bitcoin-config.h moved, but the old file is likely to still exist when
reconfiguring or switching branches. This would've caused files to not rebuild
correctly, and other strange problems.
Make the path explicit so that the old one cannot be found.
Core libs use config/bitcoin-config.h.
Libs (like crypto) which don't want access to bitcoin's headers continue
to use -Iconfig and #include bitcoin-config.h.
Adds a copyright and attribution message to the `-version` output
(the same as shown in the About dialog in the GUI).
Move the message to a function LicenseInfo in init.cpp.
- add DEFAULT_LISTEN in net.h and use in the code (shared
setting between core and GUI)
Important: This makes it obvious, that we need to re-think the
settings/options handling, as GUI settings are processed before
any parameter-interaction (which is mostly important for network
stuff) in AppInit2()!
f0a83fc Use Params().NetworkID() instead of TestNet() from the payment protocol (jtimon)
2871889 net.h was using std namespace through chainparams.h included in protocol.h (jtimon)
c8c52de Replace virtual methods with static attributes, chainparams.h depends on protocol.h instead of the other way around (jtimon)
a3d946e Get rid of TestNet() (jtimon)
6fc0fa6 Add RPCisTestNet chain parameter (jtimon)
cfeb823 Add RequireStandard chain parameter (jtimon)
21913a9 Add AllowMinDifficultyBlocks chain parameter (jtimon)
d754f34 Move majority constants to chainparams (jtimon)
8d26721 Get rid of RegTest() (jtimon)
cb9bd83 Add DefaultCheckMemPool chain parameter (jtimon)
2595b9a Add DefaultMinerThreads chain parameter (jtimon)
bfa9a1a Add MineBlocksOnDemand chain parameter (jtimon)
1712adb Add MiningRequiresPeers chain parameter (jtimon)
New RPC methods: return an estimate of the fee (or priority) a
transaction needs to be likely to confirm in a given number of
blocks.
Mike Hearn created the first version of this method for estimating fees.
It works as follows:
For transactions that took 1 to N (I picked N=25) blocks to confirm,
keep N buckets with at most 100 entries in each recording the
fees-per-kilobyte paid by those transactions.
(separate buckets are kept for transactions that confirmed because
they are high-priority)
The buckets are filled as blocks are found, and are saved/restored
in a new fee_estiamtes.dat file in the data directory.
A few variations on Mike's initial scheme:
To estimate the fee needed for a transaction to confirm in X buckets,
all of the samples in all of the buckets are used and a median of
all of the data is used to make the estimate. For example, imagine
25 buckets each containing the full 100 entries. Those 2,500 samples
are sorted, and the estimate of the fee needed to confirm in the very
next block is the 50'th-highest-fee-entry in that sorted list; the
estimate of the fee needed to confirm in the next two blocks is the
150'th-highest-fee-entry, etc.
That algorithm has the nice property that estimates of how much fee
you need to pay to get confirmed in block N will always be greater
than or equal to the estimate for block N+1. It would clearly be wrong
to say "pay 11 uBTC and you'll get confirmed in 3 blocks, but pay
12 uBTC and it will take LONGER".
A single block will not contribute more than 10 entries to any one
bucket, so a single miner and a large block cannot overwhelm
the estimates.
Use CFeeRate instead of an int64_t for quantities that are
fee-per-size.
Helps prevent unit-conversion mismatches between the wallet,
relaying, and mining code.
Previously if bitcoind is linked with an OpenSSL which is compiled
without EC support, this is seen as an assertion failure "pKey !=
NULL" at key.cpp:134, which occurs after several seconds. It is an
esoteric piece of knowledge to interpret this as "oops, I linked
with the wrong OpenSSL", and because of the delay it may not even
be noticed.
The new output is
: OpenSSL appears to lack support for elliptic curve cryptography. For
more information, visit
https://en.bitcoin.it/wiki/OpenSSL_and_EC_Libraries
: Initialization sanity check failed. Bitcoin Core is shutting down.
which occurs immediately after attempted startup.
This also blocks in an InitSanityCheck() function which currently only
checks for EC support but should eventually do more. See #4081.
Add -rpcbind command option to specify binding RPC service on one
or multiple specific interfaces.
Functionality if -rpcbind is not specified remains the same as before:
- If no -rpcallowip specified, bind on localhost
- If no -rpcbind specified, bind on any interface
Implements part of #3111.
