Subject: Re: [Bitcoin-development] Introducing BitcoinKit.framework

From: Mike Hearn <[email-masked]>
Date: Tue, 16 Jul 2013 12:59:56 +0200

I think that's a great approach. Here is the patch Satoshi sent me back in
2010. All the code has changed since but it can be a source of inspiration.

>From Satoshi:

*The simplified payment verification in the paper imagined you would
receive transactions directly, as with sending to IP address which nobody
uses, or a node would index all transactions by public key and you could
download them like downloading mail from a mail server.

Instead, I think client-only nodes should receive full blocks so they can
scan them for their own transactions.  They don't need to store them or
index them.  For the initial download, they only need to download headers,
since there couldn't be any payments before the first time the program was
run (a header download command was added in 0.3.18).  From then on, they
download full blocks (but only store the headers).

Code for client-only mode is mostly implemented.  There's a feature branch
on github with it, also I'm attaching the patch to this message.

Here's some more about it:

"Here's my client-mode implementation so far.  Client-only mode only
records block headers and doesn't use the tx index.  It can't generate, but
it can still send and receive transactions.  It's not fully finished for
use by end-users, but it doesn't matter because it's a complete no-op if
fClient is not enabled.  At this point it's mainly documentation showing
the cut-lines for client-only re-implementers.

With fClient=true, I've only tested the header-only initial download.

A little background.  CBlockIndex contains all the information of the block
header, so to operate with headers only, I just maintain the CBlockIndex
structure as usual.  The nFile/nBlockPos are null, since the full block is
not recorded on disk.

The code to gracefully switch between client-mode on/off without deleting
blk*.dat in between is not implemented yet.  It would mostly be a matter of
having non-client LoadBlockIndex ignore block index entries with null block
pos.  That would make it re-download those as full blocks.  Switching back
to client-mode is no problem, it doesn't mind if the full blocks are there.

If the initial block download becomes too long, we'll want client mode as
an option so new users can get running quickly.  With graceful switch-off
of client mode, they can later turn off client mode and have it download
the full blocks if they want to start generating.  They should rather just
use a getwork miner to join a pool instead.

Client-only re-implementations would not need to implement EvalScript at
all, or at most just implement the five ops used by the standard
transaction templates."
*

diff -u old\db.cpp new\db.cpp
--- old\db.cpp  Sat Dec 18 18:35:59 2010
+++ new\db.cpp  Sun Dec 19 20:53:59 2010
@@ -464,29 +464,32 @@
     ReadBestInvalidWork(bnBestInvalidWork);

     // Verify blocks in the best chain
-    CBlockIndex* pindexFork = NULL;
-    for (CBlockIndex* pindex = pindexBest; pindex && pindex->pprev; pindex
= pindex->pprev)
+    if (!fClient)
     {
-        if (pindex->nHeight < nBestHeight-2500 &&
!mapArgs.count("-checkblocks"))
-            break;
-        CBlock block;
-        if (!block.ReadFromDisk(pindex))
-            return error("LoadBlockIndex() : block.ReadFromDisk failed");
-        if (!block.CheckBlock())
+        CBlockIndex* pindexFork = NULL;
+        for (CBlockIndex* pindex = pindexBest; pindex && pindex->pprev;
pindex = pindex->pprev)
         {
-            printf("LoadBlockIndex() : *** found bad block at %d,
hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString().c_str());
-            pindexFork = pindex->pprev;
+            if (pindex->nHeight < nBestHeight-2500 &&
!mapArgs.count("-checkblocks"))
+                break;
+            CBlock block;
+            if (!block.ReadFromDisk(pindex))
+                return error("LoadBlockIndex() : block.ReadFromDisk
failed");
+            if (!block.CheckBlock())
+            {
+                printf("LoadBlockIndex() : *** found bad block at %d,
hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString().c_str());
+                pindexFork = pindex->pprev;
+            }
+        }
+        if (pindexFork)
+        {
+            // Reorg back to the fork
+            printf("LoadBlockIndex() : *** moving best chain pointer back
to block %d\n", pindexFork->nHeight);
+            CBlock block;
+            if (!block.ReadFromDisk(pindexFork))
+                return error("LoadBlockIndex() : block.ReadFromDisk
failed");
+            CTxDB txdb;
+            block.SetBestChain(txdb, pindexFork);
         }
-    }
-    if (pindexFork)
-    {
-        // Reorg back to the fork
-        printf("LoadBlockIndex() : *** moving best chain pointer back to
block %d\n", pindexFork->nHeight);
-        CBlock block;
-        if (!block.ReadFromDisk(pindexFork))
-            return error("LoadBlockIndex() : block.ReadFromDisk failed");
-        CTxDB txdb;
-        block.SetBestChain(txdb, pindexFork);
     }

     return true;
diff -u old\main.cpp new\main.cpp
--- old\main.cpp        Sat Dec 18 18:35:59 2010
+++ new\main.cpp        Sun Dec 19 20:53:59 2010
@@ -637,6 +637,9 @@
     if (!IsStandard())
         return error("AcceptToMemoryPool() : nonstandard transaction
type");

