Match
- Rule or Token value that matched.V
- The type of the target value.@FunctionalInterface public interface Mapper<Match,V>
| Modifier and Type | Interface and Description |
|---|---|
static class |
Mapper.Builder<K extends Grammar.Rule,M extends Mapper<?,V>,V>
A mapper builder.
|
| Modifier and Type | Method and Description |
|---|---|
static <K extends Grammar.Rule,M extends Mapper<?,V>,V> |
$()
Convenient method for building a set
of mappers.
|
V |
transform(ValueStack<ValueMapper.Value<V>> stack,
Match matcher,
Deque<ValueMapper.Value<V>> data)
Transform a rule to a node in the context
of what was previously parsed in the stack,
and what follows in the current rule.
|
V transform(ValueStack<ValueMapper.Value<V>> stack, Match matcher, Deque<ValueMapper.Value<V>> data)
stack
- The stack contains source tokens
encountered so far but not yet processed.
The stack is a work area that may be useful
for the transformation of the token.matcher
- The actual rule/token value to transform is
supplied by the parser.data
- The elements available in the current
context of this transformation.null
to discard the rule, which means that all
its arguments will be merged with the arguments
of the nested rule.static <K extends Grammar.Rule,M extends Mapper<?,V>,V> Mapper.Builder<K,M,V> $()
K
- The type of the key : Rule, or Token.M
- A subclass of Mapper.V
- The type of the target value.Copyright © 2020 Alternet. All rights reserved.


A local court in August had pronounced death penalty by hanging to the accused in the rape and murder of the nine-month-old baby of Kumarpally, Hanamkonda.
The baby, who asleep with her mother on the terrace of the house was allegedly kidnapped, raped and murdered by a Polepaka Praveen of Vasanthapur village of Shayampet mandal in Warangal Rural district in the wee hours of June 19.
Following this, the Hanamkonda police registered a case and ACP Ch. Sridhar investigated the case and filed the chargesheet in just 21 days after the incident. The police arrested the accused on the same day.


Look away now West Ham fans – this Lucas Perez stat is madness
by Tom ProcterWest Ham United fans didn’t really bat much of an eyelid when Lucas Perez was sold in the summer.
The Spaniard was one of four attackers to depart the club, with Marko Arnautovic, Javier Hernandez and Andy Carroll all leaving as well.
Perez only signed for the Hammers in the summer of 2018 from Arsenal, but couldn’t make an impact for the Londoners.
Remarkably, he managed to make his paltry £4 million fee (football.london) look expensive.
Manuel Pellegrini used him sparingly, and he could only contribute six goals in 19 appearances.
Perez left West Ham for Deportivo Alaves for around £2.2 million (Sky Sports), and most people thought they wouldn’t be hearing from him again. That they could just pretend he never happened.
Unfortunately, Perez has set about showing how good a finisher he really is.
According to The Daily Mail, Perez is statistically Europe’s most clinical forward having converted 46.1% of his chances.
He may ‘only’ have seven goals to his name so far, but in terms of putting away chances there’s nobody better right now.
Of course, the likes of Kylian Mbappe and Robert Lewandowski have far more goals, but they are in teams that create more chances for them to squander.
Perez’s rate puts him marginally ahead of the Premier League’s Jamie Vardy (45.5%), whose finishing has been next level this term.
TBR’s view – Were West Ham too hasty?
Perez’s amazing form is getting to be quite uncomfortable for West Ham supporters.
Some might have thought he’d improve back in his homeland, but nobody would have predicted this kind of prolificacy.
Having struggled at Arsenal too, some put Perez’s failings in England down to adaptability issues.
But maybe he just wasn’t given a fair crack, with both Arsene Wenger and Pellegrini mostly keeping him on the fringes.
Have something to tell us about this article?
Let us know


enum class RelevancyStatus
If the querying node is a participant in a state then it is classed as RELEVANT.
If the querying node is not a participant in a state then it is classed as NOT_RELEVANT. These types of states can still be recorded in the vault if the transaction containing them was recorded with the net.corda.v5.ledger.services.StatesToRecord.ALL_VISIBLE flag. This will typically happen for things like reference data which can be referenced in transactions as a net.corda.v5.ledger.contracts.ReferencedStateAndRef but cannot be modified by any party but the maintainer.
RELEVANT |
|
NOT_RELEVANT |


The Chemical Reaction Toolkit is a suite of tools written in Javascript that perform basic analysis of chemical reaction networks from the comfort of your web browser, without needing to install any software.
At present, the toolkit provides a convenient parser for reaction networks and efficient algorithms for computing the full set of conservation laws.
Please review CRNTK's "understanding" of your chemical reaction network before proceeding.
Additionally, you may provide specific names for each reaction: these names will be reflected in the various exported files that are available. (Note that a reversible reaction named "Rxn" will implicitly generate "Rxn_f" and "Rxn_b" in these files, referring to the forward and backward reactions separately.)
Depending on the size of the chemical reaction network, this calculation may take some time. The underlying algorithm is the "double description method" combined with a few tricks that often drastically speed up the calculation.
coming soon...
coming soon...


I'm a Enthusiastic Competitive Pragrammer.
Name:
Saurabh Mishra
Age:
21 years
Location:
Bangalore, Karnataka ,INDIA
“I Don't Believe in Taking Right Decisions, I Take My Decision And Make It Right.”
-Ratan Tata
Aug 2017 -Jun 2021
Bachelor Of Technology I pursued my B.Tech. from University Of Lucknow which is a State University. During the course i attended my subjects like Operating System, Design and Analysis of Algorithms, Theory of Computation, DBMS, etc. Online
May 2020
Stood Among Top 6% of participants from all over India in HackWithInfy 2020 which was a pure DSA based Competition.
Oct 2020
Got into top 20% in final results of Hackerrank HackFest 2020, a three day pure DSA Competition.
May 2020 - Current
Achieved 5 star Position in Problem Solving, 5 Star in Python, 4 Star in SQL on hackerrank.
“Life without knowledge is death in disguise.”
- Talib Kweli
“You can do anything you set your mind to.”
- Benjamin Franklin
“If I had asked people what they wanted, they would have said faster horses. ”
- Henry Ford


OBReadProduct2_Data_OtherProductType_Overdraft_OverdraftTierBandSet
- AuthorisedIndicator : Boolean
Indicates if the Overdraft is authorised (Y) or unauthorised (N)
- BufferAmount : String
When a customer exceeds their credit limit, a financial institution will not charge the customer unauthorised overdraft charges if they do not exceed by more than the buffer amount. Note: Authorised overdraft charges may still apply.
- Identification : String
Unique and unambiguous identification of a Tier Band for a overdraft product.
- OverdraftFeesCharges : List
- OverdraftType : String
An overdraft can either be 'committed' which means that the facility cannot be withdrawn without reasonable notification before it's agreed end date, or 'on demand' which means that the financial institution can demand repayment at any point in time.
- Enum:
- OVCO
- OVOD
- OVOT
- TierBandMethod : String
The methodology of how overdraft is charged. It can be: 'Whole' Where the same charge/rate is applied to the entirety of the overdraft balance (where charges are applicable). 'Tiered' Where different charges/rates are applied dependent on overdraft maximum and minimum balance amount tiers defined by the lending financial organisation 'Banded' Where different charges/rates are applied dependent on overdraft maximum and minimum balance amount bands defined by a government organisation.
- Enum:
- INBA
- INTI
- INWH


lexicon-STICKER
Lexicon Sticker Component
Setup
Install NodeJS >= v0.12.0 and NPM >= v3.0.0, if you don't have it yet. You can find it here.
Install local dependencies:
npm install
Build the code:
npm run build
Open the demo at demos/index.html on your browser.
Contribute
We'd love to get contributions from you! Please, check our Contributing Guidelines to see how you can help us improve.