Size specifiers are no longer needed now that we use typesafe tinyformat
for string formatting, instead of the system's sprintf.
No functional changes.
This continues the work in #3735.
The year is 2014. All supported operating systems have IPv6 support,
most certainly at build time (this doesn't mean that IPv6 is configured,
of course).
If noone is exercising the functionality to disable it, that means it
doesn't get tested, and IMO it's better to get rid of it.
(it's also not used consistently in RPC/boost and Net code...)
Prints the actual version of BerkeleyDB that is linked against, if
wallet support is enabled.
Useful for troubleshooting.
For example:
2014-05-01 07:44:02 Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)
2014-05-01 07:54:25 Using BerkeleyDB version Berkeley DB 5.1.29: (October 25, 20 11)
- introduce DEFAULT_SCRIPTCHECK_THREADS in main.h
- only show values from -"MAX_HW_THREADS" up to 16 for -par, as it
makes no sense to try to leave more "cores free" than the system
supports anyway
- use the new constant in optionsdialog and remove defaults from
.ui file
Amend to d5f1e72. It turns out that BerkelyDB was including inttypes.h
indirectly, so we cannot fix this with just macros.
Trivial commit: apply the following script to all .cpp and .h files:
# Middle
sed -i 's/"PRIx64"/x/g' "$1"
sed -i 's/"PRIu64"/u/g' "$1"
sed -i 's/"PRId64"/d/g' "$1"
# Initial
sed -i 's/PRIx64"/"x/g' "$1"
sed -i 's/PRIu64"/"u/g' "$1"
sed -i 's/PRId64"/"d/g' "$1"
# Trailing
sed -i 's/"PRIx64/x"/g' "$1"
sed -i 's/"PRIu64/u"/g' "$1"
sed -i 's/"PRId64/d"/g' "$1"
After this commit, `git grep` for PRI.64 should turn up nothing except
the defines in util.h.
As the tinyformat-based formatting system (introduced in b77dfdc) is
type-safe, no special format characters are needed to specify sizes.
Tinyformat can support (ignore) the C99 prefixes such as "ll" but
chokes on MSVC's inttypes.h defines prefixes such as "I64X". So don't
include inttypes.h and define our own for compatibility.
(an alternative would be to sweep the entire codebase using sed -i to
get rid of the size specifiers but this has less diff impact)
5770254 Copyright header updates s/2013/2014 on files whose last git commit was done in 2014. contrib/devtools/fix-copyright-headers.py script to be able to perform this maintenance task with ease during the rest of the year, every year. Modifications to contrib/devtools/README.md to document what fix-copyright-headers.py does. (gubatron)
contrib/devtools/fix-copyright-headers.py script to be able to perform this maintenance task with ease during the rest of the year, every year. Modifications to contrib/devtools/README.md to document what fix-copyright-headers.py does.
- Log a warning when bootstrap files are specified using `-loadblock`
but cannot be opened.
- Log a warning when bootstrap.dat exists in the home directory
but cannot be opened.
This changes the block processing logic from "try to atomically switch
to a new block" to a continuous "(dis)connect a block, aiming for the
assumed best chain".
This means the smallest atomic operations on the chainstate become
individual block connections or disconnections, instead of entire
reorganizations. It may mean that we try to reorganize to one block,
fail, and rereorganize again to the old block. This is slower, but
doesn't require unbounded RAM.
It also means that a ConnectBlock which fails may be no longer called
from the ProcessBlock which knows which node sent it. To deal with that,
a mapBlockSource is kept, and invalid blocks cause asynchronous "reject"
messages and banning (if necessary).
After the tinyformat switch sprintf() family functions support passing
actual std::string objects.
Remove unnecessary c_str calls (236 of them) in logging and formatting.
Allow running bitcoind without server.
