications.



Author: Senselogic
Source Code: https://github.com/senselogic/GENERIS 
License: View license

#go #golang #code 

Go Programming

Go Programming


Fuzz Testing (Fuzzing) | Write a Fuzz Test with Go (Golang)

How to write a fuzz test with Go (Golang) | Demo

Want to write a fuzz test? In this video, we are joined by Saba, a Software Engineering Manager at Google, who shows how to write a fuzz test for a simple reverse string function, run the go command, and understand the log. You will need Go 1.18 to write a fuzz test!

Go 1.18 installation instructions → https://goo.gle/3AbDsoA 

0:00 - Intro
0:19 - Prerequisites for Fuzzing
0:56 - Demo
6:16 - Wrap up

#go #golang #programming 

Tamia  Walter

Tamia Walter


Testing Microservices Applications

The shift towards microservices and modular applications makes testing more important and more challenging at the same time. You have to make sure that the microservices running in containers perform well and as intended, but you can no longer rely on conventional testing strategies to get the job done.

This is where new testing approaches are needed. Testing your microservices applications require the right approach, a suitable set of tools, and immense attention to details. This article will guide you through the process of testing your microservices and talk about the challenges you will have to overcome along the way. Let’s get started, shall we?

A Brave New World

Traditionally, testing a monolith application meant configuring a test environment and setting up all of the application components in a way that matched the production environment. It took time to set up the testing environment, and there were a lot of complexities around the process.

Testing also requires the application to run in full. It is not possible to test monolith apps on a per-component basis, mainly because there is usually a base code that ties everything together, and the app is designed to run as a complete app to work properly.

Microservices running in containers offer one particular advantage: universal compatibility. You don’t have to match the testing environment with the deployment architecture exactly, and you can get away with testing individual components rather than the full app in some situations.

Of course, you will have to embrace the new cloud-native approach across the pipeline. Rather than creating critical dependencies between microservices, you need to treat each one as a semi-independent module.

The only monolith or centralized portion of the application is the database, but this too is an easy challenge to overcome. As long as you have a persistent database running on your test environment, you can perform tests at any time.

Keep in mind that there are additional things to focus on when testing microservices.

  • Microservices rely on network communications to talk to each other, so network reliability and requirements must be part of the testing.
  • Automation and infrastructure elements are now added as codes, and you have to make sure that they also run properly when microservices are pushed through the pipeline
  • While containerization is universal, you still have to pay attention to specific dependencies and create a testing strategy that allows for those dependencies to be included

Test containers are the method of choice for many developers. Unlike monolith apps, which lets you use stubs and mocks for testing, microservices need to be tested in test containers. Many CI/CD pipelines actually integrate production microservices as part of the testing process.

Contract Testing as an Approach

As mentioned before, there are many ways to test microservices effectively, but the one approach that developers now use reliably is contract testing. Loosely coupled microservices can be tested in an effective and efficient way using contract testing, mainly because this testing approach focuses on contracts; in other words, it focuses on how components or microservices communicate with each other.

Syntax and semantics construct how components communicate with each other. By defining syntax and semantics in a standardized way and testing microservices based on their ability to generate the right message formats and meet behavioral expectations, you can rest assured knowing that the microservices will behave as intended when deployed.

Ways to Test Microservices

It is easy to fall into the trap of making testing microservices complicated, but there are ways to avoid this problem. Testing microservices doesn’t have to be complicated at all when you have the right strategy in place.

There are several ways to test microservices too, including:

  • Unit testing: Which allows developers to test microservices in a granular way. It doesn’t limit testing to individual microservices, but rather allows developers to take a more granular approach such as testing individual features or runtimes.
  • Integration testing: Which handles the testing of microservices in an interactive way. Microservices still need to work with each other when they are deployed, and integration testing is a key process in making sure that they do.
  • End-to-end testing: Which⁠—as the name suggests⁠—tests microservices as a complete app. This type of testing enables the testing of features, UI, communications, and other components that construct the app.

What’s important to note is the fact that these testing approaches allow for asynchronous testing. After all, asynchronous development is what makes developing microservices very appealing in the first place. By allowing for asynchronous testing, you can also make sure that components or microservices can be updated independently to one another.

