net: bound what a peer can make the node allocate (#73)

Three independent bounds on what an untrusted peer can make this node allocate:

- serialize.h: reject a compact size above MAX_SIZE before reading a string or a
  vector, instead of discovering it read by read. MAX_SIZE moves from main.h to
  serialize.h, where the checks live; headers_core.h includes serialize.h first,
  so every existing user still sees it.
- main.cpp: cap an orphan transaction at 10,000 inputs. Orphans are stored and
  never validated, so mapOrphanTransactionsByPrev grew with one entry per input
  of every orphan a peer cared to send.
- rpc.cpp: drop a Stratum line nested deeper than 20 before json::parse recurses
  into it. The scan tracks string state, so a worker name containing { or [ is
  no longer mistaken for nesting.

Verified: builds clean on UCRT64; the depth scanner passes a table of legitimate
Stratum lines and nesting attacks; a node built from this branch synced the chain
from genesis to 4462 with no deserialization failure and no rejected block.

1 files changed, 26 insertions, 1 deletions

diff --git a/src/rpc.cpp b/src/rpc.cpp
index 285f11b..3db8b94 100644
--- a/src/rpc.cpp
+++ b/src/rpc.cpp
@@ -681,7 +681,32 @@ static bool HandleLine(Miner* m, const std::string& rawLine,
                        int& blocksFoundThisSession)
 {
     json req;
-    try { req = json::parse(rawLine); }
+    try {
+        // Fast pre-parse depth check to prevent stack overflow in json::parse.
+        // Legitimate Stratum requests have a depth of at most 4.
+        int depth = 0;
+        bool in_string = false;
+        bool escape = false;
+        for (char c : rawLine) {
+            if (in_string) {
+                if (escape) escape = false;
+                else if (c == '\\') escape = true;
+                else if (c == '"') in_string = false;
+            } else {
+                if (c == '"') in_string = true;
+                else if (c == '{' || c == '[') {
+                    if (++depth > 20) {
+                        LogPrint("worker", "[worker] JSON too deeply nested from %s\n",
+                                 m->address.empty() ? "(unauth)" : m->address.c_str());
+                        return true;
+                    }
+                } else if (c == '}' || c == ']') {
+                    depth--;
+                }
+            }
+        }
+        req = json::parse(rawLine);
+    }
     catch (...) {
         LogPrint("worker", "[worker] JSON parse error from %s: %.80s\n",
                  m->address.empty() ? "(unauth)" : m->address.c_str(),