- Default to -server mode (of course) for bitcoind with SoftSetBoolArg
- Remove fForceServer argument from AppInit2
- Move fDaemon to a static variable in bitcoind
c3a7f51 Move `verifymessage` from rpcwallet to rpcmisc (Wladimir J. van der Laan)
723a03d Move `createmultisig` from rpcwallet to rpcmisc (Wladimir J. van der Laan)
452955f Move `validateaddress` from rpcwallet to rpcmisc (Wladimir J. van der Laan)
cd7fa8b Move `nTransactionFee` from main.cpp to wallet.cpp (Wladimir J. van der Laan)
a943bde Move `settxfee` from rpcblockchain to rpcwallet (Wladimir J. van der Laan)
16bc9aa Move `getinfo` from rpcnet to rpcmisc (Wladimir J. van der Laan)
652e156 add new RPC implementation file `rpcmisc.cpp` (Wladimir J. van der Laan)
When a InitError or InitWarning happens, the
GUI pops up but is unusable (until Init finishes).
This is caused by showNormalIfMinimized. Add a message
flag to skip this call for Init errors or warnings.
Seperate out the wallet options in HelpMessage, and
don't show them if compiled with --disable-wallet.
Also add documentation for `-disablewallet` option.
`-logtodebugger` is a strange, obscure, WIN32-only (mostly MSVC) thing.
Let's clean up the options a bit get rid of it.
test_bitcoin was using fLogToDebugger as a way to prevent logging to
debug.log. For this, add a boolean (not exposed as option) fLogToDebugLog that
defaults to true and is disabled in the tests.
The following mining-related RPC calls don't use the wallet:
- getnetworkhashps
- getmininginfo
- getblocktemplate
- submitblock
Enable them when compiling with --disable-wallet.
Remove unnecessary dependencies for bitcoin-cli
(leveldb, berkelydb, wallet, RPC server)
Build system changes:
- split libbitcoin.a into libbitcoin_common.a, libbitcoin_server.a and
libbitcoin_cli.a
Code changes (movement only):
- split up HelpMessage into HelpMessage in init.cpp and HelpMessageCli
in rpcclient.cpp
- move uiInterface from init.cpp to util.cpp
Split bitcoinrpc up into
- rpcserver: bitcoind RPC server
- rpcclient: bitcoin-cli RPC client
- rpcprotocol: shared common HTTP/JSON-RPC protocol code
One step towards making bitcoin-cli independent from the rest
of the code, and thus a smaller executable that doesn't have to
be linked against leveldb.
This commit only does code movement, there are no functional changes.
I'm writing some wallet regression tests using -regtest mode, and
need to generate an initial multi-hundred-block chain. Repeatedly
calling setgenerate to generate one block is slow and doesn't
work properly, because block creation happens asynchronously.
This adds two features to setgenerate in -regtest mode:
1) Instead of being interpreted as number of threads to start, the
third argument is the number of blocks to generate.
2) setgenerate will not return until the block creation threads
have created the requested number of blocks.
Use misc methods of avoiding unnecesary header includes.
Replace int typedefs with int##_t from stdint.h.
Replace PRI64[xdu] with PRI[xdu]64 from inttypes.h.
Normalize QT_VERSION ifs where possible.
Resolve some indirect dependencies as direct ones.
Remove extern declarations from .cpp files.
- re-work -debug help message text
- make -debug log every debugging information again (even all categories)
- remove unneeded fDebug checks in front of LogPrint()/qDebug(), as that
check is done in LogPrintf() when category is != NULL (true for all
LogPrint() calls
- remove fDebug ONLY in code which is NOT performance-critical
- harmonize addrman category name
- deprecate -debugnet usage, should be used via -debug=net and remove the
corresponding global
This adds an executable `bitcoin-rpc` that only serves as a Bitcoin RPC
client.
The commit does not remove RPC functionality from the `bitcoind` yet,
this functionality should be deprecated but is left for a later version
to give users some time to switch.
- this extends the accepted ciphersuites with TLSv1.2 ones
- also removes !AH, as I could not find documentation on it and the change
did not result in a changed ciphersuite list (checked via openssl
ciphers -v)
- closes#3096 (which also contains more details)
This removes a few unused CBlockLocator methods, and moves the
construction and fork-finding logic to CChain (which can do these
more efficiently, as it has a height-indexable chain available).
It also makes CBlockLocator independent from the validation code.
- rename URL into URI in paymentserver where correct
- add some missing Qt-coding-stuff in paymentserver
- change QSpinBox to QLineEdit as base for BitcoinAmountField in .ui files
(as this is the result when converting the BAF back into base)
- remove some c_str() and replace with QString::fromStdString()
- remove several new-lines
- remove unneeded spaces
- indentation fixes
I've seen users confused multiple times thinking they
should be using -tor to set their tor proxy and then
finding in horror that they were still connecting to
the IPv4 internet.
