initial (extremely hacky) patch for pgbouncer that caches the last search_path set on the client socket.

client-cache-search_path.patch

diff --git a/include/varcache.h b/include/varcache.h
index 4984b01..d363fb0 100644
--- a/include/varcache.h
+++ b/include/varcache.h
@@ -5,7 +5,8 @@ enum VarCacheIdx {
 	VTimeZone,
 	VStdStr,
 	VAppName,
-	NumVars
+	VSearchPath,
+	NumVars,
 };
 
 typedef struct VarCache VarCache;
diff --git a/src/admin.c b/src/admin.c
index d23d24b..fc7c927 100644
--- a/src/admin.c
+++ b/src/admin.c
@@ -242,6 +242,7 @@ static bool send_one_fd(PgSocket *admin,
 			const char *addr, int port,
 			uint64_t ckey, int link,
 			const char *client_enc,
+			const char *search_path,
 			const char *std_strings,
 			const char *datestyle,
 			const char *timezone,
@@ -255,9 +256,9 @@ static bool send_one_fd(PgSocket *admin,
 
 	struct PktBuf *pkt = pktbuf_temp();
 
-	pktbuf_write_DataRow(pkt, "issssiqisssss",
+	pktbuf_write_DataRow(pkt, "issssiqissssss",
 		      fd, task, user, db, addr, port, ckey, link,
-		      client_enc, std_strings, datestyle, timezone,
+		      client_enc, search_path, std_strings, datestyle, timezone,
 		      password);
 	if (pkt->failed)
 		return false;
@@ -308,6 +309,7 @@ static bool show_one_fd(PgSocket *admin, PgSocket *sk)
 	VarCache *v = &sk->vars;
 	uint64_t ckey;
 	const struct PStr *client_encoding = v->var_list[VClientEncoding];
+	const struct PStr *search_path = v->var_list[VSearchPath];
 	const struct PStr *std_strings = v->var_list[VStdStr];
 	const struct PStr *datestyle = v->var_list[VDateStyle];
 	const struct PStr *timezone = v->var_list[VTimeZone];
@@ -334,6 +336,7 @@ static bool show_one_fd(PgSocket *admin, PgSocket *sk)
 			   ckey,
 			   sk->link ? sbuf_socket(&sk->link->sbuf) : 0,
 			   client_encoding ? client_encoding->str : NULL,
+			   search_path ? search_path->str : NULL,
 			   std_strings ? std_strings->str : NULL,
 			   datestyle ? datestyle->str : NULL,
 			   timezone ? timezone->str : NULL,
@@ -346,7 +349,7 @@ static bool show_pooler_cb(void *arg, int fd, const PgAddr *a)
 
 	return send_one_fd(arg, fd, "pooler", NULL, NULL,
 			   pga_ntop(a, buf, sizeof(buf)), pga_port(a), 0, 0,
-			   NULL, NULL, NULL, NULL, NULL);
+			   NULL, NULL, NULL, NULL, NULL, NULL);
 }
 
 /* send a row with sendmsg, optionally attaching a fd */
@@ -412,12 +415,12 @@ static bool admin_show_fds(PgSocket *admin, const char *arg)
 	/*
 	 * send resultset
 	 */
-	SEND_RowDescription(res, admin, "issssiqisssss",
+	SEND_RowDescription(res, admin, "issssiqissssss",
 				 "fd", "task",
 				 "user", "database",
 				 "addr", "port",
 				 "cancel", "link",
-				 "client_encoding", "std_strings",
+				 "client_encoding", "search_path", "std_strings",
 				 "datestyle", "timezone", "password");
 	if (res)
 		res = show_pooler_fds(admin);
diff --git a/src/client.c b/src/client.c
index 2b01ff2..e5adebe 100644
--- a/src/client.c
+++ b/src/client.c
@@ -23,6 +23,14 @@
 #include "bouncer.h"
 
 #include <usual/pgutil.h>
+#include <usual/string.h>
+
+static inline const char *str_skip_ws(const char *p)
+{
+  while (*p && isspace(*p))
+    p++;
+  return p;
+}
 
 static const char *hdr2hex(const struct MBuf *data, char *buf, unsigned buflen)
 {
@@ -592,6 +600,85 @@ static bool handle_client_startup(PgSocket *client, PktHdr *pkt)
 	return true;
 }
 