My senior seminar project, we looked to understand, visualize, and grant easier access to Carleton's energy data. We created a system that includes an organized database, an api, a dashboard, and some analysis tools that all work together to grant understanding of energy usage and general facilities data to students and staff at the school.
This project was made to evolve a solution to a crossword given a grid. It works through having a random beginning population, assigning fitness to members of that population, and then performing 'natural' selection to get the next population. The idea is that every new generation will be more fit (a better solution) than the previous generation, and in this way, a solution will arise.
Writing an interpreter was a huge challenge as I was unfamiliar with both scheme and C at the time that I was writing it. Our interpreter could take scheme input and output either the correct result or an appropriate error message.
An Android application for money management in a group. You can enter individual debts, or group debts to make shared living situations easier and general finances streamlined.
Greenvale Community School is located in Northfield, MN and expressed a desire for more of an online presence. Myself and a group of 2 others mocked-up a possible website for the school according to the requirements we obtained in interviews with the school and the community members. We used Balsamiq to create prototypes and then worked on those prototypes over the course of several weeks while interviewing the community throughout to ensure that our mockups would suit the needs of the school.


GALLERY Brilliant work done by my students. Beautiful group theory notes by grade 8 girl. Highlight of an incredible combinatorics test paper. Grade 7 The layout and organization of this number theory computation is a model of mathematical handwriting beauty. Grade 8 girl. Proof of Ptolemy's second theorem on cyclic quadrilaterals. Grade 8. Ruler-compass construction of huge polygon by grade 6 boy. Visualization of 4D hypercube by grade 7 girl.


SOLAR AGE CALCULATOR
The current date is:
Compare a Date in Seconds with Today!
Male
Female
Calculate!


Cristin Milioti
American actress and singer. She has worked in Broadway theatre productions such as That Face, Stunning, and the Tony Award-winning musical Once. She also played the titular Mother on the sitcom How I Met Your Mother from 2013 to 2014, Teresa Petrillo Belfort in the 2013 film The Wolf of Wall Street, and Betsy Solverson in the second season of Fargo.


Eye5G is here to assist 24/7, whenever you feel like practicing.
Optional integration with your glasses.
Able to distinguish between a wide range of everyday objects.
The full source code is released under MIT and available on Github.


extract first frame from http stream before it complete ↓
fetch bytes by http and extract first frame ↓
fetching...
choose a local GIF to decode ↓
Note:The responses of GIFs have been throttled (~<=%speed%=>KB/s), so you can see the loading process.
It depends on
Service Worker,
fetch API and
Readable Stream.
loading...
extract first frame from http stream before it complete ↓
fetch bytes by http and extract first frame ↓
fetching...
choose a local GIF to decode ↓


{% extends "base.html" %} {% block title %}Create User{% endblock %} {% block content %}
User was created!
That token seems no good. :(


Checkpoint
Groups trackable objects, saving and restoring them.
Checkpoint
's constructor accepts keyword arguments whose values are types
that contain trackable state, such as tf.compat.v1.train.Optimizer
implementations, tf.Variable
, tf.keras.Layer
implementations, or
tf.keras.Model
implementations. It saves these values with a checkpoint, and
maintains a save_counter
for numbering checkpoints.
Example usage when graph building:
import tensorflow as tf import os checkpoint_directory = "/tmp/training_checkpoints" checkpoint_prefix = os.path.join(checkpoint_directory, "ckpt") checkpoint = tf.train.Checkpoint(optimizer=optimizer, model=model) status = checkpoint.restore(tf.train.latest_checkpoint(checkpoint_directory)) train_op = optimizer.minimize( ... ) status.assert_consumed() # Optional sanity checks. with tf.compat.v1.Session() as session: # Use the Session to restore variables, or initialize them if # tf.train.latest_checkpoint returned None. status.initialize_or_restore(session) for _ in range(num_training_steps): session.run(train_op) checkpoint.save(file_prefix=checkpoint_prefix)
Example usage with eager execution enabled:
import tensorflow as tf import os tf.compat.v1.enable_eager_execution() checkpoint_directory = "/tmp/training_checkpoints" checkpoint_prefix = os.path.join(checkpoint_directory, "ckpt") checkpoint = tf.train.Checkpoint(optimizer=optimizer, model=model) status = checkpoint.restore(tf.train.latest_checkpoint(checkpoint_directory)) for _ in range(num_training_steps): optimizer.minimize( ... ) # Variables will be restored on creation. status.assert_consumed() # Optional sanity checks. checkpoint.save(file_prefix=checkpoint_prefix)
Checkpoint.save
and Checkpoint.restore
write and read object-based
checkpoints, in contrast to tf.compat.v1.train.Saver
which writes and reads
variable.name
based checkpoints. Object-based checkpointing saves a graph of
dependencies between Python objects (Layer
s, Optimizer
s, Variable
s,
etc.) with named edges, and this graph is used to match variables when
restoring a checkpoint. It can be more robust to changes in the Python
program, and helps to support restore-on-create for variables when executing
eagerly. Prefer tf.train.Checkpoint
over tf.compat.v1.train.Saver
for new
code.
Checkpoint
objects have dependencies on the objects passed as keyword
arguments to their constructors, and each dependency is given a name that is
identical to the name of the keyword argument for which it was created.
TensorFlow classes like Layer
s and Optimizer
s will automatically add
dependencies on their variables (e.g. "kernel" and "bias" for
tf.keras.layers.Dense
). Inheriting from tf.keras.Model
makes managing
dependencies easy in user-defined classes, since Model
hooks into attribute
assignment. For example:
class Regress(tf.keras.Model): def __init__(self): super(Regress, self).__init__() self.input_transform = tf.keras.layers.Dense(10) # ... def call(self, inputs): x = self.input_transform(inputs) # ...
This Model
has a dependency named "input_transform" on its Dense
layer,
which in turn depends on its variables. As a result, saving an instance of
Regress
using tf.train.Checkpoint
will also save all the variables created
by the Dense
layer.
When variables are assigned to multiple workers, each worker writes its own section of the checkpoint. These sections are then merged/re-indexed to behave as a single checkpoint. This avoids copying all variables to one worker, but does require that all workers see a common filesystem.
While tf.keras.Model.save_weights
and tf.train.Checkpoint.save
save in the
same format, note that the root of the resulting checkpoint is the object the
save method is attached to. This means saving a tf.keras.Model
using
save_weights
and loading into a tf.train.Checkpoint
with a Model
attached (or vice versa) will not match the Model
's variables. See the
guide to training
checkpoints for
details. Prefer tf.train.Checkpoint
over tf.keras.Model.save_weights
for
training checkpoints.
save_counter
: Incremented when save()
is called. Used to number
checkpoints.__init__
__init__(**kwargs)
Group objects into a training checkpoint.
**kwargs
: Keyword arguments are set as attributes of this object, and are
saved with the checkpoint. Values must be trackable objects.ValueError
: If objects in kwargs
are not trackable.save_counter
An integer variable which starts at zero and is incremented on save.
Used to number checkpoints.
The save counter variable.
restore
restore(save_path)
Restore a training checkpoint.
Restores this Checkpoint
and any objects it depends on.
When executing eagerly, either assigns values immediately if variables to restore have been created already, or defers restoration until the variables are created. Dependencies added after this call will be matched if they have a corresponding object in the checkpoint (the restore request will queue in any trackable object waiting for the expected dependency to be added).
When graph building, restoration ops are added to the graph but not run immediately.
To ensure that loading is complete and no more assignments will take place,
use the assert_consumed()
method of the status object returned by
restore
:
checkpoint = tf.train.Checkpoint( ... ) checkpoint.restore(path).assert_consumed()
An exception will be raised if any Python objects in the dependency graph were not found in the checkpoint, or if any checkpointed values do not have a matching Python object.
When graph building, assert_consumed()
indicates that all of the restore
ops that will be created for this checkpoint have been created. They can be
run via the run_restore_ops()
method of the status object:
checkpoint.restore(path).assert_consumed().run_restore_ops()
If the checkpoint has not been consumed completely, then the list of restore ops will grow as more objects are added to the dependency graph.
Name-based tf.compat.v1.train.Saver
checkpoints can be loaded using this
method. Names are used to match variables. No restore ops are created/run
until run_restore_ops()
or initialize_or_restore()
are called on the
returned status object when graph building, but there is restore-on-creation
when executing eagerly. Re-encode name-based checkpoints using
tf.train.Checkpoint.save
as soon as possible.
save_path
: The path to the checkpoint, as returned by save
or
tf.train.latest_checkpoint
. If None (as when there is no latest
checkpoint for tf.train.latest_checkpoint
to return), returns an
object which may run initializers for objects in the dependency graph.
If the checkpoint was written by the name-based
tf.compat.v1.train.Saver
, names are used to match variables.A load status object, which can be used to make assertions about the status of a checkpoint restoration and run initialization/restore ops.
The returned status object has the following methods:
assert_consumed()
:
Raises an exception if any variables/objects are unmatched: either
checkpointed values which don't have a matching Python object or
Python objects in the dependency graph with no values in the
checkpoint. This method returns the status object, and so may be
chained with initialize_or_restore
or run_restore_ops
.
assert_existing_objects_matched()
:
Raises an exception if any existing Python objects in the dependency
graph are unmatched. Unlike assert_consumed
, this assertion will
pass if values in the checkpoint have no corresponding Python
objects. For example a tf.keras.Layer
object which has not yet been
built, and so has not created any variables, will pass this assertion
but fail assert_consumed
. Useful when loading part of a larger
checkpoint into a new Python program, e.g. a training checkpoint with
a tf.compat.v1.train.Optimizer
was saved but only the state required
for
inference is being loaded. This method returns the status object, and
so may be chained with initialize_or_restore
or run_restore_ops
.
assert_nontrivial_match()
: Asserts that something aside from the root
object was matched. This is a very weak assertion, but is useful for
sanity checking in library code where objects may exist in the
checkpoint which haven't been created in Python and some Python
objects may not have a checkpointed value.
expect_partial()
: Silence warnings about incomplete checkpoint
restores. Warnings are otherwise printed for unused parts of the
checkpoint file or object when the Checkpoint
object is deleted
(often at program shutdown).
initialize_or_restore(session=None)
:
When graph building, runs variable initializers if save_path
is
None
, but otherwise runs restore operations. If no session
is
explicitly specified, the default session is used. No effect when
executing eagerly (variables are initialized or restored eagerly).
run_restore_ops(session=None)
:
When graph building, runs restore operations. If no session
is
explicitly specified, the default session is used. No effect when
executing eagerly (restore operations are run eagerly). May only be
called when save_path
is not None
.
save
save( file_prefix, session=None )
Saves a training checkpoint and provides basic checkpoint management.
The saved checkpoint includes variables created by this object and any
trackable objects it depends on at the time Checkpoint.save()
is
called.
save
is a basic convenience wrapper around the write
method,
sequentially numbering checkpoints using save_counter
and updating the
metadata used by tf.train.latest_checkpoint
. More advanced checkpoint
management, for example garbage collection and custom numbering, may be
provided by other utilities which also wrap write
(tf.contrib.checkpoint.CheckpointManager
for example).
file_prefix
: A prefix to use for the checkpoint filenames
(/path/to/directory/and_a_prefix). Names are generated based on this
prefix and Checkpoint.save_counter
.session
: The session to evaluate variables in. Ignored when executing
eagerly. If not provided when graph building, the default session is
used.The full path to the checkpoint.
write
write( file_prefix, session=None )
Writes a training checkpoint.
The checkpoint includes variables created by this object and any
trackable objects it depends on at the time Checkpoint.write()
is
called.
write
does not number checkpoints, increment save_counter
, or update the
metadata used by tf.train.latest_checkpoint
. It is primarily intended for
use by higher level checkpoint management utilities. save
provides a very
basic implementation of these features.
file_prefix
: A prefix to use for the checkpoint filenames
(/path/to/directory/and_a_prefix).session
: The session to evaluate variables in. Ignored when executing
eagerly. If not provided when graph building, the default session is
used.The full path to the checkpoint (i.e. file_prefix
).