#blog #microservices #testing #caylent #contract testing #end-to-end testing #hoverfly #integration testing #microservices #microservices architecture #pact #testing #unit testing #vagrant #vcr

Waylon  Bruen

Waylon Bruen


Go-fuzz: Randomized Testing for Go

go-fuzz: randomized testing for Go

Go-fuzz is a coverage-guided fuzzing solution for testing of Go packages. Fuzzing is mainly applicable to packages that parse complex inputs (both text and binary), and is especially useful for hardening of systems that parse inputs from potentially malicious users (e.g. anything accepted over a network).

Note: go-fuzz has recently added preliminary support for fuzzing Go Modules. See the section below for more details. If you encounter a problem with modules, please file an issue with details. A workaround might be to disable modules via export GO111MODULE=off.


First, you need to write a test function of the form:

func Fuzz(data []byte) int

Data is a random input generated by go-fuzz, note that in most cases it is invalid. The function must return 1 if the fuzzer should increase priority of the given input during subsequent fuzzing (for example, the input is lexically correct and was parsed successfully); -1 if the input must not be added to corpus even if gives new coverage; and 0 otherwise; other values are reserved for future use.

The Fuzz function must be in a package that go-fuzz can import. This means the code you want to test can't be in package main. Fuzzing internal packages is supported, however.

In its basic form the Fuzz function just parses the input, and go-fuzz ensures that it does not panic, crash the program, allocate insane amount of memory nor hang. Fuzz function can also do application-level checks, which will make testing more efficient (discover more bugs). For example, Fuzz function can serialize all inputs that were successfully deserialized, thus ensuring that serialization can handle everything deserialization can produce. Or, Fuzz function can deserialize-serialize-deserialize-serialize and check that results of first and second serialization are equal. Or, Fuzz function can feed the input into two different implementations (e.g. dumb and optimized) and check that the output is equal. To communicate application-level bugs Fuzz function should panic (os.Exit(1) will work too, but panic message contains more info). Note that Fuzz function should not output to stdout/stderr, it will slow down fuzzing and nobody will see the output anyway. The exception is printing info about a bug just before panicking.

Here is an example of a simple Fuzz function for image/png package:

package png

import (

func Fuzz(data []byte) int {
    return 0

A more useful Fuzz function would look like:

func Fuzz(data []byte) int {
    img, err := png.Decode(bytes.NewReader(data))
    if err != nil {
        if img != nil {
            panic("img != nil on error")
        return 0
    var w bytes.Buffer
    err = png.Encode(&w, img)
    if err != nil {
    return 1

The second step is collection of initial input corpus. Ideally, files in the corpus are as small as possible and as diverse as possible. You can use inputs used by unit tests and/or generate them. For example, for an image decoding package you can encode several small bitmaps (black, random noise, white with few non-white pixels) with different levels of compressions and use that as the initial corpus. Go-fuzz will deduplicate and minimize the inputs. So throwing in a thousand of inputs is fine, diversity is more important.

Put the initial corpus into the workdir/corpus directory (in our case examples/png/corpus). Go-fuzz will add own inputs to the corpus directory. Consider committing the generated inputs to your source control system, this will allow you to restart go-fuzz without losing previous work.

The go-fuzz-corpus repository contains a bunch of examples of test functions and initial input corpuses for various packages.

The next step is to get go-fuzz:

$ go get -u github.com/dvyukov/go-fuzz/go-fuzz@latest github.com/dvyukov/go-fuzz/go-fuzz-build@latest

Then, download the corpus and build the test program with necessary instrumentation:

$ go get -d github.com/dvyukov/go-fuzz-corpus
$ cd $GOPATH/src/github.com/dvyukov/go-fuzz-corpus
$ cd png
$ go-fuzz-build

This will produce png-fuzz.zip archive.

