This link doesn't need any installation procedures: http://ec2-54-201-144-165.us-west-2.compute.amazonaws.com/dtc/get/40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548

Hello!

Datacoin blockchain started about two months ago. Thank you to all of you supporting Datacoin. It exists because of your support.

Now we can start developing blockchain-based web applications. Note that this feature doesn't touch sources of Datacoin daemon or qt-wallet: if you are not interested in this it you can still use Datacoins and without understanding this post. Blockchain-based web applications require a http-server that redirects HTTP requests from browser to daemon. This is implemented now with Perl (dtc_http_server.pl). Yes, I know I would have to do it using C++. I'll rewrite it later.

Why web-applications inside blockchain are good?

1. they are protected from being deleted or censored
2. they work locally and don't require a live Internet connection
3. web interface is convenient to users
4. no new technologies are required for developement: HTTP, AJAX and JSON RPC are simply linked together

Datacoin HTTP server is very simple and it is intended to work locally on end-user's machine.

Types of requests supported by Datacoin local HTTP server

NB: NET can be 'dtc' or 'dtc-testnet'

1. Get data from blockchain
http://localhost:PORT/NET/get/TXHASH -> data from tx with TXHASH will be sent back (data is assumed to be in Envelope format - see envelope.proto file)

Example:
http://localhost:8080/dtc/get/40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548

2. Call daemon's method
http://localhost:PORT/NET/rpc/METHOD(/ARGS) -> json-rpc call to daemon's METHOD will be performed and resulting json will be sent back to browser

Several arguments are possible in form arg1/arg2/arg3/...

Example:
http://localhost:8080/dtc/rpc/getblockhash/1000


NB: due to security reasons only 'getinfo', 'getmininginfo', 'getblock', 'getblockhash' and 'getrawtransaction' are supported now. Later all reading methods will be added. 'sendtoaddress' and other money-spending methods probably will be added also but some security issues are to be considered before in order to protect users from theft.

3. Call http local server's method
http://localhost:PORT/NET/lsrpc/METHOD(/ARGS) -> http server will handle this method itself (or translate to several requests to daemon).

There is only one example of lsrpc methods now: 'getenvelope'. It parses tx.data field of a given transaction as an Envelope and returns envelope in json format (without 'Data'). This method is needed to get metadata easily.

Example:
http://localhost:8080/dtc/lsrpc/getenvelope/40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548


Demo
In order to demonstrate this in action I've sent 'Block explorer' application in transaction 40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548. Here is an instruction on how to access it from your own computer with local HTTP server (actually this will be too difficult for 99% of users, I need to rewrite server using C++ and deliver it as a precompiled binary):

Before you start: DON'T do this on the machine with many coins!!! Setup a different user account on Windows (or Linux) or a virtual machine. There is a lot of possible bugs in this code that can lead to loss of money.

Now you are warned. Let's continue.

1. backup yout wallet.dat and protect it with password

2. git clone https://github.com/foo1inge/datacoin-browser.git

3. install all required CPAN modules (the way to do this depends from your Perl distribution, ask Perl guru if you don't know how to do this). Here is list of modules:


4. start Datacoin daemon ('getdata' RPC method is required. It was commited two weeks ago and probably you have to update your daemon).

5. cd datacoin-browser/perl/

6. perl dtc_http_server.pl --http-port=8080
This will start local HTTP server on port 8080. In order to see Datacoin testnet add "--testnet=1" option - it will connect to daemon working in testnet.

7. go to http://localhost:8080/dtc/get/40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548

8. enjoy

You can deploy this on any machine. Here is this application deployed on Amazon EC2 (micro instance, very slow):
http://ec2-54-201-144-165.us-west-2.compute.amazonaws.com/dtc/get/40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548

Blockexplorer application consists of three transactions:

40a3eb9624528008a87d9119dbed4041d45c9f6483ecd52a7b24f9c8b4fdf548 - blockexplorer.html
465ca75b6dedf70bc85db24548ee99bab776028f9295116afba4fa1e4838ff5f - blockexplorer.js
73b7c7165a51f604040e17681705a39145392691a0447266b9074a2ad9140327 - datacoin-logo.png

All these files are accessed by TXID (not by names!) the following way (snippets from blockexplorer.html):



Blockexplorer does following steps while starting:

1. getinfo RPC call (to get current height)
2. getblockhash / getblock for each block in cycle
3. getrawtransaction for each transaction
4. getenvelope for each transaction with data

All these calls are coded as ordinary AJAX in blockexplorer.html.