{% extends 'base.html' %} {% block content %}
The app is focused on the locations in Black Desert Online, including how they are connected to one another as well as their utility.
Kingdoms are the principle geographic divisions in Black Desert Online.
Territories are subdivions of Kingdoms and the smallest geographic divisions.
Nodes are the primary locations through Black Desert Online. They are connected to other Nodes and typically contain Resources and/or Properties.
Properties are rentable buildings that are attached to a Node. They often contain crafting Stations.


Freddie Mercury was 'scarred and deeply hurt' by devastating betrayal
Freddie Mercury has said that heartbreaking affairs had 'scarred' him but there were two people that 'deeply hurt' him with their betrayal
by James Brinsford, https://www.facebook.com/james.brinsfordFreddie Mercury was 'scarred' and 'deeply betrayed' by two people, according to his former best friend, Peter Freestone.
The Queen singer was allegedly "good a sussing people out quickly," but was left reeling by the antics of a couple of people he let get close to him.
The legendary frontman's friend, who stayed with him at One Garden Lodge in Kensington for 12 years, said that he often would advise that certain associates of the singer were only there for one thing, and it was detrimental to Freddie.
Peter recalls: "I would say, ’This person is only hanging around for your money and fame.’   I know what they’re doing but I am getting something out of it, too’
"Freddie just enjoyed the company or the sex or being amused by the situation and he’d say, ‘When I’m done, I will turn around and say ‘enough.’"
Unfortunately, it wasn't that simple in the end and Freddie found himself wounded emotionally by a couple of these 'friends' that took advantage of him.
The first was his former driver, who lost his licence but then hid the fact from Freddie.
Rather than tell the Queen singer about what had happened, he disappeared instead, causing Freddie an enormous amount of grief and worry.
The driver wouldn't return Freddie's calls but eventually he came clean in an emotional meeting at the singer's house.
Peter said that Freddie told the driver: "Darling, we could have found something else for you to do."
For lying, Freddie fired him and cut him off and he started to distrust more people that were involved in his life.
The main betrayal came at the hands of his former manager, Paul Prenter, who was portrayed as the 'villain' in Queen biopic, Bohemian Rhapsody.
Peter told Express Online: "Freddie discovered his life through Paul Prenter.
"Paul was looking after the whole band but then they got rid of him because he was spending 90% of the time with Freddie. And Freddie took him on.
"It wasn’t as bad as you see in the film. Paul is used to represent the bad side of Freddie but he is two or three people rolled into one."
Peter said that Prenter's intentions was to "steer Freddie away from the band," but in the end, "he became unreliable and Freddie knew enough was enough and let him go."
By 1986, Freddie was trying to clean up his life as he was fearing he might by HIV positive and began turning his back on partying.
Prenter continued with his wild ways and Peter recalls: "It was alright for a year and then Paul sold his story. That hurt Freddie so much. He couldn't understand why someone would do that."
Prenter cashed in to the tune of thousands for a series of lurid revelations in The Sun, during May 1987.
He revealed stories of Freddie's promiscuity along with his first homosexual experiences aged 14.
He also shared with the tabloid that the singer feared he had AIDS and sold personal photographs of Freddie.
Prenter's family defended him, saying that he did it so that he could afford HIV treatments for himself.
Freddie could not forgive Prenter's betrayal, according to Peter, who said that the Queen star was 'devastated' by the revelations.
Peter recalls: "He said ‘Why didn’t he just ask me for the money? I would have given him anything.' It made him doubt his ability to trust and judge people.
"It made him feel so vulnerable and unsure of himself. It made him even more afraid of what might happen if he ever revealed he was ill."
Freddie allegedly refused to speak to Prenter when he reached out to the singer and said that he had hurt him more then anyone else in his life.
Do you have a story to sell? Get in touch with us at<EMAIL_ADDRESS>or call us direct 0207 29 33033.