Even Jeff guesses wrong about what the knob does, so
I think we should rename it. This leaves the old
knob working, we can pull it out completely in a
later release.
Add support for a Payment Protocol to Bitcoin-Qt.
Payment messages are protocol-buffer encoded and communicated over
http(s), so this adds a dependency on the Google protocol buffer
library, and requires Qt with OpenSSL support.
- move SelectParamsFromCommandLine() from init.cpp to bitcoin.cpp to allow
to use TestNet() for Bitcoin-Qt instead of GetBoolArg("-testnet", false)
- change order in bitcoind.cpp to match bitcoin.cpp functionality
- hamonize error message strings for missing datadir and failing
SelectParamsFromCommandLine() in bitcoin.cpp and bitcoind.cpp
- use TestNet() call in splashscreen.cpp
use std::string instead of psz for WalletFile
only allow wallets within $DATADIR
Use strWalletFile in salvage/recover
fix: remove unused variable pszWalletFile
move strWalletFile to init.h/init.cpp
avoid conversion of strWalletfile to c-string
In case no database exists yet, and -txindex(=1) is passed, we currently first
check whether fTxIndex differs from -txindex (and ask the user to reindex in
that case), and only afterwards initialize the database. By swapping these
around (the initialization is a no-op in case the database already exists),
we allow it to be born in txindex mode, without warning.
That also means we don't need to check -reindex anymore, as the wiping/reinit
of the databases happens before checking.
The new class is accessed via the Params() method and holds
most things that vary between main, test and regtest networks.
The regtest mode has two purposes, one is to run the
bitcoind/bitcoinj comparison tool which compares two separate
implementations of the Bitcoin protocol looking for divergence.
The other is that when run, you get a local node which can mine
a single block instantly, which is highly convenient for testing
apps during development as there's no need to wait 10 minutes for
a block on the testnet.
- adds a reindex dialog for Bitcoin-Qt to change -txindex without the need
to supply -reindex
- now also does a -reindex, when removing the -txindex switch
Removed AreInputsStandard from CTransaction, made it a regular function in main.
Moved CTransaction::GetOutputFor to CCoinsViewCache.
Moved GetLegacySigOpCount and GetP2SHSigOpCount out of CTransaction into regular functions in main.
Moved GetValueIn and HaveInputs from CTransaction into CCoinsViewCache.
Moved AllowFree, ClientCheckInputs, CheckInputs, UpdateCoins, and CheckTransaction out of CTransaction and into main.
Moved IsStandard and IsFinal out of CTransaction and put them in main as IsStandardTx and IsFinalTx. Moved GetValueOut out of CTransaction into main. Moved CTxIn, CTxOut, and CTransaction into core.
Added minimum fee parameter to CTxOut::IsDust() temporarily until CTransaction is moved to core.h so that CTxOut needn't know about CTransaction.
Added explicit include of main.h in init.cpp, changed include of init.h to include of main.h in net.cpp.
Added function registration for net.cpp in init.cpp's network initialization.
Removed protocol.cpp's dependency on main.h.
TODO: Remove main.h include in net.cpp.
This will allow each to have its own main(), meaning that we can build a common
base client and simply link in the correct startup object to create the
appropriate binary.
- explicitly set the default of all GetBoolArg() calls
- rework getarg_test.cpp and util_tests.cpp to cover this change
- some indentation fixes
- move macdockiconhandler.h include in bitcoin.cpp to the "our headers"
section
This commit decouples the pMiningKey initialization and shutdown from the RPC
threads.
`getwork` and `getblocktemplate` rely on pMiningKey, and can also be ran
from the debug window in the UI even when the RPC server is not running.
Solves issue #2706.
Write bestblock records in wallets:
* Every 20160 blocks synced, no matter what (before: none during IBD)
* Every 144 blocks after IBD (before: for every block, slow)
* When creating a new wallet
* At shutdown
This should result in far fewer spurious rescans.
At startup, check that the expected genesis is loaded. This should prevent
cases where accidentally a datadir from the wrong network is loaded
(testnet vs mainnet, e.g.).
Bitcoin-Qt could core dump if application initialization failed in certain ways.
