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Salesforce: Which API to use without Login required?

I'm currently working on a native Android app for my company and ran into some problems with Salesforce lately.
I hope I can find some help here.
What I want to achieve:
The company has a lot of Accounts in Salesforce with 3 important fields for the app: Name, Business (Workshop or Parts Dealer) and location(latitude, longitude)
I would like to show those Accounts(Workshops/Parts Dealers) as markers on a google map in my Android app based on a radius around the user's current location. So it would be more than sufficient to get the data as JSON or XML(i read about sObjects, which would be nice too)
The app will be freely available on Google Play Store and every user should be able to see all the Workshops/Parts dealers around the world.
The problem I'm facing is that I can't find a way to fetch the data inside my app without authenticating every user with a Salesforce-Login. 
Which API is the best to use in this case?
It would be so awesome if anybody could help me with this problem.
What I tried so far: 
- SalesforceMobileSDK: If i extend SalesForceApplication() i always end up with the Salesforce-Login Screen.
It seems that every client has to be authenticated for API-calls to work. I tried using the method peekUnauthenticatedRestClient(), but this method only works on full path URL's(e.g. "https://api.spotify.com/v1/search?q=James%20Brown&type=artist"), which isn't really practical for my Use-case.
I feel like I read nearly all docs about salesforce API, but can't quite get my head around how to solve this problem, although it seems like to be a pretty common use-case.  
would a salesforce-apex method which would select all records inside a set radius around the user's location to be accessible without authentication?
Thanks for your help in advance!
Roman

Try asking on salesforce.stackexchange.com. Your question is more about licensing model than a particular programming problem. It might even be the case that you don't really need Salesforce for your project, you'd be better off on Heroku (even free tier) if the login piece is an issue...
All Salesforce APIs require some form of authentication. If you're positive you don't want to hardcode "Integration user" credentials in the app and you don't want to pay for (self-)registered user licenses in your org...
Try to read about these:
Site - piece of Visualforce running under specific "guest user", letting you view & interact with SF data without having to log in. You expose SF data to the world but that means it's your job to handle security (if any) and craft the API. You want to really display the data to human? Or just return JSON content or what...
Sites are meant to be displayin some incentive to contact you. Your product catalog / basic order form. Some map of nearby locations. Maybe a "contact us" form. There's limit on the traffic so eventually they'll explode as your app gets popular:
Customer Community - typically you need named licenses (even if they're fairly cheap) to let your customers log in to your SF. You create a Contact, click magic button - boom, this Contact now has a real matching User record with its own license. Think of it as some kind of step up from Sites - it'll still have some limits but will offer more than just raw API access and you'll have better control on what's going on.

Tips for new Android app - maps, directions, transit

I'm not asking for anyone to build me an app.
I just need some tips on getting started.
So what I wanted to do:
be able to map some routes/directions, similar to what Google Maps already has regarding the local transit in a city.
Why? Because Google's database is a bit outdated, first. Second, because I want to create a local database with the routes and with the stations. Unfortunately, I can't really do that using Google Maps and I think Leaflet could help me with this much better. This would've been a web app, where someone with an account could add/edit/delete the routes.
create an Android app that :
a) sees the routes, allows an user to find the closest path to get from point A to B using only the routes I have in my database, sort by tram/bus etc
b) allows the user to mark a location and say something like "bus no 37 was here at hour:minute:second" - this would appear for anyone else that is using the app, similar to what another app lets you do this for police cars and traffic jams
c) extra: allow users to input some data so that my app could also give predictions; for example, someone inputs it took 10m50s to get from point X to point Y on route Z. That remains in a database and then someone else inputs some data for the same path...i would create some algorithm that could get predictions on where would a bus be now if someone marked it at Station 'bla' 5 minutes ago. I know, I know, this might be pretty hard, and it would be pretty inaccurate, I should consider the time of day, but it would just be something small, as an extra. Also, would be cool if this stuff could be added automatically: like the user sets the route he's on, starts "recording", then stops it when he gets off the vehicle and the time and locations are automatically taken into consideration.
Hope you understand what I have in my mind.
Thing is, what would you recommend?
I know Java, Spring MVC and a bit of Android. JavaScript, HTML and CSS won't be a problem. I need to combine these. If I will use Leaflet, as far as I can find, I won't really be able to use it in an Android APP, I would have to create a web app. At the same time, Google Maps doesn't really let me do what I want for my "personal" database. I can't even create decent custom routes by adding waypoints because parts of the Tramway Line aren't on streets with car access. ALso, would you think this is easier/better to do as an Android app or as a web app? I'm kinda new to Android.
I hope this isn't an unsuitable thing to ask on stackoverflow.
I'm open to any ideas.

allows an user to find the closest path to get from point A to B using only the routes I have in my database, sort by tram/bus etc
Routing is hard. Multi-modal routing (tram+bus+car+walking+cycle) even more so. See pgRouting and Valhalla. If you're going to do anything with public transport, then you'll have to deal with GTFS too.
Research into OpenTripPlanner also, as there are several actors developing some similar platforms.
I hope this isn't an unsuitable thing to ask on stackoverflow.
I'm afraid it kinda is - see https://stackoverflow.com/help/on-topic, point 4.