+    if (fClient)
+        return true;
+
     // Do we already have it?
     uint256 hash = GetHash();
     CRITICAL_BLOCK(cs_mapTransactions)
@@ -1308,23 +1311,26 @@
     if (!CheckBlock())
         return false;

-    //// issue here: it doesn't know the version
-    unsigned int nTxPos = pindex->nBlockPos + ::GetSerializeSize(CBlock(),
SER_DISK) - 1 + GetSizeOfCompactSize(vtx.size());
-
-    map<uint256, CTxIndex> mapUnused;
-    int64 nFees = 0;
-    foreach(CTransaction& tx, vtx)
+    if (!fClient)
     {
-        CDiskTxPos posThisTx(pindex->nFile, pindex->nBlockPos, nTxPos);
-        nTxPos += ::GetSerializeSize(tx, SER_DISK);
+        //// issue here: it doesn't know the version
+        unsigned int nTxPos = pindex->nBlockPos +
::GetSerializeSize(CBlock(), SER_DISK) - 1 + GetSizeOfCompactSize(vtx.size(
));
+
+        map<uint256, CTxIndex> mapUnused;
+        int64 nFees = 0;
+        foreach(CTransaction& tx, vtx)
+        {
+            CDiskTxPos posThisTx(pindex->nFile, pindex->nBlockPos, nTxPos);
+            nTxPos += ::GetSerializeSize(tx, SER_DISK);

-        if (!tx.ConnectInputs(txdb, mapUnused, posThisTx, pindex, nFees,
true, false))
+            if (!tx.ConnectInputs(txdb, mapUnused, posThisTx, pindex,
nFees, true, false))
+                return false;
+        }
+
+        if (vtx[0].GetValueOut() > GetBlockValue(pindex->nHeight, nFees))
             return false;
     }

-    if (vtx[0].GetValueOut() > GetBlockValue(pindex->nHeight, nFees))
-        return false;
-
     // Update block index on disk without changing it in memory.
     // The memory index structure will be changed after the db commits.
     if (pindex->pprev)
@@ -1378,7 +1384,7 @@
     foreach(CBlockIndex* pindex, vDisconnect)
     {
         CBlock block;
-        if (!block.ReadFromDisk(pindex))
+        if (!block.ReadFromDisk(pindex, !fClient))
             return error("Reorganize() : ReadFromDisk for disconnect
failed");
         if (!block.DisconnectBlock(txdb, pindex))
             return error("Reorganize() : DisconnectBlock failed");
@@ -1395,7 +1401,7 @@
     {
         CBlockIndex* pindex = vConnect[i];
         CBlock block;
-        if (!block.ReadFromDisk(pindex))
+        if (!block.ReadFromDisk(pindex, !fClient))
             return error("Reorganize() : ReadFromDisk for connect failed");
         if (!block.ConnectBlock(txdb, pindex))
         {
@@ -1526,7 +1532,7 @@

     txdb.Close();

-    if (pindexNew == pindexBest)
+    if (!fClient && pindexNew == pindexBest)
     {
         // Notify UI to display prev block's coinbase if it was ours
         static uint256 hashPrevBestCoinBase;
@@ -1547,10 +1553,6 @@
     // These are checks that are independent of context
     // that can be verified before saving an orphan block.

-    // Size limits
-    if (vtx.empty() || vtx.size() > MAX_BLOCK_SIZE ||
::GetSerializeSize(*this, SER_NETWORK) > MAX_BLOCK_SIZE)
-        return error("CheckBlock() : size limits failed");
-
     // Check proof of work matches claimed amount
     if (!CheckProofOfWork(GetHash(), nBits))
         return error("CheckBlock() : proof of work failed");
@@ -1559,6 +1561,13 @@
     if (GetBlockTime() > GetAdjustedTime() + 2 * 60 * 60)
         return error("CheckBlock() : block timestamp too far in the
future");