Kawai K4
Multi-Mode Patch Editor
This editor will work with the Kawai K4 and the Kawai K4r.
Communicating with Edisyn
Set your K4 to receive Program Changes (RCV PGM = NORM) and Exclusive (RCV EXCL = ON). See pages 79 and 80 of the manual. You'll also probably want your send channel and receive channel to be the same. I wouldn't set the receive channel to OMNI, as this might conflict with drums.
K4 Banks
You'd think that the "A, B, C, D" buttons on the K4 designate four banks. But they don't. For purposes of sysex (and for Edisyn's purposes) the K4 only has two banks: internal and external, each with 64 patches. Edisyn designates the "A, B, C, D" as so-called groups.
All Patch Sysex
If Edisyn receives an all-patch sysex message (representing the whole memory of the synthesizer) it cannot select from it messages for this patch editor. It will select messages for the K4 (Single) editor instead.
Hints
- The following effect patches are not used by any standard single, multi, or drum patch: 3, 10, 11, 12, 14, 15, 21, 22, 23, 28
- In all standard effect patches, Submix H is always "off".
Gotchas
-
You can't make parameter changes in real-time.
- When you send a patch, the name isn't updated: but the sound has in fact been changed.
Librarian Support
Edisyn can quick-request a bank from this synthesizer via Request Bank from Synth. This is a lot faster than the patch-by-patch request method in Download Bank from Synth. So try it out.
Thanks
Thanks to Benjamin Wild<EMAIL_ADDRESS>for bug reporting.
| By
| Sean Luke
|
| Date
| August 2017
|


--- title: QuTiP Historical Benchmarks: Qobj Add --- {% include header.html %} {% include navbar.html %}


Improved UI Forms
Added new Database models. Positions, Candidate, Config
Adding automatic generation of candidate algorand address and asset-optin for candidates accounts.
Setting Voting Configs like escrow address.
Using ChartJS to visualize voting results.
Allows creation of multiple candidates and positions.
Adding utility functions to generate algorand address, opt-in asset into candidate's account, send-alogrand, validating escrow address and mnemonic, check_algorand balance.