I double-fixed this:
1) qt/bitcoin.cpp now shuts down core threads cleanly if AppInit2 returns false
2) init.cpp now exits before StartNode() if strErrors is set (no reason to StartNode if we're just going to exit immediately anyway).
Tested by triggering all of the various ways AppInit2 can fail, either by passing bogus command-line arguments or just recompiling tweaked code to simulate failure.
This is a partial fix for #2480
It is possible to have a wallet.dat file without any bestblock
record at all (if created offline, for example), which - when
loaded into a client with a up-to-date chain - does no rescan and
shows no transactions.
Also make sure to write the current best block after a rescan, so
it isn't necessary twice.
Two reasons for this change:
1. Need to always use boost::thread's sleep, even on Windows, so the
sleeps can be interrupted (prior code used Windows' built-in Sleep).
2. I always forgot what units the old Sleep took.
Create a boost::thread_group object at the qt/bitcoind main-loop level
that will hold pointers to all the main-loop threads.
This will replace the vnThreadsRunning[] array.
For testing, ported the BitcoinMiner threads to use its
own boost::thread_group.
- remove an unneeded MODAL flag, as MSG_ERROR sets MODAL
- re-order an if-clause in main to have bool checks before a function call
- fix some log messages that used wrong function names
- make a log message use a correct ellipsis
- remove some unneded spaces, brackets and line-breaks
- fix style for adding files in the Qt project
By specifying -txindex when initializing the database, a txid-to-diskpos
index is maintained in the blktree database. This database is used to
help answering getrawtransaction() RPC queries, when enabled.
Changing the -txindex value requires a -reindex; the client will abort
at startup if the database and the specified -txindex mismatch.
- it was bad, that quite some messages were just talking about a database,
I think a user should know, if we are talking about wallet db or
block/coin db
- also adds a new init message for "Verifying block database integrity..."
- this pull adds an InitMessage() function to noui.cpp, which outputs init
messages to debug.log (this allows to remove some printf() calls from
init.cpp)
- change InitMessage() in bitcoin.cpp to also write init messages to
debug.log to ensure nothting is missing in the log because of the
removal of printf() calls in init.cpp
* During block verification (when parallelism is requested), script
check actions are stored instead of being executed immediately.
* After every processed transactions, its signature actions are
pushed to a CScriptCheckQueue, which maintains a queue and some
synchronization mechanism.
* Two or more threads (if enabled) start processing elements from
this queue,
* When the block connection code is finished processing transactions,
it joins the worker pool until the queue is empty.
As cs_main is held the entire time, and all verification must be
finished before the block continues processing, this does not reach
the best possible performance. It is a less drastic change than
some more advanced mechanisms (like doing verification out-of-band
entirely, and rolling back blocks when a failure is detected).
The -par=N flag controls the number of threads (1-16). 0 means auto,
and is the default.
-checklevel gets a new meaning:
0: verify blocks can be read from disk (like before)
1: verify (contextless) block validity (like before)
2: verify undo files can be read and have good checksums
3: verify coin database is consistent with the last few blocks
(close to level 6 before)
4: verify all validity rules of the last few blocks
Level 3 is the new default, as it's reasonably fast. As level 3 and
4 are implemented using an in-memory rollback of the database, they
are limited to as many blocks as possible without exceeding the
limits set by -dbcache. The default of -dbcache=25 allows for some
150-200 blocks to be rolled back.
In case an error is found, the application quits with a message
instructing the user to restart with -reindex. Better instructions,
and automatic recovery (when possible) or automatic reindexing are
left as future work.
When the coin database is out of date with the block database, the
best block in it is automatically switched to. This reconnection
process can take time, so allow it to be interrupted.
This also stops block connection as soon as shutdown is requested,
leading to a faster shutdown.