+    if (fClient && vtx.empty())
+        return true;
+
+    // Size limits
+    if (vtx.empty() || vtx.size() > MAX_BLOCK_SIZE ||
::GetSerializeSize(*this, SER_NETWORK) > MAX_BLOCK_SIZE)
+        return error("CheckBlock() : size limits failed");
+
     // First transaction must be coinbase, the rest must not be
     if (vtx.empty() || !vtx[0].IsCoinBase())
         return error("CheckBlock() : first tx is not coinbase");
@@ -1623,13 +1632,14 @@
         return error("AcceptBlock() : out of disk space");
     unsigned int nFile = -1;
     unsigned int nBlockPos = 0;
-    if (!WriteToDisk(nFile, nBlockPos))
-        return error("AcceptBlock() : WriteToDisk failed");
+    if (!fClient)
+        if (!WriteToDisk(nFile, nBlockPos))
+            return error("AcceptBlock() : WriteToDisk failed");
     if (!AddToBlockIndex(nFile, nBlockPos))
         return error("AcceptBlock() : AddToBlockIndex failed");

     // Relay inventory, but don't relay old inventory during initial block
download
-    if (hashBestChain == hash)
+    if (!fClient && hashBestChain == hash)
         CRITICAL_BLOCK(cs_vNodes)
             foreach(CNode* pnode, vNodes)
                 if (nBestHeight > (pnode->nStartingHeight != -1 ?
pnode->nStartingHeight - 2000 : 55000))
@@ -2405,6 +2415,8 @@
         {
             if (fShutdown)
                 return true;
+            if (fClient && inv.type == MSG_TX)
+                continue;
             pfrom->AddInventoryKnown(inv);

             bool fAlreadyHave = AlreadyHave(txdb, inv);
@@ -2441,6 +2453,9 @@

             if (inv.type == MSG_BLOCK)
             {
+                if (fClient)
+                    return true;
+
                 // Send block from disk
                 map<uint256, CBlockIndex*>::iterator mi =
mapBlockIndex.find(inv.hash);
                 if (mi != mapBlockIndex.end())
@@ -2486,6 +2501,8 @@

     else if (strCommand == "getblocks")
     {
+        if (fClient)
+            return true;
         CBlockLocator locator;
         uint256 hashStop;
         vRecv >> locator >> hashStop;
@@ -2556,6 +2573,8 @@

     else if (strCommand == "tx")
     {
+        if (fClient)
+            return true;
         vector<uint256> vWorkQueue;
         CDataStream vMsg(vRecv);
         CTransaction tx;
@@ -2620,6 +2639,33 @@

         if (ProcessBlock(pfrom, &block))
             mapAlreadyAskedFor.erase(inv);
+    }
+
+
+    else if (strCommand == "headers")
+    {
+        if (!fClient)
+            return true;
+        vector<CBlock> vHeaders;
+        vRecv >> vHeaders;
+
+        uint256 hashBestBefore = hashBestChain;
+        foreach(CBlock& block, vHeaders)
+        {
+            block.vtx.clear();
+
+            printf("received header %s\n", block.GetHash().ToString().
substr(0,20).c_str());
+
+            CInv inv(MSG_BLOCK, block.GetHash());
+            pfrom->AddInventoryKnown(inv);
+
+            if (ProcessBlock(pfrom, &block))
+                mapAlreadyAskedFor.erase(inv);
+        }
+
+        // Request next batch
+        if (hashBestChain != hashBestBefore)
+            pfrom->PushGetBlocks(pindexBest, uint256(0));
     }

On Tue, Jul 16, 2013 at 12:17 PM, Wendell <[email-masked]> wrote:

> I for one would be interested in taking a look at that.
>
> In San Jose I was asking around about the possibility of hiring someone to
> complete such a patch. Pieter Wuille introduced me to Eric Lombrozo, who
> expressed interest, but has since gotten quite busy. So we haven't arrived
> at a detailed estimate of what it would involve.
>
> Maybe it would be better to start a completely new thread for this topic,
> but I would very much be interested in an open dissection of what adding
> SPV support to bitcoind would take. I am willing to fund or (ideally)
> co-fund this endeavor, if I can ever get my head around it. I'm super
> interested in all of these possibilities (including micro-stripped-VMs and
> transpilation), but would simply like to encourage the proliferation of
> _options_ whenever possible.
>
> -wendell
>
> grabhive.com | twitter.com/grabhive
>
> On Jul 16, 2013, at 11:51 AM, Mike Hearn wrote:
>
> > If you wanted to implement SPV mode in bitcoind, Gavin or I could send
> you Satoshi's old patch although of course it is no longer usable. It would
> indicate the basic cut lines though.
>
>