Important issues for web developers on how to develop applications for Datacoin

1. Start development in testnet

Testnet block explorer: http://ec2-54-201-144-165.us-west-2.compute.amazonaws.com:81/dtc-testnet/get/7fead7473c448b2d69d0e62354dedd59895a1ab099c1835155d83f7327c5156a

2. Never use specific IP or PORT in URLs - only relative URLs are meaningful (user can start local HTTP server on any IP:PORT).
In your HTML code instead of doing


use relative URL:


3. Use "--content-type" argument of dtc_put_file.pl script to set a "Content-type" HTTP attribute for your files.

Here is an example:

4. Use "--add_key" argument of dtc_put_file.pl script and save private key (it will be printed on screen) in a secure place in order to upate your application later.

Here is a full example:

NB: update feature isn't implemented yet I'm working on it now.

Datacoin development plans regarding blockchain-based web-applications:
(I don't mention here issues not related to the topic)

1. bugfixing

2. Update feature (see detailed description of update scenario in envelope.proto file)

3. Big files (more 128Kb) feature

4. C++ version of local HTTP server

5. "senddata" from local HTTP server

6. Access to P2P file sharing networks from local HTTP server (something like localhost:8080/kademlia/HASH). Needs some investigation.

This is the same question as mentioned above. In case tx fee modification will be enabled it will behave following way:

----
Sender can set any fee above technically hard-coded minimum (such a minimum is required in order to avoid tx spam).
Each miner sets his own minimum fee to accept tx into memory pool.

Auction system will really work in case tx flow is close to 1Mb per minute (max blockchain capacity). Below this limit miners are motivated to accept any tx with fee above zero.
----

NB: Second question will get it's answer also

Do you know why did Sunny King disabled -paytxfee?

In case of merged mining one of blockchains is parent (has much higher difficulty) and another one is auxiliary and has lower difficulty. This is not the case of Datacoin and Primecoin as soon as difficulties are very close to each other now: 10.x for Primecoin and 9.x for Datacoin. Thus there is no way to do merged mining in the near future.

Please see details here: https://en.bitcoin.it/wiki/Merged_mining_specification

Pools will definitely appear.
Good news is that I plan to support pools (at least pools that can mine directly to Datacoin address) in Qt wallet.

Here is a small Q&A session. I'll stay online for 1-2 hours and answer other questions.

Q1: I asked in a different thread: I have two wallets with mined balances. How can I bring them in a single one without importing each privatekey separately?

A1: you can do "sendtoaddress" RPC command or just push "Send" button and input another wallet's address.


Q2: Is the RPC getdata function already implemented ? You did not comment about it on the faq, using shell commands is fine for now.

A2: Not yet. But it will be implemented soon.


Q3: Does this means that he is officially dismissing the new development team? If yes, no problem, I'll go back to developing my own crypto currency. Maxsolnc, Mstfck and the rest, seem your hard work have gone down the drain.

A3-1: I respect your work. This is just a security issue: it's important to have one "approved" point of updates. Security is important for all people holding coins.

A3-2: I'm really surprized with a lot of activity around DataCoin. This is very good for all of us. I still need to adapt to this fact.


Q4: Another thing that bothers me about Datacoin is why has the block reward gone down so fast ?

A4: Block reward goes down with difficulty increase. It's all the same as in PrimeCoin. The difference is that you can get more in the future with tx fee (full block will give about 50 DCT in fees).


Q5: Do both wallet versions (normal and HP) store the full data blockchain ?

A5: Yes. The difference is only in mining speed (-hp uses libgmp).


Q6: And BTW if storage is so expensive, those who keep the full blockchain available in the network should be rewarded, otherwise there is not much incentive to keep a growing blockchain in your hardrive.

A6: I'm thinking now about policy that can encourage people to store and distribute blockchain data to other services. I think this shouldn't be a part of core protocol due to security reasons. All ideas are welcome.


Q7: The mining reward is so tiny, why should people mine long-term?

A7: Cummulative tx fee from one block is expected to be higher than block reward. This is different from PrimeCoin.


Q8: cryptrol -> maxsolnc: Maybe the dev is more interested in an open discussion here, instead of a private conversation with you.

A8: Both


Q9: I just thought, that including virus/malware code(not working) in blockchain can cause antivirus software to block/delete the chains. Of cousre you can exclude blockchains directory for antivirus, but there should be better solutions for this.

A9: cgminer and some other tools are recognized by antiviruses as malware. This is still not a problem. In case this will become a problem we can always encrypt blockchain on local hdd. This will not lead to hardfork or any other network related problem.


Q10: The original dev has only interest in coding DTC, but zero interest in promoting it.