How should I manage Bluetooth connections in Android?

Q. What are your best practices in managing bluetooth connectivity?
I've read the android bluetooth guide & many bluetooth connectivity tutorials. Not helpful with encapsulation-design nor best practices.
When should I open/close the connection?
Is the "connection" with a single bluetooth device called a "socket" connection?
Can a single connection send data while listening? (...or between listening states).
I've never coded connectivity with external devices before. It took two weeks for me to wrap my head around the code that scans for near-by bluetooth devices and throw them into a ListView. Listeners, Broadcasts, and Adapters!
My project will be printing 1-40 receipts every 15 minutes on a bluetooth receipt printer. At the moment, security is not an issue. On the same connection, it will also be receiving data (sending & receiving simultaneously does not appear to be necessary but would be useful). I'm not yet sure how the devices are configured on this single dongle device but I would guess the devices are connected via USB controller to the dongle.
So far, I have 1 object to manage a single I/O connection. Staticly I open an activity to select a connection (to later save the label, mac, and pin in the database). Based on tutorials, I have "open", "listen", "send", and "close" methods. What confuses me is "how" to use these functions. Can I leave a connection open all day (10hrs) and use it every 3mins? Should I open/close the connection when sending or requesting data? Where would I detect the need to reconnect?

sorry for the short answer, but from my practice with the Bluetooth API, I have found that this video describe the things very good (totally personal opinion...)
Video 1
In addition this is useful when you do NOT have any previous experience
Tutorial
And as last check out this question in stackoverflow it has a bunch of good references and examples!!
Again sorry for the shortage, but I believe that if you check these out at least most of your questions and concerns will become answered!
:)
EDIT
So, let me be a bit more descriptive and share some of my experience.
I have written an App that communicates with BLE device that has 3 functions
double sided event driven button (push the button on phone -> event is fired to the device; push the button on the BLE device -> event is fired to the phone)
send request from phone -> BLE device answers with current battery percentage
continuously reading strength signal (as aprox. distance) between the phone and the BLE device
So far so good, now the things is that the basic approach is:
Search for BLE devices (bluetooth search or "discovery" of nearby bluetooth devices)
Here you will need android permissions!
Choose the device you want to connect to
To differ the devices (maybe there are a lot around you :) ) you can use BLE device's name or UUID or ... best - use the name ;)
After both devices connect to each other you can then start the Gatt communication. The approach with state machine is a little too much overkill for me. But anyway the communication is done through bytes (in my case...)
In one of the videos/resources there was something specific and VERY HELPFUL at least for me! To be honest I don't remember it exactly, but the idea was that before any communication it's RECOMMENDED to read/get all the options from the BLE device or something similar...
Maybe it was something like discoverOptions() or something like that
Great thing will be to know your device "communication codes" or at least I call them that way.
Check this link for example: Link
** Now you can see there are tables with the USEFUL INFO! E.g. if you want to read the battery level you navigate to this page and find that in order to read the battery, the service name is UUID XXXXX and you need to send 0x01 to the BLE device and it will "answer" to your call with some data which is again in bytes.
I really hope that this is somehow helpful!
PLEASE NOTE
This is strictly coming from my experience and there could be some mismatches or wrong terms, but that's how I personally see the things and because my project was long ago, I don't remember most of the things exactly.

