From be8cfdfbc0a65ce93269281418b3ab41082a6994 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Mon, 9 Oct 2023 00:44:46 +0100
Subject: Avoid repeated calls to PQunescapeBytea

Fixes issue where accessing the blob value of a column multiple times
would free previously unescaped buffers resulting in dangling pointers.
---
 libpqpp/pq-column.cpp | 13 +++++++------
 libpqpp/pq-column.h   | 10 ++++++++--
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/libpqpp/pq-column.cpp b/libpqpp/pq-column.cpp
index 5a5f6b6..e495f2a 100644
--- a/libpqpp/pq-column.cpp
+++ b/libpqpp/pq-column.cpp
@@ -89,12 +89,13 @@ PQ::Column::apply(DB::HandleField & h) const
 		case TIMESTAMPTZOID:
 			h.timestamp(boost::posix_time::time_from_string(value()));
 			break;
-		case BYTEAOID: {
-			size_t len = 0;
-			// NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
-			buf = BufPtr {PQunescapeBytea(reinterpret_cast<const unsigned char *>(value()), &len)};
-			h.blob(DB::Blob(buf.get(), len));
+		case BYTEAOID:
+			if (sc->tuple != buffer.row || !buffer.data) {
+				buffer.data = Buffer::BufPtr {// NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
+						PQunescapeBytea(reinterpret_cast<const unsigned char *>(value()), &buffer.length)};
+				buffer.row = sc->tuple;
+			}
+			h.blob(DB::Blob(buffer.data.get(), buffer.length));
 			break;
-		}
 	}
 }
diff --git a/libpqpp/pq-column.h b/libpqpp/pq-column.h
index fa4a78a..4ef102d 100644
--- a/libpqpp/pq-column.h
+++ b/libpqpp/pq-column.h
@@ -24,8 +24,14 @@ namespace PQ {
 		const Oid oid;
 
 		// Buffer for PQunescapeBytea
-		using BufPtr = std::unique_ptr<unsigned char, pq_deleter<PQfreemem>>;
-		mutable BufPtr buf;
+		struct Buffer {
+			using BufPtr = std::unique_ptr<unsigned char, pq_deleter<PQfreemem>>;
+			size_t row {};
+			size_t length {};
+			BufPtr data;
+		};
+
+		mutable Buffer buffer;
 	};
 }
 
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