AMQP Package¶
Introduction¶
The amqp package is a wrapper and drop-in replacement for streadway/amqp, and is designed to enable automatic redialing to any code using the streadway package with no changes.
To begin using rogerRabbit/amqp, simply change your imports from:
import "github.com/streadway/amqp"
To:
import "github.com/peake100/rogerRabbit-go/amqp"
Under the hood, this library is a wrapper around streadway/amqp and would not be possible without the amazing development team behind it.
Roger, Rabbit seeks to expand on the work done by streadway/amqp, not replace it.
Basic Usage¶
As this package is a drop-in replacement for streadway/amqp, basic usage will not be covered by these docs.
The official rabbitMQ documentation has
an excellent set of tutorials using the streadway library. Simply replacing the import
statements of the official examples to "github.com/peake100/rogerRabbit-go/pkg/amqp"
will allow you to follow along as normal using this package.
Note
If you find any examples that do NOT work after such a replacement, please open a PR!
For instance, the hello world receiver example would be simply changed from this:
package main
import (
"log"
"github.com/streadway/amqp"
)
func failOnError(err error, msg string) {
if err != nil {
log.Fatalf("%s: %s", msg, err)
}
}
func main() {
conn, err := amqp.Dial("amqp://guest:guest@localhost:5672/")
failOnError(err, "Failed to connect to RabbitMQ")
defer conn.Close()
ch, err := conn.Channel()
failOnError(err, "Failed to open a channel")
defer ch.Close()
q, err := ch.QueueDeclare(
"hello", // name
false, // durable
false, // delete when unused
false, // exclusive
false, // no-wait
nil, // arguments
)
failOnError(err, "Failed to declare a queue")
msgs, err := ch.Consume(
q.Name, // queue
"", // consumer
true, // auto-ack
false, // exclusive
false, // no-local
false, // no-wait
nil, // args
)
failOnError(err, "Failed to register a consumer")
forever := make(chan bool)
go func() {
for d := range msgs {
log.Printf("Received a message: %s", d.Body)
}
}()
log.Printf(" [*] Waiting for messages. To exit press CTRL+C")
<-forever
}
To this:
package main
import (
"log"
// ONLY THIS CHANGES
"github.com/peake100/rogerRabbit-go/pkg/amqp"
)
func failOnError(err error, msg string) {
if err != nil {
log.Fatalf("%s: %s", msg, err)
}
}
func main() {
conn, err := amqp.Dial("amqp://guest:guest@localhost:5672/")
failOnError(err, "Failed to connect to RabbitMQ")
defer conn.Close()
ch, err := conn.Channel()
failOnError(err, "Failed to open a channel")
defer ch.Close()
q, err := ch.QueueDeclare(
"hello", // name
false, // durable
false, // delete when unused
false, // exclusive
false, // no-wait
nil, // arguments
)
failOnError(err, "Failed to declare a queue")
msgs, err := ch.Consume(
q.Name, // queue
"", // consumer
true, // auto-ack
false, // exclusive
false, // no-local
false, // no-wait
nil, // args
)
failOnError(err, "Failed to register a consumer")
forever := make(chan bool)
go func() {
for d := range msgs {
log.Printf("Received a message: %s", d.Body)
}
}()
log.Printf(" [*] Waiting for messages. To exit press CTRL+C")
<-forever
}
This documentation will focus on the differences from – and expansion upon – the streadway API, rather than retreading a primer on how to work with the basic API.
It is suggested that users new to amqp who have not used streadway/amqp start with the basic RabbitMQ tutorials before continuing this documentation.
When To Use This Library¶
Roger, Rabbit is designed to remove all the mental overhead involved with managing unexpected broker disconnects, it features systems to automatically recreate client / server topologies on reconnect, ensure consistent Delivery and Publish tags over reconnection events, and more.
But there are some assumptions that need to be made or such features. In general, this library should be used when:
Basic Client/Server Topology: All calls on a channel to QueueDeclare, QueueBind, ExchangeDeclare and ExchangeUnbind will be re-made every time a channel drops it’s connection and has to reconnect. In general, if you are using complex topology where Queues and Exchanges are being routinely shifted, deleted, and altered this library’s behavior may result in the re-declaration of unwanted Queues and Exchanges.
Orphaned Publications Are Nacks: Failed in-flight Publications on Channels in confirmation mode will be exposed to the end user as a Nacked publication. There is an additional extension of the streadway API to flag Orphaned publications, but such handling will require code tweaks and not be a drop-in replacement.
Delivery Acknowledgements do not Mix Per-Message and Multiple: Roger, Rabbit will detect orphaned acknowledgements and return an error when orphans occur (the broker is disconnected before a delivery is acknowledged), but mixing Ack with multiple=true and multiple=false may confuse the library, and is currently not supported by Roger, Rabbit.
Unsupported Features¶
Roger, Rabbit strives to be a complete, drop-in replacement for streadway/amqp, but is still under construction. The following features have yet to be implemented:
Transactions: Calling Channel.Tx(), Channel.TxCommit() and Channel.TxRollback() will result in a panic. Transactions are an interesting problem to solve for with robust channels and draft PRs for how to handle them are welcome!
Robust Features¶
In this section, we will examine features unique to Roger, Rabbit.
Connection Recovery¶
Both the Connection
and Channel
types are robust transport mirrors of the streadway
types by the same names, and will automatically re-connect when a connection is lost:
// Get a new connection to our test broker.
connection, err := amqp.Dial(amqpTest.TestDialAddress)
if err != nil {
panic(err)
}
// Get a new channel from our robust connection.
channel, err := connection.Channel()
if err != nil {
panic(err)
}
// We can use the test method to return an testing object with some additional
// methods. ForceReconnect force-closes the underlying transport, causing the
// robust connection to reconnect.
//
// We'll use a dummy *testing.T object here. These methods are designed for tests
// only and should not be used in production code.
channel.Test(new(testing.T)).ForceReconnect(context.Background())
// We can see here our channel is still open.
fmt.Println("IS CLOSED:", channel.IsClosed())
// We can even declare a queue on it
queue, err := channel.QueueDeclare(
"example_channel_reconnect", // name
false, // durable
true, // autoDelete
false, // exclusive
false, // noWait
nil, // args
)
if err != nil {
panic(err)
}
// Here is the result
fmt.Printf("QUEUE : %+v\n", queue)
// Explicitly close the connection. This will also close all child channels.
err = connection.Close()
if err != nil {
panic(err)
}
// Now that we have explicitly closed the connection, the channel will be closed.
fmt.Println("IS CLOSED:", channel.IsClosed())
// Output:
// IS CLOSED: false
// QUEUE : {Name:example_channel_reconnect Messages:0 Consumers:0}
// IS CLOSED: true
Topology Recreation¶
Roger, Rabbit’s Channel
type remembers all called to Channel.QueueDeclare()
,
Channel.QueueBind()
, Channel.ExchangeDeclare()
and Channel.ExchangeBind()
, and
replays those calls on a reconnection event:
Note
Calling Channel.QueueDelete()
, Channel.QueueUnbind()
, Channel.ExchangeDelete
,
and Channel.ExchangeUnbind()
will remove relevant robust queues and bindings from
the internally tracked lists. Queues invoked in these methods will NOT be recreated
on a reconnection event.
Delivery Tag Continuity¶
Delivery tags remain continuous, even across unexpected disconnects. Roger, rabbit takes care of all the internal logic of lining up the caller-facing delivery tag with the actual delivery tag relative to the current underlying channel:
// Get a new connection to our test broker.
connection, err := amqp.DialCtx(context.Background(), amqpTest.TestDialAddress)
if err != nil {
panic(err)
}
// Get a new channel from our robust connection for consuming.
consumeChannel, err := connection.Channel()
if err != nil {
panic(err)
}
// Get a new channel from our robust connection for publishing.
publishChannel, err := connection.Channel()
if err != nil {
panic(err)
}
queueName := "example_delivery_tag_continuity"
// Declare the queue we are going to use.
queue, err := consumeChannel.QueueDeclare(
queueName, // name
false, // durable
false, // autoDelete
false, // exclusive
false, // noWait
nil, // args
)
if err != nil {
panic(err)
}
// Clean up the queue on exit,
defer consumeChannel.QueueDelete(
queue.Name, false, false, false,
)
// Set the prefetch count to 1, that way we are less likely to lose a message
// that in in-flight from the broker in this example.
err = consumeChannel.Qos(1, 0, false)
if err != nil {
panic(err)
}
// Start consuming the channel
consume, err := consumeChannel.Consume(
queue.Name,
"example consumer", // consumer name
false, // autoAck
false, // exclusive
false, // no local
false, // no wait
nil, // args
)
// We'll close this channel when the consumer is exhausted
consumeComplete := new(sync.WaitGroup)
consumerClosed := make(chan struct{})
// Launch a consumer
go func() {
// Close the consumeComplete to signal exit
defer close(consumerClosed)
fmt.Println("STARTING CONSUMER")
// Range over the consume channel
for delivery := range consume {
// Ack the delivery.
err = delivery.Ack(false)
if err != nil {
panic(err)
}
// Force-reconnect the channel after each delivery.
consumeChannel.Test(new(testing.T)).ForceReconnect(context.Background())
// Tick down the consumeComplete waitgroup
consumeComplete.Done()
// Print the delivery. Even though we are forcing a new underlying channel
// to be connected each time, the delivery tags will still be continuous.
fmt.Printf(
"DELIVERY %v: %v\n", delivery.DeliveryTag, string(delivery.Body),
)
}
fmt.Println("DELIVERIES EXHAUSTED")
}()
// We'll publish 10 test messages.
for i := 0; i < 10; i++ {
// Add one to the consumeComplete WaitGroup.
consumeComplete.Add(1)
// Publish a message. Even though the consumer may be force re-connecting the
// connection each time, we can keep using the channel.
//
// NOTE: it is possible that we will drop a message here during a reconnection
// event. If we want to be sure all messages reach the broker, we'll need to
// publish messages with the Channel in confirmation mode, which we will
// show in another example.
err = publishChannel.Publish(
"",
queue.Name,
false,
false,
amqp.Publishing{
Body: []byte(fmt.Sprintf("message %v", i)),
},
)
if err != nil {
panic(err)
}
}
// Wait for all messages to be received
consumeComplete.Wait()
// Close the connection
err = connection.Close()
if err != nil {
panic(err)
}
// Wait for the consumer to exit
<-consumerClosed
// exit
// Output:
// STARTING CONSUMER
// DELIVERY 1: message 0
// DELIVERY 2: message 1
// DELIVERY 3: message 2
// DELIVERY 4: message 3
// DELIVERY 5: message 4
// DELIVERY 6: message 5
// DELIVERY 7: message 6
// DELIVERY 8: message 7
// DELIVERY 9: message 8
// DELIVERY 10: message 9
// DELIVERIES EXHAUSTED
Warning
In the above example, is possible that we will drop the publishing of message during a reconnection event. If we want to be sure all messages reach the broker, we’ll need to publish messages with the Channel in confirmation mode, which we will show in the next example.
Delivery Tag Orphans¶
When manually acking Deliveries, it is possible that between the time we get a Delivery, and the time that we ack it, a disconnection of the underlying channel has occurred and the delivery is no longer acknowledgable. In such cases, an error will be returned indicating this delivery has been orphaned:
// Get a new connection to our test broker.
connection, err := amqp.Dial(amqpTest.TestDialAddress)
if err != nil {
panic(err)
}
// Get a new channel from our robust connection for consuming.
channel, err := connection.Channel()
if err != nil {
panic(err)
}
queueName := "example_delivery_ack_orphan"
// Declare the queue we are going to use.
_, err = channel.QueueDeclare(
queueName, // name
false, // durable
true, // autoDelete
false, // exclusive
false, // noWait
nil, // args
)
if err != nil {
panic(err)
}
// Cleanup channel on exit.
defer channel.QueueDelete(queueName, false, false, false)
// Start consuming the channel
consume, err := channel.Consume(
queueName,
"example consumer", // consumer name
// Auto-ack is set to false
false, // autoAck
false, // exclusive
false, // no local
false, // no wait
nil, // args
)
// publish a message
err = channel.Publish(
"", // exchange
queueName,
false,
false,
amqp.Publishing{
Body: []byte("test message"),
},
)
if err != nil {
panic(err)
}
// get the delivery of our published message
delivery := <- consume
fmt.Println("DELIVERY:", string(delivery.Body))
// Force-close the channel.
channel.Test(new(testing.T)).ForceReconnect(context.Background())
// Now that the original underlying channel is closed, it is impossible to ack
// the delivery. We will get an error when we try.
err = delivery.Ack(false)
fmt.Println("ACK ERROR:", err)
// This error is an orphan error
var orphanErr amqp.ErrCantAcknowledgeOrphans
if !errors.As(err, &orphanErr) {
panic("error not orphan error")
}
fmt.Println("FIRST ORPHAN TAG:", orphanErr.OrphanTagFirst)
fmt.Println("LAST ORPHAN TAG :", orphanErr.OrphanTagLast)
// Output:
// DELIVERY: test message
// ACK ERROR: 1 tags orphaned (1 - 1), 0 tags successfully acknowledged
// FIRST ORPHAN TAG: 1
// LAST ORPHAN TAG : 1
Publishing Tag Continuity¶
Just like with Delivery Tags, publishing tag continuity is maintained, even across disconnection events.
// Get a new connection to our test broker.
connection, err := amqp.Dial(amqpTest.TestDialAddress)
if err != nil {
panic(err)
}
// Get a new channel from our robust connection for publishing.
publishChannel, err := connection.Channel()
if err != nil {
panic(err)
}
// Put the channel into confirmation mode
err = publishChannel.Confirm(false)
if err != nil {
panic(err)
}
confirmationsReceived := new(sync.WaitGroup)
confirmationsComplete := make(chan struct{})
// Create a channel to consume publication confirmations.
publishEvents := publishChannel.NotifyPublish(make(chan amqp.Confirmation))
go func() {
// Close to signal exit.
defer close(confirmationsComplete)
// Range over the confirmation channel.
for confirmation := range publishEvents {
// Mark 1 confirmation as done.
confirmationsReceived.Done()
// Print confirmation.
fmt.Printf(
"CONFIRMATION TAG %02d: ACK: %v ORPHAN: %v\n",
confirmation.DeliveryTag,
confirmation.Ack,
// If the confirmation was never received because the channel was
// disconnected, then confirmation.Ack will be false, and
// confirmation.DisconnectOrphan will be true.
confirmation.DisconnectOrphan,
)
}
}()
// Declare the message queue
queueName := "example_delivery_tag_continuity"
_, err = publishChannel.QueueDeclare(
queueName,
false,
true,
false,
false,
nil,
)
if err != nil {
panic(err)
}
// We'll publish 10 test messages.
for i := 0 ; i < 10 ; i++ {
// We want to wait here to make sure we got the confirmation from the last
// publication before force-closing the connection to show we can handle it.
confirmationsReceived.Wait()
// Force a reconnection of the underlying channel.
publishChannel.Test(new(testing.T)).ForceReconnect(context.Background())
// Increment the confirmation WaitGroup
confirmationsReceived.Add(1)
// Publish a message. Even though the consumer may be force re-connecting the
// connection each time, we can keep using the channel.
err = publishChannel.Publish(
"",
queueName,
false,
false,
amqp.Publishing{
Body: []byte(fmt.Sprintf("message %v", i)),
},
)
if err != nil {
panic(err)
}
}
// Wait for all confirmations to be received.
confirmationsReceived.Wait()
// Close the connection.
err = connection.Close()
if err != nil {
panic(err)
}
// Wait for the confirmation routine to exit.
<-confirmationsComplete
// Exit.
// Output:
// CONFIRMATION TAG 01: ACK: true ORPHAN: false
// CONFIRMATION TAG 02: ACK: true ORPHAN: false
// CONFIRMATION TAG 03: ACK: true ORPHAN: false
// CONFIRMATION TAG 04: ACK: true ORPHAN: false
// CONFIRMATION TAG 05: ACK: true ORPHAN: false
// CONFIRMATION TAG 06: ACK: true ORPHAN: false
// CONFIRMATION TAG 07: ACK: true ORPHAN: false
// CONFIRMATION TAG 08: ACK: true ORPHAN: false
// CONFIRMATION TAG 09: ACK: true ORPHAN: false
// CONFIRMATION TAG 10: ACK: true ORPHAN: false
Note
The Confirmation.DisconnectOrphan
is a new field for the Confirmation
type and
is unique to Roger, Rabbit.
When DisconnectOrphan
is true, it means that a Nack occurred not from a broker
response, but because no confirmation positive or negative was received from the
broker before the connection was disrupted. Orphaned messages may have reached the
broker – we have no way of knowing.
Channel Middleware¶
Roger, Rabbit allows the registration of middleware on all Channel
methods. In fact,
most of the robust Channel
features are implemented through middleware defined in
the amqp/defaultMiddlewares
package! It is a powerful tool and one of the biggest
API expansions over streadway/amqp.
Middleware signatures are defined in the amqp/amqpMiddleware
package.
Registering Middleware¶
// define our new middleware
queueDeclareMiddleware := func(
next amqpmiddleware.HandlerQueueDeclare,
) amqpmiddleware.HandlerQueueDeclare {
return func(args amqpmiddleware.ArgsQueueDeclare) (streadway.Queue, error) {
fmt.Println("MIDDLEWARE INVOKED FOR QUEUE")
fmt.Println("QUEUE NAME :", args.Name)
fmt.Println("AUTO-DELETE:", args.AutoDelete)
return next(args)
}
}
// Create a config and add our middleware to it.
config := amqp.DefaultConfig()
config.ChannelMiddleware.AddQueueDeclare(queueDeclareMiddleware)
// Get a new connection to our test broker.
connection, err := amqp.DialConfigCtx(
context.Background(), amqptest.TestDialAddress, config,
)
if err != nil {
panic(err)
}
defer connection.Close()
// Get a new channel from our robust connection for publishing. The channel is
// created with our default middleware.
channel, err := connection.Channel()
if err != nil {
panic(err)
}
// Declare our queue, our middleware will be invoked and print a message.
_, err = channel.QueueDeclare(
"example_middleware",
false,
true,
false,
false,
nil,
)
if err != nil {
panic(err)
}
// MIDDLEWARE INVOKED FOR QUEUE
// QUEUE NAME : example_middleware
// AUTO-DELETE: true
Middleware Providers¶
For more complex middleware, you can implement middleware providers, which expose methods that implement middleware. You can then register a factory method that will generate a new provider value whenever a new Connection or Channel is created, and the middleware methods will be automatically registered for you.
This can help build complex middlewares. Let’s define a custom middleware provider and factory method:
// CustomMiddlewareProvider exposes methods for middlewares that need to coordinate.
type CustomMiddlewareProvider struct {
InvocationCount int
}
// TypeID implements amqpmiddleware.ProvidesMiddleware and returns a unique type ID
// that can be used to fetch middleware values when testing.
func (middleware *CustomMiddlewareProvider) TypeID() amqpmiddleware.ProviderTypeID {
return "CustomMiddleware"
}
// QueueDeclare implements amqpmiddleware.ProvidesQueueDeclare.
func (middleware *CustomMiddlewareProvider) QueueDeclare(
next amqpmiddleware.HandlerQueueDeclare,
) amqpmiddleware.HandlerQueueDeclare {
return func(args amqpmiddleware.ArgsQueueDeclare) (streadway.Queue, error) {
middleware.InvocationCount++
fmt.Printf(
"DECLARED: %v, TOTAL: %v\n", args.Name, middleware.InvocationCount,
)
return next(args)
}
}
// QueueDelete implements amqpmiddleware.ProvidesQueueDelete.
func (middleware *CustomMiddlewareProvider) QueueDelete(
next amqpmiddleware.HandlerQueueDeclare,
) amqpmiddleware.HandlerQueueDeclare {
return func(args amqpmiddleware.ArgsQueueDeclare) (streadway.Queue, error) {
middleware.InvocationCount++
fmt.Printf(
"DELETED: %v, TOTAL: %v\n", args.Name, middleware.InvocationCount,
)
return next(args)
}
}
// NewCustomMiddlewareProvider creates a new CustomMiddlewareProvider.
func NewCustomMiddlewareProvider() amqpmiddleware.ProvidesMiddleware {
return new(CustomMiddlewareProvider)
}
We can register it on our Config so that every channel created from a connection gets a fresh instance of our provider:
// Create a config and add our middleware provider factory to it.
config := amqp.DefaultConfig()
config.ChannelMiddleware.AddProviderFactory(NewCustomMiddlewareProvider)
// Get a new connection to our test broker.
connection, err := amqp.DialConfigCtx(
context.Background(), amqptest.TestDialAddress, config,
)
if err != nil {
panic(err)
}
defer connection.Close()
// Get a new channel from our robust connection for publishing. The channel is
// created with our default middleware.
channel, err := connection.Channel()
if err != nil {
panic(err)
}
// Declare our queue, our middleware will be invoked and print a message.
_, err = channel.QueueDeclare(
"example_middleware",
false, // durable
true, // autoDelete
false, // exclusive
false, // noWait
nil, // args
)
if err != nil {
panic(err)
}
// Delete our queue, our middleware will be invoked and print a message.
_, err = channel.QueueDelete(
"example_middleware",
false, // ifUnused
false, // ifEmpty
false, // noWait
)
if err != nil {
panic(err)
}
// MIDDLEWARE INVOKED FOR QUEUE
// DECLARED: example_middleware, TOTAL: 1
// DELETED: example_middleware, TOTAL: 2
// AUTO-DELETE: true
if, for some reason, we wanted every Channel to share the same instance of the provider, we could make the following adjustment:
// Create an instance of our provider:
provider := NewCustomMiddlewareProvider()
config := amqp.DefaultConfig()
config.ChannelMiddleware.AddProviderMethods(provider)
This will add the methods once and re-use them for all Channels rather than making a fresh provider every time a channel is generated.
Note
Many of rogerRabbit’s more complex features are implemented through middleware
providers. Check the defaultmiddlewares
package to see practical examples of
middleware providers used in this library.
Testing¶
Testing is a first-class citizen of the Roger, Rabbit package. Types expose a robust
number of testing methods, and the amqpTest
offers a number of additional testing
utilities.
Note
Testing methods and utilities are heavily integrated with testify. Testify is somewhat divisive within the Go community, but as the maintainers of this repository heavily leverage it, so does Roger, Rabbit’s testing utilities.
Test() Methods¶
Both Connection
and Channel
expose a .Test()
method, which returns a testing
harness type with additional methods for running tests on it’s parent value.
Most test methods do not return an error, instead opting to report the error and immediately fail the test.
Example:
// Get a new connection to our test broker.
connection, err := amqp.Dial(amqpTest.TestDialAddress)
if err != nil {
panic(err)
}
defer connection.Close()
// Get a new channel from our robust connection for publishing. The channel is
// created with our default middleware.
channel, err := connection.Channel()
if err != nil {
panic(err)
}
// Get a channel testing harness. In a real test function, you would pass the
// test's *testing.T value. Here, we will just pass a dummy one.
testHarness := channel.Test(new(testing.T))
// We can use the test harness to force the channel to reconnect. If a reconnection
// does not occur before the passed context expires, the test will be failed.
ctx, cancel := context.WithTimeout(context.Background(), 5 * time.Second)
defer cancel()
testHarness.ForceReconnect(ctx)
// We can check how many times a reconnection has occurred. The first time we
// connect to the broker is counted, so we should get '2':
fmt.Println("RECONNECTION COUNT:", testHarness.ReconnectionCount())
// exit.
// Output:
// RECONNECTION COUNT: 2
Testify Suite¶
The amqpTesting
package makes an AmqpSuite
type that is an extension of
testify/suite.Suite
AmqpSuite
adds a number of QoL methods for quickly setting up an tearing down
integration tests with a test broker.
See the godoc documentation for more details.
Architecture¶
Overview¶
Lets dig in to some of the specifics.
Note
When we refer to an amqp.[Type], we are referring to the rogerRabbit-go/pkg/amqp implementation of that type. If we need to refer to underlying types provided by the streadway/amqp package, we will refer to them as streadway.[Type]
Warning
The file organization of the amqp
package is still in flux, though the API and
underlying logical structure is likely to remain stable. This architecture guide
will refrain from referencing specific files or paths for the time being, until
the types and helpers are done playing musical chairs.
Streadway Transport¶
The Streadway Transport
is our underlying streadway.Connection
or
streadway.Channel
and handles all of our actual communication with the
AMQP Broker
.
It is manages with by a Robust Transport
.
Robust Transport¶
A Robust Transport is an amqp.Channel
or amqp.Connection
. These types manage
their streadway.Channel
or streadway.Connection
counterparts, and expose
Exported Methods
to the caller that re-implement the methods supplied by the
Streadway Transport
they manage.
Each Robust Transport
implements the reconnects
interface, which in turn is
referenced by the Transport Manager
and used to redial the underlying broker
connection.
So why are we talking about the Transport Manager
here if it manages the
Robust Transport
? Well, because the Transport Manager
is then embedded into the
Robust Transport it is managing, and provides some of that transport’s methods.
Close()
, NotifyDisconnect()
, and all other methods that are shared between
amqp.Channel
and amqp.Connection
are actually provided by an embedded
transportManager
value which, like an ouroboros, also contains a reference to it’s
parent transport that is used to help manage the lifecycle of that transport’s
underlying streadway transport through the shared reconnects
interface.
Method Handlers¶
Each Robust Transport
(and the Transport Manager
) contains a handlers
field
which holds all the method handlers for that transport. These handlers are comprised of
the base streadway/amqp type methods wrapped in user-supplied Middleware
.
Middleware¶
Middleware
is a core component of the Roger, Rabbit amqp package. Most of the Roger,
Rabbit’s extended functionality is supplied by middleware, such as continuous Delivery
Tags over disconnects and auto-redeclaration of broker topology on reconnections.
In the early life of this package, robust features were implemented directly on the
Channel
, resulting in features which were hard to isolate and maintain. Topology
re-declaration, for instance, involves 9 methods manipulating 6 data resources over
~700 lines of code. Debugging and tracking errors with these features was incredibly
cumbersome when they were spread out over the main Channel
method calls.
By moving these features into middleware, all off the logic that supports a given feature can be housed together, greatly reducing the complexity and increasing maintainability.
The current default middleware that ships with Roger, Rabbit is:
ConfirmsMiddleware: Tracks whether
Channel.Confirms
has been called, and sets any freshly reconnected streadway Channels into the correct state.DeliveryTagsMiddleware: Ensures that Delivery tags are continuous for the caller, even over disconnects.
FlowMiddleware: Tracks the Flow state of channel and sets the correct state on Channel reconnections.
LoggingMiddlewareConnection: Facilitates logging for all Connection Operations.
LoggingMiddlewareChannel: Facilitates logging for all Channel Operations.
PublishTagsMiddleware: Ensures that Publish Confirmation tags are continuous for the caller, even over disconnects.
QoSMiddleware: Tracks QoS setting and sets up Channels on reconnect to match.
RouteDeclarationMiddleware: Handles topology recreation on Channel reconnects.
Together these middlewares implement the bulk of our robust feature set.
Transport Lock¶
The TransportLock
is a *sync.RWMutex
contained on the transportManager
used to
ensure there is no race conditions when a disconnection event occurs.
Any process that wishes to make use of the underlying streadway connection must acquire the transport lock for read.
When the transport manager redials the broke, the transport lock is acquired for write, and not released until a successful connection occurs. This blocks all other operations (like channel and connection method calls) from interacting with the underlying streadway transport until we are reconnected.
Transport Manager¶
The Transport Manager
implements all common functionality between Channel
and
Connection
. See the above section for more details.
The Transport Manager
listens for a disconnection event to occur, the grabs an
exclusive Write access to the Transport Lock
. Only then does it continuously attempt
to redial the broker using the methods exposed on out Robust Connection
through the
reconnects
interface.
The transport manager also exposes a Retry On Disconnected
method which all of our
exported Channel
and Connection
Exported Methods
invoke to complete
requests.
Redial Routine¶
The Redial Routine
is launched by the Transport Manager
. The redial routine
is responsible for reconnecting to the underlying Streadway Transport
on a
disconnection event.
Register’s a listener with the
Streadway Transport
’sNotifyOnClose
method.Blocks until the listener signals that
Streadway Connection
has closed (disconnection event)Exits if our
Robust Transport
has been closed by the caller.Acquires the
Transport Lock
for write, blockingExported Method
calls until a successful reconnection occurs.Calls the
tryReconnect
method on theRobust
transport until we get a successful result.Register’s a listener with the new
Streadway Connection
’sNotifyOnClose
method.Releases the
Transport Lock
.Restarts at step 2.
Retry On Disconnected¶
Retry On Disconnected
is a method exposed by Transport Manager
that enables
Robust Transports
(Channel
and Connection
) to automatically retry an
operation if it failed because we were disconnected from the AMQP broker.
When invoked, Retry On Disconnected
does the following:
Acquires the
Transport Lock
for read (so multiple methods can be called simultaneously).Runs the operation handed to it by the
Exported Method
, usually aMethod Handler
.Releases the
Transport Lock
.If an error occurred because the broker was not reachable, goes back to step 1.
Passes the result back to up to the caller.
Event Relays¶
Many Channel
methods like NotifyPublish
or Consume
involve sending
events along a provided or returned Go chan [Event]
value to the caller.
When a streadway.Channel
disconnects, it closes all event chan [Event]
values
it is feeding. Because we want our event chan [Event]
values to survive a
disconnect, we cannot pass the caller’s chan [Event]
directly to a
streadway.Channel
. Instead, we need to create our own temporary chan [Event]
,
pass that to the Streadway Transport
, then relay the events from our temporary
chan [Event]
to the caller’s chan [Event]
.
To do this, we launch an Event Relay
,
When a reconnection event occurs, the relay creates a new temporary chan [Event]
,
passes that to the new Streadway Transport
, and the continues to relay messages to
the caller as if nothing has happened.
Since Channel
is the only transport that needs event relays, it manages their
lifecycle. Event Relays
must be kept in careful sync with reconnection events to
ensure that data or logic races do not occur. That Event Relay
lifecycle is as
follows:
A relay is started by the
Channel.[Method]
handler using thetransportManager.retryOperationOnClosed
function so it can acquire theTransport Lock
for read when starting up (ensuring thestreadway.Channel
is not swapped out from under it).The relay runs it’s first leg until the undeerlying
streadway.Channel
disconnects.On
streadway.Channel
disconnect, the temporarychan [Event]
feeding the relay dries up. The relay waits on a new*streadway.Channel
to be sent by it’sChannel
on a successful reconnection.The
transportManager
acquires theTransport Lock
for write and callsChannel.tryReconnect
over and over until a newstreadway.Channel
is successfully connected.When a new
streadway.Channel
is successfully established,Channel.tryReconnect
does not return until all the remaining steps are completed.Channel.tryReconnect
waits for allEvent Relays
to signal that their last leg has been successfully completed.Channel.tryReconnect
sends the new*streadway.Channel
value to each relay for it to run any setup and start relaying events again.Channel.tryReconnect
waits for all relays to signal that their setup on*streadway.Channel
is complete. If we were to return and release theTransport Lock
before this, users might start taking actions that SHOULD generate events before ourstreadway.Channel
had been set up to send them, resulting in dropped events.Channel.tryReconnect
returns with the new, connected*streadway.Channel
value releasing theTransport Lock
so that callers can begin callingChannel
methods again.