IMPORTANT:
This is only a summery of STUCI's provided links above. He has since updated his answer and I have not updated/edited this summery. Topics in my summery are not explanatory but provided for reference and help in generating specific questions.
Original Post...
Thank you Stuci! Some of that was helpful:- some not. I thought it best to collect my thoughts and see what has been explained and if anything hasn't.
(I can't post this much in a comment tho, sorry)
PLEASE CALL ME ON ANYTHING THAT IS INCORRECT.
Video of Bluetooth LE
(Covers a bunch of random things)
While I "dont-like" videos of code:- I watched it because it was recommended ... and I am glad I did. While not very helpful it did introduce some concepts I was unaware of. Since I am targeting old android devices (v8+) the LE features are inconsequential.
Pushing Data: [Depending on the source feature-set], one does not need to continually pull data (ex. with a temperature sensor) but some devices can "push" it to the device on change. Seems to use the 'advertisement" design concept.
UUIDs define Services and/or Characteristics of the connected device.
Possibility to write configuration on (to) connected devices.
Characteristics which seem to be simply "settings" that can be assigned over bluetooth. Not sure if this (~19mins) applies to non-gatt connectoins but seems similar to the state-machine that controls
Advertisements which seem to be the "metadata" regarding the devices current state or config (~24mins). Again, not sure if this even applies to non LE Bluetooth.
Leaving Connections Open
Bluetooth connections can indeed remain open; starting at the point which the "startActivityForResult(...) method is successfully called.
Two basic things affect whether or not one would want to maintain an open connection:
Understand the power consumption.
Having the adapter active simply consumes additional power. If one can keep the adapter shut-off while it is not "absolutely-needed" will mearly save battery power.
Accidental disconnects are managed.
Other than leaving the connection continually connected, one could disconnect & reconnect regularly at specified intervals to ensure a connection is up.
In the thread(s) used for I/O, one could check for a disconnect and reconnect (possibly starting a new thread).
I/O Streams pr Connection
A single connection can indeed "have" simultaneous Input & Output streams. I
Since it was suggested, I re-read Android's Bluetooth Guide and under "managing a connection" (talking about a single socket) I noticed this...
Get the InputStream and OutputStream that handle transmissions through the socket, via getInputStream() and getOutputStream(), respectively.
Read and write data to the streams with read(byte[]) and write(byte[]).
...but continues with noting that read & write block each other. Something I still need to look further into. It seems like you cant I/O simultaneously on the same socket???
Max Connections
I also looked into the max connection issue Stuci added and found no documentation on the Android-side. It might exist, I cant find it. However, most people seem to agree that there is a limitation (that could be as low as 4) imposed by whatever hardware you are coding for.
Some notable links:
- How many devices we can pair via Bluetooth of BLE to Android?
- How many maximum device can we pair via Bluetooth to android device at a time?
- https://groups.google.com/forum/#!topic/android-developers/adeBD275u30

Android Word Validation

I am developing an Android word game like Scrabble. I need to check if the word a user enters is correct (aka is a String entered by a user equal to an existing word).
All that Android seems to offer is a spell-checking api which provides you with some suggestions based on your input. This just seems silly to me because these suggestions are actual words and there seems to be nothing in the api that is able to check if a word exists in it's dictionary.
I understood that there are some other web based solutions for my problem but I can't assume these web-based solutions will work forever and that users have a stable network connection. Also, my game is time based so the only proper solution would be a local one.
So, (how) can I validate a word (String) locally on Android?
inb4 it can't be done properly and wordnik is the best solution for me

Load your dictionary into SQLite and use a query to determine if it's valid.

How to handle multiple video streams in Red5?

I am writing a Red5 application that provides 1-on-1 video chat to a Flash client over RTMP.
Unfortunately most tutorials I was able to find were sketchy at best and the documentation of Red5 itself tends to be vague when it comes to API concepts and intended usage.
In short, I am a bit stuck and looking for hints on Red5 ApplicationAdapter implementation. Gnarly details are as follows:
First of all, the connections come in two flavors: visitors and consultants. A visitor should be able to indicate which consultant it wishes to communicate with. A consultant simply gets connected to the requesting visitor as long as the consultant is not busy servicing another.
Obviously, every RTMP connection has two-way traffic: both sending and receiving video. From the standpoint of the server, connections bring in a bunch of video streams that get their receiving endpoints assigned by request.
Since several video conversations can be in progress simultaneously, the main task of the application is to handle the mapping of visitor streams to consultants and provide a list indicating each consultant's state (busy/available) via AMF.
So, all in all, I have a pretty good idea what I am aiming for but how to achieve it with Red5 is still a bit of a mystery.
Hopefully someone can enlighten me in any or all of the following:
What is the easiest way to establish the connection type (visitor/consultant)?
Which API classes should be used to implement a persistent, globally accessible list of active connections for reporting the state of each consultant?
How to switch receving endpoints dynamically when the goal is to connect a specific visitor to the selected consultant?

Saul ,
1.What is the easiest way to establish
the connection type
(visitor/consultant)?
assuming that both(visitor/consultant) are using flex client via which they start publishing their live video stream ,here you need to make sure that each published video stream name is unique (HOWTO is already mentioned in demo apps)
2.Which API classes should be used to
implement a persistent, globally
accessible list of active connections
for reporting the state of each
consultant?
and for providing the list of active connections you simply need to store(preferably in your db) each user's id with the stream name (which is also available as a tutorial demo app) to connect to.
I believe all the code is available for the red5 demos Do try oflaDemo , simpleSubscriber , fitcDemo demo apps.
I hope I am closer to your solution.

Since Oflademo or red5 is capable of 1v1 chats, then replicate this code to make around 50 chats. You can maintain a table with the following columns :
chat room number (1 to 50)
user1
user2
status(0 or 1 - unoccupied or occupied)
If let say a visitor V22 wants to get consulted from consultor C33, then a program can detect the first unoccupied room from 1 to 50, if the 7th room is unoccupied then, redirect V22 and C33 to room 7 and change status to 1(occupied). After the video call, the status can be reset to 0, and the table at roomno:7 , user1 of roomno:7, user2 of roomno:7, can be set to NULL. Its like maintaining tables in a restaurant in a computer.
You can basically develop multiple chatting using 1to1 using a database and php queries, no need to edit any swf code or maintain a complicated server etc.