Now we are ready to go:

$ go-fuzz

Go-fuzz will generate and test various inputs in an infinite loop. Workdir is used to store persistent data like current corpus and crashers, it allows fuzzer to continue after restart. Discovered bad inputs are stored in workdir/crashers dir; where file without a suffix contains binary input, file with .quoted suffix contains quoted input that can be directly copied into a reproducer program or a test, file with .output suffix contains output of the test on this input. Every few seconds go-fuzz prints logs to stderr of the form:

2015/04/25 12:39:53 workers: 500, corpus: 186 (42s ago), crashers: 3,
     restarts: 1/8027, execs: 12009519 (121224/sec), cover: 2746, uptime: 1m39s

Where workers means number of tests running in parallel (set with -procs flag). corpus is current number of interesting inputs the fuzzer has discovered, time in brackets says when the last interesting input was discovered. crashers is number of discovered bugs (check out workdir/crashers dir). restarts is the rate with which the fuzzer restarts test processes. The rate should be close to 1/10000 (which is the planned restart rate); if it is considerably higher than 1/10000, consider fixing already discovered bugs which lead to frequent restarts. execs is total number of test executions, and the number in brackets is the average speed of test executions. cover is number of bits set in a hashed coverage bitmap, if this number grows fuzzer uncovers new lines of code; size of the bitmap is 64K; ideally cover value should be less than ~5000, otherwise fuzzer can miss new interesting inputs due to hash collisions. And finally uptime is uptime of the process. This same information is also served via http (see the -http flag).

Modules support

go-fuzz has preliminary support for fuzzing Go Modules. go-fuzz respects the standard GO111MODULE environment variable, which can be set to on, off, or auto.

go-fuzz-build will add a require for github.com/dvyukov/go-fuzz to your go.mod. If desired, you may remove this once the build is complete.

Vendoring with modules is not yet supported. A vendor directory will be ignored, and go-fuzz will report an error if GOFLAGS=-mod=vendor is set.

Note that while modules are used to prepare the build, the final instrumented build is still done in GOPATH mode. For most modules, this should not matter.

libFuzzer support

go-fuzz-build can also generate an archive file that can be used with libFuzzer instead of go-fuzz (requires linux).

Sample usage:

$ cd $GOPATH/src/github.com/dvyukov/go-fuzz-corpus/fmt
$ go-fuzz-build -libfuzzer  # produces fmt.a
$ clang -fsanitize=fuzzer fmt.a -o fmt.libfuzzer
$ ./fmt.libfuzzer

When run with -libfuzzer, go-fuzz-build adds the additional build tag gofuzz_libfuzzer when building code.

Continuous Fuzzing

Just as unit-testing, fuzzing is better done continuously.

Currently there are 2 services that offer continuous fuzzing based on go-fuzz:

Random Notes

go-fuzz-build builds the program with gofuzz build tag, this allows to put the Fuzz function implementation directly into the tested package, but exclude it from normal builds with // +build gofuzz directive.

If your inputs contain a checksum, it can make sense to append/update the checksum in the Fuzz function. The chances that go-fuzz will generate the correct checksum are very low, so most work will be in vain otherwise.

Go-fuzz can utilize several machines. To do this, start the coordinator process separately:

$ go-fuzz -workdir=examples/png -coordinator=

It will manage persistent corpus and crashers and coordinate work of worker processes. Then run one or more worker processes as:

$ go-fuzz -bin=./png-fuzz.zip -worker= -procs=10

External Articles

History rewrite

go-fuzz repository history was recently rewritten to exclude examples directory to reduce total repository size and download time (see #88, #114 and https://github.com/dvyukov/go-fuzz-corpus). Unfortunately, that means that go get -u command will fail if you had a previous version installed. Please remove $GOPATH/github.com/dvyukov/go-fuzz before running go get again.

Credits and technical details

Go-fuzz fuzzing logic is heavily based on american fuzzy lop, so refer to AFL readme if you are interested in technical details. AFL is written and maintained by Michal Zalewski. Some of the mutations employed by go-fuzz are inspired by work done by Mateusz Jurczyk, Gynvael Coldwind and Felix Gröbert.


If you find some bugs with go-fuzz and are comfortable with sharing them, I would like to add them to this list. Please either send a pull request for README.md (preferable) or file an issue. If the source code is closed, you can say just "found N bugs in project X". Thank you.

Author: Dvyukov
Source Code: https://github.com/dvyukov/go-fuzz 
License: Apache-2.0 license

#go #golang #testing