To define these style elements the best place to start is in the middle. Just from the word "Border", you already have a pretty good idea of what this element is. If you are already familiar with the idea that all individual elements on an HTML page are boxes, the border is a line surrounding that box. However borders do not have to be visible. All content has a border whether we can see it or not. Just look at the bottom of the screen and you will see an example of a border around the copyright. Directly below you will see the CSS code that styles this element of the page.
footer { border: 1px solid black; margin-top: 1em; padding-left: 5px; border-radius: 1em; }As you can see the border is a very simple 1 pixel solid lined black color border. In this example I have also used Margin and Padding stylings which I will describe next.
In our previous example we can see the border. The content of this element is the text. The reason I said we should start in the middle is because Margin and Padding are basically the same thing, just on different sides of the border. So... Padding is the space between the content of an element, and its border. The larger the padding of an element, the larger the element, and the farther away the border is from the content. In the previous example I have only put padding on the left side of the element at 5 pixels. This moves the content (the text) 5 pixels away from the left border. Without this styling, the C in Copyright would be touching the visible border.
Finally we have Margin. Margin is the space between the border and the very edge of an element. So the larger the margin the larger the element and the farther away the edge of the element is from its border. In our example I have put a 1em margin on the top of my footer element. This has the effect of making this blue text element and the footer element seem like they are separated. In reality, the text "box" is sitting directly on the footer "box". If I removed all the margins on the page this would become evident. So hopefully this has given you a good idea of what these 3 elements are and what they do.