A10: Somebody must work with code. I think this is very important
I appreciate all of you for doing promotion. You do this much better than I could.

Data is signed with TxInput's keys. If you change data transaction's signatures become invalid. It's the same as if you change output address or locktime. No peer would accept tx into mempool with invalid signatures.

Thanks to Zorrosv, maxsolnc and to all participating in logo creation. Current changes are pushed to datacoin-hp repo (please let me know if I did something wrong with images). Binaries will be published soon (see main post for links).

Hello!

1. I've added FAQ to the top message of this thread. I hope it will clarify plans. In case something important is missing, please add questions here.

2. Please don't post non technical issues (exchange rates, markets, etc) into this thread because it's hard to find questions I really have to answer.

1. Please don't use Primecoin's DNS seed. This will not help.

2. I've restarted both hardcoded seed nodes. They are working now.

3. New nodes will be installed by my friends. I'll hardcode these IPs too.

4. Here is the list of working nodes I've found right now:

14.158.38.21:4777
14.220.228.99:4777
14.28.52.207:4777
36.57.145.161:4777
36.57.145.16:4777
36.57.146.21:4777
37.143.201.89:4777
46.10.55.117:4777
49.67.135.67:4777
49.83.33.38:4777
77.23.239.66:4777
88.83.203.34:4777
93.189.44.49:4777
106.187.41.67:4777
108.161.145.16:4777
111.173.1.17:4777
113.124.121.18:4777
117.11.230.244:4777
117.21.226.240:4777
117.21.227.229:4777
117.93.111.112:4777
122.7.124.45:4777
123.171.107.117:4777
123.174.211.94:4777
123.9.118.54:4777
124.230.102.236:4777
124.230.77.181:4777
124.232.136.235:4777
125.211.206.16:4777
162.213.253.139:4777
162.243.47.48:4777
173.208.179.90:4777
183.86.193.42:4777
209.126.73.2:4777
209.126.74.150:4777
221.0.120.129:4777
221.234.191.176:4777
222.243.84.129:4777

I've started fixing the issue with getwork in daemon. This will take few day to complete and verify.

Yes.

Thank you for the question. Nothing stops us from modifying mintxfee as soon as txfee isn't a hard rule: block will be accepted with zero tx fee.

There is two kinds of mintxfee:

1) minimal tx fee that limits me (as a miner) to accept tx into block
2) minimal tx fee that limits me (as a node) to relay tx to other nodes

As a miner I can accept lowfee txes into my memory pool but these txes will be accepted by other nodes only with blocks I've mined myself. This means that lowfee txes will reach other nodes much slower.

Here is a short spec:

2.000.000.000 coins will be emitted.

Block reward gradually goes down as difficulty rises (no halving) as in Primecoin. But finally it is a bit different from Primecoin: tx fee is high (0.05 DTC per 1Kb) => fully loaded block (1024Kb) gives ~50DTC in plus to block reward. This is expected in future.

Block target is 1 minute.

Max block size is 1Mb.
Max tx size is 128Kb.

Sorry, I'm not clear enough
Here are details and example:

Minimal tx fee is 0.05DTC => any tx will cost at least 0.05DTC
1Kb fee is also 0.05DTC => tx fee = tx size * 0.05DTC

Let's check how this works (I use non-hp version of daemon and perl scripts from https://github.com/foo1inge/datacoin-browser):

"balance" : 31.83000000,

$ perl dtc_put_file.pl ubuntu-12.04.3-alternate-amd64.iso.torrent
db0bbf965ee6da1d6e546b5d5b0d6f8a0934687d9ea7b9fd9af91491cfb7011a

"balance" : 30.33000000,

ubuntu-12.04.3-alternate-amd64.iso.torrent is 29Kb long

Total fee for 29Kb (+ some meta information added by scripts) is 1.50 DTC (30Kb * 0.05 = 1.50).

I will also add +250 DTC for the best logo. Let's wait a week (until Nov 25) before making any decisions.

Yes, this is a min tx fee.

The fist coin with data in tx was Namecoin. The main difference is that Namecoin is a key-value storage and it applies some rules to the data (data can be correct or not). Datacoin daemon handles blobs and it doesn't care about data format.

Sending a message means that there is a receiver for this message. senddata RPC doesn't add a receiver into tx but as soon as any tx has a data field you can do this (=> needs a bit of coding but doesn't need a hardfork).

I don't think that messaging (like IM or e-mail) is a very good idea for the blockchain: IM/e-mail is a one-to-one communication and data in blockchain is more suitable for one-to-many communication model.