+static char *scan_for_set_search_path(struct MBuf *buf, const char type)
+{
+	char *spath        = (char *)buf->data + buf->read_pos;
+	const uint8_t *nul = memchr(spath, 0, mbuf_avail_for_read(buf));
+
+	if (!nul) {
+		log_debug("scan_for_set_search_path: couldn't find null terminator.");
+		return NULL;
+	}
+
+	/* Parse packet data is composed of: <string:pstmt_name>\0<string:query>\0
+	   so, to get to the query, we need to skip past the "prepared statement name" */
+	if (type == 'P') {
+		int pstmt_name_len = ((uintptr_t)nul + 1) - (uintptr_t)spath;
+		spath = spath + pstmt_name_len;
+
+		/* make sure we have a null terminated query string */
+		nul = memchr(spath, 0, mbuf_avail_for_read(buf) - pstmt_name_len);
+		if (!nul) {
+			log_debug("scan_for_set_search_path:"
+			          " couldn't find null terminator for query component of Parse packet.");
+			return NULL;
+		}
+	}
+
+	spath = (char *) str_skip_ws(spath);
+
+	/* check for SET */
+	if (strncasecmp("set", spath, strlen("set")) == 0) {
+		spath += strlen("set");
+	} else {
+		return NULL;
+	}
+
+	spath = (char *) str_skip_ws(spath);
+
+	/* check for search_path */
+	if (strncasecmp("search_path", spath, strlen("search_path")) == 0) {
+		spath += strlen("search_path");
+	} else {
+		return NULL;
+	}
+
+	spath = (char *) str_skip_ws(spath);
+
+	/* check for '=' or 'TO' */
+	if (*spath == '=') {
+		spath++;
+	} else {
+		if (tolower(*spath++) != 't') return NULL;
+		if (tolower(*spath++) != 'o') return NULL;
+	}
+
+	/* skip the last bit of whitespace, leading up to the actual search_path */
+	return (char *) str_skip_ws(spath);
+}
+
+static void client_cache_search_path(PgSocket *client, PktHdr *pkt)
+{
+	char spath[128], *p = NULL;
+
+	if ( (p = scan_for_set_search_path(&pkt->data, pkt->type)) != NULL) {
+		if (strlen(p) >= sizeof(spath)) {
+			slog_debug(client, "cache_search_path: search_path too big; skipping");
+			return;
+		}
+
+		strncpy(spath, p, strlen(p) + 1);
+
+		/* remove whitespace and semicolons from the end of the data */
+		p = (char *)spath + strlen(p) - 1;
+		while(p > (char *)spath && (isspace(*p) || *p == ';')) p--;
+		*(p+1) = 0;
+
+		varcache_set(&client->vars, "search_path", spath);
+		slog_noise(client, "cached search_path -> %s", spath);
+	}
+}
+
 /* decide on packets of logged-in client */
 static bool handle_client_work(PgSocket *client, PktHdr *pkt)
 {
@@ -606,6 +693,8 @@ static bool handle_client_work(PgSocket *client, PktHdr *pkt)
 			disconnect_client(client, true, "PQexec disallowed");
 			return false;
 		}
+		client_cache_search_path(client, pkt);
+
 	case 'F':		/* FunctionCall */
 
 	/* request immediate response from server */
@@ -625,6 +714,7 @@ static bool handle_client_work(PgSocket *client, PktHdr *pkt)
 	 * to buffer packets until sync or flush is sent by client
 	 */
 	case 'P':		/* Parse */
+		client_cache_search_path(client, pkt);
 	case 'E':		/* Execute */
 	case 'C':		/* Close */
 	case 'B':		/* Bind */
diff --git a/src/varcache.c b/src/varcache.c
index 6321dc5..33db06f 100644
--- a/src/varcache.c
+++ b/src/varcache.c
@@ -35,6 +35,7 @@ static const struct var_lookup lookup [] = {
  {"TimeZone",                    VTimeZone },
  {"standard_conforming_strings", VStdStr },
  {"application_name",            VAppName },
+ {"search_path",                 VSearchPath },
  {NULL},
 };