Back-End
Technologies:
- Java
- PL/SQL
- Node.js
- Among Others
I am a passionate person for the Software development, I worry about being up to date in the field of technology, I have an excellent ability for self-study. I have solid knowledge in back-end, front-end , best coding practices and agile methodologies. My strength is the back-end, specifically in the Java programming language and frameworks related to this. I have had the opportunity to work in large companies in which I have put into practice all my knowledge and have obtained enriching experiences of these. I consider myself a person who possesses the spirit of collaboration and service, the ability to learn quickly and on their own initiative, ability to work as a team and concerned about personal and technical growth.
Application that will be useful when you want to keep track of your budget.This application is intended to help you to view and store expenses and incomes incurred in your day by day in a simple way.
Application that will be useful during the development of your academic period. This application is intended to help you more easily the calculations of your subjects, so you can take the registry of each of your grades.
Application that will generate values at random for what you want. Among the functionality of the application you can get: - Random number. - Throw a coin. - Throw dices - Select a winner, appear from a list of data. - Sort a list of values - Formulate teams, appear from a list of values. - Create passwords according to the length and values you need.
Application that will be useful to you when you want to calculate the ideal range of your weight or body mass index. Features: - Calculate recommended and recommended maximum recommended weight. - Calculate BMI (Body Mass Index). - Calculate ideal weight. - Formula Broca - Formula Lorentz - Formula Wan der Vael - Formula Perrault
MultiNotes is an application that allows you to create notes and lists of notes in a simple way thanks to its simple graphic interface and and intuitive. Application allows you to create nota:- Notes simple.- List of tasks.


