feat(ffto): add pgsql_parse_error_response() helper with unit tests

include/PgSQLErrorFields.h

@@ -0,0 +1,39 @@
+/**
+ * @file PgSQLErrorFields.h
+ * @brief Parser for PostgreSQL ErrorResponse message fields.
+ *
+ * Extracted for unit testability. Scans ErrorResponse payload for
+ * SQLSTATE ('C') and message ('M') fields.
+ *
+ * @see PostgreSQL Protocol: ErrorResponse message format
+ */
+
+#ifndef PGSQL_ERROR_FIELDS_H
+#define PGSQL_ERROR_FIELDS_H
+
+#include <cstdint>
+#include <cstddef>
+
+/**
+ * @brief Result of parsing a PostgreSQL ErrorResponse payload.
+ */
+struct PgSQLErrorResult {
+    bool parsed;              ///< True if payload was non-null and scanned.
+    char sqlstate[6];         ///< 5-char SQLSTATE + null terminator (empty if not found).
+    const char* message;      ///< Pointer into payload at 'M' field value (null if not found).
+    size_t message_len;       ///< Length of message string.
+};
+
+/**
+ * @brief Parse a PostgreSQL ErrorResponse payload to extract SQLSTATE and message.
+ *
+ * Scans the field-type/value pairs in the ErrorResponse payload.
+ * Field format: type_byte + null_terminated_string, repeated, ending with '\0'.
+ *
+ * @param payload  ErrorResponse message payload (after the 5-byte header).
+ * @param len      Length of the payload.
+ * @return PgSQLErrorResult with parsed fields.
+ */
+PgSQLErrorResult pgsql_parse_error_response(const unsigned char* payload, size_t len);
+
+#endif // PGSQL_ERROR_FIELDS_H

lib/Makefile

@@ -110,6 +110,7 @@ _OBJ_CXX := ProxySQL_GloVars.oo network.oo debug.oo configfile.oo Query_Cache.oo
 	TransactionState.oo \
 	HostgroupRouting.oo \
 	PgSQLCommandComplete.oo \
+	PgSQLErrorFields.oo \
 	MySQLProtocolUtils.oo \
 	PgSQLErrorClassifier.oo \
 	PgSQLMonitorDecision.oo \

lib/PgSQLErrorFields.cpp

@@ -0,0 +1,37 @@
+#include "PgSQLErrorFields.h"
+#include <cstring>
+
+PgSQLErrorResult pgsql_parse_error_response(const unsigned char* payload, size_t len) {
+    PgSQLErrorResult result {};
+    result.parsed = false;
+    result.sqlstate[0] = '\0';
+    result.message = nullptr;
+    result.message_len = 0;
+
+    if (!payload || len == 0) return result;
+    result.parsed = true;
+
+    size_t pos = 0;
+    while (pos < len) {
+        char field_type = static_cast<char>(payload[pos]);
+        if (field_type == '\0') break;  // end of fields
+        pos++;  // skip field type byte
+
+        // Find the null terminator for this field's value
+        const char* value = reinterpret_cast<const char*>(payload + pos);
+        size_t value_len = strnlen(value, len - pos);
+        if (pos + value_len >= len) break;  // truncated
+
+        if (field_type == 'C' && value_len <= 5) {
+            memcpy(result.sqlstate, value, value_len);
+            result.sqlstate[value_len] = '\0';
+        } else if (field_type == 'M') {
+            result.message = value;
+            result.message_len = value_len;
+        }
+
+        pos += value_len + 1;  // skip value + null terminator
+    }
+
+    return result;
+}

test/tap/tests/unit/ffto_protocol_unit-t.cpp

@@ -16,6 +16,7 @@
 #include "proxysql.h"
 #include "MySQLProtocolUtils.h"
 #include "PgSQLCommandComplete.h"
+#include "PgSQLErrorFields.h"
 
 #include <cstring>
 #include <vector>
@@ -309,12 +310,56 @@ static void test_mysql_err_packet_empty_message() {
     ok(errmsg_len == 0, "ERR parse empty msg: empty message");
 }
 
+// ============================================================================
+// 7. PgSQL: ErrorResponse field parsing
+// ============================================================================
+
+static void test_pgsql_error_fields_basic() {
+    unsigned char payload[] = {
+        'S','E','R','R','O','R','\0',
+        'C','4','2','6','0','1','\0',
+        'M','s','y','n','t','a','x',' ','e','r','r','o','r','\0',
+        '\0'
+    };
+    PgSQLErrorResult r = pgsql_parse_error_response(payload, sizeof(payload));
+    ok(r.parsed == true, "PgSQL error parse: basic parsed");
+    ok(strcmp(r.sqlstate, "42601") == 0, "PgSQL error parse: sqlstate = 42601");
+    ok(r.message != nullptr && strncmp(r.message, "syntax error", 12) == 0,
+       "PgSQL error parse: message starts with 'syntax error'");
+}
+
+static void test_pgsql_error_fields_missing_code() {
+    unsigned char payload[] = {
+        'S','E','R','R','O','R','\0',
+        'M','s','o','m','e',' ','e','r','r','\0',
+        '\0'
+    };
+    PgSQLErrorResult r = pgsql_parse_error_response(payload, sizeof(payload));
+    ok(r.parsed == true, "PgSQL error no-code: parsed");
+    ok(strlen(r.sqlstate) == 0, "PgSQL error no-code: empty sqlstate");
+    ok(r.message != nullptr && strncmp(r.message, "some err", 8) == 0,
+       "PgSQL error no-code: message correct");
+}
+
+static void test_pgsql_error_fields_empty() {
+    unsigned char payload[] = {'\0'};
+    PgSQLErrorResult r = pgsql_parse_error_response(payload, 1);
+    ok(r.parsed == true, "PgSQL error empty: parsed (no fields)");
+    ok(strlen(r.sqlstate) == 0, "PgSQL error empty: empty sqlstate");
+    ok(r.message == nullptr, "PgSQL error empty: null message");
+}
+
+static void test_pgsql_error_fields_zero_length() {
+    PgSQLErrorResult r = pgsql_parse_error_response(nullptr, 0);
+    ok(r.parsed == false, "PgSQL error null: returns false");
+}
+
 // ============================================================================
 // Main
 // ============================================================================
 
 int main() {
-	plan(46);
+	plan(56);
 	int rc = test_init_minimal();
 	ok(rc == 0, "test_init_minimal() succeeds");
 
@@ -355,6 +400,12 @@ int main() {
 	test_mysql_err_packet_truncated();      // 1
 	test_mysql_err_packet_empty_message();  // 3
 
+	// PgSQL ErrorResponse parsing
+	test_pgsql_error_fields_basic();        // 3
+	test_pgsql_error_fields_missing_code(); // 3
+	test_pgsql_error_fields_empty();        // 3
+	test_pgsql_error_fields_zero_length();  // 1
+
 	test_cleanup_minimal();
 	return exit_status();
 }