make bulk export commands gracefully exit on SIGPIPE (for example, if piped to head)

TODO

@@ -28,5 +28,4 @@ rate limits (maybe not needed now that we have plugins?)
 
 misc
   ? periodic reaping of disconnected sockets (maybe autoping is doing this already)
-  ? export not dying on SIGPIPE, or not getting SIGPIPE
   ? why isn't the LMDB mapping CLOEXEC

src/apps/dbutils/cmd_export.cpp

@@ -32,6 +32,8 @@ void cmd_export(const std::vector<std::string> &subArgs) {
     uint64_t start = reverse ? until : since;
     uint64_t startDup = reverse ? MAX_U64 : 0;
 
+    exitOnSigPipe();
+
     env.generic_foreachFull(txn, env.dbi_Event__created_at, lmdb::to_sv<uint64_t>(start), lmdb::to_sv<uint64_t>(startDup), [&](auto k, auto v) {
         if (reverse) {
             if (lmdb::from_sv<uint64_t>(k) < since) return false;

src/apps/dbutils/cmd_monitor.cpp

@@ -54,6 +54,8 @@ void cmd_monitor(const std::vector<std::string> &subArgs) {
         }
     }
 
+    exitOnSigPipe();
+
     env.foreach_Event(txn, [&](auto &ev){
         monitors.process(txn, ev, [&](RecipientList &&recipients, uint64_t levId){
             for (auto &r : recipients) {

src/apps/dbutils/cmd_scan.cpp

@@ -34,6 +34,8 @@ void cmd_scan(const std::vector<std::string> &subArgs) {
 
     uint64_t numEvents = 0;
 
+    exitOnSigPipe();
+
     while (1) {
         bool complete = query.process(txn, [&](const auto &sub, uint64_t levId, std::string_view eventPayload){
             if (count) numEvents++;

src/global.h

@@ -16,3 +16,4 @@ uint64_t parseUint64(const std::string &s);
 std::string parseIP(const std::string &ip);
 uint64_t getDBVersion(lmdb::txn &txn);
 std::string padBytes(std::string_view str, size_t n, char padChar);
+void exitOnSigPipe();

src/misc.cpp

@@ -1,5 +1,6 @@
 #include <arpa/inet.h>
 #include <stdio.h>
+#include <signal.h>
 
 #include <algorithm>
 #include <string>
@@ -109,3 +110,10 @@ std::string padBytes(std::string_view str, size_t n, char padChar) {
     if (str.size() > n) throw herr("unable to pad, string longer than expected");
     return std::string(str) + std::string(n - str.size(), padChar);
 }
+
+void exitOnSigPipe() {
+    struct sigaction act;
+    memset(&act, 0, sizeof act);
+    act.sa_sigaction = [](int, siginfo_t*, void*){ ::exit(1); };
+    if (sigaction(SIGPIPE, &act, nullptr)) throw herr("couldn't run sigaction(): ", strerror(errno));
+}