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Mossberg 500 is a series of pump action shotguns manufactured by O.F. Mossberg & Sons. The 500 series comprises widely varying models of hammerless repeaters, all of which share the same basic receiver and action, but differ in bore size, barrel length, choke options, magazine capacity, stock and forearm materials.
Model numbers included in the 500 series are the 500, 505, 510, 535, and 590.
Sights vary from model to model, from a simple bead sight to a receiver-mounted ghost ring or an integrated base for a telescopic sight.
Mossberg shotguns currently designated "law enforcement models" are 590A1s. 590A1s differ from other 500/590 shotguns, in that they have heavy barrels, metal trigger guards, and metal safeties.


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Preparation time
30 mins to 1 hour
Cooking time
10 to 30 mins
Serves
Serves 4
Dietary
Preheat oven to 180C/350F/Gas 4.
For the pancakes, break the eggs into a bowl and whisk in the flour until it is a smooth batter. Whisk in the milk, salt and one teaspoon of vegetable oil.
Using a paper kitchen towel, smear the base of a non-stick frying pan with the remaining oil before allowing to gently heat.
When the pan is hot, ladle some of the pancake mixture in until it is evenly covering the base of the pan.
Allow the pancake to colour until golden-brown underneath before turning and cooking the other side. Once golden-brown remove from the pan and place onto a plate. It is useful to separate the pancakes using small pieces of baking parchment paper. Repeat the process until there are eight pancakes. Place the pancakes into the oven to keep warm.
For the roasted fruits, place the butter, one sprig of lavender and the honey into a non-stick, ovenproof pan and heat gently. Add the fruit to the pan and caramelise lightly before placing the pan into the oven and cooking for approximately five minutes.
Remove the fruits from the oven. Add the orange juice to the fruits and use a wooden spoon to scrape the caramelised juices off the bottom and sides of the pan. Add another sprig of fresh lavender. Leave to rest.
Remove the pancakes from the oven. To serve, place one pancake onto a plate, spoon in some of the fruit and its juice and fold or roll the pancake up. Repeat this for the rest of the pancakes.