- fix ThreadSafeMessageBox always displays error icon
- allow to specify MSG_ERROR / MSG_WARNING or MSG_INFORMATION without a
custom caption / title
- allow to specify CClientUIInterface::ICON_ERROR / ICON_WARNING and
ICON_INFORMATION (which is default) as message box icon
- remove CClientUIInterface::OK from ThreadSafeMessageBox-calls, as
the OK button will be set as default, if none is specified
- prepend "Bitcoin - " to used captions
- rename BitcoinGUI::error() -> BitcoinGUI::message() and add function
documentation
- change all style parameters and enum flags to unsigned
- update code to use that new API
- update Client- and WalletModel to use new BitcoinGUI::message() and
rename the classes error() method into message()
- include the possibility to supply the wanted icon for messages from
Client- and WalletModel via "style" parameter
- this allows the client to listen on via -bind specified addresses
(e.g. 127.0.0.1), even when a network (IPv4 in that case) was blocked
via e.g -onlynet="Tor"
- introduce enum BindFlags to avoid passing multiple bools to Bind()
- make -bind help text clear we ALWAYS listen on the specified address
- remove an unused variable
- remove 2 unneeded IsLimited() checks before calling Bind(), which does
these checks anyway
- usage case: specify -bind=127.0.0.1 -onlynet="Tor" to allow incoming
connections to a Tor hidden service, but still don't allow other IPv4
nodes to connect / get connected
Flushes the blktree/ and coins/ databases, and reindexes the
block chain files, as if their contents was loaded via -loadblock.
Based on earlier work by Jeff Garzik.
As the coinset data refers to the best block, stored in the block
tree. Flushing the coin set first can cause inconsistencies if
the process gets killed in between.
Split off CBlockTreeDB and CCoinsViewDB into txdb-*.{cpp,h} files,
implemented by either LevelDB or BDB.
Based on code from earlier commits by Mike Hearn in his leveldb
branch.
Given that the block tree database (chain.dat) and the active chain
database (coins.dat) are entirely separate now, it becomes legal to
swap one with another instance without affecting the other.
This commit introduces a check in the startup code that detects the
presence of a better chain in chain.dat that has not been activated
yet, and does so efficiently (in batch, while reusing the blk???.dat
files).
During the initial block download (or -loadblock), delay connection
of new blocks a bit, and perform them in a single action. This reduces
the load on the database engine, as subsequent blocks often update an
earlier block's transaction already.
This switches bitcoin's transaction/block verification logic to use a
"coin database", which contains all unredeemed transaction output scripts,
amounts and heights.
The name ultraprune comes from the fact that instead of a full transaction
index, we only (need to) keep an index with unspent outputs. For now, the
blocks themselves are kept as usual, although they are only necessary for
serving, rescanning and reorganizing.
The basic datastructures are CCoins (representing the coins of a single
transaction), and CCoinsView (representing a state of the coins database).
There are several implementations for CCoinsView. A dummy, one backed by
the coins database (coins.dat), one backed by the memory pool, and one
that adds a cache on top of it. FetchInputs, ConnectInputs, ConnectBlock,
DisconnectBlock, ... now operate on a generic CCoinsView.
The block switching logic now builds a single cached CCoinsView with
changes to be committed to the database before any changes are made.
This means no uncommitted changes are ever read from the database, and
should ease the transition to another database layer which does not
support transactions (but does support atomic writes), like LevelDB.
For the getrawtransaction() RPC call, access to a txid-to-disk index
would be preferable. As this index is not necessary or even useful
for any other part of the implementation, it is not provided. Instead,
getrawtransaction() uses the coin database to find the block height,
and then scans that block to find the requested transaction. This is
slow, but should suffice for debug purposes.
Corrupt wallets used to cause a DB_RUNRECOVERY uncaught exception and a
crash. This commit does three things:
1) Runs a BDB verify early in the startup process, and if there is a
low-level problem with the database:
+ Moves the bad wallet.dat to wallet.timestamp.bak
+ Runs a 'salvage' operation to get key/value pairs, and
writes them to a new wallet.dat
+ Continues with startup.
2) Much more tolerant of serialization errors. All errors in deserialization
are reported by tolerated EXCEPT for errors related to reading keypairs
or master key records-- those are reported and then shut down, so the user
can get help (or recover from a backup).
3) Adds a new -salvagewallet option, which:
+ Moves the wallet.dat to wallet.timestamp.bak
+ extracts ONLY keypairs and master keys into a new wallet.dat
+ soft-sets -rescan, to recreate transaction history
This was tested by randomly corrupting testnet wallets using a little
python script I wrote (https://gist.github.com/3812689)
Before, opening a -datadir that was created with a new
version of Berkeley DB would result in an un-caught DB_RUNRECOVERY
exception.
After these changes, the error is caught and the user is told
that there is a problem and is told how to